nasa-gesdisc/es-publications-researchareas huggingface dataset:
Assessing the spatiotemporal variation in anthropogenic heat and its impact on the surface thermal environment over global land areas (2020)

Anthropogenic heat that is mainly released in cities is rapidly rising in the context of global warming, while its impact on the land surface thermal environment is not completely clear. This study compared the anthropogenic heat flux (AHF) with the surface net solar radiation (SNSR) and analyzed the relationship between AHF and the surface urban heat island effect (ESUHI) on the basis of the estimation and analysis of global terrestrial AHF. Results indicated that the global-averaged terrestrial AHF caused by energy consumption and human metabolism increased from 0.07 to 0.15 W/m2 from 1980 to 2018. While a decrease in AHF mainly occurred in the developed cities of Europe and the United States, developing cities, particularly in eastern China, experienced an increase in AHF. The averaged terrestrial AHFs were far less than the corresponding SNSRs at the global and continental scales, whereas they were generally comparable in urban areas. AHF in the 100 largest cities around the globe was 19.56 (6.54) W/m2 in 2018 (1980) on average, which was approximately 12% (4%) of the corresponding SNSR. Additionally, we found a significantly positive correlation between AHF and ESUHI in eastern China (R2 = 0.8383, P < 0.01). These findings imply that anthropogenic heat has a considerable impact on the land surface thermal environment and is one of the most important contributors to dramatic urban warming, which needs to be considered in future climate-related policy formulation and evaluation.

Research areas: Heat
The case of Tehran's urban heat island, Iran: Impacts of urban 'lockdown'associated with the COVID-19 pandemic (2021)

The increasing expansion of urban environments with associated transformation of land-cover has led to the formation of urban heat islands (UHI) in many urbanized regions worldwide. COVID-19 related environmental impacts, through reduced urban activities, is worthy of investigation as it may demonstrate human capacity to manage UHI. We aim to establish the thermal impacts associated with COVID-19 induced urban lockdown from 20 March to 20 April 2020 over Tehran. Areal changes in UHI are assessed through Classification and Regression Trees (CART), measured against background synoptic scale temperature changes over the years 19502020. Results indicate that monthly Tmean, Tmax and Tmin values during this time were considerably lower than long-term mean values for the reference period. Although the COVID-19 initiated shutdown led to an identifiable temperature anomaly, we demonstrate that this is not a product of upper atmospheric or synoptic conditions alone. We also show that the cooling effect over Tehran was not spatially uniform, which is likely due to the complexity of land uses such as industrial as opposed to residential. Our findings provide potentially valuable insights and implications for future management of urban heat islands during extreme heat waves that pose a serious threat to human health.

Research areas: Heat
Interacting implications of climate change, population dynamics, and (2019)

Abstract
            One near-term expression of climate change is increased occurrence and intensity of extreme heat events. The evolution of extreme heat risk in cities depends on the interactions of large-scale climate change with regional dynamics and urban micro-climates as well as the distribution and demographic characteristics of people who live and work within these micro-climate areas. Here we use California as a testbed where we employ a suite of high-resolution (1.5 km) future regional climate simulations coupled with a satellite-driven urban canopy model and a spatially explicit population projection to investigate the interacting effects of climate change, population growth, and urban heat mitigation measures, such as cool roofs, on exposure to extreme heat events. We find that climate change and population growth reinforce with one another to drive substantial increases in future exposure to heat extremes, which are poised to become more frequent, longer, and more intense. Exposure to events analogous to historic high-mortality extreme heat waves increases by 3.56 folds. Widespread implementation of cool roofs can offset a substantial fraction (51%100%) of the increased heat exposure and associated building energy demand owing to climate change in urbanized regions.

Research areas: Heat
Are global cities homogenizing? An assessment of urban form and heat island implications (2022)

The rapid growth of citiesalong with the increasing connectedness of the world's social, economic, and political systemshas been hypothesized to generate a homogenization of urban form and associated environmental impacts. These hypotheses, however, have rarely been tested. Employing satellite imagery of 150 of the most populous cities in China, India, and the United States, we examine how the area and configuration of built-up land within cities has changed between 1995 and 2015 and assess impacts on the urban heat island effect. We find similar urban form trends across the three countries. The strongest evidence of homogenization is in the connectivity of urban form, while the shape of cities is linked to higher daytime surface urban heat island (SUHI) intensity. In the context of this and other research, we postulate that the identified urban form trends may lead to the homogenization of the biotic and abiotic environment of cities. Homogenization presents an opportunity for cities to learn from each other as they encounter similar ecological outcomes driven, in part, by their increasingly similar urban form.

