Perfect model?

New method to forecast monsoon early

 
By T V Jayan
Last Updated: Saturday 04 July 2015

-- scientists at the Bangalore-based Indian Institute of Science (iisc) have devised a new method to forecast the monsoon, that too eight months ahead of the rainfall season. The statistical method, developed by R N Iyengar and S T G Ravikanth, is much less complicated than the existing forecasting models, as it has a sole parameter -- the 1871-2001 rainfall data of the country. On the other hand, the model currently used by the New Delhi-based India Meteorological Department (imd) has eight varied parameters, such as the Eurasian snow cover, sea surface temperature of the oceans worldwide, and pressure and wind patterns during the months preceding the monsoon season. Moreover, this model is able to provide a forecast only two months in advance.

"Our new model can give a fairly reliable picture," claims Iyengar. During evaluation, it was successfully able to 'hindcast' (retrospective forecast) the 2002 drought. Most methods, including the 16-parameter model being used by imd at that time, failed to foresee the drought. Subsequently, imd discarded the 16-parametric and power regression model for the eight-parametric model (see: 'The rain check', Down To Earth, May 15, 2003). "The successful prediction of the 2002 drought should become the touchstone to introduce the new model in the forecasting arena," asserts J Srinivasan, head of Centre for Atmospheric and Oceanic Sciences, iisc.

However, other experts are sceptical. "The results are interesting. But the the model's capability need to be carefully examined," asserts M Rajeevan, director of long range forecasting at imd, Pune. He is not convinced about the 'science' of the model. According to him, it is difficult to believe that oceanic-atmospheric forcings prevailing around the monsoon season are not considered in the new model. Iyengar says that the forcings are a part of the rainfall pattern over the years, and hence they are indirectly considered in the model.

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