Kolkata: The city has emerged as India's most humid metro in summer, according to a recent study by the Centre for Science and Environment (CSE), exacerbating urban heat stress and challenging public health resilience.In a comprehensive study spanning 2001 to 2023, the Delhi-based think tank CSE examined the twin forces of land surface temperature (LST) and relative humidity across six major Indian metro cities — Delhi, Mumbai, Bengaluru, Chennai, Hyderabad, and Kolkata — and four smaller cities. The analysis focused on average relative humidity during the summer months of March to May, and revealed a troubling rise in urban heat stress, particularly in cities with already high baseline humidity, like Kolkata and Mumbai.Among the cities studied, Kolkata stood out for recording consistently high relative humidity during the summer over the last 13 years. With a baseline average of 73.3% for 2001-2010, the city recorded 74.4% humidity in 2023, peaking at 81.3% in 2020 and recording a lowest count of 73.9% in 2014. This trend of persistent, elevated moisture levels has placed Kolkata at the top of the humidity charts almost every year, frequently surpassing even coastal counterparts, like Mumbai and Chennai.As a result, the city experiences intensifying levels of perceived heat, making summers increasingly unbearable for residents. In 2023, Kolkata's summer relative humidity stood at 74.4%, higher than Chennai's 74.1%, with a 61.3% baseline, and Mumbai's 73.8%, with a 70% baseline. Bengaluru, traditionally less humid, recorded 66.7%, with a 67.8% baseline, Hyderabad recorded 61.0%, with a 55.4% baseline, and Delhi stood at 60.9%, with a 52.5% baseline.Even cities like Delhi and Hyderabad, known more for dry heat, are witnessing sharp increases in humidity — Delhi's relative humidity rose by 8% and Hyderabad's by 10% over the past two decades.The study also underscored a seasonal shift in thermal discomfort. Traditionally, monsoon offered a break from the intense summer heat. But now, cities like Delhi, Mumbai, Kolkata, and Chennai report higher heat indices during the monsoon months due to persistently high humidity, reducing the cooling effect of rain.This surge in humidity is particularly dangerous because it hinders the body's natural cooling mechanism — sweating. When air moisture is high, sweat evaporates more slowly, leading to ineffective thermoregulation, which can cause heat exhaustion, heat cramps, and even fatal heatstroke. Vulnerable groups, like the elderly, children, and outdoor workers, are at higher risk, the study said.Get the latest lifestyle updates on Times of India, along with Mother's Day wishes, messages, and quotes !