Divergent latitude-specific urban humid heat risks are regulated by local climate types

Cities are home to more than half of the global population, and the urban heat island effect has aroused widespread concerns. Urban-induced changes in wet-bulb temperature and their health impacts remain less systematically investigated. Here we analyze the spatiotemporal evolution and drivers of wet-bulb temperature patterns across 56 globally representative cities during 2005-2024 using high-resolution reanalysis data. We find pronounced increases in global urban wet-bulb temperature since 2020, with spatially variable responses to urbanization and local climatic conditions. Tropical coastal cities such as Jakarta and Bangkok exhibit relatively stable and high wet-bulb temperature, where warm humid climate substantially offsets the urban heat island effect. In contrast, inland cities demonstrate pronounced spatial gradients. Metropolitan regions at low-to-mid latitudes display higher spatial heterogeneity than those at high latitudes. Mechanistic analysis reveals that variable responses of wet-bulb temperature to air temperature and relative humidity determine urbanization’s influence. Extreme heat intensities reached remarkable levels during 2023-2024, posing serious health threats. Urban humid heat patterns show spatial heterogeneity at different latitudes, primarily due to the divergent local climate types, revealed by mechanistic analysis across multiple representative cities based on observational data.