Cities play a fundamental role in climate at local to regional scales through modification of heat and moisture fluxes, as well as affecting local atmospheric chemistry and composition, alongside air-pollution dispersion. Vice versa, regional climate change impacts urban areas and is expected to affect cities and their citizens increasingly in the upcoming decades when the share of the population living in urban areas is growing and is projected to reach about 70 % by 2050. This is especially critical in connection to extreme events, for instance, heat waves with extremely high temperatures exacerbated by the urban heat island effect, in particular during night-time, with significant consequences for human health.

From the perspective of recent regional climate model development with resolution achieving city scales within convection permitting RCMs, parameterization of urban processes plays an important role to understand local/regional climate change. The inclusion of the individual urban processes affecting energy balance and transport (i.e. heat, humidity, momentum fluxes, emissions) via special urban land-surface interaction parameterization of local processes becomes vital to simulate the urban effects properly. This enables improved assessment of climate change impacts in cities and planning adaptation and/or mitigation options, as well as adequate preparation for climate-related risks (e.g. heat waves, smog conditions, etc.).

We introduced this topic to the CORDEX platform, within the framework of flagship pilot studies on challenging issues and gaps in regional climate change knowledge. The main aims and progress of this activity will be presented, especially an analysis of Stage-0 experiments using case studies of heat wave and convection episode within ensemble of about 30 simulations for City of Paris with convection permitting RCMs from different groups over the world. Further outlook of long term (10 years) climate simulation with these models in common strategy to IMPETUS4CHANGE Horizon Europe Project will be presented as well,

How to cite: Halenka, T., Langendijk, G., and Hoffmann, P.: CORDEX Flagship Pilot Study URB-RCC: Urban Environments and Regional Climate Change – Where We Are and Where We Would Like to Go, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-722, https://doi.org/10.5194/icuc12-722, 2025.

With the increasing resolution of regional climate models (RCM), the representation of urban areas becomes ever more critical. However, even in a kilometer-scale resolution, many RCMs still neglect urban-specific processes and represent cities only by their specific physical parameters (e.g., albedo, roughness). The URB-RCC flagship pilot study under the framework of the CORDEX initiative aims to promote and analyze RCMs with explicit urban treatment. In the first phase, the study assesses the performance of high-resolution RCMs that include urban schemes in large cities under various weather conditions. This analysis focuses on a selected heat wave episode in August 2020 and analyzes how several RCMs capture it in the city of Paris. The urban heat island (UHI) is represented by the temperature contrast (UHI index) between several locations within and outside the Paris city center. The UHI index is calculated from station measurements and compared to the index calculated from RCM simulations in 3km resolution. Preliminary results show that while RCMs generally capture day-to-day variability and general weather patterns, there is quite a large uncertainty in the daily cycle. Some models agree well with the observations for both daily minima and maxima. On the other hand, a large set of the model ensemble tends to overestimate the UHI index derived from daily maxima. At the same time, they underestimate the UHI index in daily temperature minima. The coordinated nature of the multi-model ensemble experiment allows to address the uncertainty coming from different model formulations.

How to cite: Belda, M. and Halenka, T. and the URB-RCC FPS Team: A Regional Climate Model Ensemble Analysis of Urban Heat Island Intensity During a Heat Wave in Paris , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-614, https://doi.org/10.5194/icuc12-614, 2025.

Heat risks in cities are augmented by the urban heat island effect associated with the high density of buildings, the lack of vegetated surfaces and human activities. During heat waves, different ventilation conditions can occur, depending on large scale conditions and their interaction with the local boundary layer (Haeffelin et al., 2025). During hot nights, the sensation of suffocation is heightened when the ventilation is weak. During these stagnant conditions, the atmosphere is stable even in the city with a strong thermal stratification. The cooling effect of parks remains very local (due to reduced ventilation) and does not allow the surrounding streets to be refreshed (Haeffelin et al., 2025), intensifying the thermal contrasts between rural areas, parks, and streets (Céspedes et al. 2024).

It is therefore important to evaluate how the interaction between synoptic conditions and local dynamics and thermal stratification in the urban boundary layer are represented in available high resolution climate simulations during heat waves. The optimal objective is to have tools we can trust to assess how much the frequency of heat waves' nights with these increased health risks' conditions will evolve in future and if greening solutions can reduce the risk efficiently.

In this work, the existing convective-permitting simulations performed in the frame of CORDEX FPS "Convection over Europe" and EUCP project are analysed and compared with available observations around Paris area during the two major heat waves events in august 2003 and july 2006. This analysis may be complemented by simulations performed in the context of CORDEX FPS URB-RCC covering heat wave of august 2020.

How to cite: Bastin, S., Hersent, M., Kotthaus, S., Haeffelin, M., Cespedes, J., and Van Hove, M.: Analysis of local dynamics and associated urban heat island intensity over Paris during heat waves in an ensemble of convective-permitting climate simulations, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-908, https://doi.org/10.5194/icuc12-908, 2025.

Heatwaves are among the most dangerous climate-related natural hazards, being associated with considerable effects on population, who mostly live in urbanized areas. Under hot conditions the human body is able to regulate its core temperature via sweat evaporation, but this ability is reduced when humidity is high. The combined effect of heat and humidity invokes heat stress which, in turn, may cause dehydration, hyperthermia and heat stroke. Thus, heat stress is a multivariate problem which could affect vulnerable groups of population in different ways. A good representation of this hazard in populated areas is essential to adapt and reduce the effects of heatwaves, especially under climate change.

In order to improve the understanding of the interactions between regional climate change and urban areas, the WCRP CORDEX Flagship Pilot Study “URBan environments and Regional Climate Change” (FPS URB-RCC) is conducting coordinated experiments with a regional climate model (RCM) ensemble that includes refined urban representations. A first effort within the FPS URB-RCC (STAGE-0) consisted of the simulation of a heatwave that affected southern Europe in August 2020, causing over 300 fatalities in Paris and surroundings (the so-called Paris heatwave). An ensemble of 40 RCM simulations encompassing different models, realizations and configurations (including variations in urban schemes and land use data), was produced approximately on a 3-km grid. The present work provides an evaluation of these simulations for the Paris heatwave considering multivariate heat stress indices, with special emphasis on the intervariable relationship between temperature and humidity. Furthermore, we assess the sensitivity to the use of different models and urban representations to better understand heat stress. Improving modeling and overall understanding of heatwaves is essential for accurate risk assessment, effective urban planning and mitigation strategies to protect public health.  

This work is part of project PID2023-149997OA-I00 (PROTECT) funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU.

How to cite: Casanueva, A., Milovac, J., Fernández, J., Simón-Moral, A., Hoffmann, P., Campanale, A., and Langendijk, G. S. and the FPS-URB-RCC community: The Paris 2020 heatwave: heat stress as represented by high-resolution regional climate model simulations, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-951, https://doi.org/10.5194/icuc12-951, 2025.

The CORDEX flagship pilot study on urban environments and regional climate change (FPS-URB-RCC, Langendijk et al. 2024) has been initiated to bridge the gap in understanding interactions between regional climate and urban areas. An initial experiment (STAGE-0) was coordinated within Phase 2 of FPS-URB-RCC, involving 19 institutions to produce an inter- and intra-model ensemble of long-term simulations at convection permitting scale (~3 km) with sophisticated representations of urban environments. In particular, the Weather Research and Forecasting (WRF) model has contributed a large coordinated ensemble, consisting of 29 STAGE-0 sensitivity simulations over the Paris domain. In this study, we use the complete WRF sub-ensemble to examine the influence of model settings on the representation of the land-atmosphere feedback with a focus on urban areas, and its comparison with observational datasets over Paris. We show the sensitivity of the correlation between land-surface and boundary layer variables to available urban parameterization schemes in WRF, land-cover data (e.g., different datasets, inclusion/exclusion of local climate zones, urban area removal), coupling with the PBL and surface schemes, microphysics options, aerosol inputs, and domain size. This ensemble also enables us to quantify internal variability and distinguish it from true model sensitivity, as 10 identical WRF configurations were run on different machines or with slight variations in initial conditions.

