Urban sprawl during five decadal period over National Capital Region of India: Impact on urban heat island and thermal comfort

The urban agglomeration of Delhi, the capital city of India is projected to be the world's largest city by 2030. This study explores and attempts to quantify the change in land use/land cover due to the evolution of urban sprawl during a five decadal period (1972–2014) over the central national capital region (CNCR) of India vis-à-vis impacts on heat island intensities, thermal comfort, and other associated features using a mesoscale numerical model. With increasing urbanization, around 500 km2 of CNCR area experiences night-time canopy layer heat island (CLHI) >4 °C and new smaller areas experiencing CLHI of about 5–6 °C have emerged which were non-existent 50 years ago. Spatially averaged ambient temperatures in Delhi have been estimated to have increased by 1.02 °C in the five-decadal period of 1972–2014. Furthermore, thermal comfort based on Robba Index is analyzed in the context of increasing urban sprawl. Thermally extremely uncomfortable hours have increased from an average of 10 to 13 h a day with an increase in urban sprawls in this multi-decadal period. It is emphasized that when this impact is considered cumulatively over the entire globe with many such urban agglomerations, urban LULC changes can cause a significant impact at the macro-climate scale. There is a considerable growth (30-fold increase) of urban and built-up areas observed during recent decades over the central National Capital Region (CNCR) of India which has led to an increase in heat island intensities in the urbanized regions. Subsequently, there is an increase in extremely uncomfortable hours and a decrease in comfortable hours per day. [Display omitted] •Half a century of urbanization across Delhi studied that showed an increase in heat island intensities up to 5–6 °C.•Average near-surface average temperatures across the city have increased by 1.02 °C due to urbanization.•Increase in extremely uncomfortable hours for the urbanized localities from an average of 10 h a day to 13 h a day.