Urban Heat Island Mitigation Measures Research Articles

Determination of land surface temperature and urban heat island effects with remote sensing capabilities: the case of Kayseri, Türkiye

Kayseri, a densely urbanized province in Türkiye, grapples with pressing challenges of air pollution and limited green spaces, accentuating the need for strategic urban planning. This study, utilizing Landsat 8 and Landsat 9 satellite imagery, investigates the evolution of land surface temperatures (LST) and urban heat island (UHI) effects in key districts—Kocasinan, Melikgazi, Talas, and Hacılar—between 2013 and 2022. This research has been complemented with an analysis of the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Built-Up Index (NDBI), exploring correlations among the LST, UHI, NDVI, and NDBI changes. The findings indicate that a significant portion (65% and 88%) of the study area remained unchanged with respect to the NDVI and NDBI differences. This research’s findings reveal that a substantial portion (65% and 88%) of the study area exhibited consistency in the NDVI and NDBI. Noteworthy increases in the NDVI were observed in 20% of the region, while only 4% exhibited higher NDBI. Strikingly, the UHI displayed strong negative correlations with the NDVI and robust positive correlations with the NDBI. The LST changes demonstrated a reduced temperature range, from 21 to 51 °C in 2013, to 18 to 40 °C in 2022. Localized environmental factors, notably at the National Garden site, showcased the most significant temperature variations. Notably, the UHI exhibited strong negative correlations with the NDVI and strong positive correlations with the NDBI. The study’s results emphasize the interplay among the NDBI, LST, and UHI and an inverse relationship with the NDVI and NDBI, LST, and UHI. These findings hold implications for urban planning and policymaking, particularly in the context of resilient and sustainable land use planning and the UHI mitigation. This research underscores the intricate interplay among the NDBI, LST, and UHI, highlighting an inverse relationship with the NDVI. These findings hold crucial implications for resilient and sustainable urban planning, particularly in mitigating the UHI effects. Despite limited vacant spaces in Kayseri, geospatial techniques for identifying potential green spaces can facilitate swift UHI mitigation measures. Acknowledging Kayseri’s complex dynamics, future research should delve into the UHI responses to urban morphology and design, extending this methodology to analyze the UHI effects in other Turkish cities. This research contributes to a broader understanding of UHI dynamics and sustainable urban planning practices, offering valuable insights for policymakers, urban planners, and researchers alike.

Enhancement of heat removal from street canyons due to buoyant approaching flow: Water tunnel PIV-LIF measurements

Heat removal from street canyons to the urban boundary layer above buildings is one of physical processes that may largely determine the (local) urban heat island (UHI) effects. Only few studies show the impact of a buoyant approaching boundary layer flow on heat removal. In this study, we show that heat removal from street canyons is enhanced when the approaching flow is more buoyant as induced by upwind convective heating from a heated ground surface. For this purpose, we perform simultaneous velocity and temperature field measurements in an atmospheric boundary layer water tunnel using particle image velocimetry (PIV) and laser-induced fluorescence (LIF), respectively. Our measurements show that in this case heat removal may be doubled due to reduced suppression at canyon opening. The effectiveness of the heat removal depends highly on the aspect ratio of the street canyons and the distance between street canyon and the place where the buoyant approach flow is produced. Additionally, we show that when the upwind ground surface presents a lower surface temperature, a cooling effect is induced in the immediate downwind street canyon as cooled fluid enters the canyon. The present study suggests that the buoyancy of an approaching boundary layer should be considered in analyzing local UHI and the implications for related UHI mitigation measures are also discussed.

Mitigation measures for urban heat island and their impact on pedestrian thermal comfort

A multiscale coupled model is presented that allows for the detailed analysis of the local impact of urban heat island mitigation measures. The model uses coupled computational fluid dynamics (CFD) simulations with unsteady heat and moisture transport (HAM) in porous urban materials in order to take into account the dynamic heat and moisture storage in the built environment. A realistic case study is performed for a public urban square in the City of Zurich during heat wave conditions. The impacts of two different mitigation strategies, i.e. adding artificial wetting of pavements and adding vegetation, on pedestrian thermal comfort are evaluated and compared with the existing situation. The results show an improvement in thermal comfort in both conditions. The improvement resulting from the addition of trees is larger and lasts longer due to shadowing effects, even though a reduced ventilation and an increased relative humidity by trees have an adverse effect on the thermal comfort.