Langendijk, G.S. et al. (2024) “Towards Better Understanding the Urban Environment and Its Interactions with Regional Climate Change - The WCRP CORDEX Flagship Pilot Study URB-RCC.” Urban Climate 58:102165. https://doi.org/10.1016/j.uclim.2024.102165.

This work is a part of projects PROTECT (PID2023-149997OA-I00) funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU, and European Union’s Horizon Europe research and innovation programme IMPETUS4CHANGE (grant agreement No 101081555). JM and AS acknowledge funding by the Ministry for the Ecological Transition and the Demographic Challenge (MITECO) and the European Commission NextGenerationEU (Regulation EU 2020/2094), through CSIC's Interdisciplinary Thematic Platform Clima (PTI-Clima)

How to cite: Milovac, J., Simón-Moral, A., Fernandez, J., Fita Borrell, L., Matos Soares, P., S. Langendijk, G., Halenka, T., and Hoffmann, P. and the WRF-FPS-URB-RCC community: Land-atmosphere feedback in the WRF FPS-URB-RCC sub-ensemble of STAGE-0 simulations: Sensitivity to the model configuration, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1034, https://doi.org/10.5194/icuc12-1034, 2025.

Understanding the interactions between urban areas and regional climate is crucial for improving climate projections and informing urban adaptation strategies. The WCRP CORDEX Flagship Pilot Study URB-RCC addresses this challenge through a coordinated modeling effort that evaluates urban climate processes using different regional climate models (RCMs) with urban schemes. As part of this initiative, STAGE-0 simulations focus on the Paris region during April–September 2020, capturing both a heatwave and a heavy precipitation event.

This study compares two simulations conducted with the WRF model by the Regional Atmospheric Modeling Group at the University of Murcia. The first experiment (CTRL) follows a standard WRF configuration used across modeling groups, integrating LANDMATE PFT land cover data with Local Climate Zones (LCZs), the BEP+BEM urban scheme, and aerosol climatology from MERRA2 reanalysis. The second simulation (CHEM) employs WRF-Chem, replacing prescribed aerosols with an interactive chemistry module that accounts for pollutant transport and interactions.

Both simulations reproduce the urban heat island (UHI) effect with reasonable accuracy. The inclusion of chemistry introduces notable differences in the daily cycle of urban-rural temperatures, generally leading to a cooling in both areas. However, these differences show a strong dependence on meteorological conditions. These findings highlight the role of aerosols and pollution in shaping urban climate simulations and emphasize their impact on the WCRP CORDEX FPS URB-RCC STAGE-0 simulations for Paris.

Acknowledgements: The authors acknowledge the ARUBA project (PID2023-149080OB-I00) of the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033). ERL thanks her predoctoral contract FPU (FPU21/02464) to the Ministerio de Universidades of Spain.

How to cite: Raluy-López, E., Segado-Moreno, L. C., Garnés-Morales, G., García-Fernández, E., Gil-Guirado, S., Jiménez-Guerrero, P., and Montávez, J. P.: Assessing Aerosol-Induced Modifications of the Urban Heat Island in WRF Simulations for Paris: Findings from the WCRP CORDEX FPS URB-RCC STAGE-0, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-716, https://doi.org/10.5194/icuc12-716, 2025.

Urbanized regional climate models bridge the gap between local urban dynamics and larger atmospheric processes, covering metropolitan areas and their surroundings. These models are essential for understanding the interactions between urban areas and mesoscale dynamics, including the urban heat island’s regional impacts and extreme weather events. Therefore, km-scale models coupled with urban parameterizations are capable of capturing the complex interaction processes between atmosphere and urban land cover, having a key role for assessing heat stress and developing strategies for urban climate adaptation and mitigation.

To address this need, the bulk urban canopy parameterization, TERRA_URB (TU), was developed for the multi-layer land surface scheme of the COSMO regional atmospheric model. This parameterization resulted effective in capturing the key characteristics of urban areas, accurately reproducing prominent urban meteorological features across a range of European and global cities. As part of the transition from the COSMO model to the Icosahedral Nonhydrostatic (ICON) Weather and Climate regional model, TU was successfully ported into ICON. In this work, we present results of the TU parameterization, coupled into the ICON model, for high-resolution (2km) climate simulations driven by ERA5 reanalysis. These simulations focus on modelling extreme temperatures and urban heat islands in Bologna, a key case study in the CARMINE project (Climate Resilient Development Pathways in Metropolitan Regions of Europe, https://carmine-project.eu/). Bologna was selected due to its vulnerability to extreme heat and heatwave events, with a particular focus on enhancing urban climate resilience for vulnerable populations. The promising results of the newly urbanized ICON model, compared against high-quality observational data, contribute to advancing climate simulations for urban modeling applications, representing one of the first uses of the ICON model coupled with TU at the climate timescale, and could also serve as input data for urban models at hectometric scales.

How to cite: Campanale, A., Adinolfi, M., Raffa, M., Schulz, J.-P., and Mercogliano, P.: Evaluating the urbanized ICON atmospheric model over the Bologna case study area, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1028, https://doi.org/10.5194/icuc12-1028, 2025.

Urban areas influence regional climate dynamics, particularly through pronounced urban-rural contrasts. In South America, cities such as Porto Alegre, Buenos Aires, and Córdoba serve as major economic and population centers. These cities experience well-documented Urban Heat Islands (UHI), altered wind patterns, and humidity contrasts, which are further intensified by climate change. These effects become especially critical during heat waves, posing significant challenges for urban populations under global warming scenarios. To address these complexities, convection-permitting models have emerged as a promising tool for capturing the fine-scale urban footprint on local climates. 

This study focuses on evaluating convection-permitting simulations, developed under the CORDEX FPS-URB-RCC SESA (Southeastern South America), capture urban-rural contrasts in three selected cities: Porto Alegre, Buenos Aires, and Córdoba. A total of five models are analyzed, including UCAN-WRF433, NCAR-WRF433, USP-RegCM471, and ICTP-RegCM5pbl1 and b2, with resolutions of 4 km for all models and 12 km for USP-RegCM471. These models are assessed based on key variables, including minimum and maximum air temperature, surface wind speed, humidity, and precipitation. Additionally, the study evaluates heat wave characteristics to understand the urban response to extreme events.

Results highlight the spatial and temporal variability of urban-rural contrasts, with particular emphasis on seasonal variations and diurnal cycles of temperature, humidity, and wind intensity. The study evaluates the added value of increased spatial resolution provided by convection-permitting models. 

How to cite: Quintana, Y., Diez-Sierra, J., Solman, S. A., Fernández, J., and Milovac, J.: Evaluating Convection-Permitting Simulations for capturing urban climate over main cities in South America, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1015, https://doi.org/10.5194/icuc12-1015, 2025.

Urbanization and growing city populations amplify the risks of extreme weather events, a vulnerability worsened by climate change. Although climate models have advanced to better represent urban areas, many of their parameters, processes, and results remain insufficiently understood. As these models become more complex, it is crucial to focus on addressing key processes and enhancing climate monitoring before prioritizing further complexity, to effectively contribute to local decision-making. A previous study conducted in the Metropolitan Area of Buenos Aires (AMBA) analyzed the sensitivity of the WRF model to changes in urban canopy parameters (UCP). Results from a heat wave event showed that, while the model exhibited sensitivity in surface variables to morphological and anthropogenic parameters, the biggest changes come from the selection of the scheme itself rather than its configuration. However, further evaluation of the urban canopy schemes and UCP changes is needed to better understand the vertical influence of urban areas in urban climate simulations. Additionally, the definition of planetary boundary layer height (PBLh) requires deeper analysis, as it is highly dependent on the surface layer representation within the models. This study explores these issues using the WRF model integrated with a refined Local Climate Zone (LCZ) and three urban canopy schemes to simulate extreme weather events in the AMBA region. 

