nasa-gesdisc/es-publications-researchareas huggingface dataset:
Enhanced surface urban heat islands due to divergent urban-rural greening trends (2021)

Abstract
            
              Satellite observations show that the surface urban heat island intensity (SUHII) has been increasing over the last two decades. This is often accompanied by an increased urban-rural contrast of vegetation greenness. However, the contribution of uneven vegetation trends in urban and rural areas to the trend of SUHII is unclear, due to the confounding effects of climate change and changes in man-made infrastructures and anthropogenic heat sources. Here we use a data-model fusion approach to quantify such contributions during the peak growing season. We show that the LAI
              dif
              (the urban-rural difference of leaf area index) is increasing (
              P
              < 0.05) in 189 of the selected 228 global megacities. The increasing trend of LAI
              dif
              from 2000 to 2019 accounts for about one quarter of the trend in satellite-derived SUHII, and the impact is particularly evident in places with rapid urbanization and rural cropland intensification. The marginal sensitivity of SUHII to LAI
              dif
              is the strongest in hot-humid megacities surrounded by croplands and in hot-dry megacities surrounded by mixed woody and herbaceous vegetation. Our study highlights the role of long-term vegetation trends in modulating the trends of urban-rural temperature differences.

Research areas: Heat
Changes in urbanization and urban heat island effect in Dhaka city (2022)

The study aimed to assess the changes in urban areas and UHI effects in Dhaka city, Bangladesh, from 2001 to 2017, using Moderate Resolution Imaging Spectroradiometer (MODIS) daily day- and nighttime land surface temperature (LST) data from 2001 to 2017. The expansion of the city was calculated using the city clustering algorithm (CCA). The temperature of the identified urbanized area was analyzed and compared with the adjacent regions. The changes in urban temperature were estimated using non-parametric statistical methods. The results showed that Dhaka city's land surface area has grown by 25.33% and its inhabitants by 76.65% during 2001-2017. Urban expansion and dense settlements caused an increase in average temperature in some areas of Dhaka city nearly 3 °C compared to that at its boundary. The day and night temperature differences at Dhaka city's warmest location and the coolest point outside the city were nearly 7 °C and 5 °C, respectively. The city's annual average day- and nighttime temperatures was increasing at a rate of 0.03 °C and 0.023 °C/year over the period of the last 17 years. The rising temperature would increase the UHI effect in the future, which, combined with high humidity, may cause a significant increase in public health risk in the city if mitigation practices are not followed.

Research areas: Heat
Environmental impacts of shifts in energy, emissions, and urban heat island during the COVID-19 lockdown across Pakistan (2021)

Restrictions on human and industrial activities due to the coronavirus (COVID-19) pandemic have resulted in an unprecedented reduction in energy consumption and air pollution around the world. Quantifying these changes in environmental conditions due to government-enforced containment measures provides a unique opportunity to understand the patterns, origins and impacts of air pollutants. During the lockdown in Pakistan, a significant reduction in energy demands and a decline of 1786 GWh (gigawatt hours) in electricity generation is reported. We used satellite observational data for nitrogen dioxide (NO2), carbon monoxide (CO), sulphur dioxide (SO2), aerosol optical depth (AOD) and land surface temperature (LST) to explore the associated environmental impacts of shifts in energy demands and emissions across Pakistan. During the strict lockdown period (March 23 to April 15, 2020), we observed a reduction in NO2 emissions by 40% from coal-based power plants followed by 30% in major urban areas compared to the same period in 2019. Also, around 25% decrease in AOD (at 550 nm) thickness in industrial and energy sectors was observed although no major decrease was evident in urban areas. Most of the industrial regions resumed emissions during the 3rd quarter of April 2020 while the urban regions maintained reduced emissions for a longer period. Nonetheless, a gradual increase has been observed since April 16 due to relaxations in lockdown implementations. Restrictions on transportation in the cities resulted in an evident drop in the surface urban heat island (SUHI) effect, particularly in megacities. The changes reported as well as the analytical framework provides a baseline benchmark to assess the sectoral pollution contributions to air quality, especially in the scarcity of ground-based monitoring systems across the country.

