Distribution and influencing factors on urban land surface temperature of three main megacities in the Beijing-Tianjin-Hebei urban agglomeration

Abstract:

Rapid urbanization is usually accompanied by a series of environmental problems. For instance, urban heat island (UHI) is known as a main environmental issue for a city during its urban growth, human mobility, and socioeconomic expansion. Urban land surface temperature (ULST), as a typical UHI indicator, is a key factor of climate change associated with urban expansion, and it is also an important part of the urban ecological environment. Therefore, investigation on the formation and dynamic evolution of ULST will help us to understand the urban climate and environment. The Beijing-Tianjin-Hebei urban agglomeration (HTHUA) is the core area of the northern China's economy. The formation and evolution of UHI in HTHUA is still poorly understood. Currently, most researches in this area have focused on analyzing the overall impact of the urban agglomeration on urban environment. They underestimated the impact of UHIs in the urban core area on urban environment and did not reveal the detailed patterns of UHIs in the urban agglomeration area. In this study, three megacities of Beijing, Tianjin and Shijiazhuang in HTHUA were selected as the research sites. We used radiative transfer modeling and correlation analysis to study variation of the areas of different ULST intervals in recent 18 years. Influences of the bare soil index (BSI), modified normalized difference water index (MNDWI), normalized difference built-up index (NDBI), and normalized difference vegetation index (NDVI) on ULST were studied. The ULSTs in the three periods of 2000, 2010, and 2017 were selected to calculate the variation of areas of different ULST intervals (Fig. 1a-c). The area of each temperature interval in the three megacities showed a growing trend, but the growing rate was significantly different: Beijing > Tianjin > Shijiazhuang. It is also found that there were significantly differences in the influencing factors on ULST (Fig. 1d-f). The ULSTs in Beijing and Shijiazhuang has a higher correlation with BSI, NDBI and NDVI, while the ULST in Tianjin has a higher correlation with MNDWI, NDBI and BSI.