This study also incorporates some results from multiple years of high-resolution (1 km) urban climate simulations over AMBA with the WRF model to provide broader insights into urban climate behavior and modeling approaches. Initial results show how the presence of urbanization has a strong impact on the circulation at local scale. These additional findings offer context for understanding the dynamics of urban environments and enhancing future modeling efforts, and help to explore alternatives for a collaborative effort with local agencies to develop adaptation strategies.

How to cite: Muñoz, L., Fita, L., and Carril, A.: Urban Climate Simulation in the Metropolitan Area of Buenos Aires (SUrAMBA): Study on the vertical influence of urban areas in km resolution urban simulations., 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-411, https://doi.org/10.5194/icuc12-411, 2025.

As a result of climate change, cities, like natural areas, are already warming and will continue to do so, even without taking urbanization into account. The urban heat island (UHI) effect, i.e. the difference in night-time air temperature between urban areas and their surroundings, poses major problems for inhabitants, for example in terms of heat stress.

Climate change projections are usually derived from global climate models (GCMs) downscaled to the local scale using statistical tools, or from regional climate models (RCMs). Due to their horizontal resolution, which is often too coarse, RCMs have historically been unable to adequately represent most urban areas, so little is known about projected changes in UHI in the future. A few studies have investigated the projected evolution of UHIs in the context of climate change, using different approaches, from GCMs and RCMs to high-resolution land surface models, but with little consistency between studies and great sensitivity to the city analyzed, its climate and especially the downscaling approach used.

Thanks to increasing computational resources and model development, RCMs are now able to achieve horizontal resolutions in the order of a few kilometers and can be coupled with various urban parametrization to improve the representation of cities in climate change projections.

Here we use GCM-driven RCM simulations from the EURO-CORDEX initiative (12.5 km) and the CORDEX Flagship Pilot Study on Convection (3 km) to study the future evolution of the UHIs of several European cities at the end of the century (2090-2099) under a scenario of very high greenhouse gas emissions (RCP8.5) and in which the cities are fixed in their historical states.

We study the potential atmospheric variables driving the UHI over the historical period and their evolution in the future, and compare these relationships between climate models of varying resolution and using different urban parametrization.

How to cite: Le Roy, B. and Rechid, D.: What are the potential drivers of urban heat island changes in European cities in future regional climate simulations?, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1134, https://doi.org/10.5194/icuc12-1134, 2025.

The Copernicus Interactive Climate Atlas (https://atlas.climate.copernicus.eu, C3S Atlas in short) evolves from the frozen IPCC Atlas (Gutiérrez et al., 2021; https://interactive-atlas.ipcc.ch/) to potentially address the needs of the IPCC’s seventh assessment cycle. A key novelty in the upcoming IPCC cycle is the inclusion of a Special Report on Climate Change and Cities (Decision IPCC-LXI-5), which motivated the WCRP CORDEX FPS URB-RCC to evaluate the capacity of current CORDEX simulations to represent urban effects on climate and provide insights for CMIP6-driven CORDEX simulations (Langendijk et al., 2024, https://doi.org/10.1016/j.uclim.2024.102165). The evaluation of CORDEX-CORE (25 km) (Langendijk et al., 2025, internal review) reveals that, although limited, these simulations can capture the nocturnal and diurnal Urban Heat Island (UHI) effect in various megacities. Despite significant gaps in spatial resolution, urban schemes, and the diversity of RCMs, these analyses highlight the need to address these limitations in future studies. Results show that the models’ ability to reproduce the UHI effect improved significantly with more advanced urban schemes and an increase in spatial resolution from 25 km to 12.5 km (over Europe). These findings advocate for the use of higher resolutions and to appropriately account for urban areas using up-to-date urban parameterizations in the new CORDEX-CORE CMIP6 simulations.

This work introduces the urban climate analysis layer in the C3S Atlas, aligned with the FPS-URB-RCC initiative. The urban layer analyzes the urban effects through spatial maps and seasonal anomalies between urban areas and their surroundings for several climatic impact-drivers (CIDs). REMO and RegCM models are used for CORDEX-CORE and EURO-CORDEX, covering different scenarios (RCP4.5, RCP8.5) and Global Warming Levels (e.g., 1.5, 2, 3, and 4 ºC). This analysis will be included in the next release of the C3S Atlas (spring 2025) and will provide global perspective based on existing worldwide regional projections focused on urban aspects. 

How to cite: Diez-Sierra, J., Fernández, J., Quintana, Y., S. Langendij, G., Milovac, J., Horányi, A., Demuzere, M., Halenka, T., Hoffmann, P., Rechid, D., Nogherotto, R., Zazulie, N., Coppola, E., and Gutiérrez, J. M.: Introducing the New Urban Climate Layer in the Copernicus Interactive Climate Atlas, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-870, https://doi.org/10.5194/icuc12-870, 2025.

The representation of local processes at the urban scale becomes highly important with the increase in resolution of regional climate models (RCMs). Current state-of-the-art RCMs do not typically include a sophisticated depiction of local urban-scale dynamics, which constrains our understanding of their interaction with regional climate. The Flagship Pilot Study on the Urban Environment and Regional Climate Change (FPS-URB-RCC) is a CORDEX initiative aimed at bridging this local-regional gap, with the main objective of enabling us to investigate how urban areas affect the regional climate and vice versa. This study uses simulations at 3 km and 12 km resolution  produced within the FPS URB-RCC STAGE-0 framework to analyze how the improved representation of urban areas modifies precipitation patterns in long-term simulations. With this aim, we consider simulations with different models, different urban parameterizations, and different representations of the urban areas, including simulations with no cities. The latter are used as reference, showing an apparent increase of average precipitation over Paris, when the urban area is considered. These preliminary results are further expanded to explore urban influence during convective and frontal precipitation events, assessing the relative importance of precipitation precursors, such as wind and moisture convergence, in the multi-model, multi-physics ensemble. The STAGE-0 experimental setup also allows us to assess the robustness of our results against the unforced internal model variability.

This work is part of projects PROTECT (PID2023-149997OA-I00) funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU, and European Union’s Horizon Europe research and innovation programme IMPETUS4CHANGE (grant agreement No 101081555). JM and AS acknowledge funding by the Ministry for the Ecological Transition and the Demographic Challenge (MITECO) and the European Commission NextGenerationEU (Regulation EU 2020/2094), through CSIC's Interdisciplinary Thematic Platform Clima (PTI-Clima)

How to cite: Simón-Moral, A., Milovac, J., Fernández, J., Bastin, S., Machado, N., langendijk, G., Hoffman, P., Belda, M., Chun, K., and Halenka, T. and the FPS-URB-RCC: Urban influence on precipitation: insights from the FPS-URB-RCC regional climate simulations, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1003, https://doi.org/10.5194/icuc12-1003, 2025.

The Urban Heat Island (UHI) effect, characterized by elevated temperatures in urban areas compared to their rural surroundings, poses significant challenges to human health, energy consumption, and environmental sustainability. But how can cities influence precipitation patterns in their vicinity? Can temperature changes above urban areas alter atmospheric stability and potentially trigger convective precipitation? This study aims to address these questions by examining the impact of urbanization on the diurnal cycle of both precipitation and temperature using the high-resolution CORDEX FPS-CONV convection-permitting model simulation ensemble over the ALP-3 European domain. With its kilometer-scale resolution, the ensemble provides a powerful tool to explore the urban climate effect. Analyses of current and future climate scenarios show that large cities, such as Paris and Barcelona, can significantly impact the diurnal cycles of both temperature and precipitation, with notable differences observed between coastal and continental cities in the Mediterranean region. The ensemble members reveal considerable variability in how urbanization affects precipitation, with discrepancies not only across ensemble members but also among different cities within the same model simulation. This variability highlights the challenges in precisely evaluating the impact of urbanization on precipitation patterns and stresses the need for more detailed future studies leveraging high-resolution kilometer-scale model ensembles to better understand the complex interplay between local climate dynamics and urbanization.