Monitoring thermal environment deterioration and its dynamic response to urban expansion in Wuhan, China

Understanding how urban heat island (UHI) effect responds to urbanization is of great significance to develop appropriate UHI mitigation measures. However, the dynamic response of thermal environment to urban expansion is still less discussed. In this study, the spatiotemporal variation of thermal characteristics and its dynamic response to urbanization was monitored at the pixel level in 1987, 1996, 2007 and 2016 in Wuhan, China based on multi-temporal remotely sensed images. The results indicate that Wuhan experienced significant thermal deterioration during the 29-year period, which was largely attributed to the rapid urbanization from 1996 to 2007. Due to the high spatial heterogeneity of urban development, the thermal characteristic variation did not always spatially correspond to urbanization process. The urbanization dynamics alone can explain only 14.84% ~ 36.37% of the spatiotemporal variation in thermal environment throughout the study area. Nevertheless, the thermally deteriorated areas had good spatial consistence with the rapidly developed areas in all cases, suggesting that urban development could better explain the dynamic characteristics of thermal environment in more rapidly urbanized areas (with the R2 values of 0.7013–0.9989). An obvious “context effect” was detected during the dynamic influence of urban development on thermal environment variation. Urban development based on the increase of construction density only strengthened UHI intensity, but contributed little to the spread of thermal environment deterioration. Urban expansion with amounts of newly expanded construction land should be responsible for thermal environment deterioration. These findings provide detailed information and sound evidence to adjust urban planning options accordingly to improve thermal environment.

Sensitivity analysis of the PALM model system 6.0 in the urban environment

Abstract. Sensitivity of the PALM model 6.0 with respect to land-surface and building properties is tested in a real urban environment in the vicinity of a typical crossroads in a densely built-up residential area in Prague, Czech Republic. The turbulence-resolving PALM is able to simulate the urban boundary layer flow for realistic setups. Besides an accurate representation of the relevant physical processes, the model performance also depends on the input data describing the urban setup, namely the building and land-surface properties. Two types of scenario are employed. The first one is the synthetic scenarios altering mainly surface and material parameters such as albedo, emissivity or wall conductivity, testing sensitivity of the model simulations to potentially erroneous input data. Second, urbanistic-type scenarios are analysed, in which commonly considered urban heat island mitigation measures such as greening of the streets or changing surface materials are applied in order to assess the limits of the effects of a particular type of scenario. For the synthetic scenarios, surface parameters used in radiation balance equations are found to be the most sensitive overall followed by the volumetric heat capacity and thermal conductivity of walls. Other parameters show a limited average effect; however, some can still be significant during some parts of the day, such as surface roughness in the morning hours. The second type, the urbanistic scenarios, shows urban vegetation to be the most effective measure, especially when considering both physical and biophysical temperature indicators. The influence of both types of scenario was also tested for air quality, specifically PM2.5 dispersion, which generally shows opposite behaviour to that of thermal indicators; i.e. improved thermal comfort brings deterioration of PM2.5 concentrations.

A big picture of urban heat island mitigation strategies and recommendation for India

Climate change poses a great threat to humans and the ecosystem of the planet. There are many factors that trigger climate change, and there are many aftereffects. One of the after-effects is Urban Heat Island (UHI), recognized as the most evident characteristic of urban climate which occurs due to dark, non-reflective surfaces. These surfaces absorb the warmth of the Sun, radiate heat; Thus, increase the land surface temperature. Additionally, heat islands increase cooling loads in the summer, which tends to increase energy consumption and produce more greenhouse gases. There are numerous strategies to mitigate the UHI effect. This study reviews various UHI mitigation strategies and their effectiveness in cooling the urban environment and propose a set of recommendation based on research and analysis. Broadly, the mitigation strategies have been divided into (i) Roof strategies, (ii) non-roof strategies, and (iii) covered parking strategies. It has been found out that the simultaneous use of several UHI mitigation measures has a more significant impact on lowering the urban temperature and could be mitigated. The study highlights the importance of each mitigation strategy and presents a set of recommendations for India that can be directed at the government level to policies to mitigate the UHI effect.

