Chile has an extensive coastline on the Pacific Ocean, where important urban areas are located. Approximately 20% of the country's population resides in Coastal Metropolitan Areas. Among these is the Valparaíso-Viña del Mar Metropolitan Area (AMVV), which is home to one million inhabitants. Within this area, Población Vergara (PV) in Viña del Mar stands out for its proximity to the sea and its urban configuration, characterized like a open high buildings zone, intense daytime urban activity and a notable presence of vegetation and trees. This sector has a streets front open to the ocean, which directly influences the air circulation in its interior. To evaluate the both impact urban morphology and frontline buildings on air flow of the sea land breeze (SLB) to Poblacion Vergara, field measurements were taken in the spring at pedestrian level at three times of day: 10 am, 2pm and 8pm, as well as simulations with the ENVI-met software. The results showed that the urban configuration significantly influences the dynamics of the sea breeze, affecting both its entry and exit from the built-up area depending on the time of day. The presence of buildings, streets and vegetation determines the behavior of the air at the sea edge of the city, modifying its velocity both horizontally and vertically; high-rise buildings zone generates accelerations in air flow towards the interior of the city, while wooded vegetation contributes to mitigate these effects. These results are an advance in knowledge regarding the potential cooling and air renewal provided by the ocean in urban areas to mitigate the effects of urban heat.

How to cite: Carrasco, C. and Tapia, J.: A coastal city on the South Pacific Ocean. Urban front and sea-land breeze in Viña del Mar, Chile., 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-801, https://doi.org/10.5194/icuc12-801, 2025.

In areas with a long summer season, especially where heat stress prevails throughout the day, such as Mediterranean coastal cities, Urban Heat Island (UHI) causes further thermal discomfort and an increase in energy consumption. Previous studies have indicated a pronounced UHI in stable winter nights, whereas most studies on the UHI in the warm season have focused on individual case studies. This study analyses the characteristics of the summer UHI of Tel Aviv under different weather conditions, using meteorological data over five summer seasons (2020-2024), and develops a statistical downscaling model that predicts the UHI intensity, based on synoptic- and mesoscale variables. The Tel Aviv UHI is quite variable during summer days, depending on mesoscale variations under the semi-permanent synoptic seasonal conditions. During daytime, the UHI is weak (<2°C) and occasionally negative. The nighttime UHI ranges from <1°C to extreme (9°C) and is typically between 4-7°C. The UHI intensity is significantly dependent on the westerly wind component, i.e., the sea breeze, enhanced by the synoptic-scale Etesian winds, the height of the persistent seasonal marine inversion, and the existence and intensity of a surface inversion, observed near the city. A prediction equation for the UHI yields a 0.85 correlation with the observed values. A surprising finding is an inverse relationship between the nocturnal temperature and the UHI intensity. In several excessive nocturnal heat events, with minimum temperature >26°C, the nocturnal UHI was minimal or even disappeared. These nights were characterized by an absence of the land breeze, increased nocturnal westerly winds from the warm Mediterranean Sea, and a relatively high base of marine inversion accompanied by clouds. However, during other nocturnal heat events, the UHI was distinct, and occasionally extreme, explained by the light land breeze, clear skies, and a pronounced surface inversion or a low marine inversion base.  

How to cite: Saaroni, H., Zohar, M., and Ziv, B.: Meteorological factors affecting the summer urban heat island in a Mediterranean coastal city - the case of Tel Aviv, Israel, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-105, https://doi.org/10.5194/icuc12-105, 2025.

