Water bodies' cooling effects on urban land daytime surface temperature: Ecosystem service reducing heat island effect

The urban heat island (UHI) effect caused by urbanization is a major environmental concern. Utilizing cooling effects of water bodies as one type of ecosystem service is an important way to mitigate UHI in urban areas during the daytime. This study aims to examine the influence of water bodies' cooling effects on the urban land surface temperature (LST). The potential influence on the relationship between urban land cover and the LST are also discussed. The daytime LST in April was retrieved from Landsat-8 thermal infrared band and the grid-based method was adopted to analyze the potential influence. The results indicated that Suzhou Bay is broadly capable of lowering daytime temperatures. The cooling distance can reach 800 m in horizontal space, and the maximum cooling effect was 3.02 °C. Furthermore, the distance to the Suzhou Bay is a great factor for the relationship between land cover and the LST. We found that the cooling effects have weakened the correct quantitative correlation between land cover (e.g., green space and impervious surface) and the LST, particularly green space in the range of 200 m. In addition, the cooling effects have strengthened the "cool edge" phenomenon when analyzing the relationship between the normal difference vegetation index (NDVI) and the LST. We suggest that the distance to the water bodies should be effectively utilized in the microclimate regulation provided by ecosystem services of water bodies. When investigating the thermal effects of urban land, urban planners and designers should consider water bodies' effects on surrounding areas. These findings have implications for understanding the role of water bodies with ecosystem services of temperature mitigation, which must be fully appreciated for sustainable urban and landscape planning.