Persistent Increases in Nighttime Heat Stress From Urban Expansion Despite Heat Island Mitigation

AbstractUrban areas generally have higher near‐surface air temperature and lower air humidity than rural areas. Little is known about how heat stress, the combined effect of high air temperature and high humidity on human physiology, will be affected by future urban land expansion. Here we use a mesoscale numerical weather prediction model to examine the effects of urban land expansion from 2000 to 2050 on heat stress (measured as wet‐bulb globe temperature, WBGT) in the urban areas of China, India, and Nigeria, which are projected to account for one‐third of global urban population growth through 2050. Our results show that urban expansion slightly reduces heat stress during the day (∼0.2°C) but substantially intensifies it at night, by ∼1°C on average and by up to 2–3°C in five mega‐urban regions (MURs). These effects exist with or without climate change induced by rising concentrations of greenhouse gases (GHGs). Installing cool roofs—an urban heat island mitigation measures—can reduce the daytime WBGT by 0.5–1°C, partially offsetting the heat stress conditions caused by GHG‐induced climate change. However, even with cool roofs, the nighttime WBGTs are higher by 0.3–0.9°C over the whole countries studied, and by 1–2°C in the MURs under the urban expansion scenario, compared to the situation in which urban areas remain unchanged. These results show that future urban expansion and heat island mitigation can result in potential daytime benefits but also persistent nighttime risks.

Perceptions of urban heat island mitigation and implementation strategies: survey and gap analysis

Sustainable development of cities and communities under climate change calls for effective and pragmatic strategies to mitigate urban heat island (UHI) during hot seasons. Meanwhile, the effectiveness of UHI mitigation measures can be affected by public perceptions during planning and implementation processes. However, the general perceptions of UHI mitigation and implementation strategies have not received adequate attention in urban climate research. This study leverages the results of a carefully designed survey to fill this research gap. The perceptions of professional respondents are largely affected by the geographic areas they work in and partially affected by how familiar respondents are with the UHI-related building codes and regulations. In addition, academic literature and government reports are the two major sources for most respondents to obtain UHI mitigation information. We also identify four knowledge and implementation gaps: the lack of public education on UHI mitigation and implementation measures, the lack of effective communications between researchers and code writers, the lack of implementing UHI mitigation strategies in some countries, and the lack of trustworthy information shared on social media. Bridging these gaps are of key importance to fostering public engagement and improving the effectiveness of UHI mitigation measures.

Impact of urban heat island mitigation measures on microclimate and pedestrian comfort in a dense urban district of Lebanon

The interaction between microclimate and buildings is predominant in urban areas. Thus, the urbanization constitutes the main cause of UHI formation. During the last years, several studies exposed the critical effects of UHI in the Mediterranean climate. As a result, there is a need for sustainable systems and urban policies to reduce heat islands in urban areas. This paper aims to present the impact of some UHI mitigation strategies in a Mediterranean city, Beirut Lebanon. Numerical microclimate simulations of an existing Lebanese district of Dora in Beirut, are performed using ENVI-met software. The study focuses on the potential of UHI mitigation scenarios to create freshness in summer conditions. The strategies are based on the increase of green surfaces, on the installation of water spray and fountains, and on the increase of the albedo of the facades and roofs of the buildings. A focus is carried out on white models, dealing with the albedo modification of roads and buildings. The effect of the proposed strategies on the pedestrian comfort is also evaluated by using the physiologically equivalent temperature PET. Results pointed out that implementation of water features contributes to a significant reduction of ambient temperature reaching a maximum of 5 °C. In term of outdoor thermal comfort, the results showed the important role of green areas on the improvement of pedestrian comfort during daytime. Finally, this research supports a set of actions that could be helpful for urban designer to create cool islands in the Lebanese neighborhoods.

