Urban overheating threatens public health and energy sustainability. Traditional radiative cooling strategies, such as super cool materials with high albedo and high emissivity, produce undesired cooling during cold seasons and increase space heating demand — a phenomenon known as the heating energy penalty. A novel temperature-adaptive emissivity (TAE) roof coating, which shifts from a low emissivity under cold conditions to a high emissivity under hot conditions, has the potential to mitigate winter heating energy penalty.

In this study, we evaluate the impact of TAE roofs with and without high albedo on surface climate and building energy demand using a global climate model. Results show that TAE roofs provide effective winter warming, increasing urban temperature by an average of 0.16 °C and up to 0.54 °C (99th percentile), but have minimal effects on summer temperatures (mean change +0.05°C). Roofs with both TAE and high albedo maintains effective summer cooling benefits without exacerbating winter heating demand, especially in mid-latitude cities. Air temperature sensitivity to emissivity shows positive linear relationships with local apparent net longwave radiation, whereas its sensitivity to albedo has negative linear relationships with incoming solar radiation. Leveraging these relationships, we propose a simple parameterization framework to predict air temperature response to various roof emissivity and albedo changes, enabling a first-order assessment of climate responses to different roofing materials. Our findings highlight the significance of tailoring heat mitigation strategies specific to local climate.

How to cite: Zhang, K., Zhao, L., Oleson, K., Li, X. “., and Lee, X.: Enhancing Urban Thermal Environment and Energy Sustainability With Temperature-Adaptive Radiative Roofs, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-160, https://doi.org/10.5194/icuc12-160, 2025.

Buildings are responsible for approximately 30% of the world energy consumption and 26% of greenhouse gas emissions, making energy-efficient building design a crucial factor in climate change. Building materials properties play a major role in building energy behavior. In particular, materials radiative properties govern the heat transfer between a building and its environment through the radiative channel. They influence solar heat gain under solar radiation, radiative cooling during clear sky conditions and occupants’ thermal comfort for example. Building energy models usually account for materials radiative properties using two parameters: short wavelength albedo for solar radiation and long wavelength emissivity / absorptivity for the building interaction with its environment and the sky. Those quantities are averaged over their respective spectral ranges, UV-VIS-NIR-SWIR (up to 3 µm) for the former and MIR (above 3 µm) for the latter. On the other hand, the atmosphere exhibits a transparency window in the MIR range between 8 and 13 µm which enables a radiative cooling effect by radiative transfer between a building and the outer space at 3 K. Average radiative properties in the MIR range do not enable an accurate description of this phenomenon. In this work, we investigate the radiative cooling potential of several common building materials based on their spectral radiative properties that we measured from 200 nm up to 25 µm.  Our results reveal significant discrepancies, up to 165%, when using average radiative properties and spectral radiative values in radiative cooling calculations. We also discuss the impact of these discrepancies on the energy demand of buildings by integrating our experimentally measured spectral data into building energy models. Our study highlights the importance of accurate radiative property knowledge in optimizing material selection for building energy efficiency improvement, the implementation of passive cooling solutions and urban heat islands mitigation.

How to cite: Yan, Y., Hervé, A., Hendel, M., Bourouina, T., and Nefzaoui, E.: Impact of Materials Spectral Radiative Properties Use on Radiative Cooling and Building Energy Demand Assessment, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-635, https://doi.org/10.5194/icuc12-635, 2025.

Climate change will make heat events more frequent, triggering enhanced indoor heat loads for urban residents. However, the understanding of indoor climate conditions in existing residences remains limited. Achieving a long-term network recording indoor temperatures is challenging, making such networks scarce. Using Netatmo weather stations in bedrooms and living rooms of 93 residences in Amsterdam (the Netherlands), we record indoor air temperature, humidity and CO₂ concentrations since 2022. We also estimate thermal comfort indices Predicted Mean Vote (PMV) and the Dutch Weighted Temperature Excess (GTO). We report on the climatology and variability for these observed and estimated variables during May–September of 2023 and 2024.

During a warm period from 1–15 September 2023, the median and 95^th percentile (P95) of the daily maximum indoor temperatures over all rooms amounted to 25.2°C and 29.8°C, respectively. While the WHO indicates a comfortable indoor temperature range of 18-24°C. The corresponding median and P95 of the daily maximum CO₂ concentrations in bedrooms were 808 and 1622 ppm, respectively. Ideally, indoor CO₂ concentrations should remain close to the outdoor CO₂ concentration of 420 ppm. For thermal comfort, we performed a sensitivity analysis on PMV and GTO. The corresponding median and P95 of the estimated hourly PMV in bedrooms were -0.58–0.12 and 0.87–1.26, respectively, indicating a neutral to slightly warm thermal sensation. Similarly, the corresponding median and P95 of the estimated GTO in bedrooms were 49.0–231.3 and 264.1–568.7 hours, respectively. Putting it into perspective, the annual GTO threshold is 900 hours.

Also, we will present preliminary findings on how house characteristics (e.g., energy label, window orientation, room volume, etc.) may explain indoor temperature characteristics. This study contributes to understanding health risks and cooling demands faced by residents of Amsterdam in their homes.

How to cite: Peerlings, E. and Steeneveld, G.-J.: Exploring urban indoor thermal comfort and CO2 concentrations in Amsterdam, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-771, https://doi.org/10.5194/icuc12-771, 2025.

