Comparison of Extreme Bioclimatic Episodes in Kolkata (India) and Two Neighboring Suburban Stations

The objective of the present study is to estimate the duration of extreme thermal bioclimate conditions in and around Kolkata, one of the highly densely populated cities in India. The biometeorological conditions have been calculated by Physiologically Equivalent Temperature (PET) using the RayMan model at 05:30 h and 14:30 h (IST) based on meteorological data for the stations Kolkata (Alipore), Dum Dum, and Diamond Harbour for the period January 2020 to December 2021. Dum Dum is located to the north of Kolkata, and Diamond Harbour is situated to the south of Kolkata. The meteorological data were retrieved from the station data measured by the Indian Meteorological Department (IMD). The atmospheric variables required to calculate the PET index are air temperature, relative humidity, cloud cover, and wind speed. A recent study reported that stations outside Kolkata suffer warmer human thermal stress conditions. To account for the prolonged thermal stress periods, PET greater than 40 °C is categorized as an episode if it turns up consecutively between 1 and 5 days, 6 and 10 days, 11 and 15 days, 16 and 20 days, 21 and 25 days, and 26 and 30 days. The number distribution of days not exceeding 40 °C remains the same for all the stations. The number of episodes occurring successively for 6–10 days, 11–15 days, 16–20 days, and 21–25 days is highest in Diamond Harbour relative to Kolkata and Dum Dum at 14:30 h. Episodes occurring successively for 26–30 days appear in Kolkata and Dum Dum, whereas no episodes appear in Diamond Harbour