Displays

In recent decades, significant progress has been made in understanding the causes and impacts of urban air pollution, generally leading to improved air quality through enhanced knowledge and regulatory action. While a significant number of people still die prematurely each year from air pollution, progress continues to be made. Scientific investigation has exposed the processes by which primary pollutants, such as oxides of nitrogen and volatile organic compounds, are processed in the atmosphere, leading to their oxidation and ultimate removal, while at the same time producing secondary species such as ozone and organic aerosols.

Research has uncovered the complex chemistry of natural organic compounds released from trees and other plants. Because of the chemical structures of these compounds, they react somewhat differently than organic substances typically found in urban environments. The ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) project focuses on scientific research to understand the detailed chemistry and physics of urban air mixed with biogenic emissions with the goals to increase detailed understanding of the chemical processes and to use this knowledge to improve the performance of air quality models. Enhanced knowledge and improved models will allow society to develop better strategies to improve air quality and save lives.

The central component of ACROSS is a comprehensive summertime field study with many instruments for the measurement of primary and secondary constituents. Measurements will be made from research aircraft, a tower located in a forest, tethered balloons and/or drones, and mobile platforms. Observations from the field study will be analyzed in a variety of ways involving statistical approaches and comparisons with different types of numerical models.

This presentation describes activities in preparation of the ACROSS measurement campaign and provides information for interested parties to become involved.

How to cite: Cantrell, C., Michoud, V., Formenti, P., Doussin, J.-F., Gratien, A., and Dusanter, S. and the ACROSS team: ACROSS: An Observational Campaign to Improve Understanding of Photochemistry of Mixed Urban and Biogenic Air Masses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4157, https://doi.org/10.5194/egusphere-egu2020-4157, 2020.

This presentation is analysing a modern evolution in research and development from specific urban air quality systems to multi-hazard and integrated urban weather, environment and climate systems and services and provides an overview of joint results of large EU FP FUMAPEX, MEGAPOLI, EuMetChem and MarcoPolo projects and international WMO GURME and IUS teams. 

Urban air pollution is still one of the key environmental issues for many cities around the world. A number of recent and previous international studies have been initiated to explore these issues. In particular relevant experience from several European projects will be demonstrated. MEGAPOLI studies aimed to assess the impacts of megacities and large air-pollution hotspots on local, regional and global air quality; to quantify feedback mechanisms linking megacity air quality, local and regional climates, and global climate change; and to develop improved tools for predicting air pollution levels in megacities (doi:10.5194/asr-4-115-2010). FUMAPEX developed for the first time an integrated system encompassing emissions, urban meteorology and population exposure for urban air pollution episode forecasting, the assessment of urban air quality and health effects, and for emergency preparedness issues for urban areas (UAQIFS: Urban Air Quality Forecasting and Information System; doi.org/10.5194/acp-6-2005-2006; doi.org/10.5194/acp-7-855-2007).

While important advances have been made, new interdisciplinary research studies are needed to increase our understanding of the interactions between emissions, air quality, and regional and global climates. Studies need to address both basic and applied research and bridge the spatial and temporal scales connecting local emissions, air quality and weather with climate and global atmospheric chemistry. WMO has established the Global Atmosphere Watch (GAW) Urban Research Meteorology and Environment (GURME) project which provides an important research contribution to the integrated urban services.

Most of the disasters affecting urban areas are of a hydro-meteorological nature and these have increased due to climate change. Cities are also responsible not only for air pollution emissions, but also for generating up to 70% of GHG emissions that drive large scale climate change. Thus, there is a strong feedback between contributions of cities to environmental health, climate change and the impacts of climate change on cities and these phases of the problem should not be considered separately. There is a critical need to consider the problem in a complex manner with interactions of climate change and disaster risk reduction for urban areas (doi:10.1016/j.atmosenv.2015.11.059, doi.org/10.1016/j.uclim.2017.05.004).

WMO is promoting safe, healthy and resilient cities through the development of Integrated Urban Weather, Environment and Climate Services (IUS). The aim is to build urban services that meet the special needs of cities through a combination of dense observation networks, high-resolution forecasts, multi-hazard early warning systems, disaster management plans and climate services. This approach gives cities the tools they need to reduce emissions, build thriving and resilient communities and implement the UN Sustainable Development Goals. The Guidance on IUS, developed by a WMO inter-programme working group, documents and shares the good practices that will allow countries and cities to improve the resilience of urban areas to a great variety of natural and other hazards (https://library.wmo.int/doc_num.php?explnum_id=9903).

How to cite: Baklanov, A. and the EU FP FUMAPEX, MEGAPOLI, EuMetChem and MarcoPolo projects and international WMO GURME and IUS teams: From Urban Air Quality Forecasting and Information Systems to Integrated Urban Hydrometeorology, Climate and Environment Systems and Services for Smart Cities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8837, https://doi.org/10.5194/egusphere-egu2020-8837, 2020.

Resilience has become an important necessity for cities, particularly in the face of climate change. Mitigation and adaptation actions that enhance the resilience of cities need to be based on a sound understanding and quantification of the drivers of urban transformation and settlement structures, human and urban vulnerability, and of local and global climate change. Copernicus, as the means for the establishment of a European capacity for Earth Observation (EO), is based on continuously evolving Core Services. A major challenge for the EO community is the innovative exploitation of the Copernicus products in dealing with urban sustainability towards increasing urban resilience. Due to the multidimensional nature of urban resilience, to meet this challenge, information from more than one Copernicus Core Services, namely the Land Monitoring Service (CLMS), the Atmosphere Monitoring Service (CAMS), the Climate Change Service (C3S) and the Emergency Management Service (EMS), is needed. Furthermore, to address urban resilience, the urban planning community needs spatially disaggregated environmental information at local (neighbourhood) scale. Such information, for all parameters needed, is not yet directly available from the Copernicus Core Services mentioned above, while several elements - data and products - from contemporary satellite missions consist valuable tools for retrieving urban environmental parameters at local scale. The H2020-Space project CURE (Copernicus for Urban Resilience in Europe) is a joint effort of 10 partners from 9 countries that synergistically exploits the above Copernicus Core Services to develop an umbrella cross-cutting application for urban resilience, consisting of individual cross-cutting applications for climate change adaptation/mitigation, energy and economy, as well as healthy cities and social environments, at several European cities. These cross-cutting applications cope with the required scale and granularity by also integrating or exploiting third-party data, in-situ observations and modelling. CURE uses DIAS (Data and Information Access Services) to develop a system capable of supporting operational applications and downstream services across Europe. The CURE system hosts the developed cross-cutting applications, enabling its incorporation into operational services in the future. CURE is expected to increase the value of Copernicus Core Services for future emerging applications in the domain of urban resilience, exploiting also the improved data quality, coverage and revisit times of the future satellite missions. Thus, CURE will lead to more efficient routine urban planning activities with obvious socioeconomic impact, as well as to more efficient resilience planning activities related to climate change mitigation and adaptation, resulting in improved thermal comfort and air quality, as well as in enhanced energy efficiency. Specific CURE outcomes could be integrated into the operational Copernicus service portfolio. The added value and benefit expected to emerge from CURE is related to transformed urban governance and quality of life, because it is expected to provide improved and integrated information to city administrators, hence effectively supporting strategies for resilience planning at local and city scales, towards the implementation of the Sustainable Development Goals and the New Urban Agenda for Europe.

How to cite: Chrysoulakis, N., Mitraka, Z., Marconcini, M., Ludlow, D., Khan, Z., Holt Andersen, B., Soukup, T., Dohr, M., Gandini, A., Kropp, J., Lauwaet, D., and Feigenwinter, C.: Copernicus for Urban Resilience in Europe: the CURE Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5879, https://doi.org/10.5194/egusphere-egu2020-5879, 2020.

The urban water system is complex, comprised of water treatment and distribution, wastewater collection and treatment, and stormwater management (to avoid combined sewer overflow, flooding, and water quality permit violations). These components are often managed by separate agencies and companies, with their respective goals and budgets. In fact, they should all be working together towards the same overarching objective of urban water systems: to provide water to people and the economy for both indoor and outdoor uses at the lowest economic and energy costs and at the lowest achievable level of pollution.

We present an integrated model of urban water systems that accounts for changes in population, water consumption patterns, water saving technologies, raw water sources, water and wastewater treatment technologies, decentralization of wastewater treatment plants, water reuse demand, stormwater control measures, economic activities, electricity and other energy supply, landscape, weather, and climate. The methodological basis includes environmental life-cycle assessment (LCA) and life-cycle cost analysis (LCCA). The model is globally applicable. For effective decision making, we have created a decision making tool with an extensive, very detailed database to allow for specific, holistic analyses of the unique demographic, economic, and physical characteristics of urban areas.

The target audience for our model, tool, and results includes the government planners and regulators of the urban water system, water and wastewater agencies and companies, urban users of water (both individuals and companies), and real estate developers.

Through case studies of cities in different regions and climates over time, we show that water consumption does not have to follow population growth, in fact, it has dropped in many cities where the average per-person water consumption has been reduced due to water conservation measures. Water withdrawal and potable water production in some cities are more than four times more energy intensive than in others, and the energy intensity is expected to increase in many parts of the world due to droughts and overwhelmed water sources. Due to differing electricity mixes and corresponding greenhouse gas emissions, the average per-person water consumption in some cities is more than four times more impactful than in others, but reductions are feasible. Tailoring water quality to an application is a key to lowering energy and emissions. We show how we can diversify irrigation sources for agricultural production in and around cities, including the potential energy and emissions implications of wastewater recycling. Using the integrated decision support tool (i-DST), which allows for the comprehensive life-cycle cost and environmental assessment of gray, green, and hybrid stormwater control measures, we can estimate the needed investments in the gray and green infrastructure, and find that in areas with water scarcity, stromwater is a viable source of water.

How to cite: Horvath, A., Gursel, A. P., Chaudron, C., and Kavvada, I.: An Integrated Model of Urban Water-Wastewater-Stormwater-Energy Systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5840, https://doi.org/10.5194/egusphere-egu2020-5840, 2020.

Several opportunistic sensors (private weather stations, commercial microwave links and smartphones) are employed to obtain weather information and successfully monitor urban weather events. The ongoing urbanisation and climate change urges further understanding and monitoring of weather in cities. Two case studies during a 17-day period over the Amsterdam metropolitan area, the Netherlands, are used to illustrate the potential and limitations of hydrometeorological monitoring using non-traditional and opportunistic sensors. We employ three types of opportunistic sensing networks to monitor six important environmental variables: (1) air temperature estimates from smartphone batteries and personal weather stations; (2) rainfall from commercial microwave links and personal weather stations; (3) solar radiation from smartphones; (4) wind speed from personal weather stations; (5) air pressure from smartphones and personal weather stations; (6) humidity from personal weather stations. These observations are compared to dedicated, traditional observations where possible, although such networks are typically sparse in urban areas. First we show that the passage of a front can be successfully monitored using data from several types of non-traditional sensors in a complementary fashion. Also we demonstrate the added value of opportunistic measurements in quantifying the Urban Heat Island (UHI) effect during a hot episode. The UHI can be clearly determined from personal weather stations, though UHI values tend to be high compared to records from a traditional network. Overall, this study illustrates the enormous potential for hydrometeorological monitoring in urban areas using non-traditional and opportunistic sensing networks.

How to cite: de Vos, L., Droste, A., Zander, M., Overeem, A., Leijnse, H., Heusinkveld, B., Steeneveld, G.-J., and Uijlenhoet, R.: Opportunistic weather sensors: an Amsterdam case study of private weather stations, commercial microwave links and smartphones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10868, https://doi.org/10.5194/egusphere-egu2020-10868, 2020.

To capture complex physical processes in cities with high degree of heterogeneity, sophisticated urban land surface models (ULSMs) are used with various anthropogenic activities considered. These ULSMs can be used either offline, using atmospheric measurements as forcing inputs, or online, coupled with large-scale climate models. One downside of using ULSMs in offline mode is that most of atmospheric measurements in cities are spatially limited (e.g. a few points or sites) preventing the physical processes across extremely diverse or heterogeneous conditions in cities from being studied in their entire complexity. Coupling ULSMs with meso-scale models helps us study two-way interactions between the urban surface and atmosphere, and provides spatio-temporal information about the effect of urban climate on various city-related environmental issues such as the urban heat island and urban stormwater.

Here we couple and evaluate state-of-the-art surface urban energy and water scheme (SUEWS) with the weather research and forecasting (WRF) model. The coupled system (WRF-SUEWS) is evaluated in two UK cities: London (dense urban) and Swindon (suburban) for four two-week periods in each season. In general, WRF-SUEWS models the surface energy balance fluxes well in both cities across all periods. One strength of the coupled system is the ability to model the spatial and temporal distribution of anthropogenic heat in urban areas. We study how the difference between the anthropogenic heat flux of residential and commercial areas affects the energy balance as well as atmospheric variables over these areas.

How to cite: Omidvar, H., Sun, T., Li, Z., Zhang, N., Huang, W., Kotthaus, S., Ward, H., Luo, Z., and Grimmond, S.: The WRF-SUEWS coupled system: development and evaluation in two UK cities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7470, https://doi.org/10.5194/egusphere-egu2020-7470, 2020.

