Anthropogenic Heat Release Research Articles

Urban ecological land and natural-anthropogenic environment interactively drive surface urban heat island: An urban agglomeration-level study in China.

The surface urban heat island effect (SUHI) that occurs during rapid urbanization increases the health risks associated with high temperatures. Urban ecological land (UEL) has been shown to play an important role in improving urban heat stress, however, the impact of UEL interactions with the natural-anthropogenic environment on SUHI at the urban agglomeration-scale is less explored. In this study, the Google Earth Engine and GeoDetector were applied to characterize the spatiotemporal patterns of UEL and SUHI in the Guangdong-Hong Kong-Macao Greater Bay Area from 2000 to 2020 by extracting major built-up urban areas and quantifying the impacts of UEL and its interactions with the natural-anthropogenic factors on SUHI. The results show that the evolution of the UEL landscape structure exhibits clear spatiotemporal coupling with SUHI. Specifically, the UEL underwent a dispersion and degradation process in 2000-2015 and a convergence and restoration process in 2015-2020, the SUHI correspondingly transitioned from intensification and continuity to mitigation and contraction. The UEL landscape structure showed a notable impact on the SUHI reduction, and the dominance and richness of the patches explained an average of 19.95% and 16.03% of the SUHI, respectively. Moreover, the interaction between UEL and land urbanization rate and anthropogenic heat release had a dominant effect on SUHI, but this effect significantly declined from 2015 to 2020. With the implementation of ecological restoration projects, the interaction of UEL with topography rapidly increased and the SUHI gradually dominated by the joint interaction of UEL and natural-anthropogenic factors. A synthesis of the varying effects of several factors showed that the dynamic relationship between the development stages of the urban agglomeration's regional system and SUHI may conform to the Environmental Kuznets Curve. SUHI reduction strategies should therefore comprehensively optimize the rational allocation of UEL landscape structures and natural-human elements to promote the well-being of residents.

Assessing the environmental impact of China's tourism activities: a tourism heat footprint method.

Numerous research studies have examined carbon emissions generated from tourism activities. However, the environmental impact of anthropogenic heat release has not attracted researchers' attention. We apply the tourism heat footprint method to assess the environmental impact of China's tourism activities. The results indicate that (1) China's tourism heat footprint increased from 0.99 × 103 w/km2 in 1994 to 7.53 × 103 w/km2 in 2018, with an average annual growth rate of 8.82%. (2) Particularly during high seasons, the tourism heat footprint increases sharply; tourism transportation accounts for the highest proportion of the tourism heat footprint, ranging from 36.50 to 69.07% from 1994 to 2018. (3) The rapid growth in arrivals and transportation-related changes have contributed to the rapid growth of the tourism heat footprint. Advances in science and technology, laws and regulations, environmental pollution constraints, and national macroeconomic policy have helped reduce the tourism heat footprint. Generally, tourism activities caused by a significant increase in income are the root cause of tourism heat footprint growth. (4) Finally, some suggestions, including cultivating a low-energy tourism culture, improving energy efficiency, implementing low-energy policies, and performing spatial-temporal monitoring, are proposed. This paper expands sustainable tourism's analytical research and enriches the tourism footprint family evaluation process.

Exploring evapotranspiration characteristics in urbanized areas of Tianjin plain

To reveal the characteristics of urban-based evapotranspiration, a SEBS-Urban model was applied to estimate the monthly evapotranspiration(ET) that occurred in the plain area of Tianjin over 2015—2017 considering anthropogenic heat release. A two-step verification method was used. First, a comparative analysis was performed with the MODIS MOD16 products for rural areas. Second, the urban water dissipation (UWD) framework was used to assess the model's performance in built-up areas. The feasibility of the Budyko formula was explored based on the SEBS-Urban results. Three key results were obtained: ① The SEBS-Urban model is reliable, and the results of the built-up area ET analysis are consistent from the perspectives of an urban surface energy balance and a dualistic water cycle. ② The ET increment ranges up to 85%~115% for the built-up area but only 7.2%~8.7% for the whole study area after including considerations for anthropogenic heat. ③ The Budyko formula obtained good results for estimating evapotranspiration in the study area, suggesting that it can also be applied to urban areas. The results of this study can provide a necessary reference for studies on evapotranspiration in urbanized areas.

