Urban Heat Island Phenomenon Research Articles

A comprehensive generalizability assessment of data-driven Urban Heat Island (UHI) models

Data-driven models serve as valuable tools for understanding and tackling the UHI phenomenon that can provide user-friendly platforms for urban planners for incorporating UHI considerations in their decisions. This study aims to assess the generalizability of data-driven UHI models at the street-level resolution, particularly considering various similarity degrees of urban contexts between training and testing cities. Five cities from three countries were selected to encompass a diverse range of similarities in this comparative study. Five Random Forest models were developed. The lowest-performing model has an R2 value of 0.56 and an MAE of 0.07, and the highest-performing model has an R2 of 0.71 and an MAE of 0.05. While these models proved to be accurate for the cities they were trained for, cross-validation of the models in different cities revealed low generalizability capabilities, irrespective of the similarity degree between training and testing datasets. Small changes in feature importance resulted in significant variation in UHI derivation mechanisms and behavior, which contributes to the models’ low generalizability. The findings of this research indicate that universal mitigation strategies may not yield consistent outcomes worldwide, and a one-size-fits-all approach may be inefficient in addressing UHI. Hence, it's vital to tackle UHI locally.

Analysis of thermal comfort in urban area using Remote Sensing and Geographic Information System

The rapid development of the city of Yogyakarta has resulted in the conversion of land functions from built-up land to undeveloped areas such as residential areas, office areas, and industrial areas. This land-use change is predicted to impact changes in weather and climate in most of the cities of Yogyakarta and cause the Urban Heat Island (UHI) phenomenon. Urban Heat Island will have implications for thermal comfort which can affect the productivity of community activities. This study aims to determine the correlation between UHI and the level of thermal comfort of settlements in Yogyakarta. This research was conducted to determine the level of thermal comfort in the city of Yogyakarta using remote sensing and GIS approaches. Comfort classification was obtained from the THI analysis and analyzed the correlation between THI and UHI. The UHI variable is used to calculate the Temperature Humidity Index (THI). The results of the quantitative analysis showed that Yogyakarta City UHI had a strong positive correlation (r2= 0.93) with the level of THI and a weak negative correlation with RH (r2= 0,52). T The increase in the level of UHI shows that the humidity and thermal comfort of the city of Yogyakarta is decreasing. The results of the qualitative analysis of the study also show that more than 95% of the people feel comfortable with the thermal conditions in which they live.

Machine Learning Techniques to Map the Impact of Urban Heat Island: Investigating the City of Jeddah

Over the last decades, most agricultural land has been converted into residential colonies to accommodate the rapid population expansion. Population growth and urbanization result in negative consequences on the environment. Such land has experienced various environmental issues due to rapid urbanization and population increases. Such expansion in urbanization has a big impact on worsening the residences soon and in the long term, as the population is projected to increase more and more. One such issue is the urban heat island (UHI), which is computed based on land surface temperature (LST). The UHI effect has fundamental anthropogenic impacts on local areas, particularly in rapidly growing cities. This is due to the unplanned shifts in land use and land cover (LUALC) at the local level, which results in climate condition variations. Therefore, proper planning based on concrete information is the best policy in the long run to remedy these issues. In this study, we attempt to map out UHI phenomena using machine learning (ML) algorithms, including bagging and random subspace. The proposed research also fulfills the sustainable development goals (SDGs) requirement. We exploit the correlation and regression methods to understand the relationship between biophysical composition and the UHI effect. Our findings indicate that in the megacity of Jeddah, Saudi Arabia, from 2000 to 2021, the urban area enlarged by about 80%, while the UHI increased overall. Impervious surfaces significantly impact the UHI effect, while vegetation and water bodies have negative implications for the UHI effect. More than 80% of the total parts in Jeddah have been classified by extremely high UHI conditions, as determined by the bagging and random subspace models. In particular, the megacity’s south, north, and central-east parts were categorized by very high UHI conditions. This research is not only expected to assist in understanding the spatial patterns of the UHI in Jeddah, but to assist planners and policymakers in spatial planning. It will help to ensure sustainable urban management and improve life quality.