Sea and estuarine breezes (SEB) play a critical role for cooling air temperatures and enhancing thermal comfort during summer in coastal urban areas. This research investigates the dynamics and impacts of SEB in Lisbon (Portugal) by combining data from a mesoscale meteorological network comprising 80 stations with high-resolution wind field simulations during the thermal summer of 2022 (June 10 to October 8). SEB episodes were identified using criteria based on wind direction shifts: the disruption of prevailing northerly winds in the morning (Nortada), transitions to easterly or southerly directions (rotation between 22,6 and 292,5º), and the resumption of regional flow by late afternoon. Wind fields were modeled using GRAMM-SCI, initialized with ERA5 reanalysis data. Finally, air temperature, absolute humidity and thermal comfort (Universal Thermal Climate Index) anomalies (ΔT/Ha/UTCI_urb) were calculated to a reference site (the airport weather station) according to the distance to the riverfront area.  SEB at 10 m height, occurred on 31% of summer days, peaking in July and August, with an average duration of six hours (10:00AM – 4:00PM). Considering only the roughness effect of the city and the terrain, these breezes reduced air temperatures up to 4 km inland, with maximum cooling effects (-1.7°C) observed within 500m of the Tagus estuary. Absolute humidity increased by 4.2 g/m³ near the estuary, and UTCI values dropped by 2.2°C on typical breeze days, reaching 5.1°C during heatwave events, substantially reducing heat stress within 1.5 km of the riverfront. However, some riverside areas still experienced moderate heat stress, highlighting the importance of preserving SEB corridors through climate-sensitive urban planning. This study reinforces the importance of integrating natural ventilation processes into urban design to foster cooler and more liveable cities.

How to cite: Reis, C., Oettl, D., Lopes, A., Santos Nouri, A., and Vasconcelos, J.: Exploring the Cooling Potential of Sea and Estuarine Breezes (SEB) in a Mediterranean city’s summer climate, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-87, https://doi.org/10.5194/icuc12-87, 2025.

Coastal cities across the world have been increasingly exposed to severe storms which threaten and strain their populations, infrastructure, and economies. Despite nearly 40% of the global population residing in these cities, the processes that drive coastal urban rainfall modifications are poorly understood. During its warm season Houston, the fourth most populated metropolitan area in the United States, frequently experiences sea breeze fronts (SBFs) and intense convective thunderstorms, which makes it an ideal region to study coastal urban-precipitation modification. The primary goal of this research is to understand the dynamics of the built environment -particularly its urban heat island (UHI) and building mechanical effects- in altering these coastal and cloud processes. An isolated thunderstorm sea breeze case from the summer 2022 NSF-funded Convective-clouds Urban Boundary-layer Experiment (CUBE) and DOE Tracking of Aerosol Convective Interaction Experiment (TRACER) field campaigns was simulated and evaluated against field campaign and radar observations. The tool used in the current investigation is the urbanized Weather Research and Forecasting (uWRF) model linked to the MYNN scheme. Results illustrate the formation of a UHI “plume” circulation in response to both urban SBF bowing and downwind rainfall. The role of this circulation in vertical moisture transport and updraft enhancement is explored. Future work will use Lagrangian storm-cell tracking software to understand how these clouds are changed by traversing the urban environment.

How to cite: Pena, J. C., Ramamurthy, P., Jensen, M. P., Giangrande, S., Swain, M., Gamarro, H., and González-Cruz, J. E.: Lifecycles of Coastal Urban Thunderstorms from an Observational and Modelling Perspective, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-247, https://doi.org/10.5194/icuc12-247, 2025.

This presentation focuses on coastal cities – a nexus of climate, energy, and air quality.   The Urban Heat Island (UHI) effect is the result of surface energy balance changes and anthropogenic heat emissions which forms a two-way feedback.  In warm seasons, excess heat from the UHI is a major driver of tropospheric ozone production once combined with nitrogen emissions and with volatile organic compounds (VOCs). Building exhalations are also a major source of environmental emissions, via their ventilation systems. These systems emit VOCs and Volatile Compound products, which are suspected to be major contributors for ozone production. As such, there is direct positive feedback in warm seasons between extreme heat, energy demands, and sources for ozone production. In cold seasons, this nexus also prevails; cold climates motivate energy demands, which leads to pollutants from the gas or coal driven-building heating systems, enhancing the UHI which results in negative feedbacks.  We present a unified observation and modeling approach to investigate this nexus in the two end-use costal-cities cases of New York City and Houston.  Observations and modeling from two major summer field campaigns are used to explore ozone episode cases driven by heat waves. The modeling used an urbanized weather model, which incorporates a building energy model, and is coupled to a chemical physical model.  The modeling framework was validated against the wide range of field observations demonstrating that incorporating urban effects is indeed necessary for accurate prediction. Observations showed a complex spatial and temporal interaction between the surface meteorology, UHI, sea-breeze front, and the ozone peak ridge. Maximum ozone production takes place in the cities which is advected to the urban outskirts, where the sea-breeze collapses leading to ozone peaks.  Building energy use was found to be a key contributor to both UHI intensification and maximum ozone.