Responses of Heat Stress to Temperature and Humidity Changes Due to Anthropogenic Heating and Urban Expansion in South and North China

Due to global warming and human activities, heat stress (HS) has become a frequent extreme weather event around the world, especially in megacities. This study aims to quantify the responses of urban HS (UHS) to anthropogenic heat (AH) emission and its antrophogenic sensible heat (ASH)/anthropogenic latent heat (ALH) components and increase in the size of cities in the south and north China for the 2019 summer based on observations and numerical simulations. AH release could aggravate UHS drastically, producing maximal increment in moist entropy (an effective HS metric) above 1 and 2 K over the south and north high-density urban regions mainly through ALH. In contrast, future urban expansion leads to an increase in HS coverage, and it has a larger impact on UHS intensity change (6 and 2 K in south and north China) relative to AH. The city radius of 60 km is a possible threshold to plan to city sprawl. Above that city size, the HS intensity change due to urban expansion tends to slow down in the north and inhibit in the south, and about one-third of the urban regions might be hit by extreme heat stress (EHS), reaching maximal hit ratio. Furthermore, changes in warmest EHS events are more associated with high humidity change responses, irrespective of cities being in the north or south of China, which support the idea that humidity change is the primary driving factor of EHS occurrence. The results of this study serve for effective urban planning and future decision making.

Increases in Anthropogenic Heat Release from Energy Consumption Lead to More Frequent Extreme Heat Events in Urban Cities

With economic development and rapid urbanization, increases in Gross Domestic Product and population in fast-growing cities since the turn of the 21st Century have led to increases in energy consumption. Anthropogenic heat flux released to the near-surface atmosphere has led to changes in urban thermal environments and severe extreme temperature events. To investigate the effects of energy consumption on urban extreme temperature events, including extreme heat and cold events, a dynamic representation scheme of anthropogenic heat release (AHR) was implemented in the Advanced Research version of the Weather Research and Forecasting (WRF) model, and AHR data were developed based on energy consumption and population density in a case study of Beijing, China. Two simulations during 1999–2017 were then conducted using the developed WRF model with 3-km resolution with and without the AHR scheme. It was shown that the mean temperature increased with the increase in AHR, and more frequent extreme heat events were produced, with an annual increase of 0.02–0.19 days, as well as less frequent extreme cold events, with an annual decrease of 0.26–0.56 days, based on seven extreme temperature indices in the city center. AHR increased the sensible heat flux and led to surface energy budget changes, strengthening the dynamic processes in the atmospheric boundary layer that reduce AHR heating efficiency more in summer than in winter. In addition, it was concluded that suitable energy management might help to mitigate the impact of extreme temperature events in different seasons.

Exploring the Impact of 2-D/3-D Building Morphology on the Land Surface Temperature:A Case Study of Three Megacities in China

The urban heat island (UHI) effect in cities and its driving factors have long been investigated. 3-D buildings are key components of urban structures and have notable effect on the UHI effect. However, due to the incomplete 3-D building information in urban database, only a few studies investigated the impact of 3-D building morphology factors on the land surface temperature (LST). In this study, a total set of 14 2-D and 3-D building morphology factors were selected to investigate the correlation between UHI and building morphology across three megacities in China (Beijing, Wuhan, Shanghai) with Landsat-8 LST scenarios in summer and winter of 2018 and 2019, respectively. Both Spearman correlation and partial correlation analysis were applied at block scale after urban functional zone (UFZ) mapping. A number of significant observations were noted based on the multispatial and multitemporal experimental results:1) both 2-D and 3-D building morphology factors influence LST, among them building coverage ratio, building ground area divided by facade area (GA2FA), and sky view factor yield stronger correlations with LST; 2) UFZ mapping scheme and partial correlation method help with controlling the anthropogenic heat release, greenspace, and water bodies coverage variables when targeting at the influence of building morphology factors on LST. This study provides insights for building morphology design in future urban planning and management.

