Five years ago the short article Is the Urban Heat Island intensity relevant for heat mitigation studies? (Martilli et al, Urban Climate, 2020) was published, detailing the limitations and shortcomings of using the Urban Heat Island Intensity (UHII) as an indicator of overheating in urban areas. This is because the rural reference, used to estimate the UHII, changes in space and time, and furthermore, it does not represent thermally comfortable conditions. It was also stressed in that paper that urban areas generate unique local climate signatures, not simply perturbations added on top of rural surface climates. Consequently, the UHII is not even a measure of the maximum impact that a heat mitigation/adaptation strategy can provide. On this basis, the aims of this contribution are to: 1) critically analyze the impact of the previously mentioned article on the field, based on the more than 200 citations it has received so far, 2) define features that relevant indexes for heat mitigation strategies should include, and 3) show how they can be used to evaluate the impacts of adaptation/mitigation strategies on negative aspects of urban overheating. To illustrate the last two points, examples from modelling studies over cities in different contexts are discussed.

How to cite: Martilli, A., Krayenhoff, E. S., and Nazarian, N.: Beyond UHI – how to build and use relevant indicators for heat mitigation studies, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-839, https://doi.org/10.5194/icuc12-839, 2025.

The urban heat island is one of the most studied phenomena in urban climatology. Numerous studies have revealed the heterogeneous nature of air temperature within cities, manifesting as an urban heat “archipelago”. With the introduction of the Local Climate Zones (LCZ), close attention has been paid to the definition and description of “urban” sites. However, what remains understudied and inconsistent across studies is the “sea level” of the “archipelago”, i.e., defining the surrounding temperature, unaffected by the city. Here, we compare definitions and requirements of that “sea level”.

Most typically, professional weather stations at airports are used as a “rural” reference. However, these stations are not ubiquitously available and suffer from local effects such as a high fraction of impervious surfaces and meso-scale effects like urban heat advection when located downwind of the city. Crowd weather stations (CWS), which have gained attention in recent years in urban climate studies due to their abundance, are often affected by nearby buildings and are mostly available in urban areas. ERA5-Land reanalysis data, on the other hand, is available globally and does not consider urban areas; hence, it provides an independent reference.

In this study, all three data sources were compared against an ideal case of multiple professional weather stations placed around the city. We find that ERA5-Land data is a consistent and ubiquitously available reference for the definition of “rural”. Using it as a universal rural reference allows for comparison between cities and further enables the potential of CWS, even in regions with few stations and a lack of professional rural weather stations. Establishing a consistent “sea level” for urban air-temperature and UHI studies enables comparison between various cities globally and allows for the integration of different data sources, such as local networks of weather stations or CWS, on a larger scale.

How to cite: Kittner, J., Fenner, D., Demuzere, M., and Bechtel, B.: Finding the Sea Level - A universal rural reference for UHI-estimation, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-314, https://doi.org/10.5194/icuc12-314, 2025.

As the climate crisis is widespread, causing enormous economic loss and fatalities, a comprehensive approach on assessing the resilience of urban areas is urgently needed. Urban areas accommodate 2/3 of the world's population and – due to their prevalence of built infrastructure and sealed surfaces – is especially vulnerable towards climate extremes such as heat or flooding. The past years have shown increasing intensities and frequencies in extremes, which are expected to intensify further due to climate change. Thus, the urban system needs to be transformed in a resilient way, meaning that it is able to cope with the shock of an extreme event, return to a stable state and adapt to changing framework conditions.

Resilience indicators are a useful tool for assessing and monitoring different aspects, such as hazard intensities (e.g. indicator maximum rainfall intensity per day), or how well the governance structure are set up to deal with shocks (e.g. % of public meetings dedicated to resilience in the city). Yet, not all indicators suggested by organizations, projects or norms are useful or usable for public authority. Therefore, within ClimEmpower, we compiled a comprehensive list of indicators (~500) covering multiple sectors. These were then discussed and short-listed with regional’ representatives to ensure that the selected indicators cover their needs, as well as – if possible - linked to available data and services.

How to cite: Bügelmayer-Blaschek, M., Tötzer, T., Molina, P., Gazzaneo, P., Pavone, V., Xekalakis, G., Chatzicristaki, C., Gamallo, I., and Havlik, D.: Indicators for urban climate resilience – availability, applicability, and usefulness, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-214, https://doi.org/10.5194/icuc12-214, 2025.

Given the impact of extreme temperatures on health, particularly in urban areas, the assessment of thermal comfort has become a central topic in the scientific community since the 20th century. Among the various indices developed for this purpose, this study aims to spatially analyze the thermal comfort of the urban areas of Grenoble and Toulouse (France) using the Operative temperature (Ot). The analysis covers the period from August 11 to August 26, 2023, corresponding to the longest and most intense heatwave recorded by Météo France during the summer of 2023 in the Auvergne-Rhône-Alpes and Occitanie regions.

The choice of Ot is based on its ability to define a variable for assessing daytime thermal comfort, which can subsequently be integrated into social vulnerability models initially developed for the nighttime phase. Although thermal comfort and social vulnerability share similarities, particularly in the construction of a composite index, some parameters, such as social predisposition factors, may overlap. Ot, by incorporating thermal exchanges between an individual and their environment through measurable climatic variables (air temperature, mean radiant temperature, wind speed), serves as a relevant indicator for an integrated approach to thermal comfort and social vulnerability.