How to cite: Gonzalez-Cruz, J., Gamarro, H., and Pena, J. C.: On the Nexus of Climate, Energy and Air Quality in Coastal-Urban Environments, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-150, https://doi.org/10.5194/icuc12-150, 2025.

Outdoor thermal comfort (OTC) is essential for public health. While the negative impacts on OTC during hot periods have been extensively studied, particularly in subtropical regions, there is a lack of evidence regarding cold conditions in these regions. Existing literature indicates that residents in regions with mild winters are less adaptable to cold snaps compared to those living in regions with cold winters. Overlooking the effect of cold days in warmer regions may lead to an underestimation of their impacts on thermal comfort and health, especially for vulnerable populations. Taking Hong Kong as a case study, this study assesses the cold weather events and their impacts on OTC in subtropical regions. Cold warning days, as defined by daily minimum air temperature at or below 12℃ and 7℃ respectively by Hong Kong Observatory, were used to identify cold weather events. Results show that during 2010-2019, Hong Kong experienced 98 cold days including 11 very cold days in downtown Nam Shan Estate, and 143 cold days including 16 very cold days in the new town of Tin Shui Wai. Physiological Equivalent Temperature (PET) evaluations by ENVI-met modelling reveal that the percentage of cold discomfort in spatial patterns exceeded 50% on cold warning days for both downtown and new towns. Compared to typical winter days, cold warning days resulted in 14.3–45.5% increase in the duration of thermal cold discomfort. Outdoor open spaces with less vegetation tend to be the most vulnerable areas throughout the day, identified as ‘cold spots’ in both downtown and new towns, potentially posing health risks to the elderly who are the primary users of urban outdoor spaces. Findings of this study underscore the critical need to identify and address the potential health risks associated with cold snaps in subtropical regions, particularly for vulnerable populations.

How to cite: Yao, L., Gao, K., Lau, K., and Ng, E.: Understanding winter outdoor thermal comfort in subtropical regions: Evidence from Hong Kong's cold weather events , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-290, https://doi.org/10.5194/icuc12-290, 2025.

Coastal cities face critical challenges in managing ozone pollution due to their high population density and complex interactions between urbanization and coastal meteorology. This study uses New York City (NYC) as a case study to investigate how urban surfaces influence heatwaves, land-sea breezes, and planetary boundary layer dynamics, and how these factors shape nitrogen dioxide (NO₂) distribution and ozone formation. Using data from the 2018 Long Island Sound Tropospheric Ozone Study (LISTOS), we leverage an airborne high-spatial-resolution ultraviolet-visible spectrometer to measure NO₂ tropospheric column densities. These observations provide valuable insights into precursor dynamics and serve as a benchmark for evaluating the performance of the urban Weather Research and Forecasting model coupled with Chemistry (uWRF-Chem), which simulates interactions between urban meteorology and chemical transport. Our findings highlight key features of chemical dynamics in NYC during a high ozone and heatwave episode. Early morning urban heat island effects trigger sea-breeze fronts, concentrating ozone precursors in the city center. Building-induced drag reduces wind flow, altering advection patterns and prolonging the residence time of these precursors over the urban area. These processes ultimately result in elevated ozone levels both within the city center and in downwind regions. Together, these insights enhance our understanding of urban air quality challenges and provide a foundation for more effective pollution mitigation strategies in densely populated coastal cities.

How to cite: Gamarro, H., McDonald, B. C., Ramamurthy, P., and Gonzalez-Cruz, J. E.: Modeling Coastal-Urban Impacts on Air Quality Distribution in New York City: Evaluation Based on High-Spatial-Resolution NO2 Retrievals, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-336, https://doi.org/10.5194/icuc12-336, 2025.

