ASSESSING THE CLIMATIC IMPACT OF ROOFTOP GARDENS ON URBAN LAND SURFACE TEMPERATURE: SATELLITE-BASED EVIDENCE FROM DHAKA NORTH CITY CORPORATION

Abstract: Rapid urbanization and the widespread expansion of impervious surfaces have intensified urban heat stress in tropical megacities, amplifying the Urban Heat Island (UHI) effect and associated environmental and public health risks. Dhaka, Bangladesh, is particularly vulnerable due to its high population density, limited green space, and pronounced pre-monsoon heat extremes. Rooftop gardens have been proposed as a nature-based solution for urban heat mitigation; however, empirical, building-scale evidence from dense tropical cities remains limited. This study evaluates the cooling effects of rooftop gardens on rooftop land surface temperature (LST) in Dhaka North City Corporation (DNCC) using satellite-based observations. Building footprints were obtained from the Google Open Buildings dataset and validated using high-resolution imagery. Rooftop gardens were identified through a combined manual and remote sensing approach, classifying 2,012 buildings with rooftop gardens and 43,553 buildings without. Daytime LST was derived for the pre-monsoon period (March–May) of 2022 using Landsat 8 Collection 2 Level-2 data processed in Google Earth Engine. Statistical analyses were conducted to compare mean temperatures, thermal variability, and extreme temperature conditions between the two building categories. The results show that rooftop gardens reduce mean rooftop LST by up to 1.99 °C during peak heat in May and suppress extreme rooftop temperatures by 3.9–6.4 °C across the pre-monsoon season. Vegetated rooftops also exhibit reduced thermal variability and fewer extreme temperature occurrences. These findings demonstrate that rooftop gardens offer significant thermal benefits under extreme climatic conditions and represent a scalable, low-cost nature-based strategy for mitigating urban heat stress in rapidly urbanizing tropical cities.