How to cite: Nogherotto, R., de Leeuw, J., Zazulie, N., Raffaele, F., and Coppola, E.: Are Diurnal Precipitation and Temperature Cycle affected by Cities in a Changing Climate?, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-755, https://doi.org/10.5194/icuc12-755, 2025.

Australian urban population accounts for over 90% of total population and is concentrated in coastal areas. Projections show that the extreme precipitatio will be more intense and frequent. We investigated changes to daily mean, moderately extreme (99^th and 99.7^th percentile), and rare extreme (Annual Exceedance Probability (AEP) 1 in 10, 50, and 100) precipitation events in Australia and within its greater capital cities. We used downscaled daily precipitation data from CMIP6 models and downscaled CORDEX-CMIP6 precipitation simulations for SSP370 completed by four modelling groups in Australia (Grosse et al., 2023). This ensemble consists of 19 different host CMIP6 models and ensemble of 39 different downscaled simulations. The changes were quantified according to the rate of change per degree of global warming. The largest increases to precipitation extremes were seen over northern Australia, with the AEP 1-in-50 event in Darwin projected to increase by 11.2%/K or 13.3%/K for the CMIP6 host models and downscaled ensembles, respectively. Projected changes from the downscaled ensemble were lower though still substantial in other capital cities (7.7%/K for Brisbane, 7.1%/K for Sydney, 4%/K for Melbourne, and 5.3%/K for Perth). Large spatial differences were noted among the downscaled ensembles, with different modelling groups showing varying spatial patterns and magnitudes of change. These results highlight the influence of the downscaling approach in determining changes to precipitation extremes and show the need to consider large ensembles to ensure uncertainties in host models and downscaling can be accounted for. Presentation will also show selected results for sub-hourly analysis of rainfall changes for selected stations in Australia from using 15 member ensemble of UQ-DES CCAM downscaled simulations.

Grose, M. et al., 2023. A CMIP6-based multi-model downscaling ensemble to underpin climate change services in Australia. Climate Services, 30, p.100368.

How to cite: Syktus, J., Eccles, R., and Trancoso, R.: Projected precipitation extremes from CMIP6 and CORDEX-CMIP6 downscaled simulations in Australian capital cities, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-621, https://doi.org/10.5194/icuc12-621, 2025.

Singapore, a tropical island city-state located near the equator, experiences a year-round warm and humid climate. Its specific location and rapid urbanization make it particularly susceptible to extreme weather events, which have the potential to adversely impact large populations. Intense rainfall, accompanied by subsequent flash floods, ranks among the most severe local natural hazards experienced. Weather phenomena contributing to heavy rainfall in Singapore include localized thunderstorms, Sumatra squalls, and monsoon surges. Modelling studies suggest that urbanization significantly influences the weather in coastal cities like Singapore by altering land-atmosphere dynamics. For example, urban environments promote localized wind convergence zones that, together with differential surface heating across disparate land types, can enhance convection and increase the likelihood of heavy rainfall. This study explores a few case studies of heavy rainfall over Singapore, triggered mainly by afternoon localized wind convergence. The analysis is conducted using the uSINGV model, a customized urban version of the operational Numerical Weather Prediction system SINGV for Singapore and the region developed at CCRS/MSS based on the UK Met Office Unified Model (UM) Regional Atmosphere and Land configuration. The results will demonstrate the performance of 100-meter high-resolution model simulations compared to larger resolutions traditionally used (300 m and 1.5 km). The primary aim is to evaluate the model’s capability at different resolutions to simulate the processes driving the initiation, organization, and intensification of deep convection over urbanized regions linked to extreme rainfall events. Findings from this study will inform the advancement of urban-scale numerical modelling, enabling the provision of more detailed weather and climate insights to benefit society.

Key words: Urban weather and climate, urban modelling, extreme rainfall, uSINGV model

How to cite: Bhautmage, U., Chen, S., Roth, M., Patel, P., Furtado, K., and Zhang, H.: High-Resolution Modelling of Urban Extreme Rainfall in Singapore, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-261, https://doi.org/10.5194/icuc12-261, 2025.

Mumbai, one of India's most densely populated cities and its economic hub, is critically vulnerable to the Indian monsoon. Frequent heavy rainfall events not only disrupt daily life but also cause significant economic and infrastructural damage. Given the city's importance, improving the accuracy of rainfall predictions is essential for effective disaster management and urban resilience planning. This study employs the multilayer Weather Research and Forecasting Urban Asymmetric Convective Model (WRF-UACM) (Bhautmage et al., 2022) for Mumbai, incorporating explicit urban physics and advanced land-use data. Land-use and land-cover (LULC) data were updated using the European Space Agency (ESA) WorldCover dataset, derived from Sentinel-1 and Sentinel-2 satellite imagery at a 10-meter resolution, resampled to a 30-arc-second grid. Urban morphological parameters, including average building height, plan area density, frontal area density, and street canyon orientation, were sourced from the WUMPOD dataset (Patel et al., 2025) at a spatial resolution of 1 km² per urban grid cell. Rainfall simulations were validated against observational data from the Mumbai Mesonet rain gauge network. The study investigates the impact of these urban morphology refinements on rainfall predictions by testing multiple microphysics parameterization schemes within the WRF-UACM framework. By integrating high-resolution urban morphology data and optimizing microphysics schemes, this research provides a robust approach to improving the accuracy of rainfall simulations for complex urban environments like Mumbai.

Keywords: WRF-UACM, Urban morphology, WUMPOD, rainfall simulation, Mumbai Mesonet observations.

How to cite: Koundal, K., Parde, A. N., Bhautmage, U. P., Patel, P., Khamgaonkar, K., Wong, M. M. F., Pleim, J., Das, S. K., and Ghude, S. D.: Simulation of Rainfall in Mumbai using Detailed Urban Morphology and the WRF-UACM Model, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-889, https://doi.org/10.5194/icuc12-889, 2025.

The current effort provides an historical review of the literature on urban impacts on summer convective precipitation (PP). It then summarized the methods used in such analyses and recommended methodological techniques that provide insights into interactions between urban, synoptic, topographic, and coastal thermodynamic processes that produce the variety of observed and modeled PP impacts. It then discussed studies that have provided new insights into these processes. The review finally reevaluated the classic METROMEX urban downwind PP maximum, in light of the newer observations of urban-induced thunderstorm (TS) bifurcation. Two science questions addressed included: (i) what are the best practices to better understand the relevant urban impacts on resultant summer TS PP patterns and (ii) can the METROMEX observed downwind urban PP maximum be reconciled with the newer observed urban TS bifurcation effect? 

The most significant results from this reanalysis of the “classic” METROMEX plot of total summer TS rainfall has revealed that: (i) its downwind maximum can be revisualized to show two downwind bifurcated lateral PP maxima and (ii) the original results included storms from all directions, and thus the individual twin bifurcations PP maxima seemingly blended into a single contiguous downwind maximum. Less-cited original METROMEX analyses reproduced herein did in fact show that the original study showed: (i) a diurnal late afternoon PP peak associated with UHI initiation over the city and (ii) that the predominant NNE moving storms did produce a clearly bifurcated downwind maxima. These expanded results now are consistent with the newer results discussed in the paper.

How to cite: Bornstein, R. and Dou, J.: METROMEX redux: Is its urban precipitation maximum downwind enhancement or lateral maxima from storm bifurcation?, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-508, https://doi.org/10.5194/icuc12-508, 2025.

