Urban Heat Island Magnitude Research Articles

A new two-step estimation approach for retrieving surface urban heat island intensity and footprint based on urban-rural temperature gradients

Past decades have seen substantial efforts devoted to observing, assessing, and documenting the urban heat island (UHI) phenomenon. However, the discrepant criteria of non-urban references and ambiguous distinctions between urban and rural landscapes pose great challenges in measuring UHI magnitudes and spatial extents. This study goes beyond the conventional urban-rural dichotomy and introduces a new two-step approach based on the continuous transition of thermal environments along urban-rural gradients. The approach is applied to quantify Surface UHI (SUHI) intensities and footprints across 283 Chinese cities from 2005 to 2018 using multiple satellite-derived data sources. The results include: 1) The two-step approach avoids the limitations in subjective rural reference selections and provides reliable quantification of SUHI characteristics in various cities over time. 2) The SUHI footprints extracted by our approach are more reasonable than those obtained by two existing methods, with footprint ratios generally ranging within 0 − 6 times the urban area. 3) The two-step approach provides more concentrated estimates of SUHI intensity. Typically, ignoring heat sources in non-built-up areas can cause an overestimation of SUHI effect and misidentification of remote rural areas with high temperatures. Overall, the two-step approach enables more accurate estimates of SUHI effect, thereby facilitating policy-making for SUHI mitigation.

Biophysical Drivers of Seasonal Hysteresis of Urban Heat Islands Across Climates and Urban Landscapes

AbstractThe phenomenon of seasonal hysteresis between urban heat islands (UHIs) and background surface temperature was reported in many studies, but a unifying explanation for the causes of its magnitude, shape and looping direction remained less clear, and the impacts of urban landscapes and background climate on such hysteresis were also the subject of enquiry. Here we performed a systematic study based on a long‐term offline simulation for surface energy budgets, surface air and skin temperature of the urban‐biosphere system in East China. It was carried out with an up‐to‐date land surface model — the CLM5‐LCZs (the Community Land Model version 5 (CLM5) coupled with a newly developed urban canopy model representing diverse urban landscapes with the local climate zones classification scheme). To isolate the causes of UHIs hysteresis, a simplified framework was constructed by combining a mathematical representation of grid/subgrid model outputs, the two‐resistance mechanism method and the time‐lagged cross correlation analysis. The results exhibited distinct hysteresis patterns of UHIs such as twisted, concave‐down, concave‐up and convex‐up curve across diverse background climates and urban landscapes. The basic shapes of hysteresis depict a gradual transition from concave/convex‐up to concave/convex‐down by characterized by a larger winter UHIs from a wetter and warmer climate to a drier and colder climate. Magnitude and seasonality of surface UHIs are separately dominated by the urban‐rural contrast of evapotranspiration and heat storage at daytime and nighttime, whereas across‐climate variations of daytime and nighttime surface UHIs hysteresis are regulated by the phase shift of convection efficiency and anthropogenic heat. Urban landscapes affect the hysteresis mainly by altering the amplitude rather than the shape of looping curves. Our work could provide a fuller picture of how to mitigate urban warming considering inter‐seasonal tradeoffs over a broader region.

Associations between violent crime inside and outside, air temperature, urban heat island magnitude and urban green space

There are more incidents of violence in summer and on hot days, a trend likely to be exacerbated by climate change. Urban areas experience additional temperature modulation due to the urban form, however, to date, no studies have considered the effect of the urban heat island (UHI) or green space with respect to the temperature–violence relationship. This study modelled the relationship between the number of daily violent crime incidents that occurred inside or outside between July 2013 and June 2018, and the average surface UHI or percentage greencover (including grasses, shrubs and trees) within each local government area in Greater Sydney, Australia. Panelised negative binomial time series regression models indicated that the violent crime rate was associated with higher surface UHI for crimes committed outside (p = 0.006) but not inside (p = 0.072). Greater percentage of all vegetation was associated with significantly lower rates of violent crime committed outside (p = 0.011) but was not associated with violent crimes committed inside (p = 0.430). More socio-economic disadvantage was associated with higher rates of violent crime committed inside (p = 0.002) but not outside (p = 0.145). Greater temperature was non-linearly associated with higher rates of violent crime committed both inside and outside (p < 0.001). The findings of this study are important because both violence and heat exposure are critical health issues and will be stressed by urbanisation and climate change. The expansion of green space and/or reduction in UHI may mitigate these effects.