Research areas: Heat
How an urban parameterization affects a highresolution global climate simulation (2020)

The impact of urban areas on the global and regional climate has been assessed using the global Conformal Cubic Atmospheric Model (CCAM) including an urban canyon parameterization at a global resolution of 50 km. Simulations were produced with and without urban areas to assess urban impacts for the historical period 1980-2000. Two different land cover and urban datasets (one based on IGBP-DIS, the other on MODIS) were tested. In addition, simulations were performed for the end of the 21st century with the RCP8.5 scenario. Evaluation of the historical climate simulations indicates realistic local urban effects, such as higher daily minimum air temperatures (tasmin), higher sensible heat flux and lower latent heat flux at urban grid cells. In regions with large fractions of urban areas, some regional changes are also noted. In addition, there are significant regional effects far away from the main urban areas, which are similar in magnitude to the effects of the different non-urban land cover input datasets. Under the projected warming at the end of the 21st century (with no land cover change), there is a decrease in anthropogenic heating, primarily during wintertime. There is a slightly smaller increase in daily maximum temperature and a slightly larger increase in tasmin in urban areas compared to rural areas. This leads to a smaller increase in the diurnal temperature range within urban areas. The tasmin changes also imply an increase in the urban heat island effect for larger cities. The results of this sensitivity study show that there is a detectable impact of urban areas on high-resolution global climate simulations. Consequently, there is a need to include urban areas in global simulations, as well as in studies of land-use change.

Research areas: Heat
Lack of vegetation exacerbates exposure to dangerous heat in dense settlements in a tropical African city (2022)

Abstract
            
              Both climate change and rapid urbanization accelerate exposure to heat in the city of Kampala, Uganda. From a network of low-cost temperature and humidity sensors, operational in 20182019, we derive the daily mean, minimum and maximum Humidex in order to quantify and explain intra-urban heat stress variation. This temperature-humidity index is shown to be heterogeneously distributed over the city, with a daily mean intra-urban Humidex Index deviation of 1.2
              
              C on average. The largest difference between the coolest and the warmest station occurs between 16:00 and 17:00 local time. Averaged over the whole observation period, this daily maximum difference is 6.4
              
              C between the warmest and coolest stations, and reaches 14.5
              
              C on the most extreme day. This heat stress heterogeneity also translates to the occurrence of extreme heat, shown in other parts of the world to put local populations at risk of great discomfort or health danger. One station in a dense settlement reports a daily maximum Humidex Index of
              
                
                  
                
                
                  >
                
                
              
              40 
              
              C in 68% of the observation days, a level which was never reached at the nearby campus of the Makerere University, and only a few times at the city outskirts. Large intra-urban heat stress differences are explained by satellite earth observation products. Normalized Difference Vegetation Index has the highest (75%) power to predict the intra-urban variations in daily mean heat stress, but strong collinearity is found with other variables like impervious surface fraction and population density. Our results have implications for urban planning on the one hand, highlighting the importance of urban greening, and risk management on the other hand, recommending the use of a temperature-humidity index and accounting for large intra-urban heat stress variations and heat-prone districts in urban heat action plans for tropical humid cities.

Research areas: Heat
How the Interaction of Heatwaves and Urban Heat Islands Amplify Urban Warming (2022)

An increase in global temperature will likely result in more intense and frequent heatwaves that would last longer. Simultaneously, the growth of urban population requires more areas of land incorporated into urbanization, because most people are expected to live in cities, which will increase the intensity and duration of urban heat islands. However, the extent of the link between global warming induced heatwaves and urbanization caused heat islands is barely understood. Understanding the link would give a new information about catastrophic heat mitigation strategies. This paper, therefore, quantifies, at the sub-continental scale of Eastern North America, the effects of background perturbations by the synergies between heatwaves and urban heat islands using simulations from the Weather Research and Forecasting (WRF) model, and focusing on the responses of urban energy balances, boundary layer height and vertical profiles of heat, momentum and moisture. Results showed that urban heat islands exacerbate heatwaves by deepening the turbulent boundary layer height, modifying the urban surface energy and regional winds. The fractional energy shift from latent to sensible heat fluxes and the consequent changes to the urban planetary boundary layer tends to amplify the intensity, extent and duration of extensive heatwaves. The response of ground heat fluxes to urban surfaces lags, while urban canopy humidity dissipates earlier because at the onset of the heatwave the surface water evaporates quickly to the point where there is less water left for evaporation leaving the urbanized regions vulnerable to more heating. During the heatwave event, the mean wind speed dropped by 2.5 m/s, hence less cool air is available for ventilation. The planetary boundary layer deepens by a maximum of 90-m over urban compared to rural and this may prolong urban surface heating. Based on the results, it can be concluded that the best heat-stress management strategies from the perspectives of urban energy balance and planetary boundary layer height is an integral approach that would lower sensible heat fluxes and increase surface albedo, latent heat fluxes and wind flows towards urban centers.

