LULC transformation and urbanization impacts on thermal and ecological dynamics in the medium-sized coastal cities of Mangaluru and Udupi, Karnataka, India

Abstract Land Surface Temperature (LST) significantly influences urban environmental balance globally. Most research focuses on megacities, neglecting medium and small cities—a gap this study addresses. This research analyzes Land Use and Land Cover (LULC) transformations in Mangaluru and Udupi, two medium-sized Karnataka cities, along their connecting coastal belt from 1994 to 2024 using Landsat imagery. It investigates LST relationships with spectral indices reflecting vegetation, urbanization, and moisture content, identifies Surface Urban Heat Island (SUHI) and non-SUHI zones, and assesses urban thermal environment using Urban Thermal Field Variance Index (UTFVI). These expanding Karnataka cities remain unassessed regarding thermal characteristics and UTFVI-derived environmental impact assessment, highlighting significant research gaps. Between 1994 and 2024, urban area increased from 5.7 to 27.67%, indicating substantial urbanization. Results reveal LST negatively correlates with NDVI and NDMI, positively associates with NDBI. Mean LST rose notably from 23.25 °C in 1994 to 28.06 °C in 2024 during the winter season, and from 28.15 to 30.71 °C during the summer season. LST thresholds exceeding mean by > 0.5 standard deviations distinguished SUHI from Non-SUHI zones. UTFVI thermal stress assessment for 2024 shows 52.46% area represents excellent class, while 33.09% falls into worst category, indicating severe ecological stress from high surface temperatures, dense built-up cover, and limited vegetation. This study emphasizes analyzing land cover changes’ influence on thermal conditions through SUHI and UTFVI patterns, supporting environmentally sustainable, heat-resilient development in medium-sized cities globally.