Spatio-temporal analysis of urban heat island in Shanghai over the past 30 years with Landsat images

Abstract

The influence of urban heat island (UHI) on the environment, human health, and urban livability has been and will continue to be a source of concern for humanity. We examined the spatial distribution and intensity of UHI in a metropolitan city Shanghai utilizing long time series of satellite images and land use data. Then we properly and objectively monitored the UHI phenomenon and evaluated its driving variables. Using Landsat 5, 7, and 8 satellite data with China's Land-Use/Cover Datasets (CLCD), we retrieved land surface temperature (LST) and computed the Urban Heat Island Intensity Index (UHII) to measure UHI intensity. When investigating the correlation between impervious surface area and UHI area, we also made use of the Pearson correlation coefficient. The study found that the LST in Shanghai fluctuated upwards from 1990 to 2020, with the downtown, suburbs, and outer suburbs increasing by 5.394 degrees, 9.187 degrees, and 5.211 degrees, respectively, with the high-temperature zone expanding to the city's periphery year by year. Meanwhile, the UHII varies dramatically, the average increase of UHI in suburbs is 4.522 degrees, while the average growth of UHI in downtown and outer suburbs is only 0.728 degrees and 0.546 degrees, respectively. The Pearson correlation coefficient between UHI area and impervious surface area is 0.8698331. Shanghai's UHI has been rising year after year, owing to an increase in impervious surface area as a result of urbanization. The causes of the large changes in surface temperature and UHI have yet to be discovered and studied in depth. Overall, these findings show that urbanization has an impact on the establishment and intensity of UHI diffusion. To balance urban development with the urban thermal environment, more measures should be explored.