How the complex urban surface heteorogeneity influences wind field structures induced by tropical cyclones remains poorly understood despite its importance for disaster management. Here high-resolution numerical simulations using the Weather Research and Forecasting model coupled with two urban canopy models (WRF/UCMs) are conducted to address this issue with the case of landfalling Typhoon Lekima (2019) over the Yangtze River Delta (YRD) urban agglomeration. Detailed building morphology data is employed to capture urban heterogeneity. Results show that the WRF/UCMs reproduce the typhoon track and intensity reasonably well and the YRD urban agglomeration only slightly influences the typhoon track and intensity. The multi-layer UCM (BEP) significantly improves the overestimation and probability distribution of the 10 m wind speed compared to the single layer UCM (SLUCM) attributed to the explicit representation of building surface drag effect. The simulations accurately reproduced jet-like wind speeds near 1 km height, with urbanization enhancing vertical ascending and descending motions. During the typhoon primarily influenced period, the attenuation rate of the daytime wind speed due to urbanization at the lowest level reaches 56.6%, which is about 15.5% larger than that during pre-typhoon or post-typhoon periods, leading to a more pronounced vertical gradient in near-surface wind speeds. This is attributed to the almost vanished urban heat island effect during the typhoon influenced period, which stabilizes the daytime boundary layer conditions. As a result, the vertical mixing is reduced and consequently the vertical downward transport of momentum to the surface is weakened. Urban effects on the boundary layer asymmetries of the wind field structures and evolution during landfall are also explored. This study provides new insights into the importance of the urban land surface processes on regulating the wind structures under tropical cyclone backgrounds.

How to cite: Ao, X. and Yu, H.: Numerical simulation of urban impacts on wind field structures over the Yangtze River Delta under typhoon conditions, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-153, https://doi.org/10.5194/icuc12-153, 2025.

Complex terrain covers the vast majority of the Earth surface and affects local thermal wind flows by adding a gravitational component to the dynamics responding to local pressure gradients. The Leman Lake region, in Switzerland, thanks to its mountaineous topography, the presence of a large alpine lake and of two major cities (Lausanne and Geneva), represents an ideal testbed for studying the interaction between urban environments and lake breeze flows in complex terrain. However, most of the research investigating local fluid dynamics in the area predominantly focuses on the impact of wind flow on internal lake circulations, and limited attention has so far been given to the environmental impact of urban areas. Here, we use a set of high-resolution Weather Research and Forecast (WRF) model simulation experiments to investigate the diurnal and seasonal evolution of boundary layer dynamics in the Leman Lake region, with a focus on the environmental impacts associated with the cities of Lausanne and Geneva. In order to isolate urban impacts and explore the role of different land cover types, we compare simulation results from an “Urban” scenario featuring a realistic landscape representation, with simulation results from an hypothetical “Rural” scenario where urban areas are replaced by croplands. We also use an additional set of monthly simulations, to evaluate the potential for improved representation of physical processes offered by the integrated 1-D WRF Lake model. Analysis of results shows that urban environments, although of limited extent, are able to modify wind flows locally, e.g., by anticipating the diurnal onset of the lake breeze circulation. In turn, wind flows interact with local UHIs by advecting heat over the Leman Lake, in accordance with what has been observed by similar studies in world regions charaterized by different topographical and climatological conditions.

How to cite: Brandi, A. and Manoli, G.: Urban impacts on lake-land interactions, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-92, https://doi.org/10.5194/icuc12-92, 2025.

Dust aerosol affects the radiation balance of the atmosphere and the resulting air temperature near the ground. However, the profile of dust aerosol content in the atmosphere is usually taken from climatological data in urban climate simulations without considering daily and event-related variations. This limitation may affect the accuracy of the simulations in specific situations. This study investigates whether taking explicitly into account the dust aerosol could increase the model performance, more specifically its ability to estimate the 2 m air temperature and thermal comfort indices.

The research question is investigated in the context of a heat wave that occurred in the Paris region from 16 to 19 June 2022. During this event, a hot air mass was advected from the Sahara region, transporting a high content of dust aerosol. A simulation of this event using the Meso-NH atmospheric model coupled with the SURFEX land surface model shows low agreement with 2 meter air temperature observations when climatological aerosol were used.

To evaluate the effect of the aerosol amount on the simulation results, three simulations were performed using different assumptions about the dust aerosol content of the atmosphere, based on data from Copernicus Atmospheric Monitoring Service (CAMS) analyses:

• a reference simulation without dust aerosol,

• a simulation using the CAMS data as input of the simulation,

• a simulation using the CAMS data but its value was multiplied by 2.

The results show that compared to the reference simulation, taking into account the aerosol improves the accuracy of the simulations, especially by reducing the warm bias in near-surface air temperature (even thought it might not be the main explanation of the warm bias of the model).

How to cite: Bernard, J., Lemonsu, A., Wurtz, J., Rodier, Q., Schoetter, R., Nagel, T., and Masson, V.: To what extent can explicit consideration of dust aerosols in the atmosphere improve urban climate modelling?, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-861, https://doi.org/10.5194/icuc12-861, 2025.

This study contributes to the growing body of research on improving urban representation in climate models by investigating the global impacts of anthropogenic heat emissions (AHE). Since the 1970s, it has been recognized that AHE from urban areas can influence the global climate. Recent regional climate models (RCM) have confirmed the significance of AHE in forming urban heat islands. The objectives of this work are twofold: to develop two methods for incorporating an anthropogenic heat emission dataset into a Global Climate Model (GCM), and to test the impacts of AHE on the whole Earth by analyzing multiple short-term time-lagged "branch" ensembles. The approach is designed to be applicable to any geospatial dataset of AHE and GCM. The study uses the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) as the GCM, which was modified to read hourly inputs of AHE in units of W/m². The surface modules pertaining to land were also modified to consider AHE as excess sensible heat, set either from the surface driver or from the land surface model. The global climate for July 2023 was modeled using the Tsubame supercomputer at a resolution of 14 km. Multiple time-lagged branches were generated starting from a month-long control case that does not consider AHE. After filtering out internal variabilities using ensemble statistics, it was found that air temperatures increased globally. While the study agrees with previous RCM studies, this study finds that the AHE's influence propagates to wider areas after a day, beyond typical boundaries of RCMs. This work provides a potential link between the common gaps in scale between urban climate and global climate studies.

How to cite: Varquez, A. C. G., Nakano, M., Nakayoshi, M., Takane, Y., and Khanh, D. N.: Effects of spatiotemporal changes in anthropogenic heat emission on 14-km resolution global climate, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-627, https://doi.org/10.5194/icuc12-627, 2025.

The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides global climate projections under multiple scenarios through the end of the century, facilitating dynamical downscaling simulations to evaluate the future impact of heatwaves on urban heat risk. However, the absence of future observational data makes it challenging to define heatwave events as simulation periods, while integrating high-resolution urban canopy models into long-term simulations leads to prohibitive computational costs. These limitations hinder the investigation of the spatiotemporal distribution of heat risk in target cities. 

This study employs the Weather Research and Forecasting (WRF) Model coupled with BEP+BEM, integrates gridded urban canopy parameters data, and focuses on the Tokyo metropolitan area as the study region. First, using CMIP6 data with a spatial resolution of 1.25°, we apply the percentile threshold method to identify and analyze heatwave events in the study area under the SSP245 and SSP585 scenarios for three future periods: 2025–2045, 2050–2070, and 2080–2100. Next, we employ an averaging-then-downscaling approach to obtain representative downscaled simulations of heatwave conditions for each period under different emission scenarios. Finally, we examine changes in urban heat island intensity and the spatiotemporal distribution of the Wet Bulb Globe Temperature (WBGT) during future heatwaves. Additionally, based on WBGT, we explore the most effective mitigation measures for reducing future heat-related health risks across different subregions. We believe this study provides a scientific reference for cities to adapt and respond to increasingly severe extreme heat events in the future.

How to cite: Zhu, D. and Ooka, R.: Spatiotemporal Changes in Urban Heat Risk Driven by Intensifying Heatwaves in Global Warming Scenarios, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-348, https://doi.org/10.5194/icuc12-348, 2025.