The Greater Bay Area (GBA) in South China is a highly urbanized and densely populated megalopolis. Heatwaves (HW) in the region are often attributed to the anomalous subtropical high, as well as tropical cyclones (TC) in the South China Sea/Western North Pacific region. This study investigates the mechanisms, intensity, and trends of heatwaves associated with TCs (TC-HW) and those without TC influence (NonTC-HW) during the May–September season from 1981 to 2019. Spatiotemporal variations of the Universal Thermal Climate Index (UTCI) across the region, highlighting key drivers of thermal comfort, are also examined. Results reveal distinct dynamic drivers for the two HW types. TC-HWs are characterized by anomalous subsidence, a strengthened subtropical high and enhanced atmospheric stability, causing anomalous northwesterly surface winds that suppress sea breeze cooling in the region. NonTC-HWs, on the other hand, are driven by an upper-level Omega Block pattern centered at approximately 35–40°N, which is accompanied by anticyclonic flows that inhibit heat dissipation over GBA. Compared with NonTC-HWs, TC-HWs lead to even warmer daily maximum temperature (T-max) by approximately 0.9°C, while the daily minimum temperature (T-min) difference is minimal. Both TC- and NonTC- HWs exhibit increasing trends in frequency and duration; however only TC-HWs show a rising trend in their amplitude. We also studied the trend of UTCI in GBA; there is an increasing annual trend larger than that of surface air temperature. This can be attributed to rising vapor pressure and declining wind speed in the region. These combined effects are found to be most pronounced in highly urbanized coastal locations compared to inland areas. These findings underscore the significant roles of synoptic and local climatic factors, as well as urbanization, in shaping changes in thermal comfort in this area.

How to cite: Tam, C.-Y. F., Lau, M., Xiao, M., and Wang, Z.: Investigating Heatwaves and Thermal Comfort due to different synoptic weather systems in South China Greater Bay Area, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-610, https://doi.org/10.5194/icuc12-610, 2025.

The outdoor environment of subtropical islands with high temperature, high humidity, strong radiation and strong wind speed has a great impact on outdoor thermal safety and thermal comfort of personnel. Ensuring the thermal safety and thermal comfort of the human body is of great significance to the development of island tourism. This study conducted thermal environment monitoring and thermal comfort questionnaire experiments in Hailing Island Beach Scenic Area to explore the outdoor thermal environment and human thermal comfort in the beach area, identify the factors affecting human thermal comfort, and determine the thermal comfort benchmark for tourists in the beach area. The research results show that: 1) the beach underlying surface albedo is 0.4, which is much higher than the common urban underlying surface albedo. The beach radiation environment is strong and the thermal environment is poor in summer. 2) On sea-land breeze days, sea breeze can effectively alleviate the heat stress in the offshore areas of island beaches. 3) Forests have a significant attenuation effect on solar radiation. Even sparse coconut forests have a certain hindering effect on radiation and the thermal comfort of human beings in the forest space is relatively good. 4) Tourists’ active thermal adaptation behaviors can avoid thermal discomfort, but the effect is limited. 5) This study obtained the thermal comfort benchmarks for beach tourists, and the thermal neutral ranges were: 20.93-29.01 °C (PET), 25.91-30.50 °C (UTCI), and -29.13-50.24 W/m² (COMFA), respectively. The research conclusions can provide a theoretical basis for the creation of outdoor thermal environment in beach scenic areas and the assessment of tourists' thermal comfort.

How to cite: Mi, J. and Li, Q.: Study on Thermal Environment Characteristics and Tourists' Thermal Comfort Benchmark in Subtropical Island Beach Scenic Spots, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-799, https://doi.org/10.5194/icuc12-799, 2025.