Land Surface Model CAS‐LSM: Model Description and Evaluation

AbstractComprehensive land surface models are very important for climate and weather forecasting and for improving our understanding of the relationships between humans and the Earth system. This work presents a land surface model of the Chinese Academy of Sciences (CAS‐LSM) that considers groundwater lateral flow, human water regulation, soil freeze‐thaw front dynamics, riverine dissolved inorganic nitrogen transport, anthropologic heat release, urban water usage, and urban planning based on the Community Land Model. Global simulations with the updated CAS‐LSM were conducted to evaluate its performance, and the results show its advantages in reproducing ecohydrological processes. Groundwater lateral flow can replenish the groundwater depletion cone caused by overexploitation, where the offset rate increases as the aquifer thickness increases. The maximum thaw depth increases by 3.62 mm yr−1 in permafrost areas, and the maximum frost depth decreases by 1.89 mm yr−1 in seasonally frozen areas. Nitrogen fertilizer use and point‐source pollution increase the riverine dissolved inorganic nitrogen flow rate in western Europe and eastern China. To further verify the model's ability to simulate the effects of urban planning implementation, simulations over Beijing were conducted using the Weather Research and Forecasting (WRF) model coupled with CAS‐LSM. The results show that anthropogenic heat release enhances the sensible heat flux and temperature in the city center. In terms of urban water planning, most of the total water supply in Beijing should be used for urban irrigation, and a small part should be used for road sprinkling to obtain a greater cooling effect.

How does anthropogenic heating affect the thermal environment in a medium-sized Central European city? A case study in Szeged, Hungary

Since the estimation of anthropogenic heating is always problematic in medium-sized cities because of data lacking, we intended to test how much the omission of such data influences the physical consistency in a numerical model (Weather Research and Forecasting – WRF). It was hypothesized that anthropogenic heating is an important input for the model, even in a relatively small urban area, therefore we adapted three different approaches to quantify its spatiotemporal distribution over Szeged, Hungary. Four numerical experiments were performed in the WRF coupled with the single layer canopy scheme, which included the calculated fluxes and an anthropogenic flux-free reference case. By comparing the experiments, we had the opportunity to determine the effects of different anthropogenic heating scenarios on certain meteorological variables near the surface and in the overlying urban boundary layer. The maximum anthropogenic heat release was estimated to be ranging between 0.6 and 31.2 W/m2 in Szeged, with higher values on winter days. This heat surplus contributed to a maximum increase of 1.5 °C in the simulated near-surface air temperature. Depending on the rate of anthropogenic heat release, the urban boundary layer became deeper, and the mixing of heat and momentum was more efficient. Our results have demonstrated that without the consideration of anthropogenic heating, numerical simulations performed to cities similar to Szeged cannot be physically complete.

Urban Heat Island intensity and buildings’ energy needs in Duran, Ecuador: Simulation studies and proposal of mitigation strategies

