Heatwave spells on the rise: IMD research
Several stations in the core heat wave zone – north, northwest, central, east and northeast Peninsular India – registered the highest number of heat waves and severe heat waves, with the highest frequency in May, during this period.
The number of heat wave days in India in a decade has increased from 413 in the 1981-90 decade to 575 in 2001-10 and further to 600 in 2010-20, highlighting the impact the climate crisis is having on maximum temperatures, a study by India Meteorological Department (IMD) and Kottayam-based Institute for Climate Change Studies (ICCS) revealed.
Besides this, most of the 103 weather stations which are being studied for heat wave occurrences in the country have shown either an increase or a significantly increasing trend in heat wave frequency between April and June during the 1961-2020 period.
Heat wave trends for the 1961-2010 period were published by a team of researchers in a book titled “Observed Climate Variability and Change Over the Indian Region” in 2016. This analysis is currently being updated by IMD and ICCSresearchers.
Regions that witnessed more than eight heat wave days on an average in the months of April, May and June had increased spatially between 1991 and 2020 in comparison to the 1961-1990 period, the study revealed.
Several stations in the core heat wave zone – north, northwest, central, east and northeast Peninsular India – registered the highest number of heat waves and severe heat waves, with the highest frequency in May, during this period.
The islands, however, were not affected by heat waves, the study said.
“An increase in the spatial coverage, frequency and persistency of the heat waves and severe heat wave days were observed during recent three decades (1991 to 2020) compared to previous three decades,” DS Pai, director of Institute of Climate Change Studies and former climate scientist at IMD Pune who was part of these studies, said.
“There is a decrease in the total number of cold wave or severe cold wave days over the cold wave zone during the past three decades,” he added.
“The recent three decades have been the warmest decades for the country and globally. Extreme temperature events like heat waves are key features of global warming,” he explained.
To be sure, the data mentioned in the study does not include March, a month not normally associated with heat waves, although this year, March has been hotter than most on account of heat waves across northwest India.
IMD Pune’s Climate Hazards and Vulnerability Atlas of India covers heat wave occurrence only in April, May, June and July. The Atlas indicates that even within the core heat wave zone, parts of west Rajasthan, Andhra Pradesh and Odisha are the worst affected between the 1961 to 2020 period.
Overall, 13% of the districts and 15% of the population are moderate to very highly vulnerable to heat waves in India, according to the atlas released in January.
This time, however, the heat wave season has advanced into March mainly due to the formation of a high-pressure area over south Sindh region.
“An area of anti-cyclone has formed near the south Sindh region. The winds are rotating clockwise here, bringing hot and dry winds from southwest Rajasthan, Balochistan, central Pakistan, etc, that are now blowing over Delhi, south Haryana, southwest Uttar Pradesh etc. This along with the lack of rainfall and western disturbances has led to an unusual spike in temperatures so early in the season. Normally, western disturbances bring some light rain and thundershowers in the upper reaches in March which helps break the heat spell. But that hasn’t happened. This is an unusual year but the link with the climate crisis is that average temperatures are going up, which is accentuating the impact of heat waves,” Mahesh Palawat, vice president of climate change and meteorology, Skymet Weather, said.
HT had reported on March 29 that a 72% deficiency in rainfall over India in March was recorded by IMD. The deficit is 89% over northwest India, 86% over central India, 13% over peninsular India and 59% over east and northeast India.
