Quantitative analysis of the interannual variation in the seasonal water cooling island (WCI) effect for urban areas

Water body, as water cool islands (WCIs), is an effective factor of mitigating the urban heat island (UHI) effects through the evaporation and absorption of solar shortwave radiance. In this study, a combination of the range, amplitude, efficiency and capacity of the WCI effect (WCI_R, WCI_A, WCI_E and WCI_C as descriptors) within water buffers, is proposed to evaluate the interannual variation of the seasonal WCI effects within the fifth loop of Beijing from 2000 to 2018, further construct optimal regression models by seven impact factors with the four WCI descriptors through all-subset regression, as well as calculate the independent contribution rate (CR) of these factors by hierarchical partitioning (HP) analysis. The results indicate that (1) In terms of the interannual variation of WCI effects, the most significant trends that rise over fall produced by four descriptors generate in summer after 2009, while relatively stable states exist in spring and winter. (2) As for the impact factors, the water temperature (WT) and the percentage of vegetation (PV) contribute most for WCI_R, WCI_A and WCI_E in reaction to the interannual average, while the water temperature capacity (WTC) maintains significant impact on WCI_C from spring to autumn over 18 years but shares power with water temperature (WA) and WT in winter. (3) Considering the factor changes yearly, the dominance relationships of external ones, mainly the percentage of impervious surface (PI) and PV, gradually surpass that of WA and WTC in four seasons especially after 2009. On this basis, urban designers could propose suitable plans to better exert the cooling effect of water bodies, thereby reducing the UHI effect.