Climate change and rapid urbanization have intensified the Urban Heat Island (UHI) effect, increasing energy demand and reducing thermal comfort in cities. In the Mediterranean region, rising temperatures and environmental threats underscore the need for microclimate-sensitive urban design. This study focuses on Madrid’s Picazo neighborhood, a vulnerable area with outdated building stock, to evaluate the interactions between urban microclimate, energy efficiency strategies, and urban morphology using ENVI-met and EnergyPlus simulations.

A novel workflow is developed to integrate radiative heat exchanges into building energy models, addressing a critical gap in existing research. While thermochromic coatings have demonstrated energy-saving potential, their interaction with urban surroundings is often overlooked. By analyzing three scenarios—Base, Radiative, and Thermochromic, results reveal significant variations in cooling and heating energy use intensities (EUIs) due to urban radiative heat and thermochromism, emphasizing the need for comprehensive urban-scale modeling.

The study also evaluates façade renovation strategies for thermal comfort. Findings show that Grey ETICS outperforms existing materials, while White ETICS yields less favorable results. An assessment of public residential buildings highlights the importance of shading, natural ventilation, and wind speed variations in mitigating heat stress.

To support climate-responsive urban planning, modified weather files incorporating UHI effects are generated to assess mitigation strategies, including optimized building envelopes, reflective pavements, and green infrastructure. These measures significantly enhance outdoor thermal comfort, reduce indoor overheating, and lower heating loads.

This research underscores the role of computational modeling in urban climate adaptation and energy assessments. The proposed methodology provides valuable insights for policymakers and urban planners, offering a scalable approach for designing sustainable and thermally resilient cities.

How to cite: Giancola, E., Amin, S., Fontana, M. S., Lopez Moreno, H., and Soutullo, S.: Optimizing Urban Comfort and Energy Efficiency: Climate-Responsive Materials and Strategies for Heat Mitigation in Madrid, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-515, https://doi.org/10.5194/icuc12-515, 2025.

In the context of global aging, frailty has become a major threat to the health of the elderly. Appropriate outdoor activities can delay the frailty process of the elderly. However, in hot and humid areas, the harsh outdoor thermal environment often causes heat stroke, which seriously hinders the outdoor activities of the elderly. Therefore, exploring the outdoor thermal comfort of the elderly in hot and humid areas and creating an outdoor environment suitable for the activities of the elderly are of great significance to enhancing the health and vitality of the elderly and delaying the aging process. This study focuses on elderly care homes in Guangzhou, classifying residents into healthy, pre-frailty, and frail groups based on their health status. Through field surveys, questionnaires, thermal environment measurements, and infrared image collection, the study identifies the most suitable thermal comfort indicators for each group of elderly individuals. The research shows that compared with PET, mPET, and UTCI, SET* is more suitable for evaluating the summer outdoor thermal sensation of the elderly with different levels of frailty in humid and hot regions, and its predictive rate and expressiveness are the best. Furthermore, the study constructs a thermal comfort prediction model based on facial skin temperature, and proposes optimization strategies for outdoor thermal environments. These strategies focus on both active and passive measures aimed at enhancing the main activity spaces of elderly individuals. By adopting these strategies, the study aims to provide theoretical guidance for constructing a healthy, comfortable, and suitable outdoor thermal environment that supports various elderly activities in hot and humid regions.

How to cite: Li, Q., Wang, J., and Mi, J.: Study on Outdoor Thermal Environment Evaluation and Optimization Design Strategy of Nursing Homes in Hot and Humid Areas, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-803, https://doi.org/10.5194/icuc12-803, 2025.

The thermoregulatory and cognitive abilities of schoolchildren can be severely impaired during extreme heat events, especially in cities where urban factors tend to increase outdoor/indoor air temperatures and air pollution. Current standards for building ergonomics do not usually address the specific indoor environment of schools and the schoolchildren population. Multiple exposures are also rarely studied and require comprehensive integrative assessment methods. This contribution presents the results of a one-year-long operational research project performed in a public primary school in Strasbourg metropolis (France, VESPA project). The research project combined a two-month intensive field observation campaign of indoor human heat stress, heat perception, and air quality with a system of numerical energy balance models from urban to indoor building scales for testing different retrofit strategies on the combined exposure.

Heat stress and air pollution intensities were qualified using 4 heat stress indices (PMV, operative temperature, heat index, WBGT) and 3 indoor air pollutant concentrations (PM2.5, VOC, CO2). These, coupled with children’s heat perception, allowed the calibration of children's sensitivity to heat and pollution compared to adults. The chosen multiscale modeling system is based on the urbanised mesoscale WRF/BEP+BEM model and the EnergyPlus©/Contam©/INCA-Indoor© computation engine, which were coupled offline. The retrofit scenarios (e.g. green roofs, mechanical ventilation system modifications) were designed in collaboration with the city stakeholders of the city of Strasbourg. They were tested under current (June-July 2024) and near-future climate conditions (August 2003 heatwave as analog).

How to cite: Kohler, M., Maury-Micolier, A., Breton, F., Chambraud, L., and Blond, N.: Observations and retrofitting simulations of schoolrooms in Strasbourg (France): towards reducing heat stress and air pollution for children?, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-831, https://doi.org/10.5194/icuc12-831, 2025.