Research areas: Air Quality
Relationship between urban heat island and green infrastructure fraction in Harbin (2018)

Urbanisation contributed to the presence of urban heat island phenomenon, and aggravated urban heat island effect intensity with the improvement of urbanisation level. Overheat weather condition caused severe threat to human life and health, while green infrastructure including water bodies has been validated to be able to reduce urban land surface temperature in different extent. To examine the impact of green infrastructure on urban heat island effect in Harbin, with the aid of ENVI and geographic information system software, this paper retrieved seasonal Harbin land surface temperature from 2000 to 2015 using Landsat series and MODIS 8-day remote sensing data, and further computed surface urban heat island intensity(SUHII). Then, to build the quantitative relationship between green infrastructure fraction and urban heat island intensity applying regression analysis method. Finally, by means of ENVI-MET software, this article simulated urban heat island intensity change based on different green infrastructure scenarios. The results showed that, as far as administrative region of Harbin scale, surface urban heat island intensity both in summer and in winter reduced from 2000(6.55C in summer, 4.15C in winter) to 2015(2.6C in summer, 0.47C in winter), and SUHII in summer is higher than it in winter except 2005; Green infrastructure fraction is negative correlated with SUHII; Simulation result indicated that increase on green infrastructure would facilitate to mitigation of urban heat island effect. The result of this study would provide some help and advice for land use planning decision and urban construction in the future of Harbin.

Research areas: Heat
Evaluation of urban heat islands using local climate zones and the influence of sea-land breeze (2020)

The Local Climate Zone (LCZ) scheme is an urban form and land cover/land use classification system used to study urban heat islands (UHIs). Many studies have evaluated the relationship between LCZs and air temperature. While the intensity and spatial pattern of an UHI can be influenced by the land-sea breeze, especially in coastal cities, few studies have been done to examine this using the LCZ scheme. In this study, Sendai, Japan, has been selected as a case study to evaluate whether the LCZ scheme can be used to study UHIs that are exposed to sea-land breeze since it has two urban-rural areas: mountain side and coastal side. UHI analysis was based on LCZ classes with GIS-derived geometric and land cover properties. By dividing Sendai into two regions along its urban center, the mitigating effects of sea-land breeze on the magnitudes of UHIs in each urban-rural area were demonstrated. Based on the results of this study, two specific UHI mitigation strategies were proposed for Sendai. This study confirmed that the LCZ scheme can be used by urban planners to assess both surface UHI (SUHI) and UHI effects, and proposed a feasible process for developing targeted UHI mitigation strategies.

Research areas: Heat
New ECOSTRESS and MODIS land surface temperature data reveal fine-scale heat vulnerability in cities: A case study for Los Angeles County, California (2019)

Rapid 21st century urbanization combined with anthropogenic climate warming are significantly increasing heat-related health threats in cities worldwide. In Los Angeles (LA), increasing trends in extreme heat are expected to intensify and exacerbate the urban heat island effect, leading to greater health risks for vulnerable populations. Partnerships between city policymakers and scientists are becoming more important as the need to provide data-driven recommendations for sustainability and mitigation efforts becomes critical. Here we present a model to produce heat vulnerability index (HVI) maps driven by surface temperature data from National Aeronautics and Space Administrations (NASA) new Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) thermal infrared sensor. ECOSTRESS was launched in June 2018 with the capability to image fine-scale urban temperatures at a 70 m resolution throughout different times of the day and night. The HVI model further includes information on socio-demographic data, green vegetation abundance, and historical heatwave temperatures from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the Aqua spacecraft since 2002. During a period of high heat in July 2018, we identified the five most vulnerable communities at a sub-city block scale in the LA region. The persistence of high HVI throughout the day and night in these areas indicates a clear and urgent need for implementing cooling technologies and green infrastructure to curb future warming.

Research areas: Heat
Lower Urban Humidity Moderates Outdoor Heat Stress (2022)

Surface temperature is often used to examine heat exposure in multi-city studies and for informing urban heat mitigation efforts due to scarcity of urban air temperature measurements. Cities also have lower relative humidity, traditionally not accounted for in large-scale observational urban heat risk assessments. Here, using crowdsourced measurements from over 40,000 weather stations in ≈600 urban clusters in Europe, we show the moderating effect of this urbanization-induced humidity reduction on outdoor heat stress during the 2019 heatwave. We demonstrate that daytime differences in heat index between urban clusters and their surroundings are weak, and associations of this urban-rural difference with background climate, generally examined from the surface temperature perspective, are diminished due to moisture feedbacks. We also examine the spatial variability of surface temperature, air temperature, and heat index within these clusters—relevant for detecting hotspots and potential disparities in heat exposure—and find that surface temperature is a poor proxy for the intra-urban distribution of heat index during daytime. Finally, urban vegetation shows much weaker (∼1/6th as strong) associations with heat index than with surface temperature, which has broad implications for optimizing urban heat stress mitigation strategies. These findings are valid for operational metrics of heat stress for shaded conditions (apparent temperature and humidex), thermodynamic proxies (wet-bulb temperature), and empirical heat indices. Based on this large-scale empirical evidence, surface temperature, used due to the lack of better alternatives, may not be suitable for accurately informing heat mitigation strategies within and across cities, necessitating more urban-scale observations and better urban-resolving models.