Exploring the Differential Effects of Urban Heat Islands on Energy Use and Carbon Emissions in Warm and Cold Climates: a Case Study of North Africa and North Europe

The urban heat island (UHI) phenomenon has differential impacts on energy use and carbon emissions in buildings depending on the climate of the region and the urban planning strategies in place. This study explores the differential effects of UHI on energy use and carbon emissions in warm and cold climates, using North Africa and North Europe as case studies. We address the following research questions: 1) How does the UHI phenomenon impact energy use and carbon emissions in buildings in these regions? 2) What urban planning strategies are currently in place to mitigate the negative impacts of UHI on energy demand and emissions in these regions? 3) How effective are these strategies in mitigating the negative impacts of UHI on energy demand and emissions in both warm and cold climates? 4) What additional urban planning strategies could be implemented to reduce further the negative impacts of UHI on energy demand and emissions in both warm and cold climates? The UHI increases energy bills and emissions due to the higher demand for cooling energy in warm climates, while in cold climates, UHI reduces energy demand and emissions by decreasing the need for heating energy. Urban planning strategies, such as incorporating green space, using reflective materials, choice of colors, and designing for natural ventilation, can effectively mitigate the negative impacts of UHI on energy demand and emissions in both warm and cold climates. However, the effectiveness of these strategies varies depending on the climate of the region and the specific urban context. In this study, we will provide a recommendation for urban planning strategies that can be implemented to further reduce the negative impacts of UHI on energy demand and emissions in both warm and cold climates. Our study contributes to the understanding of the UHI phenomenon. It provides insights for urban planners and policymakers in developing effective strategies to reduce energy use and carbon emissions in buildings and cities.

Quantitative assessment of land surface temperature and vegetation indices on a kilometer grid scale.

Due to expanding populations and thriving economies, studies into the built environment's thermal characteristics have increased. This research tracks and predicts how land use and land cover (LULC) changes may affect ground temperatures, urban heat islands, and city thermal fields (UTFVI). The current study examines land surface temperature (LST), urban thermal field variance index (UTFVI), normalized difference built-up index (NDBI), normalized difference vegetation index (NDVI), and land use land cover (LULC) on a kilometer scale. According to the comparative study, the mean LST decreases by 3°C and the NDVI increases considerably. Correlation analysis showed that LST and NDVI are inversely connected, while LST and NDBI are positively correlated. NDVI and NDBI have a strong negative association, while LST and UTFVI have a positive correlation. Urban planners and environmentalists can study the LST's effects on land surface parameters in different environmental contexts during the lockout period. The urban heat island (UHI) phenomenon, in which the land surface qualities of an urban region cause a change in the urban thermal environment, forms and intensifies over an urban area. The minimum and maximum LST in grid number 1 in 2009 was 20.30°C and 29.91°C, respectively, with a mean LST of 25.1°C. There was a decline in the minimum and maximum LST in grid number 1 in 2020 with a minimum and maximum LST of 17.31°C and 25.35°C, respectively, with a mean LST of 21.33°C. There was a 3.8°C drop in the LST of this grid. The minimum and maximum NDVI were also - 0.16 and 0.59, respectively, with an average NDVI value of 0.21. Therefore, it is essential to evaluate and foresee the impact of LULC change on the thermal environment and examines the connection between LULC shifts with subsequent changes in land surface temperature (LST) along with the UHI phenomenon. Maps of the UTFVI reveal positive UHI phenomena, with the highest UTFVI zones occurring over the developed area and none over the adjacent rural territory. During the summer months, the urban area with the strongest UTFVI zone grows noticeably larger than it does during the winter months during the forecasted years. Future policymakers and city planners can mitigate the effects of heat stress and create more sustainable urban environments by evaluating the expected distribution maps of LULC, LST, UHI, and UTFVI.

Assessment of Winter Urban Heat Island in Ljubljana, Slovenia

Although the urban heat island (UHI) phenomenon is more commonly studied in summer, its influence is also important in winter. In this study, the authors focused on the winter UHI in Ljubljana (Slovenia) and its impact on the urban population, as well as in comparison with a UHI study from 2000. Through a combination of mobile and stationary temperature measurements in different parts of the city, the winter intensity of the UHI in Ljubljana was studied in a dense spatial network of measurements. It was found that the intensity of the winter UHI in Ljubljana decreases as winters become warmer and less snowy. The results showed that the winter UHI in Ljubljana intensifies during the night and reaches the greatest intensity at sunrise. During the winter radiation type of weather, the warmest part of Ljubljana reaches an intensity of 3.5 °C in the evening. In total, 22% of the urban area is in the evening UHI intensity range of 2–4 °C, and 65% of the urban population lives in this range. In the morning, the UHI in Ljubljana has a maximum intensity of 5 °C. The area of >4 °C UHI intensity covers 7% of the urban area, and 28% of the total urban population lives in this area. Higher temperatures in urban centers in winter lead to a longer growing season, fewer snow cover days, lower energy consumption and cold stress, and lower mortality from cold-related diseases compared to the colder periphery.

