The University of Reading has published a study in the journal Weather and Climate Dynamics, which reveals cyclonic storms are occurring more often during India’s summer.
Western disturbances
The cyclonic storms, known as western disturbances, typically bring heavy snow to the Himalayas from December to March. This snowpack slowly melts in spring, providing a steady supply of irrigation water for wheat and other crops downstream.
According to the report, the storms have increased in frequency by 60% from April to July over the past 70 years, reducing snowfall and increasing the risk of heavy flooding. This exacerbates the risk of catastrophic flooding while also reducing vital water supplies for millions of Indians, the university says.
Author Dr Kieran Hunt, of the University of Reading, said, “Strong storms are now twice as likely to occur in the north of India in June compared to 70 years ago. With warmer and more moist air at this time of year, these late storms are dumping heavy rainfall instead of snow. This raises the risk of deadly flooding as we saw in Uttarakhand in 2013 and around Delhi in 2023.
“Some areas of Kashmir saw no snow at all in December or January. This is a serious concern for the 750 million people in the Indus and upper Ganges basins who rely on these winter snows for water supplies. The loss of winter snow and the increasing late-season storms that heighten flood risks is a one-two sucker-punch that underscores the urgent need to respond to the far-reaching impacts of climate change in this sensitive region.”
Warming the Tibetan Plateau
The research team attributes this seasonal shift to changes in the subtropical jet stream, a high-altitude air current that steers western disturbances. The rapid warming of the Tibetan Plateau is creating a larger temperature contrast with surrounding areas, fueling a stronger jet stream that powers more frequent and intense storms.
At the same time, global warming is reportedly weakening the temperature difference between the equator and poles that normally draw the jet stream northward in summer. As a result, the jet stream is increasingly lingering at southerly latitudes later into spring and summer, allowing more storms to strike North India after the winter snow season.
Arriving in the pre-monsoon heat, these increasingly frequent late-season storms unleash heavy rainfall instead of snow, raising risks of devastating flooding. Meanwhile, the team found that the winter snowfall is declining as the region warms, threatening spring water supplies.
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