Urban Heat Island (UHI) is a phenomenon that is affecting cities across the world. In tropical climates, an increased UHI intensity can cause a significant rise in heat stress probability, both indoors and outdoors. A general increase in the air-conditioning energy consumption of buildings should also be expected as a consequence. This paper evaluates the case of Duran, Ecuador. It estimated, through a spatial distribution analysis, urban morphology parameters, properties of materials, and anthropogenic heat emissions in the streets. Twenty-eight urban, randomly selected samples were classified using the k-means clustering technique, which resulted in four preliminary clusters. Exploratory UHI simulations were carried out in the Urban Weather Generator tool (UWG) using the four clusters to investigate the relevance of the main UHI driving factors through a sensitivity analysis. Urban samples were weighted, considering the sensitivity analysis, for better classifying the driving factors. Results indicate that Duran city is strongly affected by UHI, especially in informal settlements with high anthropogenic heat release. The urban temperatures obtained by the model were compared to the experimental measurements in different locations in the city. Besides, the building cooling needs were simulated by using the TRNSYS v. 17 tool for residential and commercial buildings of the city, showing that UHI is increasing cooling-related energy consumption in a 30–70 % for residential buildings and a 10–20 % for commercial buildings. Finally, general mitigation strategies and policy implications to reduce the UHI intensity are proposed, and a set of scenarios is tested for the cluster with the highest UHI intensity.

Assessment of surface urban heat island intensity and its causes in the city of Baghdad

Recently, the differences in land surface temperature (LST) between urban and rural areas became more evident causing the formation of Surface Urban Heat Island (SUHI). The research aims to investigate the current intensity of Baghdad SUHI and determines its growing state over time. It also aims to identify the causes of this phenomenon. To find out Baghdad SUHI, the maps of LST and land use classes were assessed. This assessment was conducted by using remote sensing techniques which include the processing of Landsat 8 images in GIS ArcMap. The satellite image was acquired in July 2018. LST map was obtained by processing thermal band 10, while the land use map was identified by using the maximum likelihood classification of optical bands 1-7 of the satellite image. The results show that the maximum LST difference between Baghdad soil and built-up areas and Baghdad vegetated and water areas was about 17C°. Compared with the results of previous studies, it was found that Baghdad SUHI had significantly increased over time. The research also identified SUHI causes which include the gradual loss of vegetated and water areas, the low albedo materials, the modern grid pattern and the increase of anthropogenic heat release.

Assessing the relationship between anthropogenic heat release warming and building characteristics in Guangzhou: A sustainable development perspective

We assessed the spatial heterogeneity of warming due to total anthropogenic heat release (AHR) and building anthropogenic heat release under different heat release scenarios and its relationship with building properties in the highly urbanized portion of Guangzhou using the Weather Research and Forecasting (WRF) model. The simulation results show that different AHR scenarios result in different temperature rise outcomes. A rise of 0.40 °C and 0.23 °C results from a normal total AHR scenario and normal building AHR scenario, while a rise of 0.71 °C and 0.41 °C arises when total AHR and building AHR is doubled. This indicates that more anthropogenic heat results in a more serious warming effect. Moreover, the spatial heterogeneity of the AHR-caused temperature rise is affected by the building area. The AHR-derived warming effect is most serious in high-height-medium-density (H-M) and high-height-high-density (H-H) building areas, where temperature rose by 0.36 °C and 0.34 °C due to building AHR under two AHR scenarios, while it was least serious in low-height-high-density (L-H) and high-height-low-density (H-L) areas, where temperature rose by 16 °C and 0.25 °C under two building AHR scenarios. When AHR is doubled, the hot spot of AHR-derived warming tends to become more concentrated. The quantitative relationship between building AHR-derived warming and building property data was assessed using a multiple linear regression model. The model shows that the combination of building height and building density provides better predictor of building AHR warming than either property alone; and the relationship is best predicted in L-H and H-L areas, with R2 values of 0.68 and 0.79, respectively. Warming due to AHR should be considered as one of the most serious urban warming forces and the land surface properties are the key factors that influence AHR-derived warming. This study provides evidence for the significance of AHR in the urban environment and offers suggestions for mitigating urban thermal heating.

