AS2.2 | Urban Boundary Layer Dynamics Across Scales
EDI
Urban Boundary Layer Dynamics Across Scales
Co-organized by CL2/ERE2/NP6
Convener: Aldo BrandiECSECS | Co-conveners: Andrea ZonatoECSECS, Beatriz SanchezECSECS, Francisco Salamanca, Alberto Martilli
Orals
| Mon, 15 Apr, 14:00–15:45 (CEST)
 
Room 1.85/86
Posters on site
| Attendance Tue, 16 Apr, 10:45–12:30 (CEST) | Display Tue, 16 Apr, 08:30–12:30
 
Hall X5
Orals |
Mon, 14:00
Tue, 10:45
Urban Boundary Layer (UBL) Dynamics is determined by city morphology, latent and sensible heat fluxes (including anthropogenic heat), and interactions with rural surroundings. The physical processes in such UBLs are characterized by great strong spatial and temporal heterogeneity, and have the potential to affect societally relevant issues like human thermal comfort, air quality, aviation operations and energy supply.
The goal of this session is to highlight research work and promote discussions on this often underrepresented aspect of urban meteorology and climatology. Hence, we invite and encourage contributions on the following topics:

- Numerical modeling of urban boundary layer dynamics at all scales (from regional to street level)
- Observational methods in the UBL: field campaigns and remote sensing (e.g., flux towers, LIDAR, drones)
- Wind tunnel experiments
- Interaction between local circulations (e.g., UHIC, thermal circulation in complex terrain, sea/lake breeze) and the built environment
- Role of turbulent fluxes and impact of turbulence on wind flow
- Intra-canopy and canyon ventilation
- Impact of urban vegetation (e.g., street trees) on wind flow
- Urban air quality (e.g., pollutant transport and dispersion)
- Urban wind energy potential

Session assets

Orals: Mon, 15 Apr | Room 1.85/86

Chairpersons: Beatriz Sanchez, Andrea Zonato, Aldo Brandi
14:00–14:05
14:05–14:15
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EGU24-5608
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AS2.2
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ECS
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On-site presentation
Juan Carbone, Beatriz Sánchez, Carlos Román-Cascón, Alberto Martilli, Dominic Royé, and Carlos Yagüe

The proportion of the world’s population living in cities has increased from 37% to 56% over the last 50 years, and it is expected to continue rising further to 60% by 2030 (UN, 2022). As an essential effect of this evolution, urban land cover has expanded rapidly. In the case of Madrid, the increase in urban fraction during the period from 1970 to 2020 has been 20%. It is well known that urbanization reduces the vegetated cover and modifies surfaces properties altering the surface-atmosphere interactions and the different terms of the Surface Energy Balnace (SEB) compared to nearby rural areas. Therefore, analyzing the influence of these changes in urban land cover contributes to understand the potential risks that urban residents might face considering the urban grown and the expected temperatures increases, as this has adverse impacts on human health, livelihoods, and key urban infrastructure.

The aim of the present study is to examine the consequence of Madrid's urban growth on the near-surface air temperature and on the SEB. We conduct a modeling study using WRF-ARW with the multilayer urban parameterization BEP-BEM, in which the land use and the land cover have been modified according to urban expansion in Madrid and its surroundings from 1970 to 2020. Two scenarios of common meteorological conditions of special interest are selected for this study: a period of intense heatwave during the summer season and a short period of strongly stable atmospheric conditions in winter, both observed in 2020. The results show that in areas where the urban fraction become greater an increase in near-surface air temperature is found for both simulated periods, especially during the night, pointing out that the cooling rate decreases in urban areas. The growing of urban land cover over time also modifies the SEB and turbulent transport in Madrid and surroundings, leading to an increase in temperatures, specially for the minima ones.

How to cite: Carbone, J., Sánchez, B., Román-Cascón, C., Martilli, A., Royé, D., and Yagüe, C.: Impacts of urban development on the local weather: A comprehensive analysis from 1970 to 2020 in Madrid., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5608, https://doi.org/10.5194/egusphere-egu24-5608, 2024.

14:15–14:25
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EGU24-17845
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AS2.2
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On-site presentation
Francesco De Martin, Andrea Zonato, and Silvana Di Sabatino

It is well known that cities can modify the rainfall distributions, in particular deep moist convection is more frequently triggered over and downwind urban areas. However, the effect of cities on the most extreme convective events, such as hailstorms, downbursts or tornadoes, is poorly studied. This topic needs further investigation since exposure and vulnerability to severe storm risk is larger in cities than in the surrounding rural area. What happens if a severe convective windstorm impacts a big city? Is the storm modified by the urban land use?

Our analysis focuses on a case study that occurred on 25 July 2023, when a nocturnal downburst affected the city of Milan, in northern Italy, with measured wind gusts up to 30 m/s. The intense wind gusts downed many trees in the public parks and over the streets, blocking urban mobility. The event is investigated in depth using both observations and high-resolution numerical simulations performed with the WRF model.

Observations show that a UHI over Milan before the storm was negligible, while there was a drier air mass over the city than over the surrounding rural area. Consequently, a pool with low values of equivalent potential temperature (theta-e), a quantity that strongly influences deep moist convection, was present over the city.

Four nested WRF simulations are carried out with grid resolution from 9 km up to 333 m, and 64 vertical levels starting from 5m AGL. Two different boundary layer parametrizations are tested, namely MYJ and BouLac schemes, as well as two different microphysics schemes: Thompson and WRF Single-moment 6-class. Moreover, simulations with bulk urban parametrizations are compared with those coupled with the building effect parameterization and the building energy model (BEP-BEM), employing data of the World Urban Database and Access Portal Tools (WUDAPT).  Simulations without the urban land use (no-urban) are carried out to test the effect of the Milan urban area on the convective storm. Results of all these simulations are compared with surface observations and radar data. The simulations have a similar skill, with slightly better results using the BouLac scheme coupled with BEP-BEM. Simulations using urban parametrizations are able to reproduce the pre-storm pool with low theta-e values over Milan, while no-urban simulations do not simulate the low theta-e pool.

