Planning for a cooler metropolitan area: a perspective on the long-term interaction of urban expansion, surface urban heat islands and blue-green spaces' cooling impact.

Urbanization is widely acknowledged as a driving force behind the increase in land surface temperature (LST), while blue-green spaces (BGS) are recognized for their cooling effect. However, research on the long-term correlation between the two in highly urbanized areas remains limited. This study aims to fill this research gap by investigating the correlation and changes between urban expansion-induced LST rise and the cooling effect of BGS in the Hangzhou metropolitan area from 2000 to 2020. Our approach combines Geographic Information System (GIS), Remote Sensing (RS), and Google Earth Engine (GEE) cloud platforms, utilizing a random forest land use classification technique in conjunction with the Geographically and temporally weighted regression (GTWR) model. The findings reveal a strong relationship between land expansion and the intensification of the surface urban heat island (SUHI) effect. The spatial heat island effect exhibits an exponential expansion in area, with an interannual LST rise of 0.4 °C. Notably, urban centers exert the highest regional heat contribution, while remote suburbs have the most significant impact on reducing LST. The impact of BGS on LST varies, fluctuating more in areas close to urban centers and less in water-rich areas. This study contributes to a better understanding of the cooling potential of BGS in rapid urbanized Metropolitan, offering valuable insights for sustainable urban planning.