The WCRP CORDEX “Flagship Pilot Study URBan environments and Regional Climate Change” (FPS URB-RCC) aims to understand the interactions between urban areas and regional climate change. As part of the STAGE-0 Test simulations, which focus on double-nested downscaling of two short weather events for the region of Paris, France, this study discusses the impact of the horizontal resolution on daily precipitation during the whole period of simulation (4-5 months). The simulations are driven by ERA5.1 reanalysis data and two different resolutions are taken into account: ~ 12 and 3 km, the first covering Europe (EUR-12; PARIS-12) and the second centered over Paris (PARIS-3); in total, 23 and 29 simulations are considered for the analysis, respectively. Preliminary results were compared to EOBS data and show that basically all models were able to capture the precipitation over the city of Paris that occurred in May 2020. The PARIS-3 simulations showed some improvement in representing the averaged precipitation over the city, as well as the minimum and maximum values observed inside the domain of the city. Nevertheless, five days before the event, both resolutions overestimated a short precipitation event (by 200%), although capturing the timing. Further investigation regarding the associated synoptic condition simulated by the models in both resolutions will be explored with the aim of understanding the dynamics related to the events.

How to cite: Machado Crespo, N., Villalba Pradas, A., Belda, M., Verma, S., and Halenka, T. and the FPS URB-RCC: Impact of the horizontal resolution on precipitation in an ensemble of regional climate models from the FPS URB-RCC , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-591, https://doi.org/10.5194/icuc12-591, 2025.

Complex interactions between the urban and regional climatic processes occur in Andean cities. These are shaped by the mountainous topography and increasing urbanization, resulting in significant environmental challenges. Climate change is leading to an increased intensity and frequency of meteorological extremes, increasing the risks in these fragile urban environments. Extreme and unusual heat events in the Andes have become a pressing issue in recent times, compounded by other climate extremes like prolonged droughts and intense rainfall. This has resulted in severe impacts such as glacier loss, water shortages, extreme floods and unbearable thermal stress for local communities, especially in cities. This study examines the microclimatic variations across four Andean cities – Bogota, Cusco, La Paz and Santiago, during recent extreme heat episodes, using WRF (Weather Research and Forecast) simulations. The ERA5 reanalysis data is used to define the initial and boundary conditions of the WRF model, calibrated to represent climatology of the entire Andes region. To configure the urban morphology more accurately into the model, it is coupled with 3D urban canopy models, which are integrated with Local Climate Zones of each city generated through World Urban Database and Access Portal Tools. The modelled finer scale near surface meteorological parameters – temperatures (air and surface), wind flow patterns, relative humidity that are most relevant to determine the heat stress are analysed to understand the nature of micro-scale UHI (urban heat island) variations in each city. The results indicate how urban design and geometry influence the spatial variations in UHI for both large and medium-sized cities, during regional-scale heat extremes. This study presents the initial assessment to understand the dynamic interplay between urban microclimate and regional meso-scale climate and how it influences localised impacts of different meteorological extremes in the context of changing climate and urban development across this complex terrain.

How to cite: Bhattacharjee, S., Potter, E., Li, S., Jones, J., Ely, J., and Davis, B.: Heat Extremes and Urban Climate Dynamics in Andean cities, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1060, https://doi.org/10.5194/icuc12-1060, 2025.

How to cite: Theeuwes, N., Zonato, A., de Rooy, W., Lean, H., Knoop, S., and Masson, V.: Improving numerical weather prediction at urban to neighbourhood scales , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-616, https://doi.org/10.5194/icuc12-616, 2025.

The substantial computational resources required for dynamical downscaling (D-DS) have limited extensive exploration of urban climate prediction, particularly for long-term and high-resolution scenarios. To bridge this gap, we propose a novel downscaling approach: Land-Surface-Physics-Based Downscaling (LSP-DS). This innovative approach aims to perform high-resolution, long-term urban-specific simulations with significantly reduced computational demands.

LSP-DS integrates the widely used HRLDAS/Noah-MP land surface model with urban canopy-process physics (SLUCM) and is driven by coarse-resolution reanalysis or numerical modeling data. Our evaluation of LSP-DS focuses on simulating the interactions between the urban heat island (UHI) effect and heat waves (HWs), using the Tokyo area as a case study. The analysis, which incorporates observational data with numerous LSP-DS simulations, confirms that the impact of UHI intensifies during HW periods.

To further assess the performance of LSP-DS, we conducted a comparative analysis with conventional direct D-DS (WRF) over the past decade in the Tokyo and Singapore regions. The results reveal that the WRF model overestimates nighttime urban temperatures, leading to an overestimation of the UHI effect, while HRLDAS/Noah-MP demonstrates accurate UHI effect estimates for both daytime and nighttime. Additionally, it was found that the urban-rural 1st atmospheric layer temperature profiles of HRLDAS/Noah-MP are too similar, but the SLUCM proved to be highly effective.

This research underscores the potential of LSP-DS in urban climate prediction, offering a less resource-intensive yet accurate alternative to conventional D-DS methods, with significant implications for urban climate studies and policy-making.

How to cite: Xue, L., Doan, Q.-V., Kusaka, H., He, C., and Chen, F.: A Novel Downscaling Approach for Urban Climate: Land-Surface-Physics-Based Downscaling, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-155, https://doi.org/10.5194/icuc12-155, 2025.

Natural areas, often referred to as rural areas, are characterized by minimal or non-existent urbanization. They serve as crucial benchmarks for impartial comparisons with urban environments. Urbanization leads to significant increases in surface and air temperatures in urban areas compared to their rural surroundings, a phenomenon known as the urban heat island (UHI) effect. This study employs high-resolution climate simulations conducted with the regional climate model CNRM-AROME46t1 (at 2.5 km resolution) to develop an innovative, fully automated method for spatializing UHIs. The CNRM-AROME46t1 model incorporates a land cover classification (ECOCLIMAP) derived from high-resolution Corine Land Cover data. This land cover mask enables the extraction of urban areas without requiring prior detailed knowledge of the region or predefined climate zones. The methodology developed, referred to as the M_Method, has been applied to a domain covering metropolitan France, encompassing urban areas of varying sizes, including the highly dense Paris metropolitan area and the medium-sized city of Dijon. These two urban centers, where local weather station data are available, were used to evaluate the automatic UHI spatialization approach. Results indicate the presence of thermal biases between the CNRM-AROME46t1 simulations and observational data. However, the application of the M_Method successfully identified and mapped areas most vulnerable to UHI effects with high accuracy. This methodology holds significant potential for future climate projections and scenario analyses, offering critical insights into key climate indicators. The spatialized diagnostics generated by this approach serve as a valuable strategic resource, enabling decision-makers to assess UHI conditions across metropolitan France and prioritize policies aimed at mitigating climate change impacts. Furthermore, the framework is designed to be adaptable to other geographical and climatic contexts and can be extended to analyze additional climate variables, such as the urban-rural moisture anomaly.

How to cite: Quenum, M., Lemonsu, A., Corneille, L., and Harader-Coustau, E.: A Novel Technique for the Spatially and Automatic Estimation of Urban Heat Island from High-Resolution Climate Simulations, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-342, https://doi.org/10.5194/icuc12-342, 2025.

Urban-scale downscaling faces significant challenges due to model biases and errors propagated from initial and boundary conditions provided by reanalysis datasets or global climate models. To address these issues, we introduce a novel global-to-local modeling framework that employs one-way coupling between the Model Prediction Across Scales (MPAS) and Weather Research and Forecasting (WRF) models. This framework is applied to a short-term (10 days) summertime meteorological simulation for the Phoenix Metropolitan Area (PMA).

The MPAS-to-WRF approach maintains physics and static field representation consistency across models and reduces spatiotemporal interpolation errors from the driving data. Simulations conducted with the MPAS-to-WRF framework are compared to a traditional approach using the ERA-5 reanalysis product to drive high-resolution (2 km grid spacing) WRF simulations for a 10-day summertime period (June 1-10, 2020). Results demonstrate improved accuracy in near-surface air temperature, moisture, and wind predictions using the MPAS-to-WRF framework, for the first 4-5 days, but a tendency for degradation appears thereafter.

