The Hindu : National : South West Monsoon may be near-normal

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Thursday, Apr 17, 2008
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National

South West Monsoon may be near-normal

P. Sunderarajan

88.11 cm rainfall forecast during the four-month season

Forecast to be updated in June
IMD to keep close watch on La Nina

NEW DELHI: The India Meteorological Department on Wednesday forecast that the coming South West Monsoon is likely to be “near normal.” Rainfall may be 99 per cent of the long period average (LPA), plus or minus the model error of five per cent.

In other words, the country is likely to receive 88.11 cm of rainfall during the four-month season as the LPA — which is derived by averaging the rainfall for the 50-year period from 1941 — is put at 89 cm.

Making the announcement, Union Science and Technology Minister Kapil Sibal said the rainfall for the coming season was considered near normal.

According to a new definition finalised by the IMD recently, rainfall of 96 to 104 per cent of the LPA is defined as near normal, between 90 per cent and 96 per cent below normal, below 90 per cent deficient, between 104 per cent and 110 per cent above normal and above 110 per cent excess.

Update

The forecast, he said, would be updated in June taking advantage of more data on the parameters that determine the outcome of monsoon. It would then have a smaller model error of plus or minus four per cent.

Region-wise forecasts

In June, the IMD would also come out with a forecast for the rainfall in July, which is the most important month for agriculture. It would then prepare region-wise forecasts for the four geographical regions — south Peninsula, Central India, the north-east and the north-west regions.

About the La Nina conditions over the equatorial Pacific, Mr. Sibal said indications were that it would not have a big impact. The phenomenon, which developed in August last, had declined to moderate strength. Recent forecasts suggested that it would become weaker, though it could persist for the next three months. It was, however, uncertain what would happen after that. Experts at the IMD would keep a close watch.

The La Nina, which develops when the sea surface temperature over the equatorial Pacific becomes colder than normal, has been found to bring more rainfall over India. The IMD had made some changes to the models used for monsoon forecast this year. For the first time, dynamic models were used for south Peninsula and the north-east regions.

“For the south Peninsula and the north-east region, the statistical models were found to be wanting. For the rest of the country, they have been performing well,” Mr. Sibal said.

The IMD, he said, had also taken into account the experimental forecasts prepared by national and international institutions such as the National Centers for Environmental Prediction, U.S.; the International Research Institute for Climate and Society, U.S.; the Meteorological Office, U.K.; the European Centre for Medium Range Weather Forecasts, U.K.; the Experimental Climate Prediction Centre, U.S.; the Indian Institute of Tropical Meteorology, Pune; the Indian Institute of Science, Bangalore; the Space Applications Centre, Ahmedabad; the National Aerospace Laboratories, Bangalore; the Centre for Mathematical Modelling and Computer Simulation, Bangalore; and the National Centre for Medium Range Weather Forecasting, Noida.

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