All WRF simulations accurately reproduce the violent windstorm, both in terms of simulated wind gusts, rainfalls and radar reflectivity. Removing the city, stronger wind gusts are simulated at the surface due to the significantly reduced drag. However, rainfalls are slightly intensified downwind of the city, as well as the drop of potential temperatures associated with the downdrafts.

In conclusion, the urban canopy may have prevented the development of even more violent wind gusts in the city, due to the increased surface roughness. On the other hand, despite the presence of a pool of low theta-e values, the storm likely intensified downwind the city. A possible motivation to that intensification will be proposed in the presentation. 

How to cite: De Martin, F., Zonato, A., and Di Sabatino, S.: Can a city modify a severe convective windstorm?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17845, https://doi.org/10.5194/egusphere-egu24-17845, 2024.

14:25–14:35
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EGU24-16420
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AS2.2
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On-site presentation
Keisuke Nakao, Hideki Kikumoto, Hiroshi Takimoto, Jia Hongyuan, and Wang Xiang

 The horizontal mean wind speed profile in vertical direction within and above urban canopy (UC) is an essential information to drive the exchange of momentum, heat, moisture and pollutants in atmosphere. Well-known profiles in logarithmic and exponential layers, which express upper and lower wind over UC, respectively, are efficient assumptions used to express UC wind profile.

 This study attempted to add the intermediate layer (IL) between those two-layers to include the effect of building height variability on the mean wind speed profile. Large-eddy simulations (LESs) of UC with building height variability were conducted using a wide range of morphology parameters, that is, plan area index, aspect ratio, and the standard deviation of building height.

 A tendency of the bulk drag coefficient of the IL was expressed by the plan area index and the frontal area index at the intermediate layer. The wind speed at IL was modeled linearly by the length- and velocity-scale analysis. By parameterizing the coefficients of these three layers, we attempted to analytically represent an entire wind speed profile by the three-layer wind profiles. The results indicated reasonable consistency in the wind speeds at mean building height and the momentum flux with LES data. Effect of the thermal stratification was investigated by the correction of the length-scale in IL.

How to cite: Nakao, K., Kikumoto, H., Takimoto, H., Hongyuan, J., and Xiang, W.: Representing mean wind speed profile over urban canopy with building height variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16420, https://doi.org/10.5194/egusphere-egu24-16420, 2024.

14:35–14:45
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EGU24-6308
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AS2.2
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ECS
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On-site presentation
Gianluca Pappaccogli, Andrea Zonato, Alberto Martilli, Riccardo Buccolieri, and Piero Lionello

As climate change continues to exert an impact on urban areas, the comprehension of its effects on the urban environment becomes crucial for sustainable urban planning. This study presents a novel approach employing the Building Effect Parameterization (BEP) coupled with a Building Energy Model (BEM) in an offline configuration to simulate urban climates. The multi-layer BEP+BEM model, properly describes the vertical arrangement of urban fabric, accounting for the distribution of heat, moisture, and momentum sources throughout the urban canopy layer. Additionally, energy consumption within buildings for both cooling and heating is estimated by the BEM, providing a comprehensive perspective on the urban energy balance. Coupled with a 1-D column model of urban canopy flow, the BEP+BEM offline model accurately estimates drag coefficients and turbulent length scales based on urban fabric characteristics. In the proposed version, the model has been extended to consider additional factors such as green areas and street trees, along with existing green roofs, photovoltaic panels and the permeability of urban materials. This expansion enhances the model's capability to assess the effectiveness of sustainable infrastructure in mitigating climate change effects on urban areas. In this study, the BEP+BEM scheme is forced by data from climate projections, allowing for the dynamic representation of various Local Climate Zones (LCZs) under distinct climatic conditions. Simulations in different LCZs and under different climatic conditions are compared to evaluate the impact of climate change on urban environment, enabling the exploration of how different urban areas respond to changing meteorological forcings. The sensitivity analysis includes a range of standard urban typologies (i.e. LCZs), capturing the complexity of interactions between the built environment and the atmosphere. This approach offers an assessment of the impacts of climate change on key urban phenomena, such as urban heat islands (UHI), thermal discomfort, and heightened energy consumption by buildings. The outcomes of this study provide valuable insights for the urban climate community, policymakers, and researchers with the aim of enhancing the resilience of cities in the face of a changing climate. By bridging the gap between climate projections and urban climate simulations, a consistent framework is presented in this work for evaluating and adapting various urban environments to future climatic conditions.

How to cite: Pappaccogli, G., Zonato, A., Martilli, A., Buccolieri, R., and Lionello, P.: The Implementation of the BEP+BEM Offline Parameterization Scheme: Exploring Urban Dynamics through Climatic Projections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6308, https://doi.org/10.5194/egusphere-egu24-6308, 2024.

