Evaluating the Cooling Efficacy of Urban Cool Islands (UCIs) in Secondary Tropical Cities: A Microclimatic Analysis of Rajshahi, Bangladesh

Abstract

Rapid urbanization in Rajshahi has intensified Urban Heat Island (UHI) effect, while the cooling performance of urban blue infrastructure remains insufficiently understood. This study evaluates the cooling efficacy of the Padma River and urban ponds through satellite-derived Land Surface Temperature (LST), morphological analysis, land cover interaction, and microclimatic profiling. Landsat 9 thermal data and ESA WorldCover datasets were integrated within a GIS framework to quantify Urban Heat Island Intensity (UHII) between Rajshahi City Corporation (RCC) and surrounding Paba Upazila. Results show a mean UHII of 0.41°C, with localized extremes exceeding ±8°C. The Padma River functioned as the primary macro-scale cooling sink, extending cooling up to 1.7 km through open morphologies, while dense compact zones restricted penetration below 700 m. Large compact ponds produced the strongest localized cooling (ΔT ≈ 6.9°C), whereas interconnected small ponds stabilized urban thermal variance. The study demonstrates that blue infrastructure morphology and adjacent land cover critically regulate urban thermal resilience.