'Changes in extreme dry, wet spell patterns raise drought, flood risks' - Livemint

The South Asian summer monsoon, an annual wind-driven weather pattern responsible for 85% of India's annual precipitation, is vital for the country's agricultural sector. Photo: AFP

Washington: Stanford scientists have warned of significant changes in the patterns of extreme wet and dry events during monsoon, increasing the risk of drought and flood in central India.

Researchers, including two Indian origin-scientists, show that the intensity of extremely wet spells and the number of extremely dry spells during the South Asian monsoon have both been increasing in recent decades.

"We are looking at rainfall extremes that only occur at most a few times a year, but can have a very large impact," said senior author Noah Diffenbaugh, senior fellow at the Stanford Woods Institute for the Environment.

The South Asian summer monsoon is an annual wind-driven weather pattern that is responsible for 85% of India's annual precipitation and is vital for the country's agricultural sector.

Deepti Singh, lead author of the study, said that rainfall extremes during monsoon months can be as important as how much total water is received. For example, during critical crop growth stages, too many days without rain can reduce yields or lead to crop failure, which can weigh on India's agriculture-dependent economy. At the same time, short periods of very heavy rainfall can create humanitarian disasters, such as in 2005, said researchers.

Diffenbaugh and his team wanted to test whether the pattern of extreme wet and dry "spells" during the monsoons had changed in recent decades.

Wet and dry spells were defined as three or more consecutive days of extremely high or low rainfall, respectively.

The team studied the rainfall data gathered over a 60-year period by the Indian Meteorological Department and other sources.

They used rigorous statistical methods to compare peak monsoon rainfall patterns during two periods: from 1951 to 1980; and from 1981 to 2011.

The team looked specifically at rainfall during the months of July and August, which is the peak of the South Asian summer monsoon.

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