Willingness to Pay for Urban Heat Island Mitigation: A Case Study of Singapore

In many countries, urban heat island (UHI) effects come along with urbanization in metropolitan areas. They have relevant adverse effects on the health and wellbeing of citizens. Singapore is strongly affected by UHI. In this study, we assess Singaporeans’ willingness to pay (WTP) for UHI mitigation by implementing a contingent valuation analysis. Specifically, we employ a double-bounded dichotomous survey design on a representative sample of 1822 online respondents. We find that Singaporeans are willing to sacrifice on average 0.43% of their annual income to mitigate UHI. The total WTP for mitigation strategies among Singapore citizens and permanent residents is estimated at SGD$783.08 million per year, the equivalent of USD$563.80 per year. Our findings suggest that there is a positive and significant relationship between the size of UHI effects and the citizens’ WTP. People living in the region with the highest intensity of UHI are willing to pay 3.09 times more than those living in the region with the lowest UHI intensity. Furthermore, demographic and socio-economic characteristics are significant determinants of Singaporeans’ WTP. The WTP increases with income and education but decreases with age. Students, men, and people with children are willing to pay more. Additional analyses show that the level of UHI awareness, positive attitudes towards UHI mitigation strategies as well as preferences for outdoor activities are positively correlated with the WTP. Our findings suggest that citizens are aware of the impacts of UHI and support UHI mitigation measures to be financed by their taxes. Policy interventions to promote UHI-related education and disseminating UHI-related information might increase the support of UHI mitigation policies.

Monitoring and spatio-temporal analysis of UHI effect for Mansa district of Punjab, India

Urban heat island (UHI) is one of the most important climatic implications of urbanization and thus a matter of key concern for environmentalists of the world in the twenty-first century. The relationship between climate and urbanization has been better understood with the introduction of thermal remote sensing. So, this study is an attempt to understand the influence of urbanization on local temperature for a small developing city. The study focuses on the investigation of intensity of atmospheric and surface urban heat island for a small urbanizing district of Punjab, India. Landsat 8 OLI/TIRS satellite data and field observations were used to examine the spatial pattern of surface and atmospheric UHI effect respectively, for the month of April, 2018. The satellite data has been used to cover the larger geographical area while field observations were taken for simultaneous and daily temperature measurements for different land use types. The significant influence of land use/land cover (LULC) patterns on UHI effect was analyzed using normalized built-up and vegetation indices (NDBI, NDVI) that were derived from remote sensing satellite data. The statistical analysis carried out for land surface temperature (LST) and LULC indicators displayed negative correlation for LST and NDVI while NDBI and LST exhibited positive correlation depicting attenuation in UHI effect by abundant vegetation. The comparison of remote sensing and in-situ observations were also carried out in the study. The research concluded in finding both nocturnal and daytime UHI effect based on diurnal air temperature observations. The study recommends the urgent need to explore and impose effective UHI mitigation measures for the sustainable urban growth.

Should Cities Embrace Their Heat Islands as Shields from Extreme Cold?

AbstractThe higher temperature in cities relative to their rural surroundings, known as the urban heat island (UHI), is one of the most well documented and severe anthropogenic modifications of the environment. Heat islands are hazardous to residents and the sustainability of cities during summertime and heat waves; on the other hand, they provide considerable benefits in wintertime. Yet, the evolution of UHIs during cold waves has not yet been explored. In this study, ground-based observations from 12 U.S. cities and high-resolution weather simulations show that UHIs not only warm urban areas in the winter but also further intensify during cold waves by up to 1.32° ± 0.78°C (mean ± standard deviation) at night relative to precedent and subsequent periods. Anthropogenic heat released from building heating is found to contribute more than 30% of the UHI intensification. UHIs thus serve as shelters against extreme-cold events and provide benefits that include mitigating cold hazard and reducing heating demand. More important, simulations indicate that standard UHI mitigation measures such as green or cool roofs reduce these cold-wave benefits to different extents. Cities, particularly in cool and cold temperate climates, should hence revisit their policies to favor (existing) mitigation approaches that are effective only during hot periods.