14:45–14:55
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EGU24-4829
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AS2.2
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ECS
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Virtual presentation
Jiachen Lu, Negin Nazarian, Melissa Hart, and Scott Krayenhoff

In recent years, urban canopy models (UCMs) have been used as fully coupled components of mesoscale atmospheric models as well as offline tools to estimate temperature and surface fluxes using atmospheric forcings. Examples include multi-layer urban canopy models (MLUCMs), where the vertical variability of turbulent fluxes is calculated by solving prognostic momentum and turbulent kinetic energy (TKE, $k$) equations using length scale ($l$) and drag parameterizations. These parameterizations are based on the well-established 1.5-order $k-l$ turbulence closure theory and are often informed by microscale fluid dynamics simulations. However, this approach can include simplifications such as the assumption of the same diffusion coefficient for momentum, TKE, and scalars. In addition, the dispersive stresses arising from spatially-averaged flow properties have been parameterized together with the turbulent fluxes while being controlled by different mechanisms. Both of these assumptions impact the quantification of turbulent exchange of flow properties and subsequent air temperature prediction in urban canopies. To assess these assumptions and improve corresponding parameterization, we conducted 49 large-eddy simulations (LES) for idealized urban arrays, encompassing variable building height distributions and a comprehensive range of urban densities ($\lambda_p\in[0.0625,0.64]$) seen in global cities. We find that the efficiency of turbulent transport (numerically described via diffusion coefficients) is similar for scalars and momentum but 3.5 times higher for TKE. Additionally, the parameterization of the dispersive momentum flux using the $k-l$ closure was a source of error, while scaling with the pressure gradient and urban morphological parameters appears more appropriate. In response to these findings, we propose two changes to MLUCM v2.0: (a) separate characterization for turbulent diffusion coefficient for momentum and TKE; and (b) introduction of an explicit physics-based "mass flux" term to represent the non-Gaussian component of the dispersive momentum transport as an amendment to the existing "eddy diffusivity" framework. The updated one-dimensional model, after being tuned for building height variability, is further compared against the original LES results and demonstrates improved performance in predicting vertical turbulent exchange in urban canopies.

How to cite: Lu, J., Nazarian, N., Hart, M., and Krayenhoff, S.: A one-dimensional urban flow model with an Eddy-diffusivity Mass-flux (EDMF) scheme and refined turbulent transport (MLUCM v3.0), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4829, https://doi.org/10.5194/egusphere-egu24-4829, 2024.

14:55–15:05
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EGU24-18319
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AS2.2
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ECS
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On-site presentation
Annika Vittoria Del Ponte, Sofia Fellini, Massimo Marro, Pietro Salizzoni, and Luca Ridolfi

Inserting vegetation within the urban environment mitigates the urban heat island effect, the flooding risk, and improves air quality. However, its aerodynamic effect has remarkable impact on the pollutant transport and, consequently, on human health comfort. Indeed, the presence of vegetation within an urban canyon leads to non-trivial patterns of pollutant concentration and mass fluxes, as a consequence of complex mean and turbulent velocity fields. In addition to the vegetation density, the flow structure within canyons is influenced by their geometry and by the wind direction.

   The aim of the present study is to experimentally investigate the velocity field within a canyon, varying the vegetation density and the wind direction. We measured flow velocity statistics within an indefinitely long street canyon, with unit height-to-width ratio, subject to a neutrally stratified boundary layer modeled in the wind tunnel of École Centrale de Lyon. The aerodynamic impact of vegetation was reproduced by inserting plastic miniatures of trees along the two long sides of the canyon. We considered an empty canyon and a vegetated canyon, whose longitudinal axes are oriented with angles of 0°, 30°, and 60° with respect to the external wind flow.

  Results reveal that when the canyon is inclined with respect to the external wind direction the mean flow follows a complex helicoidal structure. The presence of trees decreases significantly the mean longitudinal velocity and weakens the transversal circulation in the inclined canyon. The dampening effect of the mean longitudinal flow is more marked increasing the inclination angle of the canyon. Turbulent fluctuations are enhanced above the tree crowns, mostly when the wind blows parallel to the canyon axis. On the contrary, turbulent fluctuations decreases at tree trunk and crown levels, in particular when the canyon is inclined of 60° with respect to the external wind direction. Spectra of the velocity signal show that the presence of trees induces an evident shift of the energy peak towards high frequencies.

  The collected data constitute a step forward to understand and modeling the urban microclimate.

How to cite: Del Ponte, A. V., Fellini, S., Marro, M., Salizzoni, P., and Ridolfi, L.: Wind tunnel study on the influence of vegetation density and wind direction on urban canyon ventilation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18319, https://doi.org/10.5194/egusphere-egu24-18319, 2024.

15:05–15:15
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EGU24-4289
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AS2.2
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ECS
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On-site presentation
Qilong Zhong, Jiyun Song, Xiaoxue Wang, and Yuguo Li

Recent years have seen more intense and frequent heatwaves across the globe. Urban overheating phenomenon induced by global warming and urban heat island (UHI) effect has adverse impact on human health. In particular, compact high-rise cities witnessed worsened wind environment, exacerbating the UHI phenomenon. Blue space such as urban lakes may help mitigate the UHI effect and improve citizens’ living environment. Under weak synoptic wind conditions, the temperature difference between built-up areas and lakes can induce wind circulation, known as lake-breeze circulation (LBC). The LBC system can transport cool and fresh air from lake surfaces into built-up areas, reducing urban air temperature and improving urban wind environment, while increasing urban air humidity. In this study, we developed a multi-scale water-energy coupled CFD model to simulate the transport processes of heat and moisture between lake surfaces and built-up areas within the urban boundary layer. The model adopted a porous turbulence model to simulate the entire urban canopy layer, a lake evaporation model and a species transport model to simulate lake dynamics, and a coordinate transformation method to simulate the effect of the background atmosphere. The model features the capability of resolving dynamics of atmospheric temperature, humidity, and wind at both street canyon scale (1 m) and city scale (50 km) with relatively low computational costs. Based on this model, we conducted sensitivity analysis to investigate the impact of urban parameters (e.g., city scale, building height and density, anthropogenic activities) and lake parameters (e.g., lake scale and lake surface temperature) on the spatial variation of temperature, humidity, wind, and thermal comfort index. Our results can provide significant references for urban planning and city design for sake of UHI mitigation.