It is a well-known fact that in urban areas, human activities result in special climatic conditions. Urban climate studies nowadays are becoming more and more important as their results can be directly used by urban planners, architects and municipal decision-makers. In the framework of a long-term cooperation between the Urban Climate Research Group of the Department of Meteorology at the Eötvös Loránd University (Budapest) and the Department of Environment at the Municipality of Újbuda (district XI of Budapest), regular urban climate measurements are carried out in the district XI of Budapest to detect the urban heat island (UHI) effect on different spatial scales.

Measuring campaigns were conducted in summer 2018 and later, in spring, summer and autumn 2019 to determine the surface temperature of various urban materials using a Voltcraft IR-280 infrared thermometer. The purpose of these measurements was to obtain information about the thermal properties of different urban surfaces, objects in order to analyse which surfaces are suitable for decreasing and hence mitigating the UHI effect. The impact of the colour of different surfaces and the role of shading are analysed as well. The measurements were carried out at two measuring sites: (i) in the largest public park of the district, called Bikás Park (with 37 measuring points), (ii) in the commercial and public transportation centre of the district, called Móricz Zsigmond Square (with 17 measuring points). Based on the compiled database, a detailed statistical analysis was performed to investigate the thermal properties of various urban surfaces, e.g. pavements, walls, street furniture, sport facilities, water and plant surfaces.

The results show that the coolest surfaces are natural covers (water, vegetation), while the hottest surfaces are concrete pavements, asphalt and rubber paving when exposed to direct solar radiation. In summer, extremely high surface temperatures can occur, the average surface temperature around noon exceeds 40 °C in the case of dark painted wood objects, asphalt and rubber-paved surfaces with sunny conditions. The analysis focusing on the concrete paving blocks with different colours shows that the average surface temperature of light grey surfaces is 5-7 °C lower than the average temperature of darker colours. During the measurement series, the highest temperatures (over 50 °C) were measured at rubber paving-covered sport facilities and playgrounds, in sunny conditions. This material is very popular because its use has many benefits. Our study shows that the extensive use of these surfaces has a negative impact on the urban climate. These surfaces warm up so much during sunny summer days that the facilities covered with this material become practically unusable due to their extremely hot surface. In the case of this surface material, shading plays an important role as it can effectively control and reduce the warming of rubber paving-covered surfaces.

How to cite: Dezső, Z., Pongrácz, R., and Bartholy, J.: Comparison of surface temperature over different natural and artificial urban surfaces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7150, https://doi.org/10.5194/egusphere-egu2020-7150, 2020.

In the recent book entitled Urban Climates (2017) by T. Oke, G. Mills, A. Christen and J. A. Voogt, there is an Epilogue section on the History of Urban Climatology (pp 454-459) which states its scientific study dates from the early 19th century (as we know, from Luke Howard’s famous works) and can be divided into four periods of activity: (a) before 1930, pioneering climatographies of selected cities and weather elements, (b) 1930-1965, the growth of micro- and local climatology of climate differentiation and new field techniques, (c) 1965 to ca. 2000, explosive increase in research interest, closer links to meteorology and emergence of physically-based models of the urban atmosphere, and (d) 2000 and beyond, a maturing of the science into a predictive science, a period called one of consolidation and prediction.   With a proliferation of interests, new entities were formed during (d) – e.g., the International Association for Urban Climate and the Board on the Urban Environment of the AMS. They are dedicated to furthering scientific work in the urban climate and meteorology field and fostering cooperation between all interested scientists and practitioners. Through experiencing period (c) and now (d) with colleagues, students, administrators, practitioners, and the public (although now as an emeritus faculty in geography and urban planning) and being exposed to these organizations, it is this latter mission of the urban climate community I would like to highlight. It is a hope that the cooperative spirit of world  scientists and practitioners is further intensified (e.g, through CitiesIPCC and other academic and applied entities) in order to achieve major global-to-local solutions for our world cities. Technologies are exploding; the hope is that there is a concomitant explosion of practice.

How to cite: brazel, A.: Ruminations of the Urban Climate Field and Hopes for the Future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5781, https://doi.org/10.5194/egusphere-egu2020-5781, 2020.

The impact of local climate change induced by urbanization or changes in the Land Use and Land Cover (LULC) has been contributing as much as ~50% of the total rise in surface air temperature over the Eastern Indian state of Odisha. While analysing the physical mechanism of such rise, it is found that the changes in the specific heat capacity of the surface regulates the changes in the surface energy budget of the region. A slight change in the energy budget may significantly disturb the regional/local climate balance thereby simulating the primary meteorological parameters such as the temperature and surface heat fluxes. LULC which characterises the surface properties can contribute immensely to the energy budget cycle through biophysical and biochemical processes like evaporation, evapotranspiration, shortwave and long wave radiation, absorption and reflection. In this study, we used observational and modeling techniques to quantify the ramifications of LULC changes on the climate of Odisha during the period 2004-2015. A significant change in the spatial pattern of temperature has been observed towards the eastern part of the region.  We try to find out whether this shift in temperature pattern is because of LULC or global climate forcing. Significant diversification in the agricultural practices have also been noticed in the region in the recent times.  To evaluate such effects, Weather Research and Forecasting (WRF) mesoscale modeling system has been enforced to visualize how significantly changes in LULC have impacted parameters like surface temperature, heat fluxes, humidity etc. However, the modeling results also follow consistency with that of the observational signatures and a rise of ~0.5-1.0 ^oC has been observed. Along with the spatial analysis, vertical profiles are also studied where we found significant impact of changed LULC on specific humidity and temperature. This study discusses the dynamics of land-atmosphere interactions instigated by local LULC effects.

Keywords: LULC, urbanization, remote sensing, numerical modeling, climate change 

How to cite: Gogoi, P. P. and Vinoj, V.: Signature of LULC induced Regional Climate Change over Eastern India: A Modeling and Observational Approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-940, https://doi.org/10.5194/egusphere-egu2020-940, 2020.

The increase in urban air temperature caused by urban heat and climate change can have negative effects on the outdoor thermal comfort (OTC) as well as on the energy demand for air-conditioning. Nature-based solutions, such as the increase in urban biomass, are often proposed to mitigate excessive urban heat. Trees are expected to decrease temperatures due to shade provision on surfaces and evapotranspiration but their canopy blocks wind flow, thus potentially induce warming by reduction of heat removal. Several studies have shown that trees have a varying potential for air temperature reduction throughout the diurnal cycle as well as in different climates. Studies that partition and attribute the temperature reduction to the aforementioned effects are still lacking though, thus making the explanation of the observed differences difficult.

To address this knowledge gap, we use the mechanistic urban ecohydrological model, Urban Tethys-Chloris (UT&C, Meili et al. 2019), which accounts for radiation, evapotranspiration and roughness effects of trees in the urban canyon. Turning these components on and off by means of virtual experiments allows us to quantify their contribution to the air and surface temperature modification caused by the tree cover. The results are analysed for compact low-rise residential areas (LCZ3) in four different climates (Phoenix, Singapore, Melbourne, Zurich).

We find that tree evapotranspiration is able to lower 2 m air temperature at maximum by 3-4°C in all four climates as stomatal closure due to high vapour pressure deficits in dry and hot cities limit the transpirative cooling effect during mid-day. Counterintuitively, tree-radiation interaction increases the 2 m air temperature up to 2°C at noon time even though a decrease in surface temperatures is observed. While the surfaces underneath the tree canopy receive less radiation due to shading, the overall absorbed solar radiation within the canyon increases due to radiation trapping. In the analysed scenarios, the presence of trees leads to a decrease in the city roughness hindering turbulent energy exchange and thus, increasing the 2 m air temperature in all climates during daytime. The tree-radiation and tree-roughness effects on 2 m air temperature during night vary in different climates due to atmospheric stability effects.

Combining the different tree effects as in the real world, leads to a distinct diurnal pattern of air temperature reduction which is consistent with the observations in the literature. The numerical experiment allows reconciling differences in temperature changes induced by trees across the diurnal cycle and in various climates. The results could be used to guide green cover and tree type selection in cities and inform future studies aimed at optimizing the role of urban greening for improving local microclimatic conditions.

Meili, N., Manoli, G., Burlando, P., Bou-Zeid, E., Chow, W. T. L., Coutts, A. M., Daly, E., Nice, K. A., Roth, M., Tapper, N. J., Velasco, E., Vivoni, E. R., and Fatichi, S.: An urban ecohydrological model to quantify the effect of vegetation on urban climate and hydrology (UT&C v1.0), Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2019-225, accepted, 2019

How to cite: Meili, N., Burlando, P., Carmeliet, J., Chow, W. T. L., Coutts, A. M., Manoli, G., Roth, M., Velasco, E., Vivoni, E. R., and Fatichi, S.: Radiation, evapotranspiration, and roughness effects of urban trees on local microclimate: A modelling study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4339, https://doi.org/10.5194/egusphere-egu2020-4339, 2020.

Currently, around 54% of the world's population is living in urban areas and this number is projected to increase by 66% by 2050. In the past years, cities have been experiencing heat wave episodes that affect the population. As the modern urban landscape is continually evolving, with green spaces and parks becoming a more integral component and with suburbs expanding outward from city centres into previously rural, agricultural, and natural areas, we need tools to learn how to best implement planning strategies that minimize heat waves.  In this study we use the Weather and Research Forecasting model (WRF) with a multi-layer layer scheme, the Building Effect Parameterization (BEP) coupled with the Building Energy Model (BEP+BEM, Salamanca and Martilli, 2010) to take into account the energy consumption of buildings and anthropogenic heat generated by air conditioning systems. The urban canopy scheme takes into account city morphology (e.g. building and street canyon geometry) and surface characteristics (e.g. albedo, heat capacity, emissivity, urban/vegetation fraction). The Community Land Surface Model (CLM) is used in WRF that uses 16 different plant functional types (PFTs) as the basis for land-use differentiation.  Furthermore, we use the Local Climate Zones (LCZ) classification which has 11 urban land use categories with specific thermal, radiative and geometric parameters of the buildings and ground to compute the heat and momentum fluxes in the urban areas.  The objective is to validate the model and establish relationships between urban morphology and land use with temperature, so that the model can be used to simulate land use scenarios to investigate the effectiveness of different mitigation strategies to lower urban temperatures during the summer months.

We test the methods with the Metropolitan Area of Barcelona (AMB) as a case study. The AMB is representative of the Mediterranean climate, with mild winters and hot summers. With a heterogeneous urban landscape, the AMB covers 636 km² (34% built, 23% agricultural, and 31% vegetation) and has more than five million habitants. We simulate the heat wave that occurred in August 2018, during which temperatures stayed between 30 and 40ºC for five consecutive days and compare results with observed data from five different weather stations. We then simulate a potential scenario changing land surface from built to vegetation, in accordance with Barcelona´s strategic climate plan, and the potential impact the land use change has on reducing heat wave episodes.

How to cite: Villalba, G., Ventura, S., Gilabert, J., Martilli, A., and Badia, A.: Assessing the impact of the urban landscape on heat wave episodes: a case study of the Metropolitan Area of Barcelona., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5728, https://doi.org/10.5194/egusphere-egu2020-5728, 2020.

It has been long understood that green infrastructure helps to mitigate urban heat island formation and therefore should be a key strategy in future urban planning practices. Due to its high level of heat resilience, the sycamore tree (Platanus) dominates the appearance of urban landscapes in central Europe. Under extreme climate conditions however, these species tend to emit high levels of biogenic volatile organic compounds (BVOCs) which in turn can act as precursors for tropospheric ozone, especially in highly NOx polluted environments such as urban areas.

Assessing the ozone air quality of a large urban area in Germany we use the state-of-the art regional chemical transport model MECO(n), with chemistry coming from the Modular Earth Submodel System (MESSy) and meteorology being calculated by COSMO. Including the latest version of TERRA_URB, the model is configured for the Rhine-Main urban area. In a second step, we implement parts of the regional atmospheric chemistry mechanism in the ENVI-met model framework in order to investigate the impact of isoprene emissions on ozone concentration at street level for the urban area of Mainz, Germany.

Whereas mesoscale model results only show moderate mean ozone pollution over the model area, at micro-scale level on selected hot spots we find a clear relationship between urban layout, proximity to NOx emitters, tree-species-dependent isoprene emission capacity and increase in ozone concentration. The ENVI-met study reveals, that next to tree species, its location is a key factor for its micro-climatic UHI and air pollution mitigation potential. We could show, that isoprene related ozone concentration is highly sensitive to leaf temperature, photosynthetic active radiation as well as to the proximity to NO2 pollution sources. In a street canyon with high traffic load we find significant correlations between diurnal boundary layer dynamics, morning and evening rush hour and ambient ozone levels. For a hot summer day in particular, we simulate ozone concentrations rising up to 500% within a weakly ventilated street canyon with a high amount of strong isoprene emitters being present.

We summarize that combining findings from meso- and microscale model systems can be an important asset for science tools for cities in the framework of climate change adaption and mitigation and air pollution abatement strategies.

How to cite: Fallmann, J., Simon, H., Sinsel, T., Barra, M., and Tost, H.: Finding the right tree for future urban planning – Meso- to microscale model coupling in urban areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9087, https://doi.org/10.5194/egusphere-egu2020-9087, 2020.