Research areas: Heat
Disproportionately higher exposure to urban heat in lower-income neighborhoods: a multi-city perspective (2019)

Abstract
            A growing literature documents the effects of heat stress on premature mortality and other adverse health outcomes. Urban heat islands (UHI) can exacerbate these adverse impacts in cities by amplifying heat exposure during the day and inhibiting the bodys ability to recover at night. Since the UHI intensity varies not only across, but also within cities, intra-city variation may lead to differential impact of urban heat stress on different demographic groups. To examine these differential impacts, we combine satellite observations with census data to evaluate the relationship between distributions of both UHI and income at the neighborhood scale for 25 cities around the world. We find that in most (72%) cases, poorer neighborhoods experience elevated heat exposure, an incidental consequence of the intra-city distribution of income in cities. This finding suggests that policymakers should consider designing city-specific UHI reduction strategies to mitigate its impacts on the most socioeconomically vulnerable populations who may be less equipped to adapt to environmental stressors. Since the strongest contributor of intra-urban UHI variability among the physical characteristics considered in this study is a neighborhoods vegetation density, increasing green space in lower income neighborhoods is one strategy urban policymakers can adopt to ameliorate some of UHIs inequitable burden on economically disadvantaged residents.

Research areas: Heat
Urban heat implications from parking, roads, and cars: A case study of metro Phoenix (2020)

To understand the transportation sectors role on influencing and mitigating heat in cities, this research quantifies added heat from pavement infrastructure and vehicle travel in the hot and automobile dependent metropolitan Phoenix, Arizona. Construction of a one-dimensional heat transfer model for local weather conditions and pavement design is combined with vehicle travel densities to simulate spatiotemporal sensible heat flux magnitudes. In metro Phoenix, sensible heat from pavements and vehicles is comprised of 67% from roadways, 29% from parking, and 3.9% vehicles. Concrete and asphalt pavement emit 15% and 37% more sensible heat compared to the bare ground, respectively. Added sensible heat from pavement peaks during summer afternoons when heat emissions relative to the ground are 26% and 46% greater for concrete and asphalt. Results indicate pavement infrastructure contributes significantly to Phoenixs urban heat balance, and areas surrounding busy vehicle corridors may be undesirable for outdoor activities during summer rush hours.

Research areas: Heat
SUMMER URBAN HEAT ISLAND OF GALATI CITY (ROMANIA) DETECTED USING SATELLITE PRODUCTS (2020)

The paper presents the main features of the urban heat island of Galati city during the summer season for a period of 16 years (2003-2018) using MODIS products. The main objectives were to analyse the extension and geometry of the urban heat island (UHI), its intensity, as well as its connection with land cover. The study is based on LST (Land Surface Temperature), a product obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors located on board of the Terra (EOS AM-1) satellite since 2001 and Aqua (EOS PM-1) satellite since 2003. The boundaries, geometry and spatial extent of the UHI were delimited primarily through the Rodionov test. Through this method, the changing points along four transects over Galati city were identified (North-South, East-West, Northeast-Southwest and Northwest-Southeast) and have been used to delimitate the UHI. Overall, the Galati UHI assessed by satellite information is stronger during the day when the UHI is split in two centres, developed over the industrial area in the west and over the residential part of the town in the east, while during the night the UHI is weaker being developed more clearly over the oldest part of the city. One of the major characteristics of the Galati UHI is that it is highly influenced by the water bodies encircling the city. During the day the intensity of UHI reaches 2-2.5C while during the night decreases below 2.0C. The relation of the UHI with land cover and the attenuation of UHI in the surrounding area are also investigated.