How to cite: Zhong, Q., Song, J., Wang, X., and Li, Y.: Modelling of urban lake breeze circulation: the implications on urban heat island mitigation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4289, https://doi.org/10.5194/egusphere-egu24-4289, 2024.

15:15–15:25
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EGU24-7011
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AS2.2
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Virtual presentation
Negin Nazarian, Jiachen Lu, Melissa Hart, and E. Scott Krayenhoff

The urban canopy layer (UCL) is characterized by a heterogeneous flow pattern that responds to heterogeneous urban geometries. The varying heights and layouts of buildings play a pivotal role in shaping this spatial variability, as they block, divert, and slow wind and determine the exchange of momentum and energy above the urban canopy. When representing these complex dynamics, however, research has conventionally relied on microscale simulations conducted over limited (often idealized) building arrays. Extending the findings to realistic urban neighborhoods and urban parameterizations presents a clear limitation, as evidenced by discrepancies in multi-model comparisons with observational data in cities.

More extensive datasets of urban airflow are needed to cover a range of realistic urban neighborhoods and provide a more holistic analysis of turbulent flow in different urban characteristics. Responding to this gap in the field, we developed a historically extensive and comprehensive dataset of Urban Turbulent Airflow based on state-of-the-art  Large Eddy Simulations (UrbanTALES). The dataset includes 400 urban layouts with both idealized and realistic configurations. Realistic urban neighborhoods were obtained from major cities worldwide, incorporating variations in plan area densities [0.0625-0.64] and height distributions [4-70m]. Idealized urban arrays, on the other hand, include two commonly studied configurations (aligned and staggered arrays), featuring both uniform and variable height scenarios along with oblique wind directions. 

UrbanTALES offers canopy-averaged data as well as 2D and 3D flow fields tailored for different applications in urban climate research. The dataset provides time-averaged wind flow properties, as well as second- and third-order flow moments that are critical for understanding turbulent processes in the UCL. Here, we describe the UrbanTALES dataset and its application, noting the unique opportunity to deploy a comprehensive representation of realistic urban neighborhoods for a) revisiting neighborhood-scale urban canopy parameterizations in various models and b) informing in-canopy flow and turbulent analyses. Furthermore, we discuss the application of this dataset for training Machine Learning algorithms for pedestrian wind speed. 

How to cite: Nazarian, N., Lu, J., Hart, M., and Krayenhoff, E. S.: UrbanTALES: A comprehensive dataset of Urban Turbulent Airflow using systematic Large Eddy Simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7011, https://doi.org/10.5194/egusphere-egu24-7011, 2024.

15:25–15:35
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EGU24-16891
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AS2.2
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ECS
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On-site presentation
Daniel Fenner, Andreas Christen, Russell Glazer, Sue Grimmond, Simone Kotthaus, Dana Looschelders, Fred Meier, William Morrison, and Matthias Zeeman

In order to better understand how urban areas modify the regional atmospheric boundary layer (ABL) and to improve and evaluate weather and climate models for urban applications and services, detailed ABL observations are needed. With new instrument technologies and advanced automatic algorithms for detection of aerosols, mixed-layer height (MLH) and boundary-layer clouds, ground-based remote sensing instruments are increasingly used in urban observational networks.

During a one-year measurement campaign in Berlin, Germany (urbisphere-Berlin, Autumn 2021 – Autumn 2022), a variety of ground-based ABL observations were carried out in the greater Berlin region. Berlin as an isolated continental city with approximately 3.8 million inhabitants provides a fairly homogeneous rural background. The urbisphere network included five inner-city, six outer-city and 14 rural sites equipped with continuously-operated Automatic Lidar and Ceilometers (ALC). The measurement network was designed and set up in a systematic and rigorous manner in order to capture intra-urban, urban-rural, and upwind-city-downwind effects of MLH, cloud-base height (CBH), and cloud cover fraction (CCF) along several transects as air masses move over the city. Based on the ALC observations, MLH, CBH and CCF were automatically derived. ALC observations are complemented by measurements of wind and temperature profiles over the city using Doppler-Wind Lidars and radiosondes concurrently released in urban and rural locations during selected days. Surface heat fluxes are continuously measured with six eddy-covariance flux towers and seven path-averaging scintillometers in urban and rural settings.

This contribution highlights the scientific considerations of the systematic measurement network design and the corresponding data analysis. We are proposing a scheme of attributing measurements to rings around the city centre representing the inner city (radius of 6 km), the outer city (radius of 18 km) and rural areas (radius of 90 km), further separated into upwind, downwind and other sectors. A detailed statistical analysis of the year-long dataset finds differences in MLH, CBH and CCF during different seasons and under different weather forcings. Selected case-study days are analysed in more detail to understand the processes controlling the interactions between surface fluxes and mixed-layer dynamics. These days are further used to evaluate the forecasting skill of hectometric dynamical-modelling runs with regard to ABL dynamics, quantifying also the sensitivity of ABL dynamics in the model to surface representation (e.g. soil moisture, heat flux partitioning).

How to cite: Fenner, D., Christen, A., Glazer, R., Grimmond, S., Kotthaus, S., Looschelders, D., Meier, F., Morrison, W., and Zeeman, M.: A systematic investigation of urban modifications of mixed layer height and cloud cover in Berlin, Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16891, https://doi.org/10.5194/egusphere-egu24-16891, 2024.