The urban heat island effect in Dutch city centres

In the Netherlands awareness regarding the Urban Heat Island (UHI) was raised relatively recently. Because of this recent understanding, there is a lack of consistent urban micro-meteorological measurements to allow a conventional UHI assessment of Dutch cities during heat waves. This paper argues that it is possible to retrieve relevant UHI information – including adaptation guidelines – from satellite imagery. The paper comprises three parts. The first part consists of a study of suited indicators to identify urban heat islands from which a method is presented based on ground heat flux mapping. The second part proposes heat mitigation strategies and identifies the areas where these strategies could be applied within the hotspots identified in the cities of The Hague, Delft, Leiden, Gouda, Utrecht and Den Bosch. The third part estimates the reduction of urban heat generated by the increase of roof albedo in the hotspots of the six cities. The six cities hotspots are located within the boundaries of the 17th century city centres. In order to avoid interference with cultural values of these historical environments most likely UHI mitigation measures regard improving the thermal behaviour of the city roofs. For instance, applying white coatings on bitumen flat roofs (or replacing them by white single-ply membranes) and replacing sloped roof clay tiles by coloured tiles with cool pigments can reduce the urban heat hotspots by approximately 1.5°C. Remote sensing provides high level information that provide urban planners and policy makers with overall design guidelines for the reduction of urban heat.

Attribution and mitigation of heat wave-induced urban heat storage change

When the urban heat island (UHI) effect coincides with a heat wave (HW), thermal stress in cities is exacerbated. Understanding the surface energy balance (SEB) responses to HWs is critical for improving predictions of the synergies between UHIs and HWs. This study evaluates observed SEB characteristics in four cities (Beijing, Łódź, London and Swindon), along with their ambient meteorological conditions, for both HW and background summer climate scenarios. Using the Analytical Objective Hysteresis Model (AnOHM), particular emphasis is on the heat storage. The results demonstrate that in London and Swindon the amount of daytime heat storage and its fraction relative to the net all-wave radiation increase under HWs. Results further demonstrate that such increases are strongly tied to lower wind speeds. The effects of different UHI mitigation measures on heat storage are assessed using AnOHM. Results reveal that use of reflective materials and maintaining higher soil moisture availability can offset the adverse effects of increased heat storage.

The Urban Heat Island: Implications for Health in a Changing Environment.

The Urban Heat Island (UHI) is a well-studied phenomenon, whereby urban areas are generally warmer than surrounding suburban and rural areas. The most direct effect on health from the UHI is due to heat risk, which is exacerbated in urban areas, particularly during heat waves. However, there may be health benefits from warming during colder months. This review highlights recent attempts to quantitatively estimate the health impacts of the UHI and estimations of the health benefits of UHI mitigation measures. Climate change, increasing urbanisation and an ageing population in much of the world, is likely to increase the risks to health from the UHI, particularly from heat exposure. Studies have shown increased health risks in urban populations compared with rural or suburban populations in hot weather and a disproportionate impact on more vulnerable social groups. Estimations of the impacts of various mitigation techniques suggest that a range of measures could reduce health impacts from heat and bring other benefits to health and wellbeing. The impact of the UHI on heat-related health is significant, although often overlooked, particularly when considering future impacts associated with climate change. Multiple factors should be considered when designing mitigation measures in urban environments in order to maximise health benefits and avoid unintended negative effects.

Multi-scale urban system modeling for sustainable planning and design

The urban heat island (UHI) phenomenon has become a concern in many major cities worldwide, as high summer temperatures and poor wind flow can have negative impacts on city dwellers, particularly increasing energy demand for artificial cooling. This paper showcases how an Integrated Multi-scale Environmental Urban Model (IMEUM) can be employed to support planners, architects and engineers to assess the combined impacts of the UHI phenomenon and rising global temperatures due to climate change. IMEUM concept derives from downscaling environmental models from global scale (25km) to mesoscale (1km) and city scale (100m). Hence, this paper showcases a computationally efficient method which couples multi-scale atmospheric models with statistical model to estimate weather parameters. Developed under Singapore context, IMEUM can be utilized to incorporate appropriate UHI mitigation measures upfront in design process, consecutively bridging the gap between global and building scale. This paper also includes calibration of the IMEUM output using observations from ground sensors. Furthermore, by using case study of a hypothetical office building, this paper showcases how the IMEUM output can be fully converted into a localized weather data file for cooling load simulation. IMEUM is currently being developed further into integrated quantitative urban environment simulation tool (QUEST), which can be used to test the immediate microclimatic impact of development plans and assess their long term impacts under future climate change scenarios.

