Analysing diurnal temperature range and extreme temperature events over Delhi and Mumbai mega cities

Amongst various form of urbanization induced climate change, changing thermal environment is the most widely studied and understood phenomenon. The impervious surfaces in urban areas absorb and re-emit the heat from solar radiation more than those of natural landscape which causes an elevated temperature in global cities. Due to increasing impervious surfaces and emissions from anthropogenic sources, the diurnal temperature range (DTR) is declining in cities while the frequency of extreme temperature events (TXX) is increasing. Hence, in this study, the trend of DTR and TXX has been examined in Delhi and Mumbai mega cities of India. For this study, India Meteorological Department (IMD) provided daily temperature data for 13 meteorological stations in Mumbai and 21 meteorological stations in Delhi. The DTR and TXX have been analysed using the RClimDex-Extraqc package while the trend of DTR and TXX has been analysed using the innovative trend analysis (ITA). The result showed that during 1991-2018, DTR has declined by about 1.5 & DEG;C in Delhi and about 0.2-0.4 & DEG;C in Mumbai, while TXX has increased by about 0.1-1.4 & DEG;C in Delhi and about 4 & DEG;C in Mumbai. The trend analysis of DTR and TXX using ITA showed that the DTR has a declining trend in both the cities while TXX has an increasing trend. The declining DTR and increasing TXX may increase the vulnerability to heat waves for the city dwellers and deteriorate the urban thermal comfort in both the cities.

Automated summary

Among the various effects of urbanization on climate change, the changing thermal environment is the most extensively studied and understood phenomenon. Impervious surfaces in cities absorb and re-emit more heat from solar radiation compared to natural landscapes, leading to elevated temperatures in global cities. Due to increased impervious surfaces and anthropogenic emissions, the diurnal temperature range is decreasing in cities while the frequency of extreme temperature events is increasing.