15:35–15:45
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EGU24-18040
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AS2.2
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On-site presentation
Simone Kotthaus, Martial Haeffelin, Jonnathan Céspedes, Jean-François Ribaud, Jean-Charles Dupont, Marc-Antoine Drouin, Pauline Martinet, and Aude Lemonsu

Atmospheric boundary layer dynamics form in response to synoptic flow and surface-atmosphere exchanges. Over cities, the complex roughness and additional heat from storage and anthropogenic emissions clearly affect atmospheric stability, with implications for heat risk and pollution dispersion. This work examines how the specific dynamics of the Paris region urban atmosphere interact with the synoptic flow using observations from a dense measurement network.

The interdisciplinary PANAME initiative is a framework coordinating the synergy of numerous projects that are studying the Paris atmosphere using both numerical modelling at various scales and novel observations. The measurement network not only includes dense surface station measurements and turbulent flux towers, but also ground-based atmospheric profile remote sensing and additional radiosonde measurements within the city. This work exploits observations from automatic lidars and ceilometers (ALC), Doppler wind lidars (DWL), and microwave radiometers (MWR) that are operated along a suburban-urban transect to collect simultaneous profiles of air temperature, wind, turbulence, and aerosol characteristics at high vertical and temporal resolution. The continuous observations from a network of compact ground-based remote sensing instruments are shown to be extremely valuable for an improved understanding of the complex processes that govern the urban atmosphere as they are highly variable in space and time.

The complex dynamics of the urban atmospheric boundary layer are explored through advanced measurement products, such as low-level jet characteristics and mixed layer heights. We evaluate how different indicators of atmospheric stability from synergy of multiple remote sensing profile data can portray the spatial and temporal variations in urban boundary layer dynamics. The work highlights the importance of atmospheric boundary layer dynamics as a crucial driver for near-surface conditions.

How to cite: Kotthaus, S., Haeffelin, M., Céspedes, J., Ribaud, J.-F., Dupont, J.-C., Drouin, M.-A., Martinet, P., and Lemonsu, A.: Linking synoptic flow and city dynamics: PANAME observations of the Paris urban boundary layer  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18040, https://doi.org/10.5194/egusphere-egu24-18040, 2024.

Posters on site: Tue, 16 Apr, 10:45–12:30 | Hall X5

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 12:30
Chairpersons: Beatriz Sanchez, Andrea Zonato, Aldo Brandi
X5.70
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EGU24-20040
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AS2.2
Siarhei Barodka, Ilya Bruchkouski, Nikita Kasushkin, Tsimafei Schlender, Piotr Silkov, and Tatiana Tabalchuk

This study is devoted to simulation of the Urban Pollution Island (UPI) phenomena over the urban territory of Minsk, Belarus and its surrounding area. We aim at recreating the common features of the air pollution spatial distribution and its time evolution on diurnal, week-long and seasonal scales. For that purpose we utilize WRF-Chem modelling system in nested runs using BEP/BEM urban parametrization schemes for the innermost high-resolution domains (500 m, 300 m, 100 m grid step). We employ two different approaches to urban morphology representation in the model (the Local Climate Zones methodology and direct representation of some of the urban parameters on the given model grid) and use ML-processed Open Street Maps (OSM) vector data and available remote sensing data to represent land use / land cover, buildings and streets parameters for Minsk urban territory and the surrounding area. A series of model runs is performed for time periods with various cases of meteorological conditions in different seasons of recent years. Anthropogenic emissions are specified for the Minsk area as several point sources (representing industrial emissions) and distributed sources over a network of main street and roads (representing vehicle emissions). By proceeding from national statistical data with estimates of main sources of atmospheric pollution in Belarus over the recent years, we formulate hypothetical distributions of emissions intensity over the specified sources and its temporal dynamics with diurnal and weekly cycles. Simulation results obtained with different configurations of the model, different weather conditions and different emission scenarios are compared to available observations: satellite remote sensing data, ground-based observations of air quality and meteorological parameters, vertical profiles of atmospheric pollution and meteorological parameters retrieved from MAX-DOAS and sodar observations.

How to cite: Barodka, S., Bruchkouski, I., Kasushkin, N., Schlender, T., Silkov, P., and Tabalchuk, T.: Dynamics and spatial distribution of air pollution over Minsk, Belarus as revealed by mesoscale and high-resolution urban WRF-Chem modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20040, https://doi.org/10.5194/egusphere-egu24-20040, 2024.

X5.71
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EGU24-7970
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AS2.2
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ECS
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Klaas Laan and Dilia Kool

EGU24-7970

Can urban heating inadvertently induce urban cooling?

Klaas Laan and Dilia Kool

 

Cities are getting hotter—and will continue to get hotter with projected climate change and increases in urbanization. However, is it possible that rising temperatures present an opportunity for enhanced evaporative cooling? Evaporative cooling generally increases linearly with an increase in the vegetative fraction. But it is also well documented that this linearity breaks down at a certain point, and that as the vegetation becomes denser, the relative increase in evapotranspiration becomes more marginal. One possible explanation is the known phenomenon that lateral heat advection enhances evapotranspiration from “scattered” or “patchy” vegetation. Lateral heat advection occurs when there is a large temperature contrast between hot, non-vegetated surfaces and much cooler vegetated surfaces. Lateral heat advection is expected to be larger at lower vegetation fractions (more source areas) and in climates that have more extreme temperatures (arid regions, future climate change-affected areas (?)). We expect that potential evaporation per unit area, enhanced by lateral heat advection, will be inversely proportional to the vegetation fraction. Thus, higher temperatures and lower vegetation fractions would result in higher evaporative cooling per unit vegetated area. This, then, could explain the non-linear relationship between evaporative cooling and vegetation fraction.

