New Delhi, April 14 Researchers at the Indian Institute of Technology Bombay (IITB) have found different climatic drivers behind back-to-back extreme heat events experienced by South Asian countries including India, Pakistan, and Afghanistan.
The study, in collaboration with a team from Johannes Gutenberg-University Mainz in Germany, focussed on unusually intense heatwave events in March and April of 2022.
The team found different atmospheric processes that compounded heatwave impacts leading to temperatures far exceeding typical ranges for that time of year.
"Our analysis shows that the March heatwave was primarily linked to a sudden increase in the amplitude of short-lived atmospheric Rossby waves, which are large-scale meanders in high-altitude winds resembling bends in a winding river," said lead author Roshan Jha, doctoral student at the Centre for Climate Studies, IIT Bombay.
"The waves grew stronger as high-altitude westerly winds near the poles (extratropical jet stream) transferred energy to westerly winds closer to the equator (subtropical jet stream) as they came closer during the heatwave," Jha added.
The study, published in the Journal of Geophysical Research: Atmospheres, showed that the April heatwave happened differently. Instead of being driven by wind patterns in high altitudes, it was largely caused by very dry soil conditions and the advection of heat to India from north-western land regions of Pakistan and Afghanistan.
Importantly, these dry conditions were partly created by the earlier March heatwave, which had already dried out the land through high temperatures and clear skies.
The research reveals a concerning pattern: one heatwave can set the stage for another, more intense heat event in the following weeks by removing moisture from the soil. When soil becomes too dry, it creates a cycle that makes the next heatwave even worse.
"Think of it like this -- when the soil has moisture, under the clear sky conditions, some of the sun's energy goes into evaporating that moisture rather than heating the air. But when the soil is already dry, all that energy goes straight into making the air hotter," explained coauthor Prof. Arpita Mondal, Associate Professor at IIT Bombay.
The experts urged the need to understand these mechanisms to improve the ability to forecast and prepare for extreme heat events in South Asia. It will also enable better prediction and mitigation of the impacts of future heatwaves.
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