Assessment of urbanization's impact on 2020 extreme and prolonged heatwave episodes over Northwest Indian cities

Abstract

Northwest Indian cities (Delhi, Jaipur, and Agra) are highly prone to heatwaves (HWs) during April to June. We address the analysis of a prolonged HW event between May 24 and May 28, 2020, using in‐situ, reanalysis, and 1.5‐km resolution Weather Research and Forecasting (WRF) model products. Both observations and reanalysis revealed that warm (˜40–44°C) and dry northwesterly winds (˜10 m·s ⁻¹ ) prevailed over northwest and central India during the HW period. The WRF model simulated the evolution of surface air temperature, relative humidity, winds, and HW duration and its spatial extent fairly well. The model could depict the nighttime intensification of HWs (˜3–7°C) in urban areas and a pronounced heat dome with vertical extension of up to 2 km. The findings reveal that weaker winds, the overlong presence of the heat dome, and a nighttime urban heat island (UHI) over urban centers exacerbate the extreme heat conditions in the cities. The altered physical processes over urban areas enhances the UHI during the night and early morning hours, thereby amplifying and prolonging the persistence of heat domes, eventually contributing to the duration and intensity of HWs. Computed statistical metrics confirm that the WRF model performed satisfactorily in predicting HW over northwestern India. Furthermore, a sensitivity test revealed a reduction in UHI intensity (about 3–5°C) when urban built‐up classes were replaced by rural classes. This research outcome is valuable to urban planners and policymakers for addressing challenges related to urbanization and increasing heat stress.