Toward cooler cities by larger homogeneous functional clusters.

Urban heat island (UHI) intensifies heat-related risks and environmental degradation in cities worldwide, yet existing mitigation strategies have largely overlooked how the spatial scale of homogeneous functional building clusters influences local climate. This scale may matter because buildings with similar functions often share similar morphology, activity schedules, and anthropogenic heat-release patterns, allowing their spatial contiguity to shape ventilation and heat accumulation. Here, we introduce the Urban Homogeneous Scale (UHS)-an indicator that measures the spatial scale of contiguous, functionally similar building clusters-and analyze 233,844 observations across 101 global cities to assess its potential for mitigating surface UHI. We find that larger UHS is associated with lower surface UHI: every 100-meter increase in UHS corresponds to 4.5% decrease in daytime UHI. This daytime cooling effect is particularly more pronounced in inland, humid, and high-income regions. In low-income regions, larger building area and higher building volume more strongly weaken UHS cooling capacity than in wealthier regions, revealing a socioeconomic inequality in UHS's mitigation benefits. Our findings identify the spatial scale of building clusters as a essential dimension of urban form associated with urban heat burden, and suggest that considering UHS alongside targeted controls on built environmental characteristics may inform future heat-mitigation planning.