How to effectively mitigate urban heat island effect? A perspective of waterbody patch size threshold

Climatic warming and urbanization have exacerbated urban heat island (UHI) effect globally. Waterbodies have significant cooling effect while the current UHI mitigation researches mostly focus on green spaces. Although the cooling effect of waterbodies has been highlighted and measured in previous studies, the impact of local socioeconomic development surrounding the waterbodies remains unclear. The scarcity of land resource in the city has also posed urgent need to explore cooling efficiency of waterbody patch size. Highly urbanized and densely scattered with waterbody, the Pearl River Delta (PRD) urban agglomeration has suffered severe UHI effect. Taking four PRD cities as the case study area, this study analyzed the impact of local socioeconomic development on the daytime cooling intensity of waterbodies, and identified the dominant impact factor as well as the threshold value of efficiency (TVoE) in diversely developed areas. The results showed that the cooling intensity of waterbodies had obvious spatial heterogeneity with an average of 1.1 degrees C and a maximum of 5.54 degrees C, which was dominated by patch size and strongly affected by local socioeconomic development. The mean cooling intensity increased along with the increasing of local socioeconomic development, and the TVoEs of waterbody patch size were 0.49 ha, 0.55 ha and 0.70 ha in such three levels of local socioeconomic development as low, medium and high, respectively. The results can provide quantitative guidance for blue landscape planning in regard to UHI effect mitigation.