Diurnal Surface Urban Heat Island Variability Across Local Climate Zones in South Asian Cities

Urban morphology exerts a fundamental control on land surface temperature (LST), governing the spatial and temporal variability of urban thermal environments. In South Asia, rapid urban expansion coupled with the increasing frequency and intensity of extreme heat events has amplified surface urban heat island (SUHI) effects, posing serious challenges to urban livability and thermal comfort. This study investigates the diurnal and spatial variability of LST across local climate zones (LCZs) in three major South Asian cities, Delhi, Bangalore, and Lahore, using multi-year Moderate Resolution Imaging Spectroradiometer (MODIS) LST observations.  Summer-specific urban LST data were analyzed to characterize grid-based diurnal thermal contrasts and intra-LCZ thermal heterogeneity under daytime and nighttime conditions. The results reveal robust diurnal thermal differentiation among LCZs, with distinct surface thermal responses across the three cities. Water-dominated LCZs consistently exhibited the lowest surface temperatures due to high thermal inertia and evaporative cooling, whereas sparsely vegetated and bare surface zones emerged as the primary contributors to elevated SUHI intensity, driven by enhanced solar absorption and limited moisture availability. Vegetated and built-up LCZs displayed intermediate thermal behavior, reflecting the combined influences of surface materials, vegetation cover, and urban forms. Spatial analyses further identified persistent thermal hotspots and coldspots, strongly regulated by underlying LCZ characteristics. The geographically weighted random forest approach revealed spatially varying controls on urban thermal extremes. Overall, the findings highlight the critical role of urban surface composition and structural configuration in modulating SUHI dynamics across South Asian cities. Our analysis provide new insights into the spatiotemporal behavior of urban thermal patterns under extreme heat conditions and offers a robust scientific basis for climate-responsive urban planning and heat-mitigation strategies.