Research areas: Heat
Complementarity of renewable energy sources in the context of the heating sector (2022)

This chapter presents an analysis of solar and/or wind-powered air-source heat pumps supplying domestic space and hot water demand in Poland. The analysis has been performed from the perspective of long-term heat demand, coefficient of performance, and renewables variability spanning across the years 19802019 with an hourly resolution. The objective of the analysis was to investigate the potential mismatch between supply and demand for three electricity supply options: only solar, only wind, and the hybrid system in a 40-years climate change approach. In the hybrid configuration, the capacities of solar and wind generators have been adjusted in such a way that electricity from PV and later wind generator used by heat pump provides exactly 50% of the annual heat demand. The results revealed a better match of wind energy when it comes to supplying heating loads in Poland. Nevertheless, a significant temporal mismatch between demand and supply calls for long-term, seasonal storage solutions.

Research areas: Energy Production/Use
Spatiotemporal Features of the Surface Urban Heat Island of Bacau City (2023)

Using MODIS and Landsat LST images, the present paper advances a series of results on the characteristics of the surface heat island (SUHI) of Bacău City (Romania) during the warm season (April to September) for a period of 20 years (2001–2020). At the same time, given their higher temporal resolution and their availability for both day and night, MODIS LST was used to understand the spatial features of the SUHI in relation to land use. In this way, a total of 946 MODIS Terra and 483 Landsat satellite images were used to outline the main LST characteristics of the days with clear sky in this middle-sized city in northeast Romania. In order to analyze MODIS LST changes in relation to land use changes in the period 2001–2018, we used the standardized CORINE Land Cover datasets. With the help of the Rodionov test, we were able to determine the geometry and intensity of the SUHI. During the day, the spatial extension of the SUHI reaches its maximum level and is delimited by the isotherm of 31.0 °C, which is 1.5–2.0 °C warmer than the neighboring non-urban areas. During the night, the SUHI has a more regulated spatial extension around the central area of the city, delimited by the 15.5 °C isotherm with LST values that are 1.0–1.5 °C warmer than the surrounding non-urban areas. Additionally, from a methodological point of view, we highlight that resampled MODIS and Landsat images at a spatial resolution of 500 m can be used with confidence to understand the detailed spatial features of the SUHI. The results of this study could help the elaboration of future policies meant to mitigate the effects of urbanization on the SUHI in an era of increasing air temperatures during summer.

Research areas: Heat
Heat wave monitoring over West African cities: uncertainties (2023)

Heat waves can be one of the most dangerous climatic hazards affecting the planet, having dramatic impacts on the health of humans and natural ecosystems as well as on anthropogenic activities, infrastructures and economy. Based on climatic conditions in West Africa, the urban centres of the region appear to be vulnerable to heat waves. The goals of this work are firstly to assess the potential uncertainties encountered in heat wave detection and secondly to analyse their recent trend in West Africa cities during the period 1993-2020. This is done using two state-of-the-art reanalysis products, namely the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) and Modern-Era Retrospective analysis for Research and Applications (MERRA), as well as two local station datasets, namely Dakar-Yoff in Senegal and Aéroport Félix Houphouët-Boigny, Abidjan, in Côte d'Ivoire. An estimate of station data from reanalyses is processed using an interpolation technique: the nearest neighbour to the station with a land sea mask ≥0.5. The interpolated temperatures from local stations in Dakar and Abidjan show slightly better correlation with ERA5 than with MERRA. Three types of uncertainty are discussed: the first type of uncertainty is related to the reanalyses themselves, the second is related to the sensitivity of heat wave frequency and duration to the threshold values used to monitor them, and the last one is linked to the choice of indicators and the methodology used to define heat waves. Three sorts of heat wave have been analysed, namely those occurring during daytime, nighttime, and both daytime and nighttime concomitantly. Four indicators have been used to analyse heat waves based on 2 m temperature, humidity, 10 m wind or a combination of these. We found that humidity plays an important role in nighttime events; concomitant events detected with wet-bulb temperature are more frequent and located over the northern Sahel. Strong and more persistent heat waves are found in the continental (CONT) region. For all indicators, we identified 6 years with a significantly higher frequency of events (1998, 2005, 2010, 2016, 2019 and 2020), possibly due to higher sea surface temperatures in the equatorial Atlantic Ocean corresponding to El Niño events for some years. A significant increase in the frequency, duration and intensity of heat waves in the cities has been observed during the last decade (2012-2020); this is thought to be a consequence of climate change acting on extreme events.