Effect urban development on urban heat island in Depok Subdistrict, Sleman Regency, Yogyakarta

Urban development follows population growth caused by various factors, both natural and non-natural. The increasing number of residents in Depok Subdistrict makes the demand for land also increase. Residential land that continues to develop can cause temperature conditions in Depok Subdistrict to increase or known as Urban Heat Island. This study purpose to determine how the influence of urban development on the Urban Heat Island phenomenon and to analyze the Urban Heat Island and land surface temperatures. This study concludes that there has been an urban heat island in Depok Subdistrict in 2014 with a distribution area of 49% of the total area of Depok Subdistrict and 51% non-UHI with a UHI threshold of 26.18°C. Meanwhile, in 2019 there was a decrease in UHI. to 30% of the total area and 70% are in non-UHI areas with a UHI threshold of 27.18°C. Although there is a decrease in UHI, the surface temperature of the soil has increased from 29.78°C to 31.10°C. In Depok Subdistrict population density does not affect the UHI value but the surface tribe value does affect the UHI index value.

Seasonal different effects of land cover on urban heat island in Wuhan's metropolitan area

Urban sprawl increases impervious surfaces and decreases vegetation cover, which exacerbates the urban heat island phenomenon. In this study, we analyzed the spatiotemporal evolution law and determined the differences between urban heat islands in winter and summer. The Land Use Contribution Index introduced a new idea for studying the relationship between land cover and heat islands. We found that with urbanization, the area of heat islands increased in the winter and summer. However, heat island intensity varied greatly depending on the season among different land types. Specifically, rivers showed the characteristics of a warm winter and cool summer, which provided new strategies for improving the urban thermal environment. Heat island intensity change maps and land transfer maps were spatially superimposed to visualize how the intensity of the heat island of the land changes with the differences in the type of cover. The results indicated that the conversion of cultivated land into construction land was the main reason for changes in the land type, and the intensity of the heat island effect of most of these converted lands was enhanced. However, the proportion of enhancement decreased gradually.

Material performance in an effort to reduce the UHI (urban heat island) phenomenon at Deo Airport, Sorong City

Domine Eduard Osok Airport is a Class I Airport in the city of Sorong which is experiencing quite rapid development. This fairly rapid development has made airport managers think of ways to be able to provide maximum service to airport users. One of these services is to reduce the occurrence of the Urban Heat Island (UHI) phenomenon in the airport area by placing several types of materials around the airport. Several types of heat-absorbing materials are natural or synthetic materials that are used to withstand high temperatures. Nature provides a choice of materials that can be applied in this effort. Raw materials contained in nature will later be processed or used directly as an effort to reduce heat. The city of Sorong is a city that has problems with the occurrence of the UHI phenomenon because recently it has experienced an increase in population. To reduce the heat generated, various materials are used to be applied. These materials include Cast concrete, Asphalt, Soil, and Paving Materials. In this study, the material performance in reducing heat is determined for the four materials. The measuring instrument used is a measuring instrument commonly used to measure temperature. Measurements were made from morning to night. The results obtained are that cast concrete material has better performance compared to other types of materials when applied as a heat-absorbing material in buildings. Meanwhile, paving material is a good material if applied as a road material. With the average temperature produced for each material morning=25.20C, afternoon=26.20C, afternoon=26.60C, and night 25.90C and morning=32.70C, afternoon=33.90C, afternoon=29.00C, and night 28.8 0C.

Evaluation of the outdoor thermal environment for three typical urban forms in Nanjing, China

Urban form has been proved to be an important factor that significantly influences the microclimate as well as the outdoor thermal comfort at the pedestrian level in urban spaces. Various kinds of urban forms arise from rapid urbanization, accompanying different thermal environments in urban spaces. However, some severe urban climate issues, such as the urban heat island phenomenon, emerge in dense urban areas frequently, especially in large cities with hot and humid climates. In this study, three different archetypes, including the freestanding, scattered, and enclosed types, were selected as the representatives of typical urban forms in the central area of Nanjing city. The outdoor microclimates of these urban forms under typical summer conditions were simulated for calculating the thermal comfort index. The effects of urban form characteristics on the thermal environment were compared and analysed. The results show that the maximum differences in average air temperature, mean radiant temperature, and PET index between these three typical plots could achieve 5.4 °C, 24.2 °C, and 12.4 °C, respectively. Furthermore, the scattered urban form was evaluated to be holding the best outdoor thermal environment in comparison to the others based on a holistic and comprehensive view. Finally, some basic design suggestions based on the results and relevant discussions were recommended for urban design in the cities with similar climate conditions.

