Meteorologists on Thursday brought cheer for the farmer by announcing a normal south west monsoon (June-September) rainfall this year.
Director National Climate Centre M Rajeevan announced that the rainfall for the whole country is likely to be 95 per cent of the Long Period Average. The LPA being 89 cm - the rainfall expected this year was around 84 cm, which is 'good for the farmers', he added.
He said the forecast was being made with a model error of five per cent plus or minus. In the worst case scenario, if the rain fell to 90 per cent of the LPA, then six to seven sub-divisions may get deficient rain. Rainfall touching 100 per cent of LPA may have just 2-3 sub-divisions deficient in rain.
Last year, IMD had projected a forecast rainfall of 93 per cent of LPA, but the actual rains were 100 per cent of LPA. Despite this, in an “unusual occurrence”, nine divisions suffered from deficient rains, he added.
However if rainfall dropped to 80 per cent of LPA it would be severe drought, one of the worst drought years was when rainfall was 79 per cent of LPA, he said.
Major indicators, which had given hope to the meteorologists is the likely formation of La Nina (cold sea surface temperature) during monsoon and European temperatures being above normal, he said.
Besides the first long-range forecast issued now, the IMD also issues an update in June 2007 as part of the second stage forecasts with separate forecasts for the July rainfall over the country as a whole and seasonal (June-September) rainfall over the four geographical regions of India.
Secretary Earth Sciences PS Goel said that the IMD had developed new models for forecasting monsoon in which new five parameter statistical forecasting system requiring data up to March will replace the existing 8 parameter model for the first forecast in April. Another new 6 parameter statistical forecasting system requiring data upto May, will replace the existing 10 parameter model for the forecast update in June.
The most important aspect of the new forecast system is the introduction of the concept of ensemble forecasts. In this method, instead of relying on a single model we have considered all the models with all possible combination of predictors, he added.
The methods used in the new forecast system and results have been documented, peer reviewed and published in 2006 in a reputed international researchy journal Climate Dynamics, he added.