High Resolution WRF Modelling of Extreme Heat Events and Mapping of the Urban Heat Island Characteristics in Athens, Greece

In recent decades, large-scale urbanisation has developed rapidly, resulting in significant changes in the local and regional environment and climate. Large metropolitan areas worldwide induce significant changes in local atmospheric circulation and boundary layer meteorology by modifying the underlying surface characteristics and through the emission of anthropogenic heat and pollutants into the atmosphere. We investigate the urban heat island (UHI) characteristics in the city of Athens, Greece, which is one of Europe’s largest metropolitan complexes with a population of approximately 3.7 million inhabitants. The UHI effect is intense due to the city’s size, dense construction, high incident solar radiation, and almost complete lack of natural vegetation, with previous studies suggesting a temperature rise of 4 °C on average in the city centre compared to summer background conditions. We used high-resolution WRF simulations (1-km horizontal grid) driven with ERA5 reanalysis data to produce surface temperature maps in the city of Athens and the surrounding areas (Region of Attiki) during the summer period of 1 July–20 August 2021. Different model parameterizations were tested, both with respect to urban characteristics and physical parameters. The daily minimum and maximum temperatures (Tmin and Tmax) derived from the model were validated against observational data from a dense network of weather stations covering metropolitan Athens and surrounding locations. We further investigate the influence of different meteorological conditions on the UHI gradients as produced by the model and the observational dataset, including the extreme heat wave of 28 July–5 August 2021, during which persistent maximum temperatures of &gt;40 °C were recorded for nine consecutive days. The results indicate a strong correlation between WRF output and recorded minimum and maximum temperatures throughout the test period (R ranges from 0.80 to 0.93), with an average mean absolute bias (MAB) of 1.5 °C, and reveal the intensity and spatiotemporal variability of the UHI phenomenon in the city of Athens, with UHI magnitude reaching 8–9 °C at times. Our work aims to maximise the potential of using high-resolution WRF modelling for simulating extreme heat events and mapping the UHI effect in large metropolitan complexes.

STUDY OF URBAN HEAT ISLAND IN YOGYAKARTA CITY USING LOCAL CLIMATE ZONE APPROACH

Yogyakarta urban area has increased significantly for the past ten years and altered ecological features, such as inducing urban heat island (UHI). Our objectives are examining UHI characteristics in Yogyakarta urban with atmospheric variables which include air temperature and relative humidity and analyzing the UHI distribution using the LCZ method. This study uses the LCZ classification to spatially compare thermal characteristic and explain how land use and building geometry affect UHI. The system comprises 17 standard classes at the local scale, using quantitative approach which includes numerical data, such as aspect ratio, building heights, and street canyons to support the classification system. Three LCZ classes found in Yogyakarta urban area are LCZ 3, LCZ 5, and LCZ 6. The LCZ variables which affect temperature and relative humidity are building heights, width of street canyons, and land use. The biggest thermal difference is ΔLCZ3-LCZ5 and ΔLCZ3-LCZ6, which happened during 08.00 – 12.00 and 16.00 – 20.00. Small UHI magnitude (&lt; 2K) is affected by small difference in morphology and fabric. Medium UHI magnitude (2 – 5K) is mostly caused by large difference in fabric and small difference in morphology. In the future, the LCZ should be widely applied for urban planning regarding climatic mitigation.

Analysis of urban Heat Island intensity through air mass persistence: A case study of four United States cities

In conjunction with the ongoing rise in global air temperature, there is evidence to suggest that mid-latitude synoptic air masses have changed in frequency and persistence. The research presented here focuses on an analysis of urban heat island (UHI) intensity through the period of synoptic-scale air mass stagnation for four UHI-prone United States cities. It is theorized that the thermal inertia associated with a stagnant air mass conducive to UHI development causes an intensification of the urban-rural temperature difference through time. Results indicate that UHI intensification is responsive to more than just the thermal characteristics of the respective air mass in place. While the magnitude of UHI was found to be smallest under a cool, dry air mass, it generally intensifies with persistence. Conversely, commonly associated with the greatest UHI intensity, a warm, moist air mass exhibits little change in UHI intensity or even a de-intensification with persistence. The warm, moist air masses that are conducive to a stronger UHI appear to be increasing in frequency, partly due to greater persistence. However, somewhat encouraging is that the results here do not show UHI intensification through the period of their persistence.