Bat bio-assisted sampling (BAS) for monitoring urban heat island

In this study, we demonstrate how urban-dwelling bats can be used to reconstruct Urban Heat Islands (UHI). We term this approach biologically-assisted sampling (BAS). We used Egyptian fruit bats to map the spatial air temperature (Tair) profile. To demonstrate the feasibility of using biologically-assisted sampled data set, we run mixed effects and Geographically Weighted Regression (GWR) models to estimate the impact of urban environment on Tair distribution. Our results suggest that vegetation is a very important mitigating factor in Tair. In the winter, we found an average Tair difference of 2–5 °C between densely urban and nearby vegetative/open areas. A distinct UHI spot was identified in the winter, centered on the Ayalon highway. These differences were lower during the summer night, probably due to a pronounced cooling sea breeze effect along the coastline. Our preliminary results also indicate that BAS sampling provide a 3D view of the UHI phenomenon: the change in Tair above the dense urban area was smaller than above the vegetative area. Since the differences in Tair between densely urban and open/green areas are the largest during the night hours, bats can serve as efficient agents to monitor UHI effects, despite the method limitations.

Investigating the Spatial Heterogeneity of Urban Heat Island Responses to Climate Change Based on Local Climate Zones

Global warming and the urban heat island (UHI) phenomenon have significant impacts on human activities, against which it is necessary to develop effective coping strategies. Based on the local climate zone (LCZ) system, this study used the land-cover and surface temperature data on the Chang–Zhu–Tan (CZT) urban agglomeration in China in 2006, 2010, 2016, and 2020 to analyze the impact of climate change on the land surface temperature (LST) under different land-cover types. The results illustrate that the LCZ map generated on the basis of the improved World Urban Database and Access Portal Tools (WUDAPT) is more accurate and efficient than the traditional method. The accuracy is increased by more than 15%. From 2006 to 2020, the main built-up types in the CZT urban agglomeration were the sparsely built, the large low-rise, and the compact mid-rise types. The low-plant type represents the most significant proportion of the natural types, followed by the water and the dense-tree types. The built-up types in the CZT urban agglomeration tend to be the high-rise, dense, and industrial types. Urban construction land is taken mainly from the sparsely built type of land. The average LST of the large low-rise and heavy-industry zones is significantly higher than the average LST of the three cities. The average LST values for the water and dense-tree zones are significantly lower than the other average LST values. The LST is stable in each LCZ, showing little correlation with the size of the LCZ area. Compact low-rise land use is ineffective against climate warming and inhibits economic growth. Compact high-rise and open high-rise land can not only effectively deal with climate warming but can also significantly stimulate economic growth. This paper helps us to understand the effect of land cover on climate warming and the economic benefits of LCZs in the CZT urban agglomeration and provides strategies to optimize the use of land resources.

Urban Green Space Analysis and its Effect on the Surface Urban Heat Island Phenomenon in Denpasar City, Bali

The Urbanization process in Indonesia’s big cities causes adverse environmental impacts such as climate change and land cover change. Urban climate change causes the warming of urban areas compared to rural areas; it is called Urban Heat Island phenomenon. Loss of vegetation due to urban development is one of several causes that contribute to urban heat islands. This study examines the availability of green spaces and their effects on the surface urban heat island in Denpasar city. This study used the spatial approach for Urban Green space mapping with digitizing methods. Landsat 8's thermal band is used for land surface temperature mapping and to conduct a spatial pattern analysis of the SUHI phenomena. The Global Moran’s Index and Local Indicator of Spatial Association (LISA) were used to determine the correlation between urban green space and SUHI. The study result shows that Denpasar City's urban green space area covers 28.22 km2. That's equal to 22.1% of the Denpasar City Administrative area. Denpasar Selatan district has the largest urban green space cover, with 14.19 km2 covered, or 50.27% of all the green space in Denpasar City. The majority of Denpasar is affected by UHI occurrences, except the northern region of North Denpasar and the southern region of South Denpasar. The maximum UHI level reaches 4-5°C, located on the east side of South Denpasar, especially in the Sanur coastal area. According to the spatial pattern study, the association between urban green space and SUHI only exists on the north side of Denpasar. The correlation between low-SUHI intensity clusters and high cover of green space is shown in the same area. However, the association between High-UHI intensity and low green space cover has not significantly happened. It indicated that other factors besides green space could affect the land surface temperature.

