Long-term global trends and influencing factors of surface urban cool and heat islands

Global warming and urbanization have intensified temperature differences (ΔT) between urban and nonurban areas, creating distinct surface urban heat islands (SUHIs) and surface urban cool islands (SUCIs). This study analyzes SUHI and SUCI trends across 1,963 global cities from 2001 to 2018, exploring their spatiotemporal patterns and drivers. Pearson correlation analysis was used to examine the relationships between ΔT and key factors, including the enhanced vegetation index (EVI), proportion of impervious surface (PIS), and climatic variables such as precipitation (PR), surface downwelling shortwave radiation (RSDS), mean daily air temperature (TAS), near-surface wind speed (Sfc Wind), near-surface relative humidity (HURS), and potential evapotranspiration (PET). Key findings include: (1) SUCIs are more common in winter but most significant in summer, with daytime SUCIs transitioning to nighttime SUHIs; (2) SUHI cities show a ΔT increase of 0.153°C per decade (P < 0.01), while SUCI cities show a decrease of −0.102°C per decade (P < 0.01); (3) HURS is the dominant climatic driver, with PR and RSDS more influential in summer, and TAS being crucial in winter. Future research should explore the dynamic interactions between climate and human factors in shaping ΔT for adaptive urban planning.