CHENNAI: The number of heatwaves in Delhi was higher than in Kolkata, Chennai, and Mumbai over the past three decades, but the risk of extreme heat stress and dangerous heat strokes triggered by relative humidity is the highest in Chennai compared to the three other metros, a study has found.
The study based on historical weather data also led scientists to conclude that extreme discomfort level during heat or non-heatwave period is higher in Kolkata and Chennai than in other cities. Scientists from the Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORAL), Indian Institute of Technology, Kharagpur, studied heatwaves in Kolkata, Chennai, Delhi and Mumbai during the summer season (April to July) from 1990 to 2019.
The results of the study were published recently in the journal ‘Science of the Total Environment’. The study used data such as daily maximum temperature, relative humidity, wind speed and solar radiation.
Heatwaves are characterised by abnormally high temperatures that exist for a significant duration, impact agriculture when associated with low humidity and affect human health leading to deaths when associated with high humidity, the study’s corresponding author Arun Chakraborty from CORAL said. Analysis shows that the probability of very strong heat stress (temperature between 38C-46C) was 98.2% in Chennai compared to 97.44%, 76.9% and 17.24% in Delhi, Kolkata and Mumbai during the heatwave period. In the non-heatwave period, the probability of very strong heat stress dropped to 58.27% in Chennai compared to 27.53% in Delhi, 1.5% in Kolkata and 2.76% in Mumbai.
Heatwaves have caused more than a lakh deaths globally between 1998 and 2017 and have been acknowledged as natural disasters in India since 2016. One of the reasons for the increase in a heatwave is due to global warming, scientists said.
The study also found that the relative humidity and temperature were both higher in Chennai city increasing the chances of heat stress. Despite the higher temperature, the possibility of heat stress was less in Delhi due to lower humidity, the study said. The temperature and heat stress were the lowest in the Mumbai region.