Roles of past, present, and future land use and anthropogenic heat release changes on urban heat island effects in Hanoi, Vietnam: Numerical experiments with a regional climate model

This study investigates the roles of land-use cover (LUC) and anthropogenic heat (AH) on the past, present, and future urban heat island (UHI) effect over the megapolitan area of Hanoi, Vietnam. We use a dynamical downscaling method with a regional climate model coupled with an urban canopy scheme to run sensitivity simulations with LUC and AH data from 1990, 2010, and 2030. The LUC data in 1990 and 2010 are derived from remote sensing data, whereas the LUC data for 2030 come from the city's master plan. The AH data are estimated from past and projected energy-use conditions. The results show that the LUC-AH coupled changes during 2010–2030 will have much greater impact on the local UHI effect than those during 1990–2010. In the urban-core area, the monthly mean surface air temperature in July is predicted to increase by 0.7 °C by 2030, double the increase of 0.35 °C during 1990–2010. We show that the temperature increase during 1990–2010 is mostly due to the change in LUC conditions, but the increase in the future AH will contribute 30–50% to the total temperature increase in the urban areas.

Impact of tourism activities on glacial changes based on the tourism heat footprint (THF) method

Nature-based tourism directly and indirectly affects the flora, fauna and environment, thereby reducing the sustainability of tourism destinations. However, the impact of tourism activities on glaciers at glacial tourism sites remains unexplored. Using two typical glacial tourism sites in China as examples, this paper uses the tourism heat footprint (THF) method to examine the impact of large-scale tourism activities on glaciers via local average temperatures. The THF method measures anthropogenic heat release (AHR) from energy consumption and human metabolism per unit area and time divided into seven components of tourism activities: transportation, accommodation, sightseeing, catering, entertainment, shopping and waste disposal. The main results show that the THF values of the Yulong and Hailuogou tourism zones are exhibiting a rapid growth trend, increasing from 8.7 × 10−3 and 4.0 × 10−4 Wm−2 in 1990 to 3.6 and 3.0 × 10−1 Wm−2 in 2017, respectively. These THFs are exerting a significant cumulative effect on the retreat of glaciers by increasing local average temperatures in conjunction with global climate change. These results show that the sustainability of glacial tourism and destinations is threatened by large-scale tourism activities. This study fills a current research gap, enriches the understanding of the impact of tourism activities on glacial resources and expands the analytical perspective of sustainable tourism research. Moreover, this study provides decision support for managing glacial scenic destinations and for the sustainable development of glacial tourism.

SEASONAL OCCURRENCE OF HEAT ISLAND PHENOMENON IN THE URBAN BUILT ENVIRONMENT

Latest analysis regarding the climate change phenomenon arises issues related to air quality, human comfort within urban environments and an increased energy demand attributed to the building sector. The Urban Heat Island (UHI) phenomenon is directly responsible for the poor quality of life in cities and for increased energy consumption. Characteristic features pertaining to a specific urban environment, such as local microclimatic conditions, urban morphology and anthropogenic heat release respectively, generate this phenomenon. Therefore, local studies must be conducted for a specific urban settlement, being very relevant for adopting suitable strategies that aim to counteract the harmful effects of UHI phenomenon. In this respect, the paper presents results of a study case comprising an investigation of the UHI occurrence and intensity for the city of Iasi, Romania. Analysed data is based on information regarding temperature values for the summer of 2013, gathered through an experimental ground-based sensor network comprising 7 observation points within the metropolitan area of Iasi city.

Seasonal climatic effects and feedbacks of anthropogenic heat release due to global energy consumption with CAM5

