Urban heat as a growing hazard: a spatiotemporal analysis of land-use/land-cover changes and land surface temperature in Ha Noi city, Viet Nam

Abstract Urban heat island (UHI) effects are increasingly recognized as a significant anthropogenic and climate‑related urban heat hazard in rapidly growing tropical cities, with profound implications for public health, energy demand, and urban ecosystems. This study examines the spatiotemporal relationship between land-use/land-cover (LULC) changes and land surface temperature (LST) in Ha Noi, Viet Nam, over a 24-year period (1998–2022), using Landsat remote sensing imagery, biophysical indices (Normalized Difference Vegetation Index (NDVI), Normalized Difference Built‑up Index (NDBI), Normalized Difference Water Index (NDWI), and Bare Soil Index (BI)), the Contribution Index (CI), and GIS-based spatial analysis. Additionally, the study evaluates UHI intensity and applies the Urban Thermal Field Variance Index (UTFVI) to assess ecological thermal stress. The results show that built-up areas increased by 174.3% while vegetation cover declined by 29.5%, contributing to an increase in mean LST from 24.13 to 25.28 °C. Maximum LST values surpassed 38 °C in central districts. UHI intensity peaked at 6.06 °C in 2022, indicating severe thermal exposure in highly urbanized zones. UTFVI analysis revealed a spatial expansion of areas classified under strong and strongest ecological stress, particularly in the urban core and new development zones. These findings underscore that LULC transitions, especially the proliferation of impervious surfaces, are primary drivers of urban thermal risk. Vegetated and water-covered surfaces demonstrated strong cooling effects, highlighting the need to preserve and expand green infrastructure. The study also identifies spatial hotspots of heat vulnerability, supporting targeted risk mitigation efforts. By integrating thermal indices and LULC dynamics, this research contributes to the growing body of literature linking urban development and climate-induced hazards. It provides a scientific foundation for climate-resilient planning, UHI risk monitoring, and disaster risk reduction in tropical megacities undergoing rapid transformation.