Too much soothsaying

How much rain?

Published: Sunday 15 June 2003

-- India's drought-stricken people must weather more uncertainty. Indeed outright confusion, for the country could receive anything from 113 per cent excess rainfall to 25 percent below normal rainfall, if monsoon forecasting models are to be believed. Such science can only leave mouths dry. On the eve of the 2003 monsoon, everything seems as sunny as a cloudburst.

IMD model
4 per cent below normal

Down to EarthThe India Meteorological Department (IMD) predicts 96 per cent of annual average rainfall of 88 cm. An associated probabilistic model says there is 21 per cent chance of drought, 39 per cent below normal and 3 per cent chance of excess rainfall

Sahay model
113 per cent excess

Down to EarthAn empirical method developed by Pune-based Indian Institute of Tropical Meteorology researcher Atul Kumar Sahay bets on an excess 113 per cent monsoon in 2003.
This model, based on sea surface temperatures alone, did foresee the 2002 drought. Still evolving, any forecast based on this model is circulated among the scientific community exclusively

IRI model
Normal monsoon

Down to EarthA multi-model probability forecast for precipitation used by the International Research Institute for Climate Prediction (IRI) of US-based Columbia University predicts a normal monsoon across the country with most factors turning favourable. The probabilistic technique uses results available from NCEP's coupled ocean-atmospheric model, its own statistical model for Indian ocean data and a global atmospheric general circulation model

NCEP model
+/- 25 per cent of normal

Down to EarthA model developed by the National Centers of Environmental Prediction (NCEP) of the US National Oceanic and Atmospheric Administration forecasts a monsoon rainfall +/- 25 per cent of normal. In parts of Gujarat, Tamil Nadu and Andhra Pradesh, monsoon failure could be over 50 per cent. The prediction is based on data available till May 2003

CMMACS model
15 per cent less than normal

Down to EarthBanglore-based Centre for Mathematical Modelling and Computer Simulation (CMMACS), using an experimental neural network-based model, forecasts an all-India summer monsoon rainfall of 74 cm, about 15 per cent less than normal. This forecast was done using a new multi-method approach after the unusual 2002 monsoon. Rains, says this model, will be below normal in most parts of western and northern India and parts of eastern India in June. In July, there will be lesser showers in south India, but bountiful in the rest of the country

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