A new study by researchers at the Indian Institute of Technology Bombay (IITB) and Johannes Gutenberg-University Mainz, Germany has uncovered why South Asian countries experienced back-to-back extreme heat events in early spring of 2022.
The research team found that these unusually intense heatwave events in March and April of 2022, which saw temperatures far exceeding typical ranges for that time of year, were driven by different atmospheric processes that compounded heatwave impacts.
“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 Roshan Jha, the study’s lead author.
“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, “
The April heatwave happened differently. Instead of being driven by wind patterns in high altitude, it was largely caused by very dry soil conditions and 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 IIT, Bombay, stated that “This 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 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 Prof. Arpita Mondal, Associate Professor at IIT Bombay and a co-author of the study.
“Understanding these mechanisms is crucial for improving our ability to forecast and prepare for extreme heat events in South Asia,” said Prof. Subimal Ghosh. “As climate change continues to affect atmospheric wind patterns, identifying these specific drivers helps us better predict and mitigate the impacts of future heatwaves.”
The study, titled “Contrasting drivers of consecutive pre-monsoon South Asian heatwaves in 2022: waveguide interaction and soil moisture depletion”, has been published in Journal of Geophysical Research: Atmospheres, scientific journal of atmospheric research published by the American Geophysical Union.