We here present a novel analysis of the dynamics of potential and actual evapotranspiration as a function of vegetation fraction using an existing urban energy balance dataset for 13 locations representing a range of climate conditions (Lipson et al., 2022; doi 10.5194/essd-14-5157-2022). A separate assessment of the horizontal component of potential evaporation and its potential implications for enhanced evaporation sheds light on whether urban heating could, to some extent, induce urban cooling.

How to cite: Laan, K. and Kool, D.: Can urban heating inadvertently induce urban cooling?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7970, https://doi.org/10.5194/egusphere-egu24-7970, 2024.

X5.72
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EGU24-16346
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AS2.2
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ECS
|
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Wanliang Zhang, Jimmy Chi Hung Fung, and Mau Fung Michael Wong

The Pearl River Delta (PRD) region in China is characterized by a large fraction of urbanized areas of which the growth rate is unprecedented. Modelling a realistic meteorological field for such a region is challenging mainly due to the uncertainties in the meso-scale numerical model, and the paucity of high-resolution profiler-type observations. In this study, we aim to improve the understanding of the urban effects on the modelled meteorological field in the PRD region by applying different fine-tuned planetary boundary layer (PBL) schemes coupled with two multi-layer urban models and leveraging the high spatial-temporal wind LiDAR observations. Particularly, the momentum in the urban roughness sublayer (RSL, about three times the building height) will be thoroughly investigated using long-lasting profiler-type observations.

The Weather Research and Forecast (WRF) model offers a variety of PBL schemes which may feature a non-local transport algorithm under unstable atmospheric conditions. Most PBL schemes utilize the surface layer fluxes calculated based on the Monin-Obukhov similarity theory, acting on the first model layer only. Although this bulk parameterization of surface layer fluxes is appropriate for urban areas occupied predominantly by low-rise buildings, it is unable to reflect the momentum drag and thermal exchange processes when the average building height (H) within a model cell greatly exceeds the height of the lowest model. Multi-layer urban models, Building Effects Parameterization (BEP), and Building Energy Model (BEM) can be coupled with PBL schemes to provide a more realistic interaction between buildings and air within the RSL. Required input for initializing the multi-layer urban models include H and average street width, which can be simply prescribed (assumed) or derived from the local climate zones.

Despite many efforts have been made to study the improvements by urban models on the surface meteorological variables, such as 10-m wind speed, 2-m temperature and moisture, little investigation of modelled results has been carried out focusing on the RSL and the entire boundary layer over a long-time series due to scarce observations. Recently, three wind LiDAR units were deployed in Hong Kong, providing us with a valuable opportunity to monitor wind profile evolution continuously at a 25-m and 1-hr resolution and to reveal the transport of surface layer fluxes to the overlying RSL.  In the result section, we first present the wind speed profiles to understand the benefits of a multi-layer urban model compared to the bulk parameterization, justified by the LiDAR observations. Secondly, as the non-local PBL scheme can transport the surface fluxes to non-adjacent cells, a comparison of the momentum flux profile will be presented between local and non-local PBL schemes under different stabilities.

How to cite: Zhang, W., Fung, J. C. H., and Wong, M. F. M.: Urban roughness sublayer characteristics: sensitivity to planetary boundary layer schemes and multi-layer urban models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16346, https://doi.org/10.5194/egusphere-egu24-16346, 2024.

X5.73
|
EGU24-15662
|
AS2.2
|
ECS
|
Fatma Başak Saka and Yurdanur Unal

The urban heat island effect, denoting the temperature difference between urban and rural areas, has become more widely recognized due to the increasing urbanization over the years. Recent studies related to the urban heat island effect mainly focus on changes in atmospheric changes and their role in triggering significant weather phenomena. Understanding these dynamics is crucial for making future projections. This research is motivated by the need to understand how the urban heat island intensity affects the boundary layer and temperature structure of İzmir, Türkiye during a record-breaking temperature period, in July 2023.  Temperatures in the Aegion region for July 2023 are above season normals of the 1991-2020 period by 1.7ºC. To investigate how urbanization contributed to the temperature changes the chosen timeframe is modeled using the Weather Research and Forecasting (WRF) Model (version 4.3). To enhance spatial resolution, we integrated the Coordination of Information on the Environment (CORINE) land cover data into the model, employing a nested domain setup ranging from outer to inner domains with resolutions of 9-3-1 km. ERA5 Reanalysis was chosen as the initial condition to force the model throughout the selected period. Following the simulations using the parameterizations set optimized for the Izmir region in July 2023, the obtained results were scrutinized through a comparison with data from meteorological observation stations to analyze the accuracy and performance of the simulations.    Then, to examine how urban areas affect atmospheric behavior under record-breaking conditions, atmospheric conditions of  July 2003 were simulated by utilizing the same parameterizations and boundary conditions with altered land use categories.   The urban land-use categories within the domain were changed to the most dominant rural land-use category.   In evaluating the city's influence on record-breaking temperatures, the analysis focused on changes in the atmospheric boundary layer and its associated parameters by comparing the simulations with urbanizations and without urbanization in İzmir.

How to cite: Saka, F. B. and Unal, Y.: How does urbanization shape the record-breaking temperatures in Izmir, Turkey ?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15662, https://doi.org/10.5194/egusphere-egu24-15662, 2024.

X5.74
|
EGU24-17628
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AS2.2
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ECS
Steven van der Linden, Judith Tettenborn, Thomas Röckmann, Stephan de Roode, and Bas van de Wiel

Last June 2023 a controlled release experiment (CRE) of methane was conducted at the campus of the Utrecht University, the Netherlands, with the aim of improving models for emission quantification. The methane was released at different flow rates and subsequently measured in the local area (along closed paths of approximately 500 m length) using vehicle mounted sensors. In addition, several wind sensors were deployed at approximately 35 meters distance of the release location covering the dominant flow pathways between the buildings.

