Urban morphology controls heatwave amplification and thermal burden in megacity Delhi: insights from LCZ-based WRF-BEP/BEM simulations

Urban heatwave amplification in rapidly expanding megacities is strongly influenced by urban morphological heterogeneity and its effects on surface-energy balance and boundary-layer processes, yet these interactions remain insufficiently represented in mesoscale atmospheric models for tropical cities like Delhi. This study investigates the influence of Local Climate Zone (LCZ)-based urban morphology on urban heat island intensity (UHII), Added Heat Load (AHL), thermal burden, and the associated surface–atmosphere exchanges, and boundary-layer evolution during the extreme pre-monsoon heat season (April–June 2024) using Weather Research and Forecasting (WRF) model coupled with the Urban Canopy Model (UCM) incorporating Building Effect Parameterization (BEP) and Building Energy Model (BEM). Four simulations were performed: (i) baseline WRF, (ii) WRF-UCM, (iii) WRF-UCM with MODIS-LCZ, and (iv) WRF-UCM with WUDAPT-LCZ. The LCZ-integrated simulations improved the representation of intra-urban thermal variability and surface energy partitioning by resolving contrasts in urban geometry, imperviousness, and anthropogenic heat emissions. Compact high-density LCZs exhibited stronger nocturnal warming due to enhanced heat storage, restricted ventilation, and weaker radiative cooling, whereas open low-rise and vegetated zones showed weaker warming. During intense heatwave episodes, nocturnal UHII exceeded 4–6 °C across densely urbanized districts, with hotspots surpassing 8 °C. AHL analysis indicated that urbanization contributed an additional 1.5–2.5 °C above the regional heatwave signal. LCZ-based simulations revealed enhanced thermal burden in compact urban sectors, associated with increased sensible heat fluxes, stronger turbulent mixing, and deeper daytime boundary layers. Among the tested configurations, WRF-UCM integrated with WUDAPT-LCZ most realistically captured urban thermal heterogeneity and hotspot persistence, demonstrating the importance of LCZ-informed urban canopy parameterization for heat-risk assessment and climate-resilient urban planning in tropical megacities.