Mean flow and turbulence in roughness sublayers (RSLs) over urban areas are complicated because of the diversified building configurations (such as size, shape and orientation, etc.). This study investigates the RSL flows over (part of) the real urban morphology of Hong Kong downtown by wind tunnel measurements. The urban models are fabricated by 3D printing using high-resolution digital maps of building morphology and topography. Vertical profiles of mean and turbulent components in three parallel transects are measured by a constant-temperature hot-wire anemometer (CTA). The wind tunnel results reveal that individual (vertical) profiles of streamwise fluctuating velocity u’’, vertical fluctuating velocity w’’ and vertical momentum flux u’’w’’ show noticeable variations in the RSL. It is largely attributed to the wakes and recirculations after the upstream high-rise buildings. A new analytical solution is proposed to predict the mean wind profiles in the RSL as well as the inertial sublayer (ISL) that is more accurate than the conventional logarithmic law of the wall (log-law). The turbulence in the RSL and ISL are examined in terms of quadrant analysis. The ejection Q2 and the sweep Q4 are stronger in the RSL than those in the ISL, collectively improving street-level air entrainment and pollutant removal.

How to cite: Mo, Z., Liu, C.-H., and Ho, Y.-K.: Flow and Turbulence Characteristics in the Roughness Sublayer over Real Urban Morphology of Hong Kong , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9854, https://doi.org/10.5194/egusphere-egu2020-9854, 2020.

Strategies for urban heat mitigation often make broad and non-specific recommendations (i.e. plant more trees) without accounting for local context. As a result, resources might be allocated to areas of lesser need over those where more urgent interventions are needed. Also, these interventions might return less than optimal results if local conditions are not considered. This project aims to assist with these interventions by providing a method to examine the urban heat profile of a city through an automated systematic approach. Using urban morphology information from databases such as WUDAPT, areas of cities are clustered into representative local climate zones (LCZs) and modelled at a micro-scale using localised features and properties. This bottom up modelling approach, using the VTUF-3D, UMEP, and TARGET models, allows these areas to be assessed in detail for their human thermal comfort performance and provide a city-wide heat map of thermal comfort. It also allows mitigation scenarios to be tested and targeted for each cluster type. A case study performed using this method for Melbourne is presented.

How to cite: Nice, K. and Broadbent, A.: Targeted urban heat mitigation strategies using urban morphology databases and micro-climate modelling to examine the urban heat profile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12795, https://doi.org/10.5194/egusphere-egu2020-12795, 2020.

Designing cities for thermal comfort should be a priority in the warming and urbanizing world. As cities continue to break extreme heat records, it is necessary to develop new sensing approaches capable of tracking thermal sensations of actual users of urban spaces. The Influence of built infrastructure on the microclimate at a human scale and residents’ thermal sensations is not well explored, but combining sensing techniques with simultaneous collection of user experiences is a promising research direction to shorten the gap.

We explored the relationships between the built environment, heat perception, and behavioral coping mechanisms in one of the most heat vulnerable Phoenix neighborhoods. Using Phoenix as an example, where extreme summer temperatures are a norm, can help to address heat challenges of other cities that have started facing temperature extremes in the recent years.

This study is an experimental citizen science project in which participants helped to create a “heat map” of the neighborhood. Participants were engaged in a 1-hour walk around the neighborhood and recorded their experience in a field guide. A smaller group participated in walking interviews and wore GPS devices and UV meters to gain deeper insights on subjective heat perception and physical body heat accumulation during the walk. Results revealed the differences in heat perception across a variety of urban landscapes. Participants identified preferred and most challenging locations, and gave ideas on what could improve their experience. Combined heart rate, UV exposure and microclimate data mapped in GIS visualized dependencies between the streetscape and physiological conditions of the study participants.

This project is one of the first to examine the impact of urban environment on dynamic psychological and physiological responses to heat. Using sensing techniques and qualitative research instruments, this research will inform the design changes in the neighborhood that will undergo redevelopment. It can serve as an example for other cities striving to adapt urban microclimates to new extremes.

How to cite: Dzyuban, Y., Redman, C., Hondula, D., Coseo, P., Middel, A., and Vanos, J.: Exploring pedestrian thermal comfort in hot climates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8439, https://doi.org/10.5194/egusphere-egu2020-8439, 2020.

Extreme temperatures during heat and cold waves are severe health hazards for humans. Residents’ exposure controls the susceptibility of the urban population to these hazards, yet the spatiotemporal population dynamics has been long overlooked in assessing the risk. In this study, we conducted comparative analysis over 16 major urban habitats under three massive heat waves and one cold wave across the contiguous United States. Incorporating WRF weather simulations with commute-adjusted population profiles, we found that the interaction between population dynamics and urban heat islands makes residents exposed to higher temperatures under extreme weather. After accounting for diurnal population movement, urban residents’ exposure to heat waves is intensified by 2.0 ± 0.8 ^oC (mean ± standard deviation among cities), and their exposure to cold wave is attenuated by 0.4 ± 0.8 ^oC. The aggravated exposure to extreme heat is more than half of the heat wave hazard (temperature anomaly 3.7 ± 1.5 ^oC). The underestimated exposure to extreme heat needs to be taken into serious consideration, especially in nighttime given the evident trend of observed nocturnal warming. Results suggest that the major driver for modified exposure to heat waves is the spatial temperature variability, i.e., residents’ exposure is more likely to be underestimated in a spread-out city. The current release of warnings for hazardous extreme weather is usually at the weather forecast zone level, and our analysis demonstrates that such service can be improved through considering spatiotemporal population dynamics. The essential role of population dynamics should also be emphasized in temperature-related climate adaptation strategies for effective and successful interventions.

How to cite: Yang, J. and Hu, L.: Refined assessment of urban residents' exposure to extreme temperatures across the United States, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-86, https://doi.org/10.5194/egusphere-egu2020-86, 2020.

Street trees are more and more regarded as a potential measure to mitigate the excessive heat in urban areas resulting from climate change and the urban heat island. However, the current knowledge of the cooling effect of street trees relies on studies at the micro-scale while potential interactions at the city-scale are yet to be understood. In fact, the vast majority of large-scale modelling studies only represent street trees outside the street canyon, neglecting important effects such as the shading and sheltering.

In order to explicitly represent street trees in coupled urban climate simulation, the multi-layer urban canopy model BEP-Tree was coupled with the regional weather and climate model COSMO-CLM. The coupled model, named COSMO-BEP-Tree, enabled simulating the radiative, flow and energy interactions between street trees, canyon surfaces and the atmosphere during weather and climate simulations.

In this study, COSMO-BEP-Tree is used to model the cooling potential of street trees during a heatwave event in Basel, Switzerland. The impact of street trees is explored in terms of near-surface air temperature and thermal comfort. The impact of greening scenarios is simulated and compared with other heat mitigation strategies.

The results highlight contrasting urban climate effects of street trees during daytime and night-time, where different processes become dominant. The daytime cooling was primarily a local effect and proportional to the local density of street trees.  In contrast, the impact was more widespread at night, where city-scale interactions become important. Beside air temperature, the model results suggest a significant impact of street trees on wind speed and canyon surface temperature. Owing to these effects, street trees produced a larger impact on thermal comfort than on air temperature. Finally, the need for further model development with respect to urban hydrology is outlined.

How to cite: Mussetti, G., Brunner, D., Henne, S., Krayenhoff, S., and Carmeliet, J.: Modelling the cooling potential of street trees at city-scale with COSMO-BEP-Tree, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19013, https://doi.org/10.5194/egusphere-egu2020-19013, 2020.

Environmental problems such as low wind speed, poor air quality and urban heat island effect are deteriorating in cities due to the rapid urbanization. Optimizing the ventilation condition in the urban canopy is an effective way to improve the urban air quality and thermal environment. To study the impact of building structure and thermal condition on local flow regime and micro thermal environment, wind tunnel experiments and CFD simulations were conducted with scale-model of idealized 2D street canyons. A series of street canyon models with aspect ratios of 1.1, 2.4, 4 and 5.67 were set up for both wind tunnel experiments and CFD simulations, with the scaled ration of 1:200. Laser Doppler Anemometer was deployed in the working section of the wind tunnel to monitor the velocity components. CFD simulations using ANSYS Fluent 15.0 were performed to study the turbulence characteristics under wind driven force and thermal buoyancy force. A solar ray tracing model and radiation models in Fluent was employed to simulate the heat effect of solar radiation in street canyons. The wind tunnel experiments and modelling revealed that a clockwise vortex existed in regular and deep street canyon while two counter-rotating vortexes appeared in extremely deep canyon. Moreover, different turbulence structures and significant spatial variation of air temperature existed in canyons with different solar elevation.

How to cite: Ling, H., Chen, L., Lin, Y., and Hang, J.: Wind-thermal environment in idealized 2D street canyon with different aspect ratios and thermal conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21100, https://doi.org/10.5194/egusphere-egu2020-21100, 2020.

The form and density of buildings modify the air flow and momentum exchange within cities, and therefore strongly affect local wind, temperature, humidity and pollution. Numerical weather prediction (NWP) models currently do not account for heterogeneity in their surface layer parameterisation. Regional models represent buildings, if at all, based on quantities such as plan and frontal area indices, and parameterise their impact at the lowest grid level, even though buildings can protrude a significant height into the atmospheric boundary layer.

To investigate how to parameterise urban roughness in NWP, we analysed high-resolution building-resolving large eddy simulations (LES) with the uDALES model over a range of heterogeneous urban neighbourhoods. The simulation setups have a similar building density and frontal aspect ratio, but vary in complexity with different building heights, plan areas and street geometries. Using the LES data we developed a parameterisation model that describes the vertical distribution of building drag inside a heterogeneous urban canopy. The drag force exerted on the atmosphere represents the momentum loss in the urban canopy due to buildings and can be incorporated as additional stress term in the momentum equations. The parameterisation represents the spatial heterogeneity effects in a one-dimensional vertical function, and links the building drag force to the heterogeneity of building layouts. A characterisation of the vertical and horizontal heterogeneity of built-up neighbourhoods is used as model input.

How to cite: Sützl, B., van Reeuwijk, M., and Rooney, G.: Distributed LES-based drag parameterisation for heterogeneous urban neighbourhoods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10461, https://doi.org/10.5194/egusphere-egu2020-10461, 2020.

How to cite: Zhang, N.: Statistical characteristics of the morphological parameters of Chinese cities and the application in WRF model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4326, https://doi.org/10.5194/egusphere-egu2020-4326, 2020.

More than 80% of people living in urban areas that exposed to air quality levels that exceed WHO guideline limits both indoors and outdoors. Road transport has been found to be one of major anthropogenic sources of aerosol particles and many gaseous pollutants in urban areas. Dispersion of pollutants emitted from vehicles over urban areas largely affects pedestrian-level air quality. A good understanding of pollutant transport, mixing process and removal mechanism is crucial to effectuate air quality management. In this study, turbulent dispersion of reactive pollutants in the atmospheric boundary layer (ABL) over hypothetical urban area in the form of an array of idealised street canyons is investigated using large-eddy simulation (LES). The irreversible ozone O3 titration oxidizes nitric oxide NO to nitrogen dioxide NO2, representing the typical anthropogenic air pollution chemistry. Nitric oxide (NO) is emitted from the ground level of the first street canyon into the urban ABL doped with ozone (O3). From the LES results, negative vertical NO flux is found at the roof level of the street canyons.  By looking into the different plume behavior and vertical flux between the inert pollutant and chemically reactive pollutant, a fundamental understanding of exchange processes of anthropogenic chemicals between an urban surface and the atmosphere is developed. 

How to cite: Wu, Z. and Liu, C.-H.: Large-eddy Simulation of Plume Dispersion over Hypothetical Urban Areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21219, https://doi.org/10.5194/egusphere-egu2020-21219, 2020.

The study of urban heat island (UHI) is of great relevance in the context of climate change (CC) and global warming. Cities accumulate heat in urban land covers as well as in built infrastructures, representing true islands of heat in relation to their rural environment, less urbanized. The literature on urban climate has highlighted the singular importance of night UHI phenomenon. It is during the night that the effects of UHI become more apparent, due to the low cooling capacity of urban construction materials and is during nighttime that temperatures can cause higher health risks, leading to the aggravation of negative impacts on people’s health and comfort in extreme events such as heat waves becoming more and more frequent and lasting longer. However, the study of nocturnal UHIs is still poorly developed, due to the structural problems regarding the availability of land surface and air temperature data for night time.

Traditional methods for obtaining nocturnal UHI have been directed either to extrapolation of data from weather stations, or obtaining air temperatures through urban transects. In the first case, the lack of weather stations in urban landscapes makes it extremely difficult to obtain data to extrapolate and propose models at a detailed resolution scale. In the second case, there is a manifest difficulty in obtaining data simultaneously and significantly representative of urban and rural zones. Another used methodology for measuring the nocturnal UHI is remote sensing from MODIS images, but the greatest limitation about this method is the low resolution, therefore it is clear the need for open source databases with better or higher resolution to quantify the night surface temperature.

This paper aims to develop a model for nocturnal UHI analysing several areas of Alta and Baja California as well as in the Mediterranean Coast, using data from the Landsat thermal bands (with an spatial resolution of 30 square meters per pixel) and contrasting Landsat's very limited nighttime images with daytime ones. The contrast allows the construction of “cooling” models of the LST based on geographical characteristics (longitude, latitude, distance to the sea, DTM, slope, orientation, etc.) and urban-spatial parameters (land uses and land covers), which are likely to be extrapolated to different time periods.

