Monsoon is normally associated with flash floods. But a team of Indian researchers found that a kind of rapidly developing drought also manifests during the prominent rainy season.

Long-term monsoon breaks — prolonged dry spells during the season — are leading to a unique phenomenon called flash droughts in India, affecting kharif crops and groundwater depletion, according to a new study by researchers at the Indian Institute of Technology (IIT)-Gandhinagar.

In a study recently published online in the journal Environmental Research Letters , IIT-Gandhinagar researchers Shanti Shwarup Mahto and Vimal Mishra found that more than 80 per cent of these extreme weather events occur during the monsoon season in the country.

Intense droughts

Flash drought, a term coined by scientists only a few years ago, refers to a severe drought kind of situation that develops very rapidly. “Unlike conventional droughts that develop over months, flash droughts intensify very quickly. This happens because rains stay away for 15-20 days at a stretch,” said Mishra, an associate professor of earth sciences and civil engineering at the IIT.

“It is widely believed that such flash droughts will occur during the summer months as was reported in the Western countries, mostly driven by heat waves and very high temperature. But much to our surprise, we found that in India, 82 per cent of such extreme weather events happen during the monsoon period,” said Mishra, whose team recorded as many as 39 such country-wide events between 1951 and 2018. Besides, there are many more region-specific flash droughts, too, during the study period.

Using India Meteorological Department observation data, they ran a model they developed to estimate soil moisture levels. When they dug deeper, the scientists found that when there is a monsoon break of 15-20 days, temperatures shoot up. This combination of monsoon breaks and increased temperatures depletes soil moisture very quickly, precipitating a very severe drought.

Impact on agriculture

“This has tremendous implications for agriculture and water management. “When there is a standing crop and no rains, farmers have no other way but to pump groundwater to sustain the crop,” Mishra said.

Their study found that each year, 10-15 per cent of area under rice and maize crops is affected by flash droughts. It also revealed that flash droughts have had significant impact on crop production, particularly in three years — 1979, 1986 and 2001.

“Monsoon variability combined with increased warming may lead to more such events in India,” said Mishra. This increasing frequency of flash droughts during the monsoon season in future can have implications for agriculture production and irrigation water demands in India, he added.

According to the scientists, the intensity of flash droughts has been increasing in some regions of the country, but not across it. For instance, in the Indo-Gangetic plains, where rainfall has been declining, there have been more instances, said the scientists who had divided the country into six different regions for the story. Two regions where flash droughts have been occurring mainly in non-monsoon periods are the peninsular region and the Himalayan region.