The cooling effects of urban waterbodies and their driving forces in China

Continuous climatic warming and urbanization exert serious urban heat island (UHI) effects. Waterbodies can mitigate surrounding temperatures with an environmentally friendly cooling effect. However, the mechanism and threshold value of efficiency (TVoE) of the cooling effects of waterbodies in different climate zones are not well understood. We quantified the cooling effects and identified the driving factors and TVoEs of 933 waterbodies in 32 major cities across 7 climatic zones in China. The cooling effects of waterbodies varied geographically among climate zones, with tropical and subtropical humid areas showing higher cooling area, cooling efficiency and lower cooling intensity than arid areas. The characteristics of the waterbody was the most important factor explaining over 44% variation in cooling effect of waterbodies in each climate zones. Anthropogenic factors were more important in humid and hot climate zones and less important in cold desert zones than the climate factors. In general, The TVoEs increased as the precipitation decreased, and national average TVoE of waterbody patches was 0.34 ha, and of waterbody perimeter was 0.51 km. Over 33% of urban waterbodies, mainly located on the North China Plain and Northeast Plain, would transform to other climate zones in the 2071-2100 period under the RCP8.5 scenario, meaning that the cooling effects and TVoEs of these waterbodies in varying climate zones will change greatly in the future. These findings provide quantitative guidance for better understanding the cooling effects of waterbodies and for improving urban resilience and mitigating UHIs in different climate zones.