Identification of Critical Urban Clusters for Placating Urban Heat Island Effects over Fast-Growing Tropical City Regions: Estimating the Contribution of Different City Sizes in Escalating UHI Intensity

The incessant rise of artificial surfaces has increased the temperatures of cities, distressing urban health and sustainability. Fast-growing tropical cities particularly call for an understanding of this phenomenon, known as the urban heat island (UHI). The present study was conducted to detect UHI dynamics over the National Capital Region of India. Stretching over more than 32 000 km 2 , this region consists of urban centers of varying sizes. Landsat thermal bands were processed to extract temperature patterns between 1999 and 2019. Urban climate change was prominent, as a 2349-km 2 expansion in UHI area was spotted. Urban clusters of different sizes were demarcated by applying the k-nearest neighbor algorithm on the normalized difference building index maps. This empirical analysis helped to form a logarithmic relation between city size and UHI intensity. Observed results set a framework to assess the thermal environment of numerous urban centers from any tropical country. UHI intensity values for various city sizes were computed, as they were crucial to decide the outdoor comfort zones based on the base temperature conditions of other cities. Further, the critical zones in each urban cluster were identified using the vegetation index, and scopes of landscaping were suggested based on the observed building morphologies of different local climate zones.