Impact of Urban Heat Islands on Rainfall Patterns in Coastal Cities of South India: A Case Study of Mangaluru

Abstract

Rapid urbanization along the southwestern coast of India has significantly altered local microclimatic conditions, with complex feedbacks between the Urban Heat Island (UHI) effect and monsoon precipitation dynamics. This study investigates the influence of UHI intensification on rainfall distribution and extreme precipitation events in Mangaluru — a fast-growing coastal city in Karnataka, India, situated between the Arabian Sea and the Western Ghats. Multi-decadal Land Use and Land Cover (LULC) data derived from Landsat satellite imagery (1994–2024), India Meteorological Department (IMD) gridded rainfall records (0.25° × 0.25°), and MODIS Land Surface Temperature (LST) datasets were used to quantify spatiotemporal shifts in surface thermal anomalies and correlate them with changes in monsoon precipitation behavior. Urban built-up cover expanded from 5.70% to 27.67% between 1994 and 2024, while mean Land Surface Temperature in the urban core rose by 4.89°C. Surface Urban Heat Island Intensity (SUHII) reached 5.21°C by 2024. Mann-Kendall trend analysis indicates a statistically significant increase in extreme rainfall events (≥150 mm/day), from 3.1 events/year in the 1980s to 7.9 events/year in 2020–2024. Weather Research and Forecasting (WRF-ARW) model simulations suggest an estimated 8–12% increase in Convective Available Potential Energy (CAPE) associated with urbanization-induced surface changes, though large-scale climatic drivers cannot be excluded. The interaction of UHI dynamics with Arabian Sea moisture supply and Western Ghats orography creates a unique precipitation amplification mechanism in this coastal setting, with significant implications for agricultural water availability, monsoon-dependent crop planning, and food security in coastal Karnataka.