Monsoon forecast till 2020: Dry patches will not reign

AS Vidarbha’s drought belt seeks a lifeline in the Prime Minister’s relief package for farmers, a new trend analysis of nationwide rainfall patterns since 1901 offers more hope — the “possibility” of fewer droughts until 2020, though the July rainfall shows a dipping trend.

“Statistics indicate the frequency of dry years will be less till 2020,” says M Rajeevan, director, National Climate Centre, Pune, which has released the analysis based on over a century's nationwide data from 1,476 rain gauge stations. “There will be more years with more rain.”

At the Indian Institute of Tropical Meteorology, director BN Goswami confirms that monsoon chasers expect the monsoon to move from a negative to a positive phase in the near future. “But it’s tricky business to predict the transitions.”

Goswami was based at the Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore until recently. There, his team reported a “close relationship” between North Atlantic sea surface temperatures and the monsoon's 30-year wet or dry episodes. Their paper was published in the international Geophysical Research Letters in January.

“The El Nino link is well-known, but this is the first time we’ve established a physical mechanism linking the Atlantic climate and Indian monsoon,” says Goswami.

Statistically, 1901-1930 was a dry monsoon phase, 1931-60 was wet and 1961-90 was again a dry phase. So the Pune analysis anticipated a possible wet phase between 1991 and 2020.

North Atlantic temperatures plotted on a long time scale reveal the Atlantic Multidecadal Oscillation (AMO) with alternating 30-year phases like the monsoon. When AMO temperatures are above normal, the multidecadal monsoon period tends to be wetter. When AMO temperatures dip below normal, the monsoon’s multidecadal phase is drier.

“We're making hypotheses now,” says Goswami. “Modelling studies are needed to predict annual variations.”