This study evaluates the performance of the Weather Research and Forecasting (WRF) model, enhanced with multi-layer urban canopy parameterizations (BEP-BEM), in capturing the unique microclimates of Caribbean coastal-urban environments. Leveraging Local Climate Zone (LCZ) mapping developed under the World Urban Database and Access Portal Tools (WUDAPT) framework, this study incorporates detailed representations of urban land cover and morphology. While LCZ methods have been widely applied to urban environments, this is among the first applications to tropical coastal cities in Puerto Rico and the United States Virgin Islands (USVI), highlighting their utility for small island settings. The simulations focus on the extreme summer heat experienced in the Caribbean during the summer of 2023, a period characterized by record-breaking temperatures and amplified urban heat stress. Using a nested domain setup at 9 km, 3 km, and 1 km resolutions (D01, D02, D03), the simulations are driven by ERA5 Reanalysis (~27 km resolution) to resolve key physical processes. The primary focus is to assess the ability of the urban WRF to capture coastal-urban boundary-layer dynamics, urban heat islands, and localized convection over small islands in the Caribbean. A key innovation of this study is the application of BEP-BEM schemes, which account for building energy exchanges and urban morphology, enabling a detailed representation of urban-atmosphere interactions. Preliminary results highlight the model's ability to capture fine-scale phenomena, including coastal breezes and urban-induced temperature gradients, critical for understanding the energy-air quality nexus and extreme weather behavior in these regions. This approach provides valuable insights into the fidelity of modeling tools for coastal-urban systems, particularly for small islands where urban footprints significantly influence atmospheric processes. By focusing on a specific extreme heat event, this study enhances understanding of coastal-urban interactions and informs climate resilience strategies for vulnerable regions.

How to cite: Gonzalez-Cruz, J. and Oppong, F.: Dynamic Downscaling of Coastal-Urban Caribbean Islands Extreme Weather Events Using High-Resolution Urban WRF, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-151, https://doi.org/10.5194/icuc12-151, 2025.

Reducing urban heat through climate-responsive design has become a priority in tropical cities, where high temperatures and intense solar radiation exacerbate outdoor thermal stress. Solar-reflective materials on pavements and façades have been proposed as effective strategies to mitigate surface heat accumulation and improve outdoor thermal conditions. This study evaluates the impact of cool pavements and cool-coated façades through field experiments and numerical simulations in Singapore, providing insights for their integration into urban planning.

Field experiments were conducted by applying high solar-reflectance coatings to asphalt pavements and concrete façades, increasing their reflectance by approximately 0.3 and 0.4, respectively. Mobile thermal stations were deployed to assess air temperature and mean radiant temperature (MRT) at pedestrian level (1.2 m), while thermocouples and thermal cameras captured surface temperature variations. ENVI-met simulations further analyzed the vertical distribution of air temperature and MRT from 0.3 m to 1.5 m.

Results indicate that cool pavements significantly reduce surface temperatures, while air temperature at pedestrian height exhibits a slight decrease. However, MRT at pedestrian level increases due to enhanced shortwave reflectance from the pavement surface, highlighting the need for careful material selection and urban design considerations. The study also examines the potential benefits of cool-coated façades in mitigating outdoor heat stress. These findings contribute to the development of urban cooling strategies, emphasizing the trade-offs of reflective surface treatments and their applicability across different urban contexts. By integrating these materials into long-term urban planning frameworks, cities can enhance climate resilience and improve outdoor thermal environment.

How to cite: Xu, R., Tong, S., Tan, E., and Wong, N. H.: Evaluating the Impact of Solar-Reflective Cool Pavements and Façades on Outdoor Thermal Conditions in a Tropical City, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-994, https://doi.org/10.5194/icuc12-994, 2025.

Hailstorms are a leading contributor to insured losses in cities in Australia and are expected to be affected by climate change, yet changes to hailstorm damage potential under climate change are not well quantified. Hail damage grows with the size of the hailstones produced by a storm, and is exacerbated by the co-occurrence of strong winds. Here, we show the first projections for hail size and co-occurring wind strength for Australian cities under a climate change scenario. Convection-permitting downscaled simulations were run for major cities and a remote region, in total covering 65% of Australia's population, for a historical period and a scenario with ~2.8 degrees Celsius of global warming over pre-industrial temperatures. Using extreme value analysis, we show that in the future scenario hail damage potential increased in some regions. In particular, overall hail frequency was projected to increase around Sydney/Canberra and Brisbane, while there were projected increases in maximum hail size for domains covering Melbourne, Sydney/Canberra, a remote region in Western Australia, and Perth. Strong winds coincident with hail were projected to decrease around Melbourne, Sydney/Canberra, and Perth. These results are important for urban design and city planning in a changing climate and can inform future climate risk planning in Australian cities.

How to cite: Raupach, T. and Aldridge, J.: Projected changes in hail damage potential in Australian cities under climate change, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1107, https://doi.org/10.5194/icuc12-1107, 2025.