Although the setup enables us to relate the variability in wind direction and concentration peaks in the direct vicinity of the release, the limited spatial extent of the setup still makes it challenging to determine the dispersion of methane on the larger campus scale. Therefore, we explore the possibility to use meter-scale Large-Eddy Simulations (LES) in which the flow around the buildings is explicitly resolved with an immersed boundary method. With this approach, we aim to provide detailed information on the dispersion of methane ranging from the street-level to the campus scale.

Here, we will show the first results of our simulations and a comparison with the observations. The controlled release experiment and wind measurements serve as validation for the LES, with the LES ideally reproducing the observed concentrations and wind directions in a statistical sense. We will discuss the model complexity required to accurately model observed dispersion features and look at the dependence of this result to changes in model setup. For example, how the model result changes with respect to a change in the prescription of large-scale meteorological conditions.

Such validated urban LES may in the future be used not only for forward-in-time prediction of pollutant concentrations but also for inverse modelling to estimate the location of pollutant release, when only a limited number of observations are available.

How to cite: van der Linden, S., Tettenborn, J., Röckmann, T., de Roode, S., and van de Wiel, B.: Large-Eddy Simulations of Methane Dispersion at the Utrecht University Campus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17628, https://doi.org/10.5194/egusphere-egu24-17628, 2024.

X5.75
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EGU24-19058
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AS2.2
Siqi Yu, Dong Liu, and Zhu Liu

The planetary boundary layer (PBL) is crucial for environmental pollution and climate change. LIDAR, with its high spatiotemporal resolution, has a strong advantage in automatically and continuously acquiring the planetary boundary layer height (PBLH). In this study, LIDAR was used in simultaneous observations of three stations in different climatic zones, Jinhua, Hefei and Lanzhou, to establish a multi-site boundary layer height inversion method, which was used to invert, statistically and analytically analyze the planetary boundary layer height. The results show that the planetary boundary layer heights over Jinhua, Hefei, and Lanzhou are characterized by different seasonal and diurnal variations. The planetary boundary layer heights over Jinhua and Hefei are lower than those over Lanzhou in spring, summer and fall. The time when the boundary layer height over Lanzhou starts to increase and decrease coincides well with the time of sunrise and sunset, while the boundary layer height over Hefei does not increase significantly until several hours after sunrise. The monthly mean diurnal mixed layer heights over Jinhua, Hefei and Lanzhou are highest in September, August and June, respectively, and the corresponding monthly mean maximum mixed layer heights are in September, August and July, respectively. The study demonstrates that the spatial and temporal distribution pattern of PBLH reflects the local climate characteristics, which can provide important data for air pollution control, weather forecasting and climate prediction.

How to cite: Yu, S., Liu, D., and Liu, Z.: Study of boundary height layer evolution patterns in different climate zones based on LIDAR observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19058, https://doi.org/10.5194/egusphere-egu24-19058, 2024.

X5.76
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EGU24-13329
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AS2.2
Konstantin Kuznetsov, Paul Sylvestre, Pavel Litvinov, Oleg Dubovik, and David Fuertes

The computational demands of Computational Fluid Dynamics (CFD) often limit its real-time or large-scale applications, particularly in scenarios requiring multiple simulations based on varying input parameters. This study introduces a surrogate reduced order model (ROM) that not only addresses the computational challenges of CFD but also underscores its potential for broad applicability.

We focus on the dynamics of the Urban Boundary Layer (UBL), a key factor in understanding urban microclimates and their impact on energy consumption, thermal comfort, and local weather phenomena. Using a representative urban test case from the city center of Paris, we illustrate the effectiveness of our approach. During the offline phase, the ROM is constructed by assembling a database of Dynamic Mode Decomposition (DMD) modes [1] associated with various aspects of UBL dynamics, such as temperature distribution, wind patterns, and turbulence characteristics. These modes are determined based on a set of meteorological conditions defined through k-means clustering analysis. During the online phase, we interpolate these DMD modes from the database, enabling us to determine the dynamic characteristics of the UBL within the domain without initiating computationally intensive code_saturne calculations.

Our validation for the UBL dynamics in central Paris indicates that the online phase can achieve a Normalized Root Mean Square Error (NRMSE) of 2-8%. A distinctive aspect of our approach is the incorporation of DMD during the code_saturne computation process. Some modifications of DMD can be seamlessly integrated into numerous code_saturne simulations, harnessing the advantages of DMD with minimal computational trade-offs. This ROM approach offers a promising tool for urban climate studies, urban planning, and environmental management, providing a more efficient means to simulate and understand the complex dynamics of the Urban Boundary Layer.

How to cite: Kuznetsov, K., Sylvestre, P., Litvinov, P., Dubovik, O., and Fuertes, D.: A Versatile Reduced Order Model of Urban Boundary Layer Dynamics in the Center of Paris, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13329, https://doi.org/10.5194/egusphere-egu24-13329, 2024.

X5.77
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EGU24-15233
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AS2.2
Measurement of evapotranspiration on small urban surfaces. Application to green roofs.
(withdrawn)
David Ramier, Fabrice Rodriguez, and Pascal Keravec
X5.79
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EGU24-18500
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AS2.2
Andrea Zonato and Natalie Theeuwes

In this work, various very-high-resolution simulations with the Harmonie-AROME Numerical Weather Prediction (NWP) model are performed for the city of Paris during an intense heatwave event in the summer of 2022, to evaluate the capability of the model to reproduce real conditions, at various resolutions and incorporating different kinds of landuse and urban morphology types.