The urban heat island effect in Dutch city centres

In the Netherlands awareness regarding the Urban Heat Island (UHI) was raised relatively recently. Because of this recent understanding, there is a lack of consistent urban micro-meteorological measurements to allow a conventional UHI assessment of Dutch cities during heat waves. This paper argues that it is possible to retrieve relevant UHI information – including adaptation guidelines – from satellite imagery. The paper comprises three parts. The first part consists of a study of suited indicators to identify urban heat islands from which a method is presented based on ground heat flux mapping. The second part proposes heat mitigation strategies and identifies the areas where these strategies could be applied within the hotspots identified in the cities of The Hague, Delft, Leiden, Gouda, Utrecht and Den Bosch. The third part estimates the reduction of urban heat generated by the increase of roof albedo in the hotspots of the six cities. The six cities hotspots are located within the boundaries of the 17th century city centres. In order to avoid interference with cultural values of these historical environments most likely UHI mitigation measures regard improving the thermal behaviour of the city roofs. For instance, applying white coatings on bitumen flat roofs (or replacing them by white single-ply membranes) and replacing sloped roof clay tiles by coloured tiles with cool pigments can reduce the urban heat hotspots by approximately 1.5°C. Remote sensing provides high level information that provide urban planners and policy makers with overall design guidelines for the reduction of urban heat.

Secondary effects of urban heat island mitigation measures on air quality

Abstract This study presents numerical simulations analysing the effect of urban heat island (UHI) mitigation measures on the chemical composition of the urban atmosphere. The mesoscale chemical transport model WRF-Chem is used to investigate the impact of urban greening and highly reflective surfaces on the concentrations of primary (CO, NO) as well as secondary pollutants (O3) inside the urban canopy. In order to account for the sub-grid scale heterogeneity of urban areas, a multi-layer urban canopy model is coupled to WRF-Chem. Using this canopy model at its full extend requires the introduction of several urban land use classes in WRF-Chem. The urban area of Stuttgart serves as a test bed for the modelling of a case scenario of the 2003 European Heat Wave. The selected mitigation measures are able to reduce the urban temperature by about 1 K and the mean ozone concentration by 5–8%. Model results however document also negative secondary effects on urban air quality, which are closely related to a decrease of vertical mixing in the urban boundary layer. An increase of primary pollutants NO and CO by 5–25% can be observed. In addition, highly reflective surfaces can increase peak ozone concentration by up to 12% due to a high intensity of reflected shortwave radiation accelerating photochemical reactions.

都市流域の地表面地物要素へのヒートアイランド緩和策に対する実流域シミュレーション評価

The promotion of heat island mitigation measures is an urgent need in Tokyo. This study simulated evapotranspiration, land surface temperature, and watershed averaged land surface temperature for each individual land-surface feature in the Upper Kanda River Watershed, implementing a water-permeable pavement for roads and green roofs as heat island mitigation measures. The simulation took an advantage of TET model that can express the amount of evapotranspiration, accounting for changes in soil moisture and permeable characteristics of individual land-surface features. As a result, it was found that the state of the soil moisture had a significant effect in the impact assessment of urban heat island mitigation measures.

Relationships between the properties of an urban street canyon and its radiant environment: Introduction of appropriate urban heat island mitigation technologies

The relationships between the properties of urban canopy components and the radiant environment in an urban street canyon are examined considering the introduction of appropriate urban heat island mitigation technologies. Radiant heat transfers between walls and roads are calculated according to Gebhart’s radiant absorption coefficients and using the Monte Carlo method. Roads are classified as either north–south or east–west; intersections are also considered. The key property of an urban street canyon is expressed by its aspect ratio W/H. A simple street canyon model and two actual urban street canyon areas are used as the objects of examination. Distributions of surface temperatures and solar radiation gains on street canyon roofs, roads, and walls are analyzed. The top priority for the implementation of urban heat island mitigation measures concerns the buildings with large roof areas. The other high-priority areas for implementing mitigation measures focus on smaller roofs and roads for which the street canyon aspect ratio W/H is greater than 1.5; the lowest-priority area is the walls.