Spatial and temporal characteristics of near‐surface air temperature across local climate zones in a tropical city

AbstractThe present study examines the temporal and spatial variability of near‐surface air temperature and the canopy layer urban heat island (UHI) in Singapore. Observations collected at 20 locations across the island city‐state and during 6 years make this one of the most extensive studies carried out in a tropical city. Local climate zones (LCZs), defined as urban built and rural land cover types which produce a unique air temperature response, are used to standardize intersite comparison. The results show that the choice of the rural reference can affect the night‐time UHI magnitude by up to 2°C under “ideal” (dry, clear, calm) conditions. The most frequently observed median UHI magnitude increases from 2.8 during all‐weather to 3.7°C during “ideal” conditions, respectively. A seasonality is present with lowest (highest) mean all‐weather values of ~2.0°C (~3.3°C), observed during the wet (dry) December–January (April–October) period. Mean night‐time UHI intensity across seven built‐type LCZs ranges between 1.8 and 3.5°C (2.5 and 4.3°C) for all‐weather (“ideal”) conditions. Corresponding daily values are 1.1–2.3°C (1.5–2.7°C). The lowest (highest) night‐time magnitudes are associated with open low‐rise LCZ 6 (compact high‐rise LCZ 1) built type. In the middle of the day LCZ 1 can experience a cool island effect. The average UHI values presented here give an indication of the extra warmth experienced in the built‐up spaces of Singapore relative to one possible rural reference land cover type (scattered trees LCZ B). Highest daytime heat exposure is observed in LCZs 3 and 8 which are characterized by low building heights, high impervious surface fraction and lack of vegetation. The present results can be used to support the development and evaluation of urban climate models, develop urban planning policies and improve local weather forecasts and the delivery of integrated urban services.

Confounding effects of harvesting on urban heat island intensity in a mid-sized city in Brazil

Urban heat island (UHI) studies have traditionally focused on the relative difference between air temperatures measured at an urban area and those at a rural location, taken as a reference. Whereas the influence of urban areas on UHI intensity has been abundantly explored, the impact of the choice of an adequate rural reference location, due to the frequent agricultural use of rural areas, still remains understudied. The issue of climate variability of rural areas is a determining factor for assessing UHI intensity. Brazil is the world's largest sugarcane producer, with a 33% share of the global market. Many mid-sized cities in the Brazilian state of São Paulo are located close to sugarcane fields, which all undergo the sugarcane growth cycle with defined pre-harvest and post-harvest stages. The aim of this study is to understand the interference of seasonal harvesting periods in sugarcane plantations on the development of UHI magnitudes in and around (at suburban locations) Piracicaba, located in the state of São Paulo, Brazil, at 22° 42′ 30“ S and 47° 38’ 01” W and characterized by Köppen-Geiger's Cfa, humid subtropical climate. We deployed a fully-equipped weather station at the site of a sugarcane crop at post- and pre-harvest and a small network of three weather stations provided with air temperature and humidity sensors in the city center and in suburban neighborhoods in Piracicaba. Pre-harvest showed the highest UHI intensities, though not confounding the analysis of intra-urban temperature differentiation patterns. Results stress the relevance of the choice of the baseline rural station in terms of temporal variability related to the sugarcane harvesting cycle.

Urbanization-induced changes in convective and frontal precipitation events in Ankara

Urbanization has been demonstrated to alter precipitation characteristics. However, there is a lack of modeling-based examination of the interaction between urbanization and precipitation in Turkey. Here, we analyze the urban impacts on two precipitation events with different synoptic backgrounds in Ankara using the Weather Research and Forecasting model. The rainfall occurrences were selected considering the urban heat island (UHI) intensity over the urbanized area. We conceptualize urban and nourban configurations using the CORINE land cover data and create ensemble simulations. Our findings underline the dissimilarity in the urban impacts on the precipitation pattern of the selected events. The urban scenario suppressed the rainfall over the downwind and upwind of the urban center by more than 10 mm for the summertime event, reshaping the rainfall pattern to be more spatially distributed and protracting the rainfall duration. By contrast, the urban impact on the springtime event is less discernible, with less than 1% change in the rainfall amounts over the urban center. Strong synoptic forcing and significantly less UHI magnitude for the springtime event are responsible for the masked urban impacts on precipitation. Regardless, the urban land use changed the surface energy balance, reducing the moisture content over the highly urbanized area.