How to cite: Roca, J. and Arellano, B.: Measuring night-time urban heat island. Still a pending issue, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19577, https://doi.org/10.5194/egusphere-egu2020-19577, 2020.

Local Climate Zones (LCZ) have now been widely accepted and used by the urban climate community (Ching et al., 2018). However, their use over Sub-Saharan Africa has still been limited because of data scarcity in the region. Brousse et al. (2019, 2020) demonstrated the added value of applying spatially variant urban canyon parameters derived from LCZ in the urban climate model TERRA_URB – embedded in the COSMO-CLM model. Despite its promising results, thermal and morphological parameters extracted out of the ranges proposed by Stewart and Oke (2012) are mostly derived from Western cities. Hence, uncertainties related to the use of unascertained urban forms and functions of African cities for urban climate modelling have not yet been evaluated.

To quantify the sensitivity of the model to more representative urban canopy parameters of African cities, this study sets up a methodology for: (i) obtaining from in situ measurements archetypal parameters of LCZ classes for Kampala (Uganda); and (ii) simulating the potential effect of the newly defined urban structure on the local climate.

In situ data were obtained during field work held in the summer months of 2018. A representative sample of 1300 measurement points was selected throughout the city of Kampala, for which both quantitative (road width, distance between houses, heights of buildings) and qualitatively estimated (vegetation fraction, road-wall-roof material) variables were collected.  These variables enabled the development of an updated LCZ map of the city of Kampala.

To evaluate the model’s sensitivity to the new spatially explicit urban morphological and thermal parameters, this new information was fed into the TERRA_URB scheme at a horizontal resolution of 1 km for a 3-months period (December 2017 – February 2018). The run was nested within a 12 km simulation forced by ERA-Interim reanalysis data. Results show tangible effects of the updated parameters on the 2-meter air temperature, land surface temperature and surface energy balance components. Still, no major improvements in model skill compared to the default LCZ framework proposed by Brousse et al. (2020) were found. [1] [WT2] This study is among the first studies to test the sensitivity of an urban climate model to more realistic urban parameters in Africa and aims at triggering more research to be done in the area with a variety of urban climate models.

How to cite: Brousse, O., Van de Walle, J., Arnalsteen, L., Demuzere, M., Thiery, W., Wouters, H., and van Lipzig, N. P. M.: Are detailed urban canopy parameters necessary for modelling the urban climate in Africa?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17692, https://doi.org/10.5194/egusphere-egu2020-17692, 2020.

The presented study is devoted to the investigation of the spatial patterns of the urban-induced air temperature anomaly, known as the urban heat island (UHI) effect, based on the example of Moscow megacity. The numerous previous studies have already shown that Moscow exhibits urban-induced climatic effects (Varentsov e al., 2018) and could serve as a good test-bed for urban climate studies. In the presented study, we have further analyzed the UHI using high-quality observations from the official meteorological networks in Moscow region as well as the uncertified crowdsourcing observations from Netatmo network. The official meteorological networks include more than 70 observational sites in the city and surroundings, while the Netatmo network additionally provides the data from more than 1500 citizen weather stations (CWSs) in Moscow region. Previous studies have shown that CWS observations could be used for urban climate studies after application of the special quality control and filtering routines (Meier et al., 2017).

The analysis performed for a number of summer and winter seasons has revealed the seasonal variations of the UHI spatial patterns. In order to investigate the driving factors of the observed spatial heterogeneity of the air temperature within the city, we have analyzed its linkages with different qualitative and quantitative parameters of the urban environment, including the Local Climate Zone (LCZ) type, the impervious area fraction, building density, vegetation area fraction, etc. These parameters were obtained using the Landsat and Sentinel satellite images, Copernicus Global Land Cover data and OpenStreetMap data. We have shown that the UHI spatial patterns are shaped both by local and non-local driving factors. The factors such as LCZ type represent the local features of the urban environment, while the non-local drivers represent the influence of remote parts of the megacity, transformed by the atmospheric diffusion and advection. The non-local effects are reflected e.g. in the dependence between the UHI intensity and the distance from the city center; in the differences between similar LCZs, located in the different parts of the city; in the heat advection to the leeward side of the city. The findings of the study clearly illustrate the importance of taking the non-local effects into consideration in urban planning applications, biometeorological assessments and when applying the LCZ approach for big cities.

Acknowledges: The processing and analysis of the official and crowdsourcing observations were supported by Russian Foundation for Basic Research (project no. 19-35-70009). The analysis of the impervious surface area fraction data was supported by Russian Foundation for Basic Research (project no. 18-35-20052). The analysis of the impacts of urban vegetation on the urban heat island was supported by Russian Science Foundation (project no. 19-77-30012).

References:

Meier F., Fenner D., Grassmann T., Otto M., & Scherer D. (2017). Crowdsourcing air temperature from citizen weather stations for urban climate research. Urban Climate, 19, 170–191.

Varentsov M., Wouters H., Platonov V., & Konstantinov P. (2018). Megacity-Induced Mesoclimatic Effects in the Lower Atmosphere: A Modeling Study for Multiple Summers over Moscow, Russia. Atmosphere, 9(2), 50.

How to cite: Varentsov, M., Samsonov, T., Konstantinov, P., Kargashin, P., Fenner, D., and Meier, F.: A study on the spatial patterns of the Moscow megacity urban heat island based on the dense official and crowdsourcing observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15827, https://doi.org/10.5194/egusphere-egu2020-15827, 2020.

Alpine Pumping refers to a thermally driven circulation between the Alps and the Alpine foreland in southeastern Germany, which occurs regularly under clear and calm weather conditions (e.g. Lugauer and Winkler (2005)). Earlier studies suggest, that the ventilation of the city of Munich, and thus the urban temperature distribution, could be influenced by this regional wind system.

The present work was conducted in a cooperation framework between the city of Munich and the German Meteorological Service. The occurrence of Alpine Pumping and its effect on the temperature distribution in the city of Munich were investigated by temporary and operational wind measurements as well as numerical simulations. The thermal wind system was simulated with the regional climate model COSMO-CLM and the characteristics of Alpine Pumping deduced from this simulation used as input for the high-resolution urban climate model MUKLIMO_3.

Using a radiation-based criterion, Alpine Pumping occurs on about 60 days per year, mostly in the summer months when the heat load is highest. The wind fields of temporary measurements in the rural areas south of Munich show the expected daily cycle of the wind system, especially the southerly flow during the night, which transports cold air from the mountains into the city. An influence of the regional circulation pattern on the temperature in the city area was found in a case study with the urban climate model MUKLIMO_3. Especially at night and in the morning hours, the cooler air from the surroundings ventilates the city area. Furthermore, the model results show a spatial shift of the maximum heat island in Munich during the course of the day.

The findings show, that Alpine Pumping is a rather frequent phenomenon in the study area and represents an important contribution to the natural ventilation of different areas within the city.

References:

LUGAUER, M., WINKLER, P., 2005: Thermal circulation in South Bavaria - climatology and synoptic aspects. Meteorologische Zeitschrift. 14, 15-13.

How to cite: Sedlmeier, K., Koßmann, M., Winderlich, K., Graf, M., and Mühlbacher, G.: Does “Alpine Pumping” have an effect on the ventilation of Munich? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11498, https://doi.org/10.5194/egusphere-egu2020-11498, 2020.

The urban heat island (UHI) is a serious climatological phenomenon that is likely to exacerbate the effects of climate change. It has adverse effects on the thermal comfort of urban dwellers, building energy consumption and the general health of vulnerable demographics (i.e. older people). To understand the effects of UHI and therefore devise efficient methods to mitigate it, it is important that we understand the many factors affecting UHI and the magnitude of their contribution on the manifestation of UHI, especially in urban areas. Consequently, in the current study, we study the effect of sky conditions and urban geometry on UHI in Seoul city, South Korea. The climatic data detailing diverse sky conditions, categorized by the amount of cloud cover, was collected from 28 Automatic Weather Stations (AWS) located in Seoul city. Information on urban geometry such as building density, gross floor area ration and building area ratio was obtained from satellite imagery. Our results indicate that the levels of UHI, quantified using urban heat island intensity (UHII), are dependent on the prevailing sky conditions. We found that, UHII was highest under cloudy sky conditions (r = 0.71) and lowest under clear sky conditions (r = 0.66). Furthermore, we found that UHII was correlated with building area ratio and gross area ratio; areas with high building area ratios and gross area ratios tended to also experience high UHII levels. The results presented in the current study are useful to policy makers or urban designers that wish to curb the increasing effects of UHI in urban areas and consequently improve thermal comfort in urban areas, reduce building energy consumption for space cooling purposes and prevent heat-related mortalities in old and vulnerable populations.

How to cite: Joen, S. J., oh, J. W., Ngarambe, J., Nzivugira Duhirwe, P., Aye Su, M., and Yun, G. Y.: The effect of sky conditions and urban morphology on urban heat island in Seoul city, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12656, https://doi.org/10.5194/egusphere-egu2020-12656, 2020.

Fast urbanization is one of the aggrandizement factors to global warming, but the effects of urbanization on extreme temperature change is still not quantitatively assessed. Based on high-resolution land cover map, this study classified 613 meteorological stations in China into three classes, namely, urban station, suburban station and rural station to simulate the trends of extreme minimum temperature (TNN), mean temperature (Tavg) and extreme maximum temperature (TXX) of each meteorological station. The roles of urbanization in temperature change in the period 1960-2016 were then assessed. The results indicated that annual temperature increased significantly, but seasonal temperature increased with varied degrees. Temperature in high latitudes increased faster than that in low latitudes. Temperature in summer increased slower than that in other seasons. The effects of urbanization on TNN, Tavg and TXX were all statistically significant, but the effects on TNN and Tavg were more noticeable than TXX. The aggrandizement effects of urbanization presented by low-altitude meteorological stations are significant in South China and East China for all temperature indices, despite no statistical significance presented by high-altitude meteorological stations in Southwest China. This paper can provide a reference for understanding the regional temperature changes and the effects of urbanization on its changes in China.

How to cite: Qiu, J., Yang, X., Cao, B., Chen, Z., and Li, Y.: Effects of Urbanization on Regional Extreme-Temperature Change in China，1960-2016, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3514, https://doi.org/10.5194/egusphere-egu2020-3514, 2020.

Urban expansion encroaches on natural habitat, which seriously affects carbon storage which plays an important role in global climate change. The projection of future effects of urban expansion on carbon storage have been the subject of attention, previous studies explored its direct impacts but ignored indirect effects: cropland loss caused by urban expansion needs to compensation from natural habitat for food security, which also affects carbon storage. China, as a populated country, is at an important stage of cropland conservation policies reform, rapid urbanization, and constructing of eco-civilization. In this case, it’s vital to figure out the change of carbon storage due to the direct and indirect impacts of urban expansion in the future. Taking Hubei as the study area, the aim of this study is to project both direct impacts (DI) and indirect impacts (II) of urban expansion on carbon storage during 2010–2030. Three scenarios are developed by integrating the current situation and policies: the scenarios where urban continues to expand and the cropland conservation policies are implemented with the priority to cropland in quantity (S₁), with the priority to cropland in quantity and quality (S₂), with the priority to cropland in quantity and quality, and ecological protection is also concerned (S₃). Results show that, the total loss of carbon storage caused by urban expansion will be 1.83Tg•C (DI: 0.95Tg•C; II:0.88Tg•C) under the S₁ scenario, will be 2.15Tg•C (DI: 1.46Tg•C; II:0.69Tg•C) under the S₂ scenario, and will be 1.49Tg•C (DI: 0.94Tg•C; II: 0.55Tg•C) under the S₃ scenario. This indicates that ignoring the indirect impacts of urban expansion on carbon storage will lead to the underestimation of real impacts of urban expansion with 48%, 32%, and 63%, respectively. This study highlights the importance of taking the carbon storage loss caused by the indirect impacts of urban expansion into consideration.

How to cite: Tang, L. and Ke, X.: Projection of future direct and indirect impacts of urban expansion on carbon storage: A case study in Hubei, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21945, https://doi.org/10.5194/egusphere-egu2020-21945, 2020.

City of Suceava, located in the NE Region of Romania, is an attraction pole for the regional inhabitants through its commercial, academic and tourist functions. The city population increased from 114462 in 1992 to 122654 in 2018. The urban area suffered major modifications between 1990 and 2018 which transposed themselves in the values of the climatic elements.

The general objective of the study consists in the evaluation of the climatogen impact of the mutations occurred in the city’s demography, in the features of the active surface between 1990 (the period which followed immediately to the communist system) and 2018.

The working algorithm adopted consisted of: i) identification of modifications in the active surface structure, ii) identification of the land cover flows which determine the evolution of the artificial surfaces, iii) intersection of CORINE Land Cover sets, for the years 1990 and 2018, in ArcGis through the overlay technique, iv) obtaining a matrix of land cover categories, v) identification of the land cover flows according to the working technology implemented by the European Environment Agency, vi) highlighting the correlations between the modification of the artificial areas surfaces and the evolution of the climatic elements of Suceava’s atmosphere.