The calculation of the variables necessary for composing the index was carried out using three models in urban climatology: SOLWEIG, URock, and TARGET. These models were forced by open-access geographical data (from IGN) and atmospheric data (ERA-5). The result is a composite index expressed as an equivalent temperature, with a spatial resolution of one meter. This methodology makes it possible to identify the most severely affected zones in the urban areas studied during the daytime heatwave. Finally, this analysis also aims to assess the relevance of the Ot index for thermal comfort studies in comparison to other commonly used indices (such as UTCI, SET*, PET, PMV, etc.).

How to cite: Lagelouze, T., Rome, S., Hidalgo, J., and Bigot, S.: Application of operative temperature to characterize daytime thermal comfort in urban areas during a heatwave: the case of two French cities, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-416, https://doi.org/10.5194/icuc12-416, 2025.

Historically, urban heat island intensity has been a measure of urban heating and multiple researchers across the world have mapped the UHII for various cities. The limited signature of the urban heat island intensity is unable to explain and assess varied impacts of extreme heat on human settlements. The urban heat island intensity as a concept is limited to temperature variations and intensities whereas the challenge of extreme heat in cities goes beyond “hot-spot” identification, it is more about the impact of heat on various factors like human health, infrastructure, energy consumption, etc. The impact of extreme heat is more than just heating, it revolves around other heat indices which are governed by “Local Threshold”. The subject of local threshold remains underdeveloped and unexplored. Since the climate varies from location to location, the concept of a EHEs and its threshold often depends upon location, geographical conditions, degree of adaptation of the population and many other factors. This makes it necessary to have regionally specific warning regimes. Hence, it is important to address differential heat risks through the development of local thresholds at city level or even for a particular climatic region. The threshold values are set at a level associated with a negative human response as indicated by the long-term relationship between some measures of heat indices. There is a need to design the guidelines of heat resilience around “local threshold”. The study tries to propose the idea of hyperlocal local threshold centric approach for planning of heat resilience in a city. The study has 4 parts – determining mortality based local threshold, conducting LCZ based heat exposure study considering the local threshold and lastly, highlighting the importance of local threshold.

How to cite: Kotharkar, R.: Local Threshold as an effective heat index for building heat resilient cities., 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-449, https://doi.org/10.5194/icuc12-449, 2025.

The performance of a number of urban cooling techniques has been thoroughly studied by the scientific community. However, decision-makers lack simple tools to spatially analyze their deployment as part of their urban cooling and climate change adaptation strategies. Among other indicators, a spatial assessment of the cooling potential of a given area is lacking.

To this end, we analyze the physical mechanisms on which these techniques are based and identify corresponding geographical indicators that influence their cooling performance. Depending on the cooling target, different energy balance equations are relevant. Solar irradiance, existing material properties and urban vegetation stand out as essential indicators for this purpose. These data also offer the advantage of often being easily accessible at high spatial resolutions by urban stakeholders. A simple empirical combination of these parameters is proposed for the analysis of daytime Urban Cooling Potential (UCP) which can be analyzed using GIS software.

Over the last ten years, our team has evaluated urban cooling techniques for approximately 20 different sites under radiative conditions, with fixed and mobile weather station monitoring, while the UCP has been mapped for a number of these sites.

In this communication, the UCP indicator will be presented and compared with daytime microclimatic measurements conducted at several monitored sites, in particular those studied during the ERDF UIA OASIS project, where ten schoolyards were monitored before and after transformation to evaluate the cooling effects of their transformation. The correlation of UCP and relative heat stress levels is discussed as well as paths for improvement of the UCP indicator as well as certain use cases by municipalities.

How to cite: Hendel, M., Giove, M., Karam, G., Parison, S., and Royon, L.: Physical and Geographical Analysis of Urban Heat: the Urban Cooling Potential Indicator, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-1043, https://doi.org/10.5194/icuc12-1043, 2025.

The evaluation of thermal comfort in urban outdoor spaces has become increasingly important due to growing concerns about climate change and heat island effects. Many thermal comfort indices have been developed, but existing indices, such as the SET, assume steady-state conditions. Hence, it may not adequately capture outdoor thermal comfort in the short-term, especially under rapidly changing thermal environments (e.g., walking from indoors to outdoors). To address these limitations, this study proposes the Dynamic Standard Effective Temperature (D-SET), an index based on the principles of SET and the two-node model. D-SET provides a simplified yet approach to represent dynamic thermal comfort without necessitating the use of complex human physiological models. To develop the proposed index, comprehensive subject walking experiments were conducted in diverse climatic regions in Japan, France, and Indonesia. These experiments measured both physiological and psychological responses, such as skin temperature and thermal sensation votes (TSV), during transitional phases from indoor to outdoor environments. D-SET may enable the assessment of time-dependent thermal comfort and risks with reduced computational complexity, particularly in wide-area microclimate simulations and risk studies. By integrating temporal variations into the analysis, D-SET enhances the understanding and management of thermal risks in urban spaces, supporting the development of more adaptive and sustainable urban strategies. 

How to cite: Hiroki, R., Varquez, A. C. G., Khanh, D. N., Renard, F., Alonso, L., Agung Junnaedhi, I. D. G., Kanda, M., and Inagaki, A.: Development of Dynamic Standard Effective Temperature (D-SET) for evaluation of the change in thermal comfort over time. , 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-662, https://doi.org/10.5194/icuc12-662, 2025.