Research areas: Heat
Global urban population exposure to extreme heat (2021)

Significance
            Increased extreme heat exposure from both climate change and the urban heat island effect threatens rapidly growing urban settlements worldwide. Yet, because we do not know where urban population growth and extreme heat intersect, we have limited capacity to reduce the impacts of urban extreme heat exposure. Here, we leverage fine-resolution temperature and population data to measure urban extreme heat exposure for 13,115 cities from 1983 to 2016. Globally, urban exposure increased nearly 200%, affecting 1.7 billion people. Total urban warming elevated exposure rates 52% above population growth alone. However, spatially heterogeneous exposure patterns highlight an urgent need for locally tailored adaptations and early warning systems to reduce harm from urban extreme heat exposure across the planets diverse urban settlements.
          , 
            
              Increased exposure to extreme heat from both climate change and the urban heat island effecttotal urban warmingthreatens the sustainability of rapidly growing urban settlements worldwide. Extreme heat exposure is highly unequal and severely impacts the urban poor. While previous studies have quantified global exposure to extreme heat, the lack of a globally accurate, fine-resolution temporal analysis of urban exposure crucially limits our ability to deploy adaptations. Here, we estimate daily urban population exposure to extreme heat for 13,115 urban settlements from 1983 to 2016. We harmonize global, fine-resolution (0.05), daily temperature maxima and relative humidity estimates with geolocated and longitudinal global urban population data. We measure the average annual rate of increase in exposure (person-days/year
              1
              ) at the global, regional, national, and municipality levels, separating the contribution to exposure trajectories from urban population growth versus total urban warming. Using a daily maximum wet bulb globe temperature threshold of 30 C, global exposure increased nearly 200% from 1983 to 2016. Total urban warming elevated the annual increase in exposure by 52% compared to urban population growth alone. Exposure trajectories increased for 46% of urban settlements, which together in 2016 comprised 23% of the planets population (1.7 billion people). However, how total urban warming and population growth drove exposure trajectories is spatially heterogeneous. This study reinforces the importance of employing multiple extreme heat exposure metrics to identify local patterns and compare exposure trends across geographies. Our results suggest that previous research underestimates extreme heat exposure, highlighting the urgency for targeted adaptations and early warning systems to reduce harm from urban extreme heat exposure.

Research areas: Heat
Urban Heat Management in Louisville, Kentucky: A Framework for Climate Adaptation Planning (2019)

We explore the potential for cities to develop urban heat management plans to moderate rising temperatures and to lessen the impact of extreme heat on human health. Specifically, we model the impacts of heat management strategies, including tree planting and other green infrastructure, cool roofing and paving, and a reduction in waste heat emissions from buildings and vehicles, on estimated heat-related mortality across Louisville, Kentucky. Our assessment finds a combination of urban heat management strategies to lessen summer temperatures by as much as 10F on hot days and to reduce estimated heat-related mortality by more than 20 percent.

Research areas: Heat
Urban heat island in current and future climates for the island of Montreal (2018)

Urban regions with their distinct surface characteristics modify energy and water partitioning, leading to higher temperatures in comparison to the adjoining non-urban regions. This phenomenon, referred to as the Urban Heat Island (UHI), is studied for the island of Montreal situated in central-eastern Canada in the province of Quebec, for current and future climates, for the summer and fall seasons. Projected changes to the UHI for the region are studied using offline high-resolution (250 m) simulations performed with a land surface scheme, the Canadian Land Surface Scheme (CLASS), with and without the urban representation from the Town Energy Balance (TEB) model, for the RCP 8.5 scenario. Projected changes to land surface and 2 m air temperature fields suggest significant increases for both urban and nonurban regions, with small increases in the UHI intensity. The small increases in UHI intensity are due to the slightly higher increase in urban surface temperatures compared with nonurban regions, associated with increase and decrease in sensible and latent heat fluxes, respectively, for the urban regions. Furthermore, analysis of the projected changes to the number of hot days suggests significant increases, with urban regions augmenting the increases by 58 days in summer and 25 days in fall.

Research areas: Heat
Diurnal and seasonal trends and associated determinants of surface urban heat islands in large Bangladesh cities (2021)

Many surface urban heat island (SUHI) studies have been conducted around the globe, however there is still a lack of information available regarding the intensity of SUHI (SUHII) in Bangladesh cities. This study focused on diurnal and seasonal SUHI variability, temporal trends and possible drivers in five major cities. Mean annual daytime SUHII ranged from 2.88 C for Dhaka to 0.84 C for Rajshahi, while nighttime intensity varied from 1.91 C (Chittagong) to 0.30 C (Sylhet). The pre-monsoon period exhibited the greatest magnitude and the seasonal amplitude during the winter season was positive for Dhaka and Khulna but negative for the other cities. Correlation analysis indicated that a dense city population, a high degree of imperviousness and the absence of greenery were likely to act singly, or in combination, to increase urban warming within these cities. An increasing warming trend during daytime was observed. The urban population of Bangladesh is projected to increase substantially in future (i.e., to 81.4 million by 2029), so the findings of this study provide valuable insights into this warming issue and will assist in the development of effective local-scale climate change adaptation plans.

Research areas: Heat