Anthropogenic heat release (AHR) is the heat generated in global energy consumption, which has not been considered in global climate models generally. The global high-resolution AHR from 1992 to 2013, which is estimated by using the Defense Meteorological Satellite Program (DMSP)/Operational Linescan System (OLS) satellite data, is implemented into the Community Atmosphere Model version 5 (CAM5). The seasonal climatic effects and possible feedbacks of AHR are examined in this study. The modeling results show that AHR increases the global annual mean surface temperature and land surface temperature by 0.02 ± 0.01 K (1σ uncertainty) and 0.05 ± 0.02 K (1σ uncertainty), respectively. The global climatic effect of AHR varies with season: with a stronger climatic effect in the boreal winter leading to global mean land surface temperature increases by 0.10 ± 0.01 K (1σ uncertainty). In the selected regions (40°N–60°N, 0°E–45°E) of Central and Western Europe the average surface temperature increases by 0.46 K in the boreal summer, and in the selected regions (45°N–75°N, 30°E–140°E) of northern Eurasia the average surface temperature increases by 0.83 K in the boreal winter. AHR changes the height and thermodynamic structure of the global planetary boundary layer, as well as the stability of the lower troposphere, which affects the global atmospheric circulation and low cloud fraction. In addition, at the surface both the shortwave radiation flux in the boreal summer and the down-welling longwave flux in the boreal winter change significantly, as a result of the change in low clouds caused by the effect of AHR. This study suggests a possible new mechanism of AHR effect on global climate through changing the global low-cloud fraction, which is crucial for global energy balance, by modifying the thermodynamic structure and stability of the lower troposphere. Thus this study improves our understanding of the global climate change caused by human activities.

Urban Heat Island Mitigation Effectiveness under Extreme Heat Conditions in the Suzhou–Wuxi–Changzhou Metropolitan Area, China

AbstractCool roofs and green roofs are two important methods used to mitigate the urban heat island (UHI) effect. The Weather Research and Forecasting Model was used to investigate the UHI effect and the effectiveness of cool and green roof mitigation strategies in the Suzhou–Wuxi–Changzhou metropolitan area during an extreme heat wave episode in the summer of 2013. Both urban land-cover change and anthropogenic heat releases exacerbated high temperatures in the urban area. Notably, urban land-cover change and anthropogenic heat release were responsible for 64% and 36% of the UHI intensity, respectively. Both cool and green roofs decreased near-surface air temperatures. The most dramatic decrease in near-surface air temperature occurred in the late morning; nocturnal air temperature decreased slightly because of the decrease in urban heat storage associated with the cool roof strategy. In addition, the UHI mitigation strategies affected the entire urban boundary layer. The decrease in the potential temperature and static stability created a stable urban boundary layer in which turbulent kinetic energy (TKE) decreased simultaneously. Analysis of an urban belt near a large water body showed that the decrease in the surface skin temperature difference between land and the water body weakened the daytime lake breeze. This effect was observed in both the inflow in the boundary layer and the return flow above the boundary layer, and it decreased the heat and moisture exchange between the lake and land boundary layers.

Evaluation of an urban canopy model in a tropical city: the role of tree evapotranspiration

A single layer urban canopy model (SLUCM) with enhanced hydrologic processes, is evaluated in a tropical city, Singapore. The evaluation was performed using an 11 month offline simulation with the coupled Noah land surface model/SLUCM over a compact low-rise residential area. Various hydrological processes are considered, including anthropogenic latent heat release, and evaporation from impervious urban facets. Results show that the prediction of energy fluxes, in particular latent heat flux, is improved when these processes were included. However, the simulated latent heat flux is still underestimated by ∼40%. Considering Singapore’s high green cover ratio, the tree evapotranspiration process is introduced into the model, which significantly improves the simulated latent heat flux. In particular, the systematic error of the model is greatly reduced, and becomes lower than the unsystematic error in some seasons. The effect of tree evapotranspiration on the urban surface energy balance is further demonstrated during an unusual dry spell. The present study demonstrates that even at sites with relatively low (11%) tree coverage, ignoring evapotranspiration from trees may cause serious underestimation of the latent heat flux and atmospheric humidity. The improved model is also transferable to other tropical or temperate regions to study the impact of tree evapotranspiration on urban climate.