Results. There were identified three types of land cover flows specific to the artificial surfaces, caused by six types of processes. The biggest share is held by LCF2 (urban residential sprawl) represented by a single type of land cover flows, urban diffuse residential sprawl (lcf22) which cumulated an area of 861.74ha (2.12% of study area total). The second category shows the intraurban space conversion, defined LCF1 (urban land management) with the presence of two types of specific processes: urban development/infilling (lcf11) with a surface of 75.82ha (0.19% of the study area) and recycling of developed urban land (lcf12) with an area of 376.88ha (0.93% of study area). In the end, there was identified a small share of conversions which show the third category LCF3 (sprawl of economic sites and infrastructures) with a total of 284.66ha (0.70% of study area) and which contains three types of processes: sprawl of industrial and commercial sites (lcf31) with 129.09ha (0.32%), sprawl of airports (lcf34) with 10.27ha (0.03%) and construction (lcf37) with 145.3ha (0.36%). In total, the anthropic space from the study area was affected by conversions on a surface of 1599.1ha (3.93% of the total study area of 40685.73ha) for period 1990-2018. Meteorological data obtained from Suceava Weather Station (1961-2018) and from the urban meteorological stations SV1 and SV2 for the interval 2009-2019 were correlated by the statistics of conversions.

Conclusions. At Suceava suburban weather station temperature increased with 0,4°C in the decade 1991-2000, with 0,5°C in decade 2001-2010 and with 0,9°C more in decade 2011-2019. Only in the interval 2009-2019 with hourly data from all 3 stations, the urban-suburban thermal difference was of +1,7°C in the city's favour. If the increase of temperature from suburban is allocated to the regional heating, the urban-suburban thermal difference was attributed to the amplification of the city’s topoclimatic role per se.

How to cite: Prisacariu, A., Horodnic, V.-D., Mihăilă, D., and Bistricean, P.-I.: Changes in the urban climate parameters due to the anthropic factors. Case study: Suceava metropolitan area from Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-744, https://doi.org/10.5194/egusphere-egu2020-744, 2020.

Climate change, extreme weather conditions, and local scale urban heat island (UHI) effect altogether have substantial impacts on people’s health and comfort. The urban population spends most of its time in buildings, therefore, it is important to examine the relationship between weather/climate conditions and indoor environment. The role of buildings is complex in this context. On the one hand UHI effect is mostly created by buildings and artificial surfaces. On the other hand they account for about 40% of energy consumption on European average. Since environmental protection requires increased energy efficiency, the ultimate goal from this perspective is to achieve nearly zero-energy buildings. When estimating energy consumption, daily average temperatures are taken into account. The design parameters (e.g. for heating systems) are determined using temperature-based criteria. However, due to climate change, these critical values are likely to change as well. Therefore, it is important to examine the temperature time series affecting the energy consumption of buildings. For the analysis focusing on the Carpathian region within central/eastern Europe, we used the daily average, minimum and maximum temperature time series of five Hungarian cities (i.e. Budapest, Debrecen, Szeged, Pécs and Szombathely). The main aim of this study is to investigate the effect of changing daily average temperatures and the rising extreme values on building design parameters, especially heating and cooling periods (including the length and average temperatures of such periods).

How to cite: Dian, C., Talamon, A., Pongrácz, R., and Bartholy, J.: Relationship between heating/cooling period and changing temperature conditions in the urban areas of Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-783, https://doi.org/10.5194/egusphere-egu2020-783, 2020.

ABSTRACT

Cities around the world develop energy balances that are different to their surroundings. This study examines the application of allometric scaling to the thermal emission of cities in temperate and tropical regions. Overpasses of UK and Nigeria of the Moderate Resolution Imaging Spectroradiometer (MODIS), covering the period between 2000 and 2017 were sampled to examine the seasonal variability in night-time clear-sky upwelling long-wave energy for selected cities of the two countries. Total (area-integrated) emitted energy was calculated per city and interpreted by looking for ‘allometric’ (power law) scaling against the total population of the urban areas. Both sets of cities produce strong correlations (R² ³ 0.8 and R²≥0.7) of log (total emission) against log (population). Total night-time emitted energy is found to scale sub-linearly (i.e. with power law index < 1) with population on both countries. However, the slope derived from UK allometry (0.85 ± 0.03) is quite different from that derived for cities in Nigeria (0.4 ± 0.05). When scaled against log (city area), both sets of cities produce linear scalings, demonstrating that the total area of built surface is a more general predictor of thermal emissions than total population, a surprising result given the differences in built form in the two sets of cities. These results are robust to the method chosen to delineate the city boundary. We further investigate the factors underlying these allometric relationships using Local Climate Zone (LCZ) classifications.    

How to cite: Abdulrasheed, M.: The allometric scaling of thermal emissions from temperate and tropical cities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1152, https://doi.org/10.5194/egusphere-egu2020-1152, 2020.

Extreme heat and associated health risks are increasingly becoming threats to urban populations, especially in developing countries of the tropics. Although human thermal exposure in cities has been studied across the globe, biometeorological conditions in mixed-used spaces, informal economic activity settings, and informal settlements have received little attention. We present a comparative analysis of outdoor thermal comfort for informal micro-entrepreneurial communities in Kolkata and Mumbai. Both cities belong to the Aw Köppen Climate Classification, which signifies tropical hot and dry or Savannah climate. Due to excessive humidity, uncomfortable thermal conditions persist year-round in both cities.

An extensive thermal comfort perception survey was conducted between November 2018 and August 2019 in three similar neighborhoods in each city with over 650 valid samples. The microentrepreneurial locations included two pottery markets (Kumbhadwada in Mumbai,  Kumartuli in Kolkata); two flower markets that are linear stretches of informal activity areas along very important transportation networks (Dadar in Mumbai, Mallickghat in Kolkata); a book selling and book binding market (Boipara in Kolkata); and an informal commercial area with apparel shops (Fashion Street in Mumbai).

Results show that outdoor thermal comfort varied by city, micro-enterprise, and season. Overall, Kolkata respondents reported warmer sensations compared to Mumbai respondents. During the winter, neutral Physiologically Equivalent Temperature (PET) was 27.50^oC in Kolkata and 23.75^oC in Mumbai. Annual neutral PET was 22.7°C and 26.5°C in Mallickghat and Boipara, respectively. Respondents in Boipara were more sensitive towards warmer sensation than in Mallickghat. Even during the winter, people reported warmer sensation votes. PET was a better predictor of the mean Thermal Sensation Vote (mTSV) compared to air temperature. In Mumbai, we report higher neutral PET for activities at the clothing market compared to other microentrepreneurial activities. Acclimatization significantly improved comfort in the summer, while evaporative cooling was beneficial in the winter. We further employed an ANCOVA to analyze the impact of various non-climatic variables on thermal comfort. Results reveal that behavioral and physiological attributes (presence in the location, expectation, beverage intake) impact the overall sensation in both cities. Availability of shading was a significant parameter in Kolkata, while shading had a negligible effect on outdoor thermal sensation in Mumbai neighborhoods.

This is the first study to assess outdoor thermal comfort conditions and perceptions of populations involved in various outdoor informal economic activities in India. Findings of this study help understand the heat health risks of informal communities and inform the design and revitalization of such spaces to improve thermal comfort.

How to cite: Banerjee, S., Middel, A., and Chattopadhyay, S.: Bio-meteorological assessment of outdoor micro-entrepreneurial informal communities in extreme heat- A case of two tropical Indian megacities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1160, https://doi.org/10.5194/egusphere-egu2020-1160, 2020.

The world’s population is becoming increasingly urbanized. Urbanization development significantly modifies the moisture, radiation balance, thermal stability, and aerodynamic properties at the surface level. Urban areas often are several degrees warmer than the surrounding countryside. Overall, a warmer climate will lead to increased energy consumption, air pollution and a higher risk of human mortality.

This study focuses on examining the ability of the GEM-Surface model to reproduce the diurnal cycle of the meteorological parameter, including fluxes over Warsaw as well as the thermal and turbulent structure of the atmosphere downwind from Warsaw with the resolution of 1 km. The  Town Energy Balance (TEB) module was run on-line in an interactive mode, where it contributed to the energy balance of the host meteorological model. Urban effects in the GEM model are described with the TEB parameterization.

The impact of the modified atmospheric stability over Warsaw on the distribution of the pollutants will be studied using the GEM-AQ model.

How to cite: Sattari, A., W. Kaminski, J., Struzewska, J., and Gawuc, L.: Application of GEM-Surface to high resolution modelling - A case study for Warsaw, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1793, https://doi.org/10.5194/egusphere-egu2020-1793, 2020.

The summer of 2019 featured significantly too warm conditions in Germany during all summer months. This included several distinct warm episodes and heat waves, the most pronounced of these appearing around end of July.

Within the framework of the interdisciplinary research project Abc (Augsburg bleibt cool – Augsburg stays cool) – funded by the German Federal Ministry for Environment, Nature Conservation and Nuclear Safety – it is intended to detect and quantify urban thermal hot-spots with respect to outdoor and as well indoor air temperatures in the city of Augsburg (Bavaria, SE Germany). The knowledge of such spatiotemporal patterns of thermal and especially heat-stress exposure are an indispensable basis for any further aspired local climate modeling and adaptation studies.

To this end, in June 2019 around 500 low-cost thermometers and around 50 thermo-hygrometers have been distributed among residents of the central city parts of Augsburg to record ambient indoor temperatures during summer. As high indoor air temperatures are suspected to be health relevant in particular during night, participants placed the thermometers in their bedrooms.

Outdoor temperature and humidity have been recorded simultaneously by an already existing comprehensive urban climate measuring network.

In this contribution we present main features of the data set of indoor temperatures and show and discuss first analyses concerning temporal and spatial variability of indoor air temperatures during summer 2019. This includes a comparison of indoor and outdoor temperatures, analyses of the influence of urban structures (e.g. in terms of local climate zones) and as well the influence of building characteristics (e.g. age, building material, ...) on indoor air temperatures.

How to cite: Beck, C., Fritsch, M., Linder, M., Völkel, J., Beckmann, S., Hiete, M., Martin, K., Repper, A., and Schneider, M.: Indoor and outdoor ambient air temperatures during summer 2019 in Augsburg, Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2734, https://doi.org/10.5194/egusphere-egu2020-2734, 2020.

The Chinese New Year (CNY, also called Spring Festival), which officially lasts for 7 days, is the most important holiday in China. Chinese people in large cities usually return to their hometowns for family reunions before the CNY holiday and return afterward. Nearly half of Beijing’s population has been reported to leave the city for family reunions before the CNY holidays in the past several years. Hourly automatic weather station (AWS) data during CNY 2010-2015 were used to analyze the changes in the temporal and spatial distribution of the Beijing urban heat island intensity (UHII) and the impact of mass human migration on urban temperature. Soil moisture, 10-m wind speed, and cloud cover were considered and indicated nearly no change during the pre-CNY period (2 to 4 weeks before CNY) and CNY week, which means that UHII variation was mainly affected by the mass human migration. Daily UHII during CNY week was lower than during pre-CNY period. UHII for daily maximum temperature decreased by 55% during CNY week than the pre-CNY period (0.6 °C during pre-CNY period vs. 0.27 °C during CNY week) due to mass human migration, which was much larger than the reduction in UHII for the daily maximum temperature (5%, 4.34 °C during the pre-CNY period vs. 4.11 °C during the CNY week). The spatial distribution of the UHII difference between CNY week and the pre-CNY period is closely related to the locations of functional population zones. UHII for daily maximum temperature decreases most (80%, 0.40 °C during the pre-CNY period vs. 0.08 °C during the CNY period) between the Third and Fourth Ring Roads (RRs), an area which experiences high human activity and has the highest floating population percentage. This study can provide suggestions for optimizing the layout of urban space and land-use structures.

How to cite: Dou, J. and Miao, S.: Impact of mass human migration during Chinese New Year on Beijing urban heat island, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6250, https://doi.org/10.5194/egusphere-egu2020-6250, 2020.

Urban areas will be subjected to temperature increases from a combination of global-scale climate change and local-scale urban heat island drivers. The resultant combined heat risk – urban overheating – will notably challenge cities in securing the resilience of public health to combined urban overheating. Although global climate change research is ubiquitous, the urban climate and biometeorological research literature of this century reveals a lag of (sub-) tropical Asian regional studies behind Europe and North America. Through a systematic research review of international urban-scale climate and biometeorological literature from 2000-2019, we propose to reflect the state of the art of the urban overheating issue in Asia alongside its penetration in the regional climate resilience discourses.

The review reveals (i.) a rise of the number of urban overheating studies throughout in the region in conjunction with rapid demographic and developmental change, except for the central Asia region; (ii.) a “metropolitisation” of the urban heat and biometeorological knowledge, meaning a spatial organization of the knowledge reinforcing the leading position of the Asian national and regional primate cities; (iii.) distinct themes of more research into: large focus on remote-sensed urban heat mapping of Chinese and Indian urban clusters, evaluation of heat mitigation strategies from modeling experiments in nations having economies in transition, compared to more focus on urban-wide heat mortality epidemiological studies in countries already facing aging issues.

Considering the lack of global climate change considerations in urban overheating and biometeorological studies, the review appeals for a more systematic vision of the urban heat issues where urban overheating consequences (i.e. thermal discomfort, heat morbidity, and mortality) are analyzed and discussed conjunctly with the geographical background of the cities, its urban fabric properties, and its socio-demographic dynamics.

How to cite: Kohler, M. and Chow, W. T. L.: A thematic review of recent urban overheating impacts research in Asia and its applications to climate resilience, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6346, https://doi.org/10.5194/egusphere-egu2020-6346, 2020.

