The study of regional thermal environments in urban agglomerations using a new method based on metropolitan areas

Urban agglomerations (UAs) are an outcome of regional urbanization reaching relatively advanced stages of development. The advancement of UAs in regional-spatial organization has been recognized worldwide. However, due to dense regional urbanization, UAs are threatened by various regional eco-environmental stresses. The topic of UAs is a hotspot of geo-science and sustainability science, which seek to analyse whether UAs may be a solution to regional eco-environmental problems. This study proposes a new method of analysing the regional thermal environment (RTE) of 3 world-class UAs in China based on Remote sensing and Geographic Information System (RS&GIS) technology using the metropolitan area (MA) as the basic unit and by using data obtained from MODIS land surface temperature (LST) products from 2000 to 2015. The results showed that MAs caused the LST of their influenced range (including the interior of the MA and its surface urban heat island footprint (FP)) to increase from 0.45 to 2.23 °C with a few built-up areas. The threat of the FP to the RTE was caused mainly by large-area warming areas, but the threat was small in terms of the temperature increase. We found that 23% of the influence of MAs on the RTE was caused by fringe areas and that this heat was superimposed on the FPs of core areas, which caused FPs to significantly increase in capacity of heat island and area. In this study, the influence of the spatial organization of UAs was emphasized. We believe that this result is more consistent with actual conditions in research on the thermal environment of UAs. Meanwhile, the authors hope that these findings will serve as a reference for sustainable development research on UAs all over the world.