The impact of urbanization and climate change on urban temperatures: a systematic review

Cities have elevated temperatures compared to rural areas, a phenomenon known as the “urban heat island”. Higher temperatures increase the risk of heat-related mortality, which will be exacerbated by climate change. To examine the impact of climate change and urban growth on future urban temperatures and the potential for increased heat stress on urban residents. We conducted a systematic review of scientific articles from Jan 2000 to May 2016. The majority (n = 49, = 86%) of studies examined climate change and the urban heat island in isolation, with few (8) considering their combined effect. Urban growth was found to have a large impact on local temperatures, in some cases by up to 5 °C in North-east USA. In some locations climate change increased the heat island, such as Chicago and Beijing, and in others decreased it, such as Paris and Brussels. When the relative impact of both factors was considered, the temperature increase associated with the urban heat island was always higher. Few studies (9) considered heat stress and its consequences for urban populations. Important contributors to urban temperatures, such as variation in urban density and anthropogenic heat release, were often excluded from studies. We identify a need for an increased research focus on (1) urban growth impact on the urban heat island in climate change studies; (2) heat stress; and, (3) variation in urban density and its impacts on anthropogenic heat. Focussing on only one factor, climate change or urban growth, risks underestimating future urban temperatures and hampering adaptation.

Mitigating the surface urban heat island: Mechanism study and sensitivity analysis

In a surface urban heat island (SUHI), the urban land surface temperature (LST) is usually higher than the temperature of the surrounding rural areas due to human activities and surface characteristics. Because a SUHI has many adverse impacts on urban environment and human health, SUHI mitigation strategies are very important. This paper investigates the mechanism of a SUHI based on the basic physical laws that control the formation of a SUHI; five mitigation strategies are proposed, namely: sprinkling and watering; paving a pervious surface; reducing the anthropogenic heat (AH) release; using a “white roof”; increasing the fractional vegetation cover or leaf area index (LAI). To quantify the effect of these mitigation strategies, 26 sets of experiments are designed and implemented by running the integrated urban land model (IUM). The results of the sensitivity analysis indicate that sprinkling and watering is an effective measure for mitigating a SUHI for an entire day. Decreasing the AH release is also useful for both night- and daytime SUHI mitigation; however, the cooling extent is proportional to the diurnal cycle of AH. Increasing the albedo can reduce the LST in the daytime, especially when the solar radiation is significant; the cooling extent is approximately proportional to the diurnal cycle of the net radiation. Increasing the pervious surface percentage can mitigate the SUHI especially in the daytime. Increasing the fractional vegetation cover can mitigate the SUHI in the daytime but may aggravate the SUHI at night.

Temporal trends of surface urban heat islands and associated determinants in major Chinese cities

There are many studies focusing on spatial variations of surface urban heat islands (SUHIs) in literature. In this study, MODIS land surface temperature (LST) data and China's Land Use/Cover Datasets (CLUDs) were used to examine the temporal trends of SUHIs in 31 major Chinese cities during 2001–2015 using three indicators: SUHI intensity (SUHII), area of the SUHI (AreaSUHI) and percentage of area with increasing SUHII (PAISUHII). Correlation analyses between SUHII and background (rural) LST (extracted from MODIS LST), vegetation coverage (reflected by MODIS EVI data) and anthropogenic heat release (reflected by nighttime light data) were performed from temporal rather than spatial perspectives. Our findings showed that the SUHII and AreaSUHI in urbanized areas increased significantly in most cities in summer days, whereas they increased significantly in approximately half and more than half of the cities in summer and winter nights, respectively. In summer days, summer nights and winter nights, the PAISUHII was approximately 80% and over 50% in union areas and the 20km buffer, respectively. Correlation analyses indicated that the SUHII in stable urban areas was negatively correlated with the background LST in summer and winter days for most cities, especially in northern China. A reduction in vegetation contributed to the increasing SUHII in urbanized areas in summer days and nights. The increasing anthropogenic heat release was an important factor for increases in the SUHII in urbanized areas.