Surface urban heat island (SUHI) shows higher surface thermal intensification in urban areas than the suburban areas and countryside. Green spaces are widely recognized as the dominant nature-based strategy to mitigate thermal stress. In contrast, natural cooling processes of urban blue spaces are seldom addressed. In this study, we applied the Google Earth Engine (GEE) to map SUHI intensity and blue spaces in order to explore the cooling effect and efficiency of blue spaces in the Pearl River Delta Metropolitan Region. Significant in-situ cooling is observed, with a 10% increase in water-body coverage leading to a depression of SUHI intensity by 11.33%. The irregular shape of lakes and reservoirs may weaken the cooling effect, but the reshaping of rivers may not. Our results indicate ex-situ cooling spillover of water bodies that will benefit the surrounding areas within an envelope of 100-m effective cooling distance. Such findings underline the importance of urban blue infrastructure in alleviating the thermal discomfort and advocate blue spaces as an essential component of urban infrastructure to minimize the SUHI effect.

城市地表热岛（SUHI）在城市地区的地表热强度高于郊区和农村。众所周知，绿色空间是缓解自然压力的主要自然策略。相反，很少涉及城市蓝色空间的自然冷却过程。在这项研究中，我们应用Google Earth Engine（GEE）绘制了SUHI强度和蓝色空间的地图，以探索珠江三角洲都会区蓝色空间的冷却效果和效率。观察到明显的原位冷却，水体覆盖率增加了10％，导致SUHI强度降低了11.33％。湖泊和水库的不规则形状可能会削弱冷却效果，但河流的重塑可能不会减弱。我们的结果表明水体的非原位冷却溢出将有益于有效冷却距离为100 m范围内的周围区域。这些发现强调了城市蓝色基础设施在缓解热不适方面的重要性，并主张将蓝色空间作为城市基础设施的基本组成部分，以最大程度地减少SUHI效应。