Delhi:Scientists have developed a new model for estimating variability and trends in rainfall over different climate regions of the country, which is set to help in improving the existing weather forecasting for both the southwest and northeast monsoons.

The new statistical model based on multiple linear regression (MLR) has been developed by scientists from the Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORAL), IIT Kharagpur, the Indian Institute of Tropical Meteorology (IITM), Pune, and the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad.

“Indian monsoon, both southwest and northeast is complex. It depends on various climatic forcings (conditions) like El Nino, Indian Ocean Dipole, which affect rainfall in different regions, in different ways. We studied these factors and assigned a value to each," said professor Arun Chakroborty from IIT Kharagpur.

Researchers highlight that current dynamic models used for monsoon forecast face two major problems. First, they respond a little too much to El Nino Southern Oscillation (ENSO). Second, the relationship between Equatorial Indian Ocean Oscillation (EQUINOO) and summer monsoon in models has been found to be opposite to actual observation.

“In observation, we find a positive co-relation between EQUINOO and monsoon, but it is opposite in the models. So, if we can improve our understanding of EQUINOO’s impact on monsoon, then we can make corrections in the dynamic model and improve our teleconnections. This will help us get an accurate monsoon forecast," said Dr P.A. Francis, from INCOIS, highlighting that it is also one of the objectives of the National Monsoon Mission.

The study published recently in Scientific Reports also analysed changes in the monsoon from 1979 to 2017 and found a significant positive trend (0.43mm/day/decade) in northwest India for the southwest monsoon. “But it showed a decline in south and northeastern states," said first author P.J. Nair, from IIT Kharagpur.

“It’s significant to note that the increase/decrease of rainfall, for both summer and winter monsoon is not uniform in all regions and so is the effect of these climatic factors. For instance, for most of mainland, El Niño is bad, but for the northeastern parts of the country, it is not that bad," said co-author Professor J. Kuttippurath from IIT Kharagpur.

The research is one of the first to have analysed the variability of the Indian monsoon because of these factors together. It confirmed with statistical analysis, that ENSO and EQUINOO are two major drivers for Indian monsoon and explain around 50% variability in monsoon.

With the accuracy of current monsoon forecast models limited because of the lack of data and adequate information on climatic processes, researchers said such studies would help scientists to better tune their models for accurate weather prediction.

The research assumes significance as the monsoon decides the livelihood of more than a billion people and influences the agrarian economy which is largely dependent on its accurate forecast. The situation warrants continuous surveillance of Indian rainfall.

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