Surface urban heat island (SUHI) is a major anthropogenic alteration of the urban environment, and its geospatial pattern remains poorly understand over a larger area. SUHI has been investigated in many regions of the world, but the complete understanding of its dynamics over a large area, across different climatic regime is missing, especially in India. In this study, Moderate Resolution Imaging Spectroradiometer (MODIS), land surface temperature (LST) data from 2003 to 2018 is used to investigate the diurnal, seasonal, and interannual variations in the SUHI intensity, difference in urban and rural LST, across 150 major Indian cities situated over different climatic zones. The result shows the presence of surface urban heat/cool island depending upon climatic zones and seasons. The general sequence of mean SUHI intensity observed over different climatic zones is winter nighttime>summer nighttime>winter daytime>summer daytime. During the daytime, the cities situated in tropical monsoon (Am) (coastal cities), hot steppe (BSh), and hot desert (BWh) climatic zone shows a cool urban island, especially in summer. The nighttime SUHI intensity showed less obvious seasonal variations and always showed positive heat intensity. The cities situated in the humid subtropical (Cwa) zone, which is mainly Indo-Gangetic plain and a major hub of the Indian population, shows strong daytime as well as nighttime SUHI intensity. Mann-Kendall and Sen’s slope estimator test are used to detect the long-term trend of SUHI intensity in different climatic zones. The results show the presence of a decreasing trend in most of the cities during the daytime as compared to nighttime in both the summer/winter season.

How to cite: Mohammad, P. and Goswami, A.: Surface urban heat island variation over major Indian cities across different climatic zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6444, https://doi.org/10.5194/egusphere-egu2020-6444, 2020.

Changes in surface and atmosphere characteristics in urban areas can alter radiation, heat and water balance and generate excessive heat load in those areas. One of the associated consequences is higher temperatures in built-up areas compared to the rural surrounding, also known as urban heat island (UHI). Here, summer heat load in Zagreb, the largest city of Croatia, is investigated. Summer season is in the focus of the study, not only because it is shown that trend in summer temperatures in Zagreb is stronger compared to the winter one, but also as it is the season when intense and prolonged extreme weather events, like heat-weaves, are likely to occur.

In this work, urban climate model MUKLIMO_3 with 100 m horizontal resolution is applied for a broader area of Zagreb. To explore the effect of climate change on the heat load, two separate experiments with the same land-use (corresponding to the current state of the city), but for different climate conditions are made. Daily data measurements for the period 1951–1980 are used as past climate, while 1981–2010 period represents the current climate conditions. Heat load is here estimated by a number of days with the maximum air temperature above 25 °C, i.e. by summer days. Both simulations indicated the lowest values of heat load in mountainous forest area accompanied by increased values in densely built-up regions and old city center. However, lower number of summer days is also found for green and blue areas within the city. The spatial pattern of difference in the number of summer days between considered periods is mainly influenced by orography with a much lower increase in the mountain area of the domain than in the lowland city region.

How to cite: Nimac, I., Herceg Bulić, I., and Žuvela-Aloise, M.: Modeling summer heat load in Zagreb due to climate change effect , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7049, https://doi.org/10.5194/egusphere-egu2020-7049, 2020.

Urban areas show higher nocturnal temperature comparing to rural areas, which is denoted by urban heat island. This effect can intensify the impact of global warming in urban areas especially during heat waves, that leads to higher energy demand for cooling the building and higher thermal stress for residents.  

The aim of this study is to identify the Urban Heat Island (UHI) effect during the heat spell 2018 and 2019 in order to calculated human thermal comfort for Berlin. Berlin, the capital city of Germany covers an area of 892km² and its population is growing, therefore more residential areas will be planned in future through higher building. The methodology of this research is to divide Berlin into Local Climate Zones (LCZ's) regarding the concept of Stewart & Oke (2012). Then to evaluate the accuracy of this concept using 30 microclimate stations. Estimating the magnitude of urban heat island and its seasonal changes in combination with human thermal perception in different LCZ during summer time is another objective of this research. 

Ten LCZ's for Berlin were selected, as class 1 (compact high rise), class 3 (compact low rise), class 7 (lightweight low-rise), class C (bush, scrub), class E (bare rock or paved) and class F (bare soil or sand) don't exist in Berlin. Class A (dense trees) is with a fraction of 18.6% in a good agreement with the percentage of dense trees reported from the city administration of Berlin (18.4%), class G (water) has a coverage of 5.1% through our classification instead of 6.7% reported by the city administration. In summary, the LCZ 1-10 cover 59.3% (more than half) of the city area.

Regarding temperature measurements, which represent a hot summer day with calm wind and clear sky the difference of Local Climate Zones will be calculated and the temperature variability in every LCZ's regarding sky view factor values show the hot spot of the city.

The vulnerability of LCZ's to heat stress will be ranked and discussed regarding ventilation and other factors.

Literature

Matzarakis, A. Mayer, H., Iziomon, M. (1999) Applications of a universal thermal index: Physiological equivalent temperature: Intern. J. of Biomet 43 (2), 76-84.

Stewart, I.D., Oke, T.R. (2012) Local climate zones for urban temperature studies. Bull. Amer. Meteor. Soc. 93 1879-1900. DOI: 10.1175/BAMS-D-11-00019.1.

How to cite: Langer, I., Pasternack, A., and Ulbrich, U.: Human thermal comfort in Local climate zones of Berlin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7741, https://doi.org/10.5194/egusphere-egu2020-7741, 2020.

Models for weather and climate have been actively populated with urban canopy models in the last decade. Urban canopy models are available with different levels of complexity. In an earlier study several urban canopy models have been evaluated in offline mode (Grimmond et al. 2011). However, in reality these schemes operate within a numerical weather prediction model, and are coupled with the atmospheric boundary layer. Within the SUBLIME model intercomparison study, single-column models equipped with urban canopy models are evaluated against observations for a clear sky case over London. As such we aim to unravel whether model sensitivity for urban morphological parameters is similar in coupled and uncoupled model. Moreover, the SUBLIME project provides a benchmark for future model evaluation and further development. The SUBLIME experiment consists of a forecast task over a 54 hour period (23-25 July 2012), during which clear sky conditions persisted over London. It consists of two main stages, firstly an offline urban canopy model run, to determine how the surface scheme performs. This is followed by a run in which the urban canopy model is coupled to a single-column model to simulate the coupling to the urban boundary layer. Model forcing data were provided by flux tower, LIDAR and radiosonde observations. Additional external forcings for geostrophic wind speed and advection of heat, moisture and momentum which could not be directly observed were simulated using, 3-D WRF (Weather Research and Forecasting model) model runs. This presentation will discuss the modelling results using the new revised external forcings. We evaluate model outcomes against surface radiation and energy balance observations for both stages. For the second stage, modelled vertical profiles of wind, temperature and humidity as well as boundary-layer height are compared against observations and between models. Finally, differences in model results are identified and the physical processes responsible for these are explored using process diagrams.

How to cite: Steeneveld, G.-J. and Tsiringakis, A. and the SUBLIME: The Single-column Urban Boundary Layer Intercomparison Modelling Experiment (SUBLIME): results of revised recipe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8070, https://doi.org/10.5194/egusphere-egu2020-8070, 2020.

In a world with increasing extreme weather events, such as dry or extreme rain periods, due to climate change and an ever growing population specifically in urban areas, a forsighted planning and adaption of cities and their urban surroundings is becoming more and more important. Here, particularly health and comfort of the urban population, such as thermal comfort, air quality, ventilation or UV exposure, but also other aspects like safety and environmental sustainability play an important role. In order to create the cities of tomorrow that meet the real requirements to host healthy and firendly living conditions, city planners are relying on scientific models where they can simulate how changes in the urban environment can effect its climate. The PALM-4U (Parallelised Large-Eddy Simulation Model for Urban Applications) model was specifically developed to be able to simulate a large variety of parameters on short timescales and at the high resolution that is required to resolve single buildings or obstacles like trees within the city.

In September 2019, the second phase of the German research project MOSAIK (model-based city planning and application in climate change), a module within the large over-arching project [UC]² (Urban Climate Under Change) that focusses on the further development of the model, has started.

In this overview, we will present the PALM-4U‘s current capabilities and outline the planned future development in the coming years like windbreak modelling, coupling with traffic flow models, including biogenic volatile organic compounds in urban air quality modelling. Furthermore, our PALM-4U community model strategy will be explained.

How to cite: Hettrich, S., Maronga, B., and Raasch, S.: PALM-4U – A building-resolving microscale model to support future adaptation of cities in a changing urban climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8513, https://doi.org/10.5194/egusphere-egu2020-8513, 2020.

Extreme hot events have profound impacts on human health. Especially, consecutive hot days without heat relief during nighttime can significantly increase the rates of mortality and morbidity. Using an urbanized global earth system model and treating urban and rural land as subgrid units, the urbanization effect on long-term changes in three types of summertime hot extremes (i.e., independent hot days, independent hot nights, and compound events) is simulated under the present-day climate and two future scenarios in China. The model is first evaluated using a homogenized observational dataset drawn from over 2,000 meteorological stations. The results show that the model can well capture urban and rural temperature changes during the historical period from 1961 to 2000. The urban and rural temperatures are both increased under two future scenarios, but the urban heat island intensities (i.e., urban minus rural) do not show significant changes. However, urbanization has a significant impact on the frequencies of summertime hot extremes under two future scenarios. The increasing frequencies of independent hot days and independent hot nights in urban areas are less than that in rural areas, but more importantly, the increasing frequency of compound events in urban areas is larger than that in rural areas. This suggests that urbanization will aggravate the trend of the extreme hot events changing from independent hot days and independent hot nights to compound events, and seriously increase the health risks of urban residents in the future.

How to cite: Liao, W., Li, D., and Liu, X.: Examination and Projection of Urbanization Effect on Summertime Hot Extremes in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8611, https://doi.org/10.5194/egusphere-egu2020-8611, 2020.

Clouds in the urban boundary layer interact with the urban land surface via different linkages, resulting in prominent spatial and temporal patterns over or downwind of cities - called here patterns of urban cloud modifications. Depending on meteorological context, an enhancement of fair-weather cumulus clouds or a faster dissipation of fog and low stratus can be encountered. As the role of clouds in the climate system is among the largest remaining uncertainties in climate science, a more complete understanding of cloud systems is required and the dynamic urban setting may serve as a testbed. 

The aim of the study is the spatiotemporal quantification of urban cloud patterns and properties over Europe. Changes of low-cloud properties including cloud occurrence frequency and microphysical properties are spatially and seasonally mapped for the urban centres of Europe using satellite observations (MODIS, SEVIRI). The identification of spatial patterns of urban cloud modifications for specific cloud types and season will provide essential information on location, thermodynamic conditions and intensity of urban centres impacting low clouds. A systematic quantification of the overall spatial and temporal patterns of urban clouds would therefore set a basis for studying drivers of urban cloud modifications and their feedbacks on the urban climate.

How to cite: Fuchs, J. and Cermak, J.: Patterns of urban cloud modifications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8847, https://doi.org/10.5194/egusphere-egu2020-8847, 2020.

Different roof materials are deployed for mitigating the urban heat, which significantly affects
our life. However, the performance of specific roof materials could be influenced by the
background climate. To evaluate the effectiveness of roof materials on temperature reductions in
a subtropical monsoon climate region, this study performs field experiments using four different
roof materials (gray and white surfaces, solar panel, and grass surface) from December 2017 to
July 2018. The results show that the white surface reduced the average daily surface temperature
by 3.37 °C. This cooling effect increased with the increase in surface albedo and incoming solar
radiation. However, the average cooling effect of the grass surface was much lower (0.43 °C).
This is attributable to the low soil moisture, which was influenced by the monsoon, thereby
indicating that irrigation is required to improve the thermal performance of grass roofs even in
humid regions. The solar panel reduced the daily surface temperature by 0.59 °C but exerted
strong warming (7.36 °C) during midday and cooling effects (4.03 °C) during midnight because
of its low albedo, low emissivity, and low heat capacity. Our results suggest that, for the roof
treatments explored here, white roofs are more effective for mitigating urban heat in a
subtropical monsoon climate under the present climatic conditions and especially for drier
climates predicted for the future, while grass roofs are not a sustainable method as they require
irrigation to achieve a cooling effect and solar panels may heat the urban atmosphere.

How to cite: Chen, X. and Jeong, S.: Mitigating the warming in urban areas: Experimental study of different roof materials in a subtropical monsoon climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9117, https://doi.org/10.5194/egusphere-egu2020-9117, 2020.

Understanding the dynamics of mass and heat exchange between a street canyon and the overlying atmosphere is crucial to predict air quality and microclimatic conditions within dense urban areas. Previous studies have demonstrated that the bulk transfer between the street and the overlying flow is entirely governed by the intensity of turbulent fluctuations within the street. The aim of this experimental study is to evaluate how the geometry of the street canyon and the solar radiation on building façades influence the turbulent velocity field within a two-dimensional street canyon and thus the global street canyon ventilation. The study was carried in a wind tunnel. The boundary conditions inside the canyon were modified by heating its windward and leeward walls and by changing the cavity aspect-ratio. The flow field in a cross-section of the street canyon was measured with particle image velocimetry. Temperatures were measured by means of thermocouples. The velocity and vorticity fields are analysed and discussed.

How to cite: Salizzoni, P., Fellini, S., and Ridolfi, L.: Effect of wall heating on street canyon ventilation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9613, https://doi.org/10.5194/egusphere-egu2020-9613, 2020.

