Patterns of nighttime urban heat island patch in mega urban agglomerations: a case study in the Pearl River Delta, China

Urban heat islands (UHI) effects across metropolitan areas poses substantial threats to both ecosytems and local residents with the risks associated with intensifying nighttime temperature, however, the patterns and evolution of nighttime UHI remain poorly understood. Taking the Pearl River Delta (PRD) in China as a case of mega urabn agglomeration, this study first integrated geostatistical models and exponential decay models to extract the urban heat island patches (UHIP) from 2003 to 2019, then evaluated the UHI effects and spatial patterns of UHIP, and finally investigated the influencing factors of the nighttime UHI intensity (UHII). The results showed that: (1) a significant clustering pattern of nighttime UHII and an increasing trend of annual nighttime UHII were observed. (2) Patch expansion categories revealed diverse UHI evolution modes, of which the spatial-temporal dynamics were found with landscape metrics, and the UHII in enclave-type, infill-type, and edge-type patches decreased successively. (3) Socioeconomic factors showed a significant positive correlation with UHII, simultaneously, environmental and landscape factors exhibited spatially dependent impacts both within and outside the UHIP. These findings underscore the need for urban planning strategies considering the heterogeneity and dynamics of nighttime UHI towards climate adaptation and urban resilience improvement in mega agglomerations.