Relationships between surface urban heat island and vegetation across a regional climatic gradient: the case of southeastern Brazil

The Surface Urban Heat Island (SUHI) is a well-known phenomenon, but there is no established understanding of how urban and rural vegetation influence it across regional climatic gradients. We investigated the seasonal and regional patterns of daytime land surface temperature (LST), vegetation condition (NDVI), and SUHI across 69 localities distributed along a regional climatic gradient in southeastern Brazil. Using Landsat data corrected for altitude, SUHI was estimated as the difference between median urban temperature and a local cold reference defined by the p5 of LST. Results revealed a regional LST gradient of up to ≂7°C, consistent with near ground air temperature. SUHI intensities were highest during the austral summer (DJF), with median values reaching up to ≂11°C, and weaker during the dry–wet transition season (ASO), with values up to ≂7°C. In summer, when temperature rises and the regional temperature gradient weakens, the dominant driver of SUHI was urban heating, which was therefore more strongly controlled by urban NDVI and its cooling capacity. In contrast, during the dry–wet transition, SUHI was more influenced by non-urban temperature and thus depended on rural NDVI, as seasonal declines in rural biomass increased background temperatures and weakened the urban–rural thermal contrast. Across both seasons, ΔNDVI consistently emerged as a robust predictor of SUHI, highlighting the relational nature of urban surface warming. The SUHI did not show a categorically organized spatial pattern with the regional temperature gradient, but during summer it highlighted clusters of colder locations (< 5°C) in the southeastern sector of the territory, whereas in the far northeastern sector the highest values (> 8°C) clustered together. These results from southeastern Brazil suggest that urban heat mitigation strategies should highlight the role of urban vegetation, particularly during summer—when heat waves are stronger—because of its substantial local cooling capacity.