Energy consumption, such as building energy use and traffic, is one of the key sources of anthropogenic heat flux in cities (Q_F), which influences the urban climate. Different methods have been proposed to quantify Q_F, such as using the inventory data and satellite observations of the land surface temperature. In this study, we develop an analysis framework based on urban surface energy balance and inverse calculation of the expected change of thermodynamic state as a result of different sources of energy consumption. This framework enables us to link the energy consumption data with remotely sensed land surface temperature (LST). Thus, the contribution of different sources of anthropogenic energy consumption to the urban land surface temperature can be readily quantified. We apply this method to ECOSTRESS LST, traffic volume and building energy consumption for cities in the US. We show that the exhaust heat from traffic and building energy use contributes differently to the surface urban heat island effect: the contributions differ in cities with different background climates, urban morphologies and green area fractions. Overall, the combined model-observation framework demonstrates potential in quantifying the impact of two major anthropogenic heating sources on urban climate, in particular with increasingly available high-quality urban energy-use data and fine-resolution satellite observations.  

How to cite: Yu, Z., Li, Q., Sun, T., and Hu, L.: The Contribution of Anthropogenic Energy Use to Urban Heat Island: Combining Energy Consumption Data with Satellite Observation of Land Surface Temperature , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10645, https://doi.org/10.5194/egusphere-egu2020-10645, 2020.

The temperature in the cities is affected by both global climate change and local changes due to human activities and the different land use compared to rural surroundings. These local changes, which modify the surface energy budget in urban areas, include the replacement of the natural surfaces by buildings and pavements and the heat of anthropogenic origin (heating, air conditioning, traffic). Madrid city (Spain) has a current population of near 3.3 million people and a larger metropolitan area reaching around 6.5 million people. Hence, it is affected by the phenomenon called urban heat island (UHI), which indicates that a higher temperature is found in the city compared with the surrounding rural areas. UHI is defined as the temperature difference between the urban observatory and the rural one and especially affects the minimum temperatures since urban areas cool down to a lesser extent than the neighbouring rural sites. Moreover, the intensity of the UHI is modulated by the meteorological conditions (wind, cloudiness, surface pressure, precipitation), highly associated with different synoptic situations. In this work, we use the Madrid-Retiro meteorological station as the urban one, which has regular and homogeneous data from the beginning of XX century; and the station at Barajas airport (12 km from the city centre) as well as other stations out of Madrid city (but within a range of 20 km from the city centre) as the rural stations. They all have a common measuring period from 1961 until present. The main objectives of the work are: 1) to identify temperature trends in the meteorological stations (both urban and rural); 2) to evaluate the intensity of the UHI for the different rural stations; 3) to apply a systematic and objective algorithm to classify each day in different categories (related to synoptic situation) that produce a different degree of UHI intensity; and, 4) to evaluate possible trends in the UHI intensity.

How to cite: Maqueda, G., Yagüe, C., Román-Cascón, C., Serrano, E., and Arrillaga, J. A.: Analysis of temperature trends and urban heat island in Madrid, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10969, https://doi.org/10.5194/egusphere-egu2020-10969, 2020.

15 year re-analysis of the urban climate of Amsterdam using WRF

Sytse Koopmans¹ (Sytse.koopmans@wur.nl), Gert-Jan Steeneveld¹, Ronald van Haren², Albert A.M. Holtslag¹.

¹ Wageningen University and Research, the Netherlands:

² Netherlands eScience Center, the Netherlands:

Ongoing world-wide climate change and urbanization illustrate the need to understand urban hydrometeorology and its implications for human thermal comfort and water management. Numerical weather prediction models can assist to understand these issues, as they progress increasingly towards finer scales. With high model resolutions (grid spacing of 100m), effective representation of cities becomes crucial. The complex structures of cities, configuration of buildings, streets and scattered vegetation, require a different modelling approach than the homogeneous rural surroundings. The current urban canopy-layer schemes account for these city specific characteristics, but differ substantially amongst each other due to uncertainty in land use parameters and incomplete physical understanding. Therefore, the hindcasting of the urban environment needs improvement.

In this study, we improve the WRF (Weather Research and Forecasting) mesoscale model performance by incorporating observations of a variety of sources using data assimilation (WRF-3DVAR) and nudging techniques on a resolution up to 167 meter. Data assimilation aims to accurately describe the most probable atmospheric state by steering the model fields in the direction of the observations. Specific to urban boundary layers, a novel approach has been developed to nudge modelled urban canyon temperatures with quality controlled urban weather observations. Adjusting the urban fabric accordingly is crucial, because of the large heat storage within urban canopies. The road and wall layers of the urban canopy are adjusted depending on the bulk heat transfer coefficient and urban geometry. Other data assimilation sources consists of WMO synoptic weather observations and volume radar data.

The results of the 15-year climatological urban re-analysis are here presented and it is subdivided in three key questions. First, we attempt to answer how large the trends are in human thermal comfort over the 15 year period. Second, we investigate if there are seasonality’s detected in maximum urban heat island intensities. Earlier found hysteresis-like curves were reproduced to a large extent for for pedestrian level air temperatures. Lastly, we analyse trends in extreme precipitation using simulated precipitation data on one second interval.

How to cite: Koopmans, S., Steeneveld, G.-J., van Haren, R., and Holtslag, A.: 15 year re-analysis of the urban climate of Amsterdam using WRF , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11560, https://doi.org/10.5194/egusphere-egu2020-11560, 2020.

Urban canopy layer (UCL) is generally considered in numerical study of urban meteorology. The weather research and forecasting Model (WRF) coupled with urban canopy layer scheme is used to simulate a heavy rainfall case in Beijing. Comparative analysis is applied for the case between coupled simulation and non coupled simulation and therefore exhibits the effect of the UCL on the rainfall. Sensitive experiments are performed to investigate anthropogenic heat source and urban area extension to affect the precipitation. The results show that the coupled UCL model has captured the rainfall characteristics at the regional scale. The coupled simulation has improved accuracy of the rainfall area, the peak value and the rainfall duration compared to the non coupled simulation. The main effect achieves as longer duriation of the ascending motions and enhancement of the layers unstabilities. Although the intensity of the vertical motion has a little reduction, the time of the motion has increased 2 hours in a day. Sensitive experiments present an obvious influence on precipitation intensity, precipitation centralization and heat island effect. The precipitation center moves toward the urban center, the accumulated rainfall increases 78.5 mm and the center moves by distance 13 km when anthropogenic heat source is perturbed to double. Urban area extension induces increase of the precipitation area and intensity due to high humidity and ascending motion. The experment also reveals shift of the island heat effect.

How to cite: ma, M.: Influence of Urban Canopy Layer on a heavy rainfall over Beijing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12190, https://doi.org/10.5194/egusphere-egu2020-12190, 2020.

The Building Effect Parameterization + Building Energy Model (BEP+BEM) with a detailed urban parameterization coupled with the Weather Research and Forecasting (WRF) model is used to simulate the summertime local circulation in the Houston, Texas metropolitan area. Six numerical model simulations at 3km horizontal resolutions (within the nested parent domain of 9km) are performed using land use data representative of 2010, and 2100.They include:

(a) Control Simulation (with 2010 land use with current and future climate)

(b) same as (a) but with less aggressive urban expansion

(c) same as (a) but with more aggressive urban expansion

For future climate simulation, CCSM4 data (RCP8.5 scenario) were used to generate the climate perturbation, which was then applied to the current forcing data (NCEP final analyses) used for the numerical model simulations. Validation is based on comparison between model simulations and observations and it shows reasonably good model performance. Numerical simulations show an important interaction between the sea breeze and the urban heat island (UHI) circulation. The UHI forms a strong convergence zone in the center of the city and accelerates the sea-breeze front toward it. This phenomenon raises several questions.  (1) With urban expansion, how is the sea breeze penetration modified?  What is its impact on energy consumption in the city during the summer season, (2) After the dissipation of the UHI, how does the penetration of sea breeze change?  (3) How is the speed of the sea breeze modified with climate change and/or urban expansion? We will discuss our approach and present our results that help answer these questions.

How to cite: Tewari, M., Singh, J., Ray, P., Georgescu, M., Salamanca, F., and Treinish, L.: Impact of urban expansion and warming climate on sea-breeze circulations: A numerical study in the Greater Houston Metropolitan Area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12480, https://doi.org/10.5194/egusphere-egu2020-12480, 2020.

Here we verify an off-line urban building energy model (CM-BEM) against ‘observed’ anthropogenic heat and electricity consumption at Tokyo (Yoyogi) residential area. Anthropogenic heat (Q_F) due to electricity air-conditioning (AC) use (Q_{F, AC}) is estimated by continuous simultaneous observations of atmospheric O₂, CO₂ and turbulent CO₂ and heat fluxes. Here we explain the outline of how to estimate Q_{F, AC}. (1) The O₂:CO₂ exchange ratio (oxidation ratio, OR) is used for the partitioning of CO₂ into emissions from gas fuels and gasoline (see detail in Ishidoya et al. 2020), which allow estimating Q_F from gas fuels and gasoline (Q_{F, gas} and Q_{F, traffic}), respectively. (2) Total Q_F is estimated by turbulent heat fluxes and net radiation observations using a heat balance equation within the constant flux layer. Finally (3) the Q_{F, AC} is estimated by ‘Total Q_F – (Q_{F, gas} + Q_{F, traffic})’. This estimation allows verifying directly simulated Q_{F, AC} by the CM-BEM. Our aim is an improvement of the CM-BEM to develop more realistic Q_F and CO₂ inventory data. Here we compare simulated Q_{F, AC}, electricity consumption, and turbulent heat fluxes against observations during winter (Jan-Feb 2017) and summer (July-Aug 2018) seasons at Tokyo. Our results will be reported at the conference.

Ref.

Ishidoya et al. 2020: Consumption of atmospheric O₂ in an urban area of Tokyo, Japan derived from continuous observations of O₂ and CO₂ concentrations and CO₂ flux. Atmospheric Chemistry and Physics Discussions. under review.

How to cite: Takane, Y., Nakajima, K., Kikegawa, Y., Sugawara, H., Ishidoya, S., Terao, Y., Yamaguchi, K., Kaneyasu, N., and Hara, M.: Off-line urban building energy model reproducibility against ‘observed’ anthropogenic heat and electricity consumption, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12496, https://doi.org/10.5194/egusphere-egu2020-12496, 2020.

Wind speed modeling on microscale can be important not only for local authorities but also for citizens.  Due to the heterogeneity of urban development in the Moscow region, wind gusts geography and thermal comfort conditions at different points in the same territory will differ noticeably with the same meteorological parameters. Thus, it is necessary to study such parameters  at the microscale. Therefore, within the framework of this study, in order to inform the public about the negative impact of the weather, and further to minimize the consequences on the human body, an attempt was made to develop an operational system for predicting dangerous conditions  of wind gusts and  thermal comfort.

In order to collect climate statistics, climate data were calculated for comfort conditions for the MSU campus using the RayMan model. Wind gusts modeling was performed using ENVI-MET model.   Therefore, it is possible to analyze the changes in biometric conditions and wind speed in recent years and track trends in various locations.

Since the input parameters for the RayMan diagnostic model, which processes only text documents, serve as predictive data for the Canadian GEM global meteorological parameters in grib2 format, a program for converting files using Command.exe and Fortran-90 language allowed us to create an online module for predicting biometric indices (UTCI, PET and mPET).

For the convenience of perception of information, the results of calculations are visualized on the basis of Yandex maps.

Research was supported by the grant program of Russian Foundation of Basic Research (project no. 19-35-70009 mol_a_mos ). The work of Pavel Konstantinov, Elizaveta Nikolaeva and Sergey Bukin was supported by Russian Science Foundation (project no. 19-77-30012)

How to cite: Konstantinov, P., Perkhurova, A., Nikolaeva, E., Bukin, S., and Varentsov, M.: Real-time modelling of dangerous wind speed gusts and thermal comfort conditions in campus of Moscow State University (Moscow, Russian Federation), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12780, https://doi.org/10.5194/egusphere-egu2020-12780, 2020.

Urban parks can effectively mitigate the urban heat island (UHI) effect. Many studies have investigated the relationship between the shape, size, interior components and cooling effect of the park, little attention have been given to explore the relationship between land surface temperature (LST) of central park and buildings in the neighboring areas. This study has explored the effect of the neighboring building on LST of central park, taking Beijing as the study area. The results showed that the cold island footprint of the park in summer was larger than that in winter (with an average area of 0.15 km² larger). The components of building in cold island footprint of the park were dominated by middle-rese building (MRB). LSI of MRB and AREA_SD of LMB were identified as the key explanatory variables in summer and winter, respectively, which could explained 16.8% and 13.9% of the variance in the park’s LST. This study could extend scientific understanding of the effect of building on park’s LST, and could provide guidance to urban planners on how to mitigate the UHI effects through the rational allocation of buildings.

How to cite: Han, D., Yang, X., Cai, H., Xu, X., Qiao, Z., and An, H.: Exploring the effect of neighboring building on land surface temperature of central park, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13117, https://doi.org/10.5194/egusphere-egu2020-13117, 2020.