Numerical Study on the Influence of Rivers on the Urban Microclimate: A Case Study in Chengdu, China

The urban heat island phenomenon in large cities is becoming increasingly serious as urbanization continues to develop, seriously affecting the lives of urban residents. Rivers can effectively alleviate urban heat islands and improve the thermal comfort of riverfront space in summer. Thus, the effect of rivers on the urban microclimate environment is studied in this work. A section of the Fu River in the inland city of Chengdu was selected as the research object, and a combination of experimental and numerical simulation methods was employed. ENVI-met software was used to study the river’s influence on the air temperature, relative air humidity, and the thermal comfort of the riverfront space. The measured experimental parameters are first used to verify the accuracy of the ENVI-met software simulation results, which are then employed to carry out simulation research. The simulation results suggest that the different types of underlying surfaces have varying impacts on the air temperature and relative air humidity. Rivers have a significant cooling effect on the regional thermal environment, and roads have a warming effect on the air temperature. The order of influence of different underlying surfaces on air temperature is as follows: rivers > roads > trees. Rivers have an obvious humidifying effect on the air, and roads have little effect on relative air humidity. The order of influence of different underlying surfaces on relative air humidity is as follows: rivers > trees > roads. The results of the outdoor predicted mean vote (PMV) reveal that rivers, trees, and green plants can effectively improve the comfort of individuals downwind.

Application of Multi-Temporal Landsat Images to Analyze the Relationship Between the Land Surface Temperature (LST) and the Land Use Land Cover (LULC) in Ho Chi Minh City

Urban sprawl has changed the land use land cover (LULC) in Ho Chi Minh City (HCMC). It has caused the gradual decline of the natural vegetation and rapid increase of the impervious surface, which leads to the heat storage capacity of the urban surface being on the rise. There is a land surface temperature (LST) difference between the urban center and surrounding areas and it creates the urban heat island phenomenon (UHI). This study used Landsat 4, 5, and Landsat 8 satellite image data from 1990 to 2020 with the GIS algorithms on ENVI and ArcGIS to analyze and estimate the correlation between the LULC and the LST in HCMC. The Kappa coefficients of the LULC classifications were all over 0.8 in 1990 – 2020 period. The total area of impervious surface has increased by 57,338 hectares over the past 30 years; while the total area of natural green has decreased by 19,116 hectares. The LST has remarkably increased in the areas of construction lands, industrial zones, and impervious surfaces, with an average increase from 22°C to 27°C. While the LST in the others such as the vegetation surface and water surface were slower, from 20°C to 23°C. The solution of enhancing the urban green space was suggested to mitigate the increasing LST impact on HCMC.

Analyzing the Urban Heat Island in Ho Chi Minh City in Relation to Urban Planning Processes from 2010 to 2020

This study aims to analyze the variation of land surface temperature (LST) and its effect on the urban heat island (UHI) in relation to the urban planning processes of Ho Chi Minh City (HCMC) from the years 2010 to 2020. These changes have impacted the urban environmental conditions and the city development. The study used the time series of Landsat 5 TM and Landsat 8 OLI acquired for the years 2010, 2015, and 2020, and used the algorithms for calculating the land surface temperature (LST), the normalized difference vegetation index (NDVI) and the normalized difference built-up index (NDBI) to investigate the relationships between these phenomena in the city planning processes. The results highlight the increase in land surface temperature was related to the dense of impervious surface area and the decrease of vegetation area. The UHI zones occurred in the areas with high LST and NDBI values, and low NDVI values (concentrated in the central districts and the planned areas) compared to the surrounding areas with lower LST and NDBI and higher NDVI. The recommend planning solutions for the new urban development areas should focus on increasing the amount green areas to combat the UHI phenomenon and environmental problems against the development.

Can retro-reflective materials replace diffuse highly reflective materials for urban buildings’ wall to improve outdoor thermal comfort?