The Impact of Climate Change on Urban Thermal Environment Dynamics

The human population is increasing. The ongoing urbanization process, in conjunction with climate change, is causing larger environmental footprints. Consequently, quality of life in urban systems worldwide is under immense pressure. Here, the seasonal characteristics of Maribor’s urban thermal environment were studied from the perspectives of surface urban heat island (SUHI) and urban heat island (UHI) A remote sensing thermal imagery time series and in-situ measurements (stationary and mobile) were combined with select geospatial predictor variables to model this atmospheric phenomenon in its most intensive season (summer). Finally, CMIP6 climate change scenarios and models were considered, to predict future UHI intensity. Results indicate that Maribor’s UHI intensity maximum shifted from winter to spring and summer. The implemented generalized additive model (GAM) underestimates UHI intensity in some built-up parts of the study area and overestimates UHI intensity in green vegetated areas. However, by the end of the century, UHI magnitude could increase by more than 60% in the southern industrial part of the city. Such studies are of particular concern, in regards to the increasing frequency of heat waves due to climate change, which further increases the (already present) heat stress in cities across the globe.

Evaluation of seasonal variability in magnitude of urban heat islands using local climate zone classification and surface albedo

Evaluation of seasonal variability in magnitude of urban heat islands using local climate zone classification and surface albedo

Urban Heat Islands during Heat Waves: A Comparative Study between Boston and Phoenix

AbstractIn this study, we simulate the magnitude of urban heat islands (UHIs) during heat wave (HWs) in two cities with contrasting climates (Boston, Massachusetts, and Phoenix, Arizona) using the Weather Research and Forecasting (WRF) Model and quantify their drivers with a newly developed attribution method. During the daytime, a surface UHI (SUHI) is found in Boston, which is mainly caused by the higher urban surface resistance that reduces the latent heat flux and the higher urban aerodynamic resistance ra that inhibits convective heat transfer between the urban surface and the lower atmosphere. In contrast, a daytime surface urban cool island is found in Phoenix, which is mainly due to the lower urban ra that facilitates convective heat transfer. In terms of near-surface air UHI (AUHI), there is almost no daytime AUHI in either city. At night, an SUHI and an AUHI are identified in Boston that are due to the stronger release of heat storage in urban areas. In comparison, the lower urban ra in Phoenix enhances convective heat transfer from the atmosphere to the urban surface at night, leading to a positive SUHI but no AUHI. Our study highlights that the magnitude of UHIs or urban cool islands is strongly controlled by urban–rural differences in terms of aerodynamic features, vegetation and moisture conditions, and heat storage, which show contrasting characteristics in different regions.

Influences of wind speed, sky conditions, land use and land cover characteristics on the magnitude of the urban heat island in Seoul: An exploratory analysis

Prevailing weather conditions and urban morphology are among the fundamental drivers of the radiative and turbulent exchange processes that inherently result in an urban heat island (UHI). The influence of such drivers varies with temporal changes and must be estimated using recent and sufficiently large meteorological and land-use datasets. We used the most recent in-situ temperature observations collected from a spatially extensive network of 54 automatic weather stations (AWS) gathered over a period of nine years to quantify the influence of wind speed, cloud coverage and land use characteristics on the magnitude of UHI in Seoul city. Through an analysis of variance and combined clustering techniques, we found increased UHI intensities (UHII) under low wind speeds, clear skies and densely built areas. Changes of 0.5 m/s in wind speeds and 1 octa in cloud coverage corresponded to 0.20 °C and 0.24 °C reductions in UHII, respectively. Also, statistically significant differences in peak diurnal UHII values of 1.2 °C were estimated between densely built and sparsely built areas. The obtained results shed light on the factors likely to influence UHI development in Seoul city, and fuel scientific discourse on the development of sustainable cities and effective policies for the management of the built environment.

Urban heat island (UHI) intensity and magnitude estimations: A systematic literature review.

