Linking maximum-impact and cumulative-impact indices to quantify the cooling effect of waterbodies in a subtropical city: A seasonal perspective

Numerous studies have explored how waterbodies mitigate the urban heat island (UHI) effect by determining their maximum impact. However, their cumulative impact resulting from spatial continuity should also be considered. Moreover, waterbody cooling effects have previously been quantified in summer, yet little attention has been paid to other seasons. We investigated 436 waterbodies in urban central Fuzhou, China. Cooling effects in each season were determined based on two cumulative-impact indices (waterbody cooling intensity and waterbody cooling gradient [WCG]) and four maximum-impact indices (maximum cooling intensity [MCI], maximum cooling efficiency [MCE], maximum cooling area [MCA], and maximum cooling distance). Results showed that the waterbody areas overlapped cold-spot areas by 58.08%, 60.27%, 65.72%, and 44.60% in spring, summer, autumn, and winter, respectively. Season significantly affected MCI and WCG but not MCA or MCE. Waterbody patch area had the largest influence on MCI and WCG in all seasons. Smaller waterbody patches with more complex shapes had strong cooling effects. The threshold values of efficiency of waterbodies increased with increasing land surface temperature. The most effective waterbody area was 0.54 ha when integrating all indices. These results could be used by urban planners and designers to mitigate the UHI effect through future urban planning.