Grid-based assessment of heat stress and population exposure in Brahmaputra and Barak valley cities of Assam, India

Abstract Heat stress has emerged as a critical environmental issue in rapidly growing tropical cities. However, grid-level assessment linking heat stress to exposed population remains limited in tier-III cities of Assam. The study examined UTFVI (Urban Thermal Field Variance Index) induced heat stress exposure across 7 prominent urban centers of Assam. Landsat 8 data of May and December 2023 were analyzed along with gridded population data. Kruskal Wallis test & Dunn’s post hoc test were employed to evaluate inter-city variations and pair wise comparison of LST (land surface temperature). The composite Z-score analysis was utilized to classify grid-level heat stress zones for assessing exposed population in selected cities. Results revealed that all cities exhibit a high mean LST in summer with highest observed in Nagaon (28.36 °C) and lowest in Tezpur (26.61 °C). In winter, Silchar records the highest mean LST (20.81 °C), while Tinsukia exhibits the lowest (17.92 °C). Statistical analysis reveals significant inter-city disparity of LST. UTFVI reveals Dibrugarh and Tezpur cities contain major areas under strongest UHI (Urban heat island), whereas Silchar and Nagaon occupy considerable Non-UHI zones. The Z-score analysis reveals Silchar and Dibrugarh occupy larger area under very high heat stress exposure (VHHSE) class. However, Nagaon records the highest number of residents exposed to VHHSE, while Sivasagar exhibits the lowest exposure. In all cities, only a minimal population resides in the very low heat stress exposure (VLHSE) zone. Findings reflect the emergence of thermally stressed cities and provide a useful framework for heat mitigation in rapidly urbanizing tropical cities.