Wind course, dry soil caused 2022 heatwaves: Study

Mumbai: In 2022, much of South Asia reeled under back-to-back heatwaves which straddled the months of March and April. Scientists at IIT-Bombay and Johannes Gutenberg University Mainz in Germany began to trace the fingerprints of a changing atmosphere. What they found was not a single reason, but a complex matrix of wind and heat, soil and sky — each compounding the next.
"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." This fast-moving, high-altitude drama sent temperatures soaring in March.
But April told a different story. This time, the heat came not from above, but from the earth itself. With the soil already parched from March's searing temperatures and cloudless skies, the land had no moisture left to act as a buffer. Heat rolled in from Pakistan and Afghanistan, unchallenged. "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-B and a coauthor 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 of IIT-B. "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, published in the Journal of Geophysical Research: Atmospheres, sounds a clear warning: a heatwave dries the land, stripping it of its natural defences, and sets the stage for an even more intense assault. "This is how climate extremes cascade," said Ghosh. "One event primes the system for the next."
Mumbai: In 2022, much of South Asia reeled under back-to-back heatwaves which straddled the months of March and April. Scientists at IIT-Bombay and Johannes Gutenberg University Mainz in Germany began to trace the fingerprints of a changing atmosphere. What they found was not a single reason, but a complex matrix of wind and heat, soil and sky — each compounding the next.
"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." This fast-moving, high-altitude drama sent temperatures soaring in March.
But April told a different story. This time, the heat came not from above, but from the earth itself. With the soil already parched from March's searing temperatures and cloudless skies, the land had no moisture left to act as a buffer. Heat rolled in from Pakistan and Afghanistan, unchallenged. "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-B and a coauthor 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 of IIT-B. "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, published in the Journal of Geophysical Research: Atmospheres, sounds a clear warning: a heatwave dries the land, stripping it of its natural defences, and sets the stage for an even more intense assault. "This is how climate extremes cascade," said Ghosh. "One event primes the system for the next."