This study introduces a robust method for short-term urban downscaling and highlights the potential for future research to incorporate data assimilation for enhanced long-term simulation accuracy. Future work - ongoing - will incorporate data assimilation methods to improve predictability for monthly to seasonal scale summertime simulations, and potentially, beyond.

How to cite: Georgescu, M. and Moustaoui, M.: A Novel Framework for Short-Term Urban Meteorological Simulations, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-819, https://doi.org/10.5194/icuc12-819, 2025.

Urban latent heat processes are neglected or oversimplified in most mesoscale models in previous studies, leading to large uncertainties in modelling urban climate. By coupling our newly developed urban hydrological parameterization scheme in the mesoscale model WRF/BEP+BEM, we conducted three one-month simulation tests to quantify the impact of latent heat processes on urban climate, which is induced by urban ground greening, green roofs and surface water, respectively. It is found that urban latent heat significantly reduces maximum temperatures and thus improves comfort, especially during heatwaves, but it does not markedly influence mean air temperature. Compared to ground greening, green roofs provide enhanced cooling advantages. Overall, all three latent heat processes produce a more spatially heterogenous distribution of precipitation with a reduction of 25% in total precipitation amount. This can be attributed to the reduced urban heat island intensity by latent heat and the enhanced stability of the planetary boundary layer. The finding has implication for the measures that can be taken in reducing the adverse impact induced by rapid urban expansion.

Highlights

• A state-of-the-art urban hydrological scheme coupled to WRF/BEP+BEM was used to quantify the impact of latent heat on urban climate.
• Urban latent heat can significantly reduce maximum temperatures and improve comfort.
• The latent heat cooling efficiency of green roofs is more prominent, especially during heatwaves.
• Urban latent heat reduces contributes to a 25% decrease in total rainfall and promotes a more dispersed distribution of precipitation.

How to cite: Yu, M.: Quantifying the impact of latent heat on urban climate: a perspective from a novel parameterization scheme, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-824, https://doi.org/10.5194/icuc12-824, 2025.

This study presents the integration of a novel three-dimensional urban parameterization, the Three-Dimensional Urban Canopy Model (3DUCM), into the Weather Research and Forecasting (WRF) model (WRF/3DUCM). Differently from traditional urban sub-grid scale parameterizations implemented into mesoscale meteorological models that consider a simple two-dimensional canyon geometry, representative of the average urban morphology of the mesoscale model grid cell, 3DUCM is a single-layer urban canopy model taking into account every single building of the urban area for the evaluation of the energy budget. It considers canyon orientation and also includes canyon edge effects, i.e., explicit crossroads modelling. Model output incorporates not only average grid cell variables, but also predicted fields down to the building scale. In this work, WRF/3DUCM is tested in the city of Rome during a summer heat wave. Simulations benefit from detailed information on the geometric characteristics of the city, whereas physical properties of urban materials are assigned based on the local climate zone framework. Simulation results obtained with WRF/3DUCM are compared with those from simulations performed with WRF coupled with the default single-layer and multi-layer urban canopy parameterizations and evaluated against an observational dataset. The results highlight the potential of incorporating single-building details to improve the representation of urban microclimates with mesoscale meteorological models.

How to cite: Di Santo, D., Ravizza Garibaldi, G., Conigliaro, E., Leuzzi, G., Monti, P., and Giovannini, L.: Integrating a three-dimensional urban canopy model into WRF for enhanced microclimate representation, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-226, https://doi.org/10.5194/icuc12-226, 2025.

This study presents significant updates to the BEP-BEM (Building Effect Parameterization - Building Energy Model) urban canopy parameterization, aiming to improve the representation of atmospheric flows in urban areas. The enhancements include the coupling of BEP-BEM with a hybrid LES-RANS planetary boundary layer (PBL) scheme and the incorporation of a novel urban gardens model. Furthermore, the urban vegetation fraction is computed in greater detail using the Corine Land Cover, improving the representation of vegetation-atmosphere interactions within urban environments. These advancements collectively aim to enhance the accuracy of urban climate modeling under extreme weather conditions such as heat waves.

Traditional RANS-based PBL schemes struggle to capture horizontal turbulence and urban canopy-layer interactions effectively. To overcome these limitations, this study introduces a novel 3D TKE Scale-Adaptive PBL scheme. This scheme blends local and non-local components to enable the concurrent application of 3D TKE, RANS, LES, and BEP-BEM. This approach ensures a more physically consistent representation of turbulence within the boundary layer.

To validate these updates, a detailed case study is conducted for the Ruhr area, Germany, during the July 2019 heatwave (July 19–28). The model evaluation leverages ~1700 quality-controlled crowd weather stations from the Netatmo network, providing a unique opportunity to assess the performance of urban parameterizations at high spatial density. Three urban morphology datasets are compared, including one refined using WUDAPT_INTERP, which applies W2W-based interpolation techniques to improve LCZ mapping precision.

Findings indicate that the newly developed 3D TKE LES-RANS closure with BEP-BEM, combined with the refined urban morphology dataset, significantly enhances temperature predictions, particularly for minimum temperatures. This improvement suggests a better representation of horizontal advection processes and stable boundary layer structures. Moreover, the integration of urban gardens as a distinct urban canopy element introduces additional surface heterogeneity, demonstrating localized cooling effects and a potential improvement in thermal comfort.

How to cite: Zonato, A., Martilli, A., Demuzere, M., Pappaccogli, G., Kamath, H., and Kittner, J.: Enhancing BEP-BEM for Urban Climate Modeling: Coupling with a 3D-TKE Scale-Adaptive PBL Scheme, Refining Urban Morphology, and Incorporating Urban Gardens, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-695, https://doi.org/10.5194/icuc12-695, 2025.

Urban Heat Island (UHI) is a phenomenon where urban areas experience significantly higher temperatures than their rural surroundings. This effect is primarily due to heat retention in buildings and roads, reduced evapotranspiration, and heat generated by vehicles, industrial activities, and air conditioning. Accurate UHI modelling is crucial for understanding its impacts and helping urban planners and policymakers in developing effective strategies to mitigate heat stress in cities. Advanced urban canopy schemes within atmospheric models play a key role, as they aim to realistically represent the complex interactions between urban surfaces and the atmosphere. The TERRA_URB (TU) model, developed within the COSMO Consortium, parametrizes the effects of buildings and streets on energy and moisture exchanges between the surface and atmosphere. Additionally, it accounts for the anthropogenic heat flux as a heat source from the surface to the atmosphere. TU requires the definition of parameters describing the geometrical and thermal urban features, such as street aspect ratio, building surface fraction, building height, impervious surface area, anthropogenic heat flux. These parameters were derived from the Local Climate Zone (LCZ) classification, using both global and local dataset. This study evaluated the performance of the TU scheme, implemented within the ICON model, by simulating past heat waves over Turin at 500 m resolution in hindcast mode. The ability of the TU scheme to reproduce UHI effects was assessed by comparing ICON simulations, with and without TU, against observational data. These included ground-level measurements from the Arpa Piemonte meteo-hydrological network and vertical temperature profiles from radiometers located in both the city center and surrounding areas. Furthermore, a denser crowdsourced air temperature network, NetAtmo, was evaluated to assess the potential of the citizen science data for improving urban climate studies. The results demonstrated that the TU scheme significantly improved the representation of the UHI effect.

How to cite: Garbero, V., Houget, T., Salizzoni, P., and Milelli, M.: Modelling the Urban Heat Island over Turin during past heat waves, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-808, https://doi.org/10.5194/icuc12-808, 2025.