 

In particular, simulations are performed using ECWMF operational forecasts at 9 km resolution as boundary conditions, for the operational 2.5 km runs. Moreover, two 500 m and 100 m resolution domains have been one-way nested in the parent one.

For considering the impact of urban areas, the state-of-the-art urban canopy parameterization Town Energy Balance (TEB, Masson et al., 2000), has been employed within the modeling system, and its single-layer and multi-layer options have been compared to evaluate the improvements brought by the multi-layer capability.

 

To test the impact of various urban morphologies, simulations have been run with 1) the default ECOCLIMAP-SG landuse at 300-meter resolution, which considers urban areas as 10 different categories, derived from the WUDAPT Local Climate Zones Classification, and 2) the Geoclimate urban morphology at 100-meter resolution, derived from the Open Street Map (OSM) database (Bernard et al., 2022). The latter employs the Open Street Map database to estimate close-to-reality urban geometries, with the help of a random forest technique to estimate missing building heights in the dataset.

 

The comparison with 79  in-situ observations shows that all the simulations are able to currently represent urban air temperature trends for homogeneous areas, such as the Paris city center and compact homogeneous areas. 

On the other hand, heterogeneous and scattered urban areas temperatures are not well represented by both higher-resolution simulations and the category-based ECOCLIMAP-SG landuse.On the contrary, the OSM-based landuse is sensible to city heterogeneity and horizontal variability.

 Considering the 100-m simulations, it is clear that category-based land uses are not suitable for very-high-resolution urban canopy layer simulations, since they cannot truly capture the neighborhood-scale variation within the same city.

For this reason, it is important, with increasing NWP resolution, to employ suitable landuse datasets, coherent with the employed horizontal resolution and applicable physical parameterizations.

How to cite: Zonato, A. and Theeuwes, N.: Very-high-resolution simulations with Harmonie-AROME of a heatwave case for the city of Pari with different landuse datasets., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18500, https://doi.org/10.5194/egusphere-egu24-18500, 2024.

X5.80
|
EGU24-18760
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AS2.2
Toward Data-Driven Urban Canopy Models
(withdrawn)
Rémi Alas, Michael Bauerheim, Corentin Lapeyre, and Thomas Jaravel
X5.81
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EGU24-18976
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AS2.2
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ECS
|
Dana Lüdemann, Niels Troldborg, Jan Pehrsson, and Ebba Dellwik

Airborne LiDARs can provide updated and highly accurate information of the 3D urban layer. This presentation focuses on transforming such information into boundary conditions for urban flow models.

When addressing buildings, we use a method called City3D [1], which outputs a watertight geometrical model at a specified level of detail (LoD).This resulting model is then utilized in the computational fluid dynamics (CFD) solver EllipSys [2]. We demonstrate how a novel implementation of the immersed boundary method (IBM) [3] simulates the wind flow and dispersion around the building. Additionally, we explore how different LoD
influence the simulation results.

The LiDAR data can also be used to model the drag force of trees. We demonstrate this process based on recent observations of a real tree. Finally, we discuss the relative importance of trees and buildings in an urban modelling context, highlighting the significance of including more details in the 3D urban layer.

References
[1] Jin Huang, Jantien Stoter, Ravi Peters, and Liangliang Nan. City3d: Large-scale building reconstruction from airborne lidar point clouds. Remote Sensing, 14(9), 2022.
[2] Jess A. Michelsen. Basis3D - a Platform for Development of Multiblock PDE Solvers: - release, volume AFM 92-05. Technical University of Denmark, 1992.
[3] Niels Troldborg, Niels N. Sørensen, and Frederik Zahle. Immersed boundary method for the incompressible reynolds averaged navier–stokes equations. Computers Fluids, 237:105340, 2022.

How to cite: Lüdemann, D., Troldborg, N., Pehrsson, J., and Dellwik, E.: Integrating Airborne LiDAR Data into Urban Flow Models: A Focus on Buildings and Trees, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18976, https://doi.org/10.5194/egusphere-egu24-18976, 2024.

X5.82
|
EGU24-19030
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AS2.2
Effect of nocturnal urban boundary layer stability and mixing on temperature contrasts between built-up environments and urban parks
(withdrawn)
Martial Haeffelin, Jean-François Ribaud, Simone Kotthaus, Jean-Charles Dupont, Aude Lemonsu, and Valéry Masson
X5.83
|
EGU24-19930
|
AS2.2
Jian Zhong, Yanzhi Lu, Jenny Stocker, Victoria Hamilton, and Kate Johnson

Cities have higher peak temperatures compared to surrounding rural areas. The urban-rural surface air temperature difference is known as the urban heat island (UHI). As extreme heat exposure can lead to adverse health effects, information on UHI characteristics of cities is important for future urban climate planning strategies. This study applied the ADMS-Urban Temperature and Humidity model to investigate the key processes driving the UHI in Birmingham, UK, at the neighbourhood scale. This model was configured with a range of input datasets (such as meteorological data, landuse data, building data, anthropogenic heat sources etc) and run on the University of Birmingham’s BlueBEAR HPC. This urban climate modelling was evaluated against the temperature measurement datasets from UK Met Office and Weather Underground. The spatiotemporal variations of surface air temperature in Birmingham, UK were captured by this model. This modelling study can be further applied to explore the impacts of local urban head island mitigation strategies.

How to cite: Zhong, J., Lu, Y., Stocker, J., Hamilton, V., and Johnson, K.: Modelling the urban heat island in Birmingham, UK at the neighbourhood scale , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19930, https://doi.org/10.5194/egusphere-egu24-19930, 2024.