The Landsat 8 satellites retrieve land surface temperature (LST) values at 30-m spatial resolution since 2013, but the urban climate studies frequently use a limited number of images due to the problems related to missing data over the area of interest. This paper proposes a procedure for building a long-term LST data set in an urban area using the high-resolution Landsat 8 imagery. The methodology is demonstrated on 94 images available through 2013-2018 over Bucharest (Romania). The raw images contain between 1.1% and 58.4% missing data. Based on an Empirical Orthogonal Filling (EOF) procedure, the LST missing values were reconstructed by means of the function dineof implemented in sinkr R packages. The output was used for exploring the LST climatology in the area of interest. The gap filling procedure was validated by comparing artificial gaps created in the real data sets. At the best of our knowledge, this is the first study using full spatial coverage high resolution remote sensing data for investigating the urban climate. The validation pursued the comparison between LST and Ta at 3 WMO stations monitoring the climate of Bucharest, and returned strong correlation coefficients (R2 > 0.9). Further research may be envisaged aiming to update the data set with more recent LST information and to combine data from various sources in order to build a more robust urban LST climatology.

This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI -
UEFISCDI, project number COFUND-SUSCROP-SUSCAP-2, within PNCDI III.

How to cite: Cheval, S., Dumitrescu, A., and Amihăesei, V.: High resolution LST climatology in an urban area using Landsat 8 thermal data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13555, https://doi.org/10.5194/egusphere-egu2020-13555, 2020.

Typical Meteorological Year (TMY) datasets are widely used in building energy design simulations to assess needs (cooling/heat). Currently, TMY data used are representative of the past climate (from observations) of the region and generally do not account for urban climate or building-city interactions. Here we use an urban land surface model, SUEWS (Surface Urban Energy and Water Balance Scheme) driven by ERA5 reanalysis data to bridge this gap.

Using 0.25 ° large-scale ERA5 reanalysis data (1979–2018) with SUEWS we generate an urbanised TMY (uTMY) dataset for Changsha, a city with more than 4.4 million residents in the hot-summer-cold-winter region of China, to demonstrate the proposed workflow. The SUEWS simulation are evaluated at the Leifeng site (WMO code 57687) for 2016.

Through comparison of DOE EnergyPlus simulations, we also assess the impact on design building energy consumption using uTMY and cTMY (conventional TMY) data. The building design energy needs evaluation is for a common Chinese apartment building. This should allow for more spatially explicit building design, and hence more sustainable.

How to cite: Sun, T., Tang, Y., Xiong, J., Omidvar, H., and Grimmond, S.: Urbanisation of weather data lead for more sustainable building design: urban land surface model used to generate Typical Meteorological Year (TMY) datasets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15069, https://doi.org/10.5194/egusphere-egu2020-15069, 2020.

Large cities and urban regions are highly sensitive to impacts caused by extreme events, e.g. heavy rainfall, since they cause fatalities and economic damages. Moreover, due to regional consequences of global climate change, problems caused by hazardous atmospheric events are expected to intensify in future. Thus adequate adaptation planning of urban infrastructure not only requires further research on potential impacts under changing precipitation patterns, but also practical feasibility for end users like insurances or fire brigades.

According to this we relate heavy precipitation events over Berlin to the available data on time and location of the respective fire brigade operations, within the research program “Urban Climate Under Change” ([UC]²) funded by the BMBF. For this purpose multiple data sets like station, radar and model  based data with a high temporal resolution will be used.  Thus an improved assessment of the spatial and temporal evolution of severe precipitation events can be made,  which is consequently also of aid in the investigation of a connection to related impacts in the urban area.

How to cite: Pasternack, A., Langer, I., Rust, H., and Ulbrich, U.: Utilization of fire brigade data in the impact analysis of extreme precipitation events over Berlin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17934, https://doi.org/10.5194/egusphere-egu2020-17934, 2020.

Urban Heat Island (UHI), a phenomenon characterized by significantly higher air and land surface temperatures (LSTs) in urban areas than in suburban areas, results in land use change from non-urban to urban land and is accompanied by increases in anthropogenic heat release. A variety of land use contribution indexes have been proposed to quantitatively calculate the impact of land use types on UHI. However, these indexes can only show the impact of specific land use types on UHI. In fact, the area and the intensity (which also can be considered as the average temperature) of land use change jointly determine the regional UHI. The purpose of this paper is to develop an algorithm to quantitatively reveal the influence of the area and the intensity of land use change on regional UHI. MODIS LST products and 1:1,000,000 land use data sets were used to quantitatively calculate the seasonal and interannual contributions of land use change on regional UHI between 2005 and 2018 in China. These results have theoretical and practical significance for further understanding the formation mechanism of urban thermal environment and its mitigation measures.

How to cite: Qiao, Z., Liu, L., Han, D., Sun, Z., and Xu, X.: Quantifying the contribution of land use change to the surface urban heat island in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18702, https://doi.org/10.5194/egusphere-egu2020-18702, 2020.

As part of the research programme "Urban Climate Under Change” [UC²] the project “Strategies for Reduction of Critical Urban Climate Load Situations in Augsburg” (MIKA) focuses on the application of the LES model PALM-4U to the medium-sized city of Augsburg, Southern Germany. The main objectives of the project include the model evaluation with special emphasis on three-dimensional observations of the urban boundary layer with unmanned aircraft systems but also utilizing ground-based long-term observations of multiple meteorological and air-quality variables. Furthermore, factors and mechanisms influencing the spatio-temporal evolution of situations with critical thermal load as well as high particulate matter concentrations within the city are investigated. Finally, the development, simulation and evaluation of short- and long-term strategies for minimization of these critical situations is another aim, carried out in cooperation with the city administration of Augsburg. Possible side-effects of these measures, e.g. remote effects in the surroundings of the city, are studied.

First model runs with PALM-4U for a test domain within the city of Augsburg have been carried out and are presented and discussed.

How to cite: Straub, A., Beck, C., and Philipp, A.: Simulation of Critical Urban Climate Load Situations in Augsburg, Southern Germany, using PALM-4U, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18723, https://doi.org/10.5194/egusphere-egu2020-18723, 2020.

The Urban Wind Island (UWI), a small but persistent positive wind anomaly over the city as a whole, has previously been revealed using a simplified conceptual model of the convective atmospheric boundary layer. However, the urban boundary layer is strongly heterogeneous and complex, and many interactions with surrounding land-use are not taken into account with the conceptual model used. Additionally, the transition to a stable or neutral nocturnal boundary layer substantially influences wind speed, for instance leading to nocturnal jets, which could also lead to UWI formation. This study extends the UWI research into less idealised cases by using the 3D WRF mesoscale model for Amsterdam (the Netherlands) and its surroundings, at 500m resolution. Two summers of forecast results for in total 173 days are used to identify whether the UWI persists in a 3-dimensional modelling environment, and which conditions are optimal for its formation and persistence. In order to focus only on wind modified by surface processes, large-scale influences which modify wind speed, such as frontal passages, are identified and eliminated from the dataset. We find that a positive UWI is present roughly half the time, with an order of magnitude that is similar to the previous work (~ 0.5 m/s). In addition we find an evening UWI that is caused by the delayed onset of the transition from an unstable to a stable or a neutral boundary layer in the urban area, while the rural area is already stable and calm.

How to cite: Droste, A., Steeneveld, G.-J., Holtslag, B., and Wouters, H.: The urban wind island from a three-dimensional perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19457, https://doi.org/10.5194/egusphere-egu2020-19457, 2020.

We welcome participants in the new project to evaluate land surface models (LSMs) in urban areas at multiple sites. Urban-PLUMBER will evaluate both specialised urban parameterisations and general LSMs typically used in weather/climate simulations. Assessment will be offline (uncoupled with an atmosphere model), with driving meteorology and general site characteristics provided at the neighbourhood scale.

The project builds upon the PLUMBER project (PALS Land sUrface Model Benchmarking Evaluation pRoject) by assessing models using simple benchmarks as well as error metrics. The PLUMBER experience indicates benchmarking can reveal where LSMs are not utilising available information effectively, helping focus future model development.

The project’s two phases are: 1) initial evaluation at one suburban site and 2) evaluation across multiple sites with varying degrees urbanised and vegetation/pervious fractions. The project will establish where on the urbanised/vegetated continuum models are more skilful, and assess the progress made in modelling urban areas over the last decade since the last major offline urban model comparison project (PILPS-Urban).

We expect the project to benefit both participating modelling groups and improve understanding of modelling urban areas as a whole. Contact us to get involved.

How to cite: Lipson, M. J., Grimmond, S., Best, M. J., Abramowitz, G., Pitman, A. J., and Ward, H. C.: Urban-PLUMBER: A new evaluation and benchmarking project for land surface models in urban areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20987, https://doi.org/10.5194/egusphere-egu2020-20987, 2020.

As urban populations increase, urban heat island effect is enhanced and urban heat stress and air pollutant concentrations increase. Sensitivity experiments of changing the albedo, emissivity, and heat capacity of urban facets can provide information to mitigate the heat island effect and allow the model to study urban climate more accurately. Experiments on sensitivity of the surface energy balance of albedo, emissivity and heat capacity in the metropolitan area of ​​Seoul were conducted using Met-Office-Reading Urban Surface Exchange Scheme (MORUSES) of Unified Model Local Data Assimilation and Prediction (UM LDAPS) model. The analysis period is a heat wave period from July 15 to 21, 2018, which is a clear day without cloud and precipitation. Comparing 1.5-m temperature of AWS data, it overestimated about 0.5-2K in the model. If the albedo decreases, the net radiation, storage heat, sensible heat and ground heat fluxes increase after sunrise. Storage heat becomes negative in the afternoon, and sensible heat is positive during the night. When the albedo decreases, the air temperature increases. As the emission rate decreases, the air temperature increases as storage heat decreases and sensible, latent and geothermal heat increases, which is more intense at night than during the day. When heat capacity decreases, sensible and ground heat increase during the day, storage heat decreases, and vice versa at night. Air temperature increases during midday when solar radiation is strong and decreases elsewhere. Considering that the LDAPS-MORUSES model underestimates the air temperature, albedo and emission rates can be reduced to achieve more accuracy.

Acknowledgement: This research was supported by the Korea Meteorological Administration’s National Institute of Meteorological Sciences "Development of Biomechanical Meteorological Technology" (1365003004).

How to cite: Moon, B.-K., Hong, S.-O., Byon, J.-Y., Ha, J.-C., and Wie, J.: Sensitivity study of urban energy balance to albedo, emissivity and heat capacity in Seoul Metropolitan Area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20995, https://doi.org/10.5194/egusphere-egu2020-20995, 2020.

As citizens face increasing heat risk due to climate change with urban heat island effect, heat risk assessments in urban have been conducted focusing on thermal diseases related to heatwave of vulnerable people. Although they provided a basis to establish adaptation strategies such as cooling centers, they could not consider citizens’ daily thermal comfort of diverse groups. Thermal comfort could be a part of heat risk because associated with work performance such as productive capacity as well as health. In particular, pedestrians’ thermal comfort can represent daily heat risk of outdoor urban environment. The past studies of pedestrians’ thermal comfort were evaluated using PMV (Predicted Mean Vote), an index based on temperature, wind velocity, relative humidity and a fixed number of metabolic rate depending on the subject’s activity level. The PMV ranges from -3 to +3 and higher value indicates higher discomfortable. Including metabolic factor, PMV did not actually consider an individuals’ physiological response (IPR) such as heart rate, skin temperature, etc. To overcome PMV’s limitation, IPR should be considered together with climatic factors when assessing pedestrians’ thermal comfort. Therefore, we aim to develop a new function of thermal comfort by incorporating PMV and IPR, especially heart rate, with validation using personal perception of thermal comfort based on survey. We selected a route of 500m length in Suwon, South Korea and 9 volunteer pedestrians walked the selected route 8 times at 2-4 pm. The walk experiment was repeated for 4 days. During the experiment, air temperature, relative humidity, and wind velocity were monitored using portable meteorological sensors. The real-time heart rate of each pedestrian was recorded using wearable sensor (Mi-band3). After every day walk, we asked each pedestrian 10 questions regarding satisfaction of thermal environment, perceived temperature, etc. The average value of PMV was 2.99 belonging to very discomfort category. Although heart rate increased with the length of exposure time to heat, the heart rate over time did not consistently increase with air temperature. It was probably because our temperature range (31.9℃- 35.2℃) during the experiment was not large enough and heart rate was influenced by other factors such as wind velocity. In the survey, 50% of volunteer pedestrians responded ‘discomfort’ and the others answered ‘slightly discomfort’. Comparing the survey (discomfort and slightly discomfort) with PMV (very discomfort), PMV generally overestimated. thermal comfort. We will categorize thermal comfort level according to heart rate increase between walking activity in outdoor and indoor. Here, the higher heart rate increase than average increase level indicates worse individual thermal comfort condition. This individual thermal comfort effect can modify the existing calculation of thermal comfort using air temperature, wind velocity, and humidity by adding modification factor of individual heart rate response (Ex. Thermal comfort=weighting factor(0.189*air temperature-0.775*wind velocity+0.195*relative humidity)). The final thermal comfort will be calculated based on the function and examined the precision of function through comparative analysis with the personal thermal perception of survey. As heart rate is an individual variable, we expect our function can be a tool evaluating the personalized heat risk.

How to cite: Kim, A. and Yoo, G.: Urban heat risk assessment for pedestrians considering thermal environment and physiological change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21615, https://doi.org/10.5194/egusphere-egu2020-21615, 2020.