The severity of urban heat islands (UHIs) is increasing due to global and urban climate change. The damage caused by UHIs is also increasing. To establish a plan to improve the deteriorating thermal environment in cities due to UHIs and to minimize the damage, further research is needed to accurately estimate and analyze the intensity and magnitude of UHIs. This systematic literature review (SLR) is an in-depth review of 51 studies obtained through a five-step filtering process focusing on their analysis of the spatial extent of UHIs, the UHI concept that was used for UHI estimation, and the UHI estimation and analysis methods. This SLR confirmed the need for accurate UHI intensity and magnitude estimation and analysis to reset the existing UHI classification based on the variety of vertical and horizontal ranges where UHIs occur. The results also indicated that the existing UHI energy concepts for estimating UHIs need to be modified and developed to reflect the three-dimensional physical form of the city. Finally, this SLR clarifies the need to develop an optimized analysis method for UHI research. The review results of this SLR will inform future studies and be the cornerstone for establishing policies and plans that can accurately predict and respond to the damage caused by UHIs.

Spatial variation of surface urban heat island magnitude along the urban-rural gradient of four rapidly growing Indian cities

The unplanned and uncontrolled urbanization of Indian cities has put them under different ecological and environmental threats. Urban heat island (UHI) is one such critical ecological hazard, whereby an urban area is experiencing higher land surface temperature (LST) as compared to the surrounding rural area. In the present study, the relationship of LST and surface urban heat island (SUHI) with the degree of impervious surface (IS) and green spaces (GS) in four rapidly growing Indian cities is presented. This study utilizes different geospatial techniques, including urban-rural gradient analysis, surface urban heat island estimation using Landsat OLI/TIRS data. The results signify a strong negative correlation of LST with the IS for Ahmedabad, Jodhpur, and Nagpur, while a positive correlation is seen over Guwahati. The negative correlation is the manifestation of the urban cool island, pertaining to higher LST over rural areas. On the other hand, Guwahati is surrounded by green vegetation, which provides natural cooling and thus lowers the LST, resulting in positive SUHI. The density of GS is found to be a significant contributor of SUHI in Guwahati city, whereas in the other three cities, its impact is insignificant due to its presence in very less amount in rural surroundings.

A Spatio-Temporal Assessment and Prediction of Surface Urban Heat Island Intensity Using Multiple Linear Regression Techniques Over Ahmedabad City, Gujarat

The present study intends to understand the variability in land surface temperature and urban heat island over Ahmedabad city, Gujarat, from 2003 to 2018 using MODIS thermal data. The spatio-temporal variability of land surface temperature dynamics is understood by pixel to pixel linear regression analysis along with Mann–Kendall and Sen's slope estimator tests. A Gaussian fitting technique is employed to estimate the surface urban heat island (SUHI) signature with respect to the surrounding rural area. An overall increase in the surface urban heat island magnitude is profoundly visible during the winter season. The spatial extent of SUHI shows a uniform distribution of urban heat inside the city and its accumulation within a high dense central urban area in both summer and winter seasons. A multiple linear regression method is used to predict the SUHI magnitude in the next 16 years, i.e. in 2034, based on enhanced vegetation index, white sky albedo, and evapotranspiration as predicting variables considering two different scenarios presuming the present rate of change of predicting variables as first scenario and a double changing rate as compared to present rate in the second scenario.

Spatial variation in temperature of urban space and urban heat island differentials in Warri metropolis, Nigeria

Urban Heat Island (UHI) has become one of the greatest problems associated with urban growth and industrialization. This is because of the elevated temperature associated with it. This paper examined spatial variation in temperature of urban space and magnitude of Urban Heat Island in Warri Metropolis, Nigeria. The study proceeded by stratifying the study area into four (Jakpa, Giwa-Amu, Airport Road and Okumagba Layout) and selected a peri-urban conurbation (Oha) as a control. Quasi-experimental (ex-post-facto) research design was adopted for the study. Secondary data of minimum and maximum temperature for a period of 30 (1992-2021) years was used. The study found that mean annual maximum temperature for Warri was 31 ºC compared to that of Oha (27.3 ºC). Minimum temperature for Warri was 23.2 ºC while Oha was 21 ºC. Generally, the mean temperatures for the Warri locations were higher than that of Oha. The UHI values, for Jakpa and Airport road were similar with UHI values of 1ºC respectively. Giwa Amu recorded 1.1 ºC, while Okumagba recorded UHI value of 1.2 ºC. The ANOVA model comparing the temperature values for the study area was significant at P&lt;0.05 (F-62.7; sig-.000). Implying that there is a significant spatial variation in temperature of Warri; and Oha was significantly cooler with a temperature of 27.1 ºC. The paired sample t test comparing mean temperature in Warri and Oha was significant at p&lt;0.05 (t-22.9; sig-.000). This implied that there is a significant difference between mean temperature in Warri and that of Oha. Therefore, tree planting, urban planning was among the recommendations advanced in the study.

