NEW DELHI: Increasing concretization and humidity levels are exacerbating heat stress in India's megacities, which are not cooling down at night at the same rate as a decade ago, according to a new report by the Centre for Science and Environment (CSE).

The CSE analysed summer air temperature, land surface temperature, and relative humidity data for six megacities -- Delhi, Mumbai, Chennai, Kolkata, Hyderabad and Bengaluru -- from January 2001 to April 2024.

The think tank found that increased humidity is worsening heat stress across all climate zones, even nullifying the marginal drop in air temperatures in Delhi and Hyderabad.

Barring Bengaluru, summertime average relative humidity has increased by 5-10 per cent in the other five megacities from 2014-2023 compared to the 2001-2010 average.

The study said rising humidity levels have also made monsoons in Delhi, Mumbai, Kolkata, and Chennai hotter than pre-monsoon periods.

The study showed that Green cover has declined in Mumbai, Kolkata, and Chennai. The built-up area in Chennai has doubled in the last two decades, while its green cover shrank by almost 14 percentage points.