In recent years, there have been numerous studies on the application of retroreflective (RR) materials to exterior building walls to relieve the urban heat island (UHI) phenomenon and save building energy consumption instead of diffuse highly reflective (DHR) materials. Experimental measurements were undertaken to investigate the impact of applying DHR and RR materials to building exterior walls on the outdoor thermal environment. DHR and RR walls were tested with three canyon aspect ratios (H/ D) of 0.5, 1.0, and 1.5, respectively, with seven environmental indexes recorded and compared, including air temperature (Ta), relative humidity (RH), sol-air temperature (SAT), operative temperature (OT), standard effective temperature (SET*), change in operative temperature (COT), and real-time solar reflectance (ρ). The results show that the RR wall is more effective in improving the outdoor thermal environment, where SAT decreased by 4.5 °C, SET* decreased by 0.5 °C, and COT decreased by 1.2 °C, on average, while it can also improve the real-time solar reflectance (ρ) by 12% on average compared to the DHR wall. Moreover, it gets more effective in scenarios with a higher canyon aspect ratio.

EFFECT OF GREEN FACADE ON THE URBAN MICROCLIMATE WITH DIFFERENT STREET CANYON

Using simulation tools, this study investigates the effect of green walls (GWs) on the urban heat island (UHI) phenomenon within different street sizes. It can be planted without taking up more area and could enhance the microclimate environment, which is why it has a wide range of use potential in urban areas. Because Mina City has a threat of UHI, it was chosen for this study. The temperature within various street sizes in the research region was evaluated using only software called ENVI-met that simulates climate, and three common scenarios were chosen. In the first experiment, green walls extending over an area of 50 m in the south facades of the street building, including a 3m Street width, are simulated to show the effect of GWs on UHI. In the second experiment, the Street width changed to 6 m, and the GWs are placed in the same condition. The last experiment is the same with a 9m street width. Temperature decreases from each green wall were contrasted with the street canyon situation as it was at the time of evaluation 1's highest heat. In comparison to evaluation 1, the temperature decreases achieved by evaluation alternatives 2, 3, 4, and 5 were 2.17 °C, 1.97 °C, 1.78 °C, and 0.90 °C, accordingly. Conclusion: A well-planned urban green wall can significantly improve UHI in tropical Lebanon.

Micro-scale UHI risk assessment on the heat-health nexus within cities by looking at socio-economic factors and built environment characteristics: The Turin case study (Italy)

Today the most substantial threats facing cities relate to the impacts of climate change. Extreme temperature such as heat waves and the occurrence of Urban Heat Island (UHI) phenomena, present the main challenges for urban planning and design. Climate deterioration exacerbates the already existing weaknesses in social systems, which have been created by changes such as population increases and urban sprawl. Despite numerous attempts by researchers to assess the risks associated with the heat-health nexus in urban areas, no common metrics have yet been defined yet. The objective of this study, therefore, is to provide an empirical example of a flexible and replicable methodology to estimate the micro-scale UHI risks within an urban context which takes into account all the relevant elements regarding the heat-health nexus. For this purpose, the city of Turin has been used as a case study. The methodological approach adopted is based on risk assessment guidelines suggested and approved by the most recent scientific literature. The risk framework presented here used a quantitative estimate per each census tract within the city based on the interaction of three main factors: hazard, exposure, and vulnerability. Corresponding georeferenced maps for each indicator have been provided to increase the local knowledge on the spatial distribution of vulnerability drivers. The proposed methodology and the related findings represent an initial stage of the urban risk investigation within the case study. This will include participatory processes with local policymakers and health-stakeholders with a view to guiding the local planning agenda of climate change adaptation and resilience strategies in the City of Turin.

Diurnal Outdoor Thermal Comfort Mapping through Envi-Met Simulations, Remotely Sensed and In Situ Measurements

Physiological equivalent temperature (PET) is one of most used indices for outdoor human well-being evaluation; its determination is particularly helpful for adaptation strategies in built-up areas affected by the urban heat island (UHI) phenomenon. In this work, we presented a methodology to compute spatially and temporally resolved PET values during a heatwave at the city level, based on a combination of satellite products, in situ measurements and Envi-met model runs upscaled from specific test areas to the broader city. The method exploits the ECOSTRESS sensor to detect surface thermal patterns at different diurnal times by developing an hourly based index called hUHTI (hourly urban heatwave thermal index) that serves as a proxy. A case study on Prato (Italy) municipality during the 2021 summer heatwave events is presented. Based on the available satellite products, a set of six hourly diurnal PET maps at 10 m spatial resolution were derived and daytime outdoor thermal patterns and trends were investigated according to land cover. hUHTI index resulted a more suitable tool as PET proxy compared to the sole ECOSTRESS land surface temperature (LST) product, especially for morning and evening times. Hourly PET maps were summarized by the use of an average exceedance map providing public administrations and stakeholders a synthetic tool for urban regeneration purposes at city scale.