Abstract
The process of the surface urban heat island (SUHI) varies with latitude, climate, topography and meteorological conditions. This study investigated the seasonal variability of SUHI in the Tehran metropolitan area, Iran, with respect to selected surface biophysical variables. Terra Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature (LST) was retrieved as nighttime LST data, while daytime LST was retrieved from Landsat 8 Thermal Infrared Sensor (TIRS) using the split-window algorithm. Both data covered the time period from September 2013 to September 2015. To assess SUHI intensity, we employed three SUHI indicators, i.e., the LST difference of urban-rural, that of urban-agriculture and that of urban-water. Physical and biophysical surface variables, including land use and land cover (LULC), elevation, impervious surface (IS), fractional vegetation cover (FVC) and albedo, were selected to estimate the relationship between LST seasonal variability and the surface properties. Results show that an inversion of the SUHI phenomenon (i.e., surface urban cool island) existed at daytime with the maximal value of urban-rural LST difference of −4 K in March; whereas the maximal value of SUHI at nighttime yielded 3.9 K in May. When using the indicators of urban-agriculture and urban-water LST differences, the maximal value of SUHI was found to be 8.2 K and 15.5 K, respectively. Both results were observed at daytime, suggesting the role of bare soils in the inversion of the SUHI phenomenon with the urban-rural indicator. Maximal correlation was observed in the relationship between night LST and elevation in spring (coefficient: −0.76), night LST and IS in spring (0.60), night LST and albedo in winter (−0.53) and day LST with fractional vegetation cover in summer (−0.41). The relationship between all surface properties with LST possessed large seasonal variations, and thus, using these relationships for SUHI modeling may not be effective. The only exception existed in the correlation between elevation and IS, which may be useful to simulate the SUHI at night. This study suggests that in semi-arid cities, such as Tehran, with the urban-rural indicator, a surface urban cool island may be observed in daytime while SUHI at nighttime; with other indicators, SUHI can be observed in both day and night. Thus, SUHI studies require the acquisition of remote sensing image data at both daytime and nighttime and careful selection of SUHI indicators.
Highlights
The urban heat island (UHI) is a well-known effect of urbanization, a phenomenon whereby urban areas experience higher temperature than the surrounding rural areas [1]
This study suggests that in semi-arid cities, such as Tehran, with the urban-rural indicator, a surface urban cool island may be observed in daytime while surface urban heat island (SUHI) at nighttime; with other indicators, SUHI can be observed in both day and night
We analyzed the seasonal SUHI variations in Tehran, Iran, by using Land Surface Temperature (LST) derived from Terra Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat 8 from 2013 to 2015
Summary
The urban heat island (UHI) is a well-known effect of urbanization, a phenomenon whereby urban areas experience higher temperature than the surrounding rural areas [1]. 5% to 10% increase in demand for electricity [6]; (3) air pollution; UHI increased the production of ozone near the ground [7] and, in the form of mesoscale wind, dispersed air pollution [8]; (4) reducing water quality; rapid temperature changes in the water ecosystems caused by surface runoff from hot pavements and roofs covered with asphalt, mostly stressful and fatal for aquatic life [9]; and (5) increase in per capita water consumption in summer time [10]. With the concern of global warming, the UHI issue will be more complicated in the future [13,14]
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