Warming amidst depopulating: insights from surface urban heat island in China's shrinking cities

Adapting to extreme heat is increasingly imperative for sustainable urban development. Concurrently, pervasive urban shrinkage driven by sustained population decline is fundamentally reshaping the socio-spatial realities of cities worldwide. Yet, the characteristics of surface urban heat islands (SUHI) in cities experiencing significant depopulation remain poorly understood. To address these gaps, we delineate the physical boundaries of 423 shrinking cities in China, exploring the spatiotemporal patterns and key drivers of SUHI effects from 2010 to 2020. Our findings suggest that larger cities experience substantially stronger SUHI effects, with daytime SUHI Intensity (SUHII) reaching 4.25 °C in cities over 100 km² compared with 1.64 °C in 5–10 km² cities, while nighttime variability remains more unstable in large cities. Population decline generally weakens SUHI, and cities that have lost more than 30% of their population exhibit a pronounced long-term cooling trend. Distinct regional patterns are evident, with cities in western and northeastern China being most sensitive to population change, while some shrinking cities in the east continue to warm. In terms of driving factors, population size and density stand out as key socio-economic predictors. At the landscape level, continuous, compact, and evenly distributed green infrastructure proves to be effective in mitigating SUHI effects. Predictive analyses across various scenarios reveal that SUHI dynamics vary between urban and non-urban areas, as well as between daytime and nighttime conditions, underscoring the necessity for context-specific climate adaptation strategies.