Linking Urban Growth and Surface Temperature Change in Capital and Secondary Cities of Southeast Asia

Rapid urbanization exacerbates heat-related environmental issues. Yet urban expansion patterns and associated heat risks in developing countries remain poorly understood. We selected sixteen capitals and secondary cities in Southeast Asia and characterized urban growth and heat hazards in their fringes using three spectral indices: PLAND (percentage of built-up areas), NDVI (Normalized Difference Vegetation Index), and LST (Land Surface Temperature). Over the past two decades, PLAND and LST in the fringes increased by 11.93% and 1.39℃, respectively. LST in the fringes of capital cities was 1.70℃ higher than in secondary cities. LST increases exceeded those in urban cores, particularly in secondary cities (+0.35℃). Highly populated and wealthier urban clusters showed marked PLAND increases and NDVI declines, but not necessarily elevated LST. We identify priority areas for land cover management and urban heat mitigation by city type and geographic location to inform sustainable regional planning.