Analyzing the Characteristics of UHI (Urban Heat Island) in Summer Daytime Based on Observations on 50 Sites in 11 LCZ (Local Climate Zone) Types in Xi’an, China

Urbanization has induced significant changes on local climate in urban areas. For sustainable urban planning, it is necessary to identify the distribution characteristics of urban heat island (UHI) and the effects of land cover properties. In situ measurements are frequently carried out to obtain critical data in urban climate studies. However, long-time continuous observations on multiple sites are still rare, even though they would be useful in mapping the distribution of UHI intensity. In the current work, three observation campaigns were carried out in Xi’an, China. Pedestrian- level air temperatures (PLAT) were measured with potable micro-environment stations on 50 sites in 11 local climate zone (LCZ) types. The normalized PLAT was used to investigate the canopy layer UHI characteristics and the effects of LCZ types. Results revealed that the land coverage type and the surface structure have significant influence on the local climate. The PLAT in high-surface-fraction building covered areas was higher than that in low-surface-fraction building covered areas. In areas with similar building surface fraction, building height influences the UHI magnitude as well, as tall buildings would provide more shielding on the pedestrian level. The average UHI magnitude and the standard deviation within each LCZ type were calculated by statistical analysis of the observed results, which proved to be useful for UHI mapping based on the LCZ classification results in urban areas.

Estimating the expansion of urban areas and urban heat islands (UHI) in Ghana: a case study

This research is focused on identifying urban sprawl pattern and extent in two rapidly growing major Ghanaian cities (Accra and Kumasi) and how urban expansion affected heat island effect over the period of 2002–2017 using remote sensing imagery. The research employed remotely sensed images from Landsat 7 and 8 missions for mapping the urban sprawl. Land cover classification was done by using object-based image analysis, and for land surface temperature estimation single-channel algorithm was used. The intensity and magnitude of urban heat island were estimated. The results showed that urban expansion was more dominant process than densification in both cities. A significant area of bare soils and sparsely vegetated lands became built-up accompanied by total disappearance of forest belt of Kumasi. The intensity and magnitude values indicated the presence and expansion of urban heat island in both cities. However, there was a significant amount of bare lands and sparsely vegetated areas with relatively high surface temperature in and around these cities. From the results of this work, we note that bare or sparsely vegetated land cover types in urban areas located in tropical climates can escalate overall urban temperatures. The urban heat island magnitude values were relatively higher compared to values for European cities during the heat wave of 2016. Although urban configurations and climatic conditions may be the reason for the differences, this shows how alarming and dangerous urban heat islands could be in tropical cities.

An integrated approach to project the future urban climate response: Changes to Lisbon's urban heat island and temperature extremes

Most state-of-the-art climate simulation ensembles misrepresent the effects of urbanization on local climate due to computational restrictions, posing a major limitation for urban climate projections. We circumvent this shortcoming by employing the SURFEX land-surface model coupled to TEB (Town Energy Balance) urban canopy model, forced by EURO-CORDEX regional climate simulations. We demonstrate the added-value of CORDEX-SURFEX-TEB compared to EURO-CORDEX in reproducing Lisbon’s temperature observations, halving the bias and improving the PDF matching by ~5%. Furthermore, the proposed framework allows characterizing the urban heat island (UHI) effect. Over Lisbon, the annual-mean UHI was ~+3 ºC (city warmer than rural) during nighttime, and around -0.5 to -1ºC (city cooler than rural) during daytime. The CORDEX-SURFEX-TEB climate projections for Lisbon, under fixed land-use and RCP8.5 scenario, showed a warming of ~+1ºC by 2021-2050 and ~+3.5ºC by 2070-2099. Despite the large multi-model spread, these long-term temperature changes were roughly constant for all hours and for urban and rural environments (corresponding to roughly constant UHI magnitude). Our results also reveal large seasonality of Lisbon’s UHI effect and of long-term warming. Finally, the projections show a striking growth in the number of extreme hot days and nights, respectively nearly tripling and quintupling its current value by 2070-2099.