The IPCC AR6 Working Group 2 report (https://www.ipcc.ch/report/ar6/wg2/chapter/chapter-6/) states 'evidence from urban and rural settlements is unequivocal; climate impacts are felt disproportionately in urban communities, with the most economically and socially marginalised being most affected.' However, climate information at the urban scale remains limited, as urban areas have historically been excluded from climate models, and recent attempts to incorporate them vary in complexity.

To assess the role of urban land surface description in climate projections, we conducted three convection-permitting climate model (CPM) experiments (4 km grid length) over Southeast Asia (1981-2000), covering Bangkok, Hanoi, Ho Chi Minh, and Phnom Penh. Each simulation progressively enhances land surface detail, utilizing high-fidelity datasets (WorldCover and World Settlement Footprint 3D) to refine land cover and building morphology representation. Initial findings indicate that these improvements significantly impact temperature (1-2°C), with variations by city. The CPM experiments are still running and we will present our results in full once they have completed.

High-resolution climate projections capable of resolving urban areas are rare. Our results advance understanding of how urban areas influence their climate and provide valuable insights for future urban CPM projections, with the potential to contribute to the AR7 Special Report on Climate Change and Cities.

How to cite: Redmond, G., Blunn, L., and Lipson, M.: Evaluating the Representation of Cities in a Convection Permitting Climate Model over Southeast Asia, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-834, https://doi.org/10.5194/icuc12-834, 2025.

Increasing the albedo of urban surfaces, through strategies like white roof installations, has emerged as a promising approach for urban climate adaptation. Yet, modeling these strategies on a large scale is limited by the use of static urban surface albedo representations in the Earth system models. In this study, we developed a new transient urban surface albedo scheme in the Community Earth System Model and evaluated evolving adaptation strategies under varying urban surface albedo configurations. Our simulations model a gradual increase in the urban surface albedo of roofs, impervious roads, and walls from 2015 to 2099 under the SSP3-7.0 scenario. Results highlight the cooling effects of roof albedo modifications, which reduce the annual-mean canopy urban heat island intensity from 0.8°C in 2015 to 0.2°C by 2099. Compared to high-density and medium-density urban areas, higher albedo configurations are more effective in cooling environments within tall building districts. Additionally, urban surface albedo changes lead to changes in building energy consumption, where high albedo results in more indoor heating usage in urban areas located beyond 30°N and 25°S. This scheme offers potential applications like simulating natural albedo variations across urban surfaces and enables the inclusion of other urban parameters, such as surface emissivity. 

How to cite: Sun, Y., Fang, B., Oleson, K., Zhao, L., Topping, D., Schultz, D., and Zheng, Z.: Improving Urban Climate Adaptation Modeling in the Community Earth System Model (CESM) Through Transient Urban Surface Albedo Representation, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-33, https://doi.org/10.5194/icuc12-33, 2025.

Rising climate risks in urban areas, driven by global warming and rapid urbanization, pose significant challenges to thermal comfort and urban sustainability. Global warming and urbanization effects on megacities remain uncertain. While considering urbanization in the form of spatial changes in urban parameters and anthropogenic heating (AH), this study models the present and future climate of Tokyo, Cairo, and Jakarta in 2050 under three CMIP6-based Shared Socioeconomic Pathways (SSP126, SSP245, and SSP370) at 1.5-km spatial resolution. To incorporate both global warming and detailed urban distributions, we used the pseudo-global warming (PGW) method and the WRF model 4.6, which explicitly considers the spatial distribution of urban parameters and AH in the single-layer urban canopy modeling framework. Extending our focus beyond temperature changes to thermal comfort, we further estimated the UTCI from the empirical UTCI-Fiala model. Results show global warming has a greater overall impact on air temperature and UTCI increases compared to future urbanization and AH change, with the effect intensifying from SSP126 to SSP245 to SSP370 and UTCI rising more sharply. However, urbanization and AH changes introduce significant spatial variability in temperature and UTCI changes within each city, with some locations having similar scale of increases as background climate. Global warming scenarios evidently influence the temperature increases from present to future across all cities, with monthly variations driven by seasonal differences. Additionally, the influence of urbanization on temperature and UTCI varies across seasons and cities. The mechanisms behind them are further examined by inspecting other modeled meteorological variables, such as climate-change influence on background winds and precipitation. From feature importance analysis, we find that while the overall urbanization effect on temperature and UTCI change remains consistent across scenarios, variations arise due to differing influences of urbanization on other factors, such as mean radiation temperature, wind speed, and relative humidity.

How to cite: Jin, X., Varquez, A. C. G., Do, N. K., Tomohiko, I., Norihiro, I., kanda, M., and Inagaki, A.: Inter-comparison of present and future urban climates of three cities considering multiple CMIP6 scenarios and urbanization, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-709, https://doi.org/10.5194/icuc12-709, 2025.

One relevant effect of urbanization is the modification of atmosphere-surface interactions, which modulate urban microclimate and human thermal comfort. The Universal Thermal Climate Index (UTCI) is commonly employed to quantify the impact of heat on the human body, accounting for not only air temperature influence but also the variability of other relevant weather variables such as wind speed, air humidity and radiation. The irregularity of urban morphology (e.g. building height and layout) across the city leads to high spatial heterogeneity of the micrometeorological variables. Therefore, analyzing the impact of urban geometry and the past changes in urban land cover on heat stress contributes to understanding the potential risks that urban residents might face considering the future urban growth and future climate.

The purpose of the present work is to investigate the impact of urban development and climate on outdoor thermal comfort in Madrid for summer weather conditions under past and future climate. A modeling study is conducted using the Weather, Research and Forecasting (WRF) model adapted to estimate the heat and momentum exchanges between buildings and atmosphere (BEP-BEM urban scheme), as well as the recent development incorporated into BEP-BEM to quantify heat stress through UTCI values and its subgrid variability. Past urban scenarios are performed considering the realistic urban expansion and morphology from 1970 to 2020, and the expected urban development is used for the future scenario. Even though the urban layout has barely changed in the center of Madrid over the last 50 years, results show an increase in the UTCI values due to the influence of the surrounding urban expansion. In addition, these results show the relative contribution of urbanization and climate effects on the heat stress changes across the city under the past and future climates.

How to cite: Sanchez, B., Martilli, A., Santiago, J. L., Rivas, E., Martin, F., Royé, D., Carbone, J., and Yagüe, C.: Past and future changes in the spatiotemporal distribution of heat stress in Madrid, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-917, https://doi.org/10.5194/icuc12-917, 2025.

Climate change is driving a global rise in temperatures. In Ireland, increasing temperatures pose a significant challenge, as residents are not naturally acclimated to extreme heat. The escalation of thermal risks is attributed to the accelerating pace of urbanization. Additionally, variations in land cover and urban environments lead to differing levels of thermal risk across regions.

This study investigates the relationship between local climate zones (LCZs) and thermal stress (measured via the Universal Thermal Climate Index, UTCI) to inform heat risk mitigation in Ireland’s future development. High-resolution (~4 km) regional climate projections were generated by dynamically downscaling CMIP6 data using atmosphere-only and coupled atmosphere-ocean-wave regional climate models (RCMs). Outer domains (12 km for COSMO-CLM and 20 km for WRF) aligned with the Euro-CORDEX framework were nested to refine Ireland-specific projections. Data from a 30-year reference period (1981–2010) and three future 30-year periods (2021–2050, 2041–2070 and 2071–2100) were used for the analysis of the Irish climate for each of the four RCP-SSP scenarios. The estimated UTCI is subsequently analysed in tandem with LCZs.

By evaluating the correlation between heat risk and LCZs, this research aims to inform climate-resilient planning and development in Ireland. The findings provide valuable insights for thermal risk mitigation strategies across different urban morphologies, particularly crucial as cities adapt to increasing thermal stress under climate change scenarios.

How to cite: Rahul, A., Clarke, J., and Nolan, P.: Thermal Stress Dynamics Across Local Climate Zones: A High-Resolution Analysis of Ireland's Future Climate, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-932, https://doi.org/10.5194/icuc12-932, 2025.