The impact of urban spatial forms on marine cooling effects in mainland and island regions: A case study of Xiamen, China

The marine cooling effect (MCE) plays a crucial role in mitigating urban heat island (UHI) in coastal cities. However, limited research has explored how urban spatial forms (USF) influence MCE, particularly between mainland and island regions, which may exhibit distinct cooling dynamics. This study proposes a marine cooling spatial impact value (SIV) index to quantify the impacts of USF on MCE. Utilizing interpretable machine learning models, we explore the nonlinear impacts of key USF on MCE. The research shows that MCE extends further on Xiamen Island than on the mainland. Specially, water bodies enhance MCE, while both impervious surfaces (Im_p) and building density (BD) weaken it. Moreover, elevation - waters interaction enhances their MCE contribution on the mainland, while waters - canopy height (CHM) interaction boosts CHM's contribution on island. This study emphasizes the significant role of the 3D structure of urban forms in shaping MCE, highlighting notable differences between island and mainland regions. Our findings offer a new framework for quantifying the USF-MCE relationship and provide valuable guidance for coastal urban planners to optimize spatial layouts and effectively mitigate UHI effects by considering regional differences in MCE.