Research areas: Heat
Exploring the seasonality of surface urban heat islands using enhanced (2023)

Understanding the seasonal variations in surface urban heat island (SUHI) in different local climate zones (LCZs) is crucial to efforts to reduce the impacts of urban warming on local residents. However, such an understanding is constrained by the lack of land surface temperatures (LSTs) at both high spatial and temporal resolutions. This study created time series LSTs by fusing Landsat 8 satellite data and gap-filled MODIS products to further analyses of the SUHI seasonality in a semi-arid city, Xi'an, China. The results showed that LSTs of the open building types were generally lower than those of the compact building types. The highest SUHI intensity (7.17 C) was found in compact mid-rise buildings (LCZ2), whereas lowest (3.62 C) was found in open high-rise buildings (LCZ4) in July. The SUHI intensity peaked about 1723 days later than the background LST. The annual SUHI hysteresis cycles exhibited an anti-clockwise concave-up pattern in the monsoon-influenced hot-summer humid continental climate (Dwa per Koppen-Geiger climate scheme). The SUHI intensity in autumn was higher than in spring under the same background LST. These results provide valuable information for developing heat mitigation strategies in different seasons.

Research areas: Heat
Comparisons of the Urbanization Effect on Heat Stress Changes in (2023)

While rapid urbanization promotes social and economic development, it exacerbates human outdoor thermal comfort, which increases the risks to human health. This paper uses four thermal comfort indices and multiple satellite observations to explore the urbanization effect on summer heat stress in Guangdong from 1979–2018, a coastal province of China. Two types of thermal comfort index are used here, namely the direct thermal comfort index (Heat Index, HI; Temperature–Humidity Index, THI; Discomfort Index, DI) and the physiological thermal comfort index (Universal Thermal Climate Index, UTCI). We compare the differences in the urbanization effects on the changes in the three direct thermal comfort indices (HI, THI, and DI) and a physiological thermal comfort index (UTCI). The results show that all four thermal comfort indices indicate an overall warming trend. Of them, urban sites show a higher warming trend than rural sites, indicating that heat stress changes are significantly influenced by urbanization from 1979–2018, which is consistent with the effect of urbanization on surface air temperature. However, except for the UTCI, this warming of direct thermal comfort indices affected by urbanization has become insignificant under the regional vegetation greening from 2004–2018 (also consistent with surface air temperature). This is primarily attributed to the different effects of wind speed on the physiological thermal comfort index in urban and rural areas: Decreasing wind speeds in urban areas lead to an increase in UTCI, while wind speeds in rural areas increase instead and decrease UTCI, thus widening the UTCI differences between urban and rural areas. Our results indicate that urbanization has a different effect on thermal comfort indices. When using the thermal comfort index, it is necessary to consider that different thermal comfort indices may bring different results. UTCI considers more factors that affect human heat perception, so it can better describe human outdoor thermal comfort. It also highlights the importance of urban ventilation and urban greenness in mitigating urban outdoor thermal comfort in the sustainable construction of future urbanization in coastal cities.

Research areas: Heat
Changes in air pollution, land surface temperature, and urban heat (2023)

COVID-19 has notably impacted the world economy and human activities. However, the strict urban lockdown policies implemented in various countries appear to have positively affected pollution and the thermal environment. In this study, Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and aerosol optical depth (AOD) data were selected, combined with Sentinel-5P images and meteorological elements, to analyze the changes and associations among air pollution, LST, and urban heat islands (UHIs) in three urban agglomerations in mainland China during the COVID-19 lockdown. The results showed that during the COVID-19 lockdown period (February 2020), the levels of the AOD and atmospheric pollutants (fine particles (PM2.5), NO2, and CO) significantly decreased. Among them, PM2.5 and NO2 decreased the most in all urban agglomerations, by >14 %. Notably, the continued improvement in air pollution attributed to China's strict control policies could lead to overestimation of the enhanced air quality during the lockdown. The surface temperature in all three urban agglomerations increased by >1 C during the lockdown, which was mainly due to climate factors, but we also showed that the lockdown constrained positive LST anomalies. The decrease in the nighttime urban heat island intensity (UHIInight) in the three urban agglomerations was greater than that in the daytime quantity by >25 %. The reduction in surface UHIs at night was mainly due to the reduced human activities and air pollutant emissions. Although strict restrictions on human activities positively affected air pollution and UHIs, these changes were quickly reverted when lockdown policies were relaxed. Moreover, small-scale lockdowns contributed little to environmental improvement. Our results have implications for assessing the environmental benefits of city-scale lockdowns.

Research areas: Heat