New Delhi: The growing concretisation and Humidity level Heat waves are increasing in India’s metropolitan cities, where nighttime cooling is not increasing at the same rate as a decade ago, according to a new report from the . Centre for Science and Environment (CSE)CSE analysed the air temperature in summer, land surface temperatureAnd relative humidity Data for six metros – Delhi, Mumbai, Kolkata, Hyderabad, Bengaluru and Chennai – from January 2001 to April 2024.

The think tank found that rising humidity was aggravating heat stress across all climate zones, with even modest drops in air temperatures being neutralised in Delhi and Hyderabad.

The average summer relative humidity in the five metropolitan cities except Bengaluru has increased by 5–10 per cent from 2014–2023 compared to the 2001–2010 average.

The CSE report comes at a time when severe heat is affecting health and livelihoods in large parts of India.

“To assess changing trends in heat, relative humidity, and land surface temperature over time, day and night.” night temperature It is necessary to develop a comprehensive heat management scheme For Urban Centresaid Anumita Roychowdhury, Executive Director, Research and Advocacy at CSE.

Aavikal Somvanshi, senior programme manager at CSE’s Urban Lab, said it is particularly important to deal with the combination of high heat and humidity, as it can affect the human body’s main cooling mechanism, sweating.

“Evaporation of sweat from the skin cools our bodies, but high humidity levels limit this natural cooling. As a result, people can suffer heat stress and illness, and at very low ambient temperatures this can be fatal,” he explained.

The study has shown that it is not getting cooler at night in the metros.

The land surface temperature will fall by 6.20-13.20 degrees Celsius from the daytime maximum temperature to the nighttime minimum temperature during the 2001-2010 summers. The night-time temperature has fallen by 6.20-11.50 degrees Celsius in the last 10 summers (2014-2023), CSE said.

“Hot nights are as dangerous as the afternoon maximums. If temperatures remain high throughout the night, people get very little chance to recover from the day’s heat,” Somvanshi said.

A study published in The Journal of Neurology Lancet Planetary Health”The risk of death from extremely hot nights could increase by about six times in the future. This forecast is far greater than the mortality risk from daily average warming suggested by climate change models,” he said.

The study said that due to increasing levels of humidity, the weather has become hotter in Delhi, Mumbai, Kolkata and Chennai than the pre-monsoon period.

It said that the use of concrete has increased in all major cities in the last two decades, leading to heat stress. CSE highlighted that increasing greenery is not effective in reducing night heat.

The study found that in Kolkata Highest Percentage The metropolises have the highest land under concrete and the lowest green area, while Delhi has the lowest area under concrete and the highest green area.

Green cover has declined in Mumbai, Kolkata and Chennai. Built-up area in Chennai has doubled in the past two decades, while its green cover has declined by about 14 percentage points.