Predicting monsoon

The India Meteorological Department's prediction that the total rainfall in the coming monsoon season (June-September) is likely to be 95 per cent of the long-period average with an error margin of 5 per cent is good news for agriculture, hydel power, navigation and other water-based economic activities. But the point to remember is this is neither the last word (as the forecast is slated to be updated in June), nor is it of much value for prior planning for most of these sectors. The more useful information on the expected onset of the monsoon and the distribution of rainfall would be available much later, when it is already too late for remedial measures. In any case, the impact of the monsoon on agricultural growth has been shrinking over the years. The rabi season's contribution to the total production is now almost equal to that of the kharif season. The last two years' experience is a case in point. Agricultural growth was a handsome 6 per cent in 2005-06, when the monsoon rainfall was 99 per cent. The growth dropped to 2.7 per cent in 2006-07, when the monsoon rainfall was even better at 100 per cent.

This shows that while there is a need for a long-term forecast, steps must be taken to strengthen and revamp the monsoon prediction capability so that the region-wise and time-wise rainfall pattern could be visualised much earlier. From that point of view, it is noteworthy that the IMD has this year taken a couple of new initiatives. First, it has evolved and used two entirely new prediction models even though these are statistical models that have in the past tended to err at crucial times like droughts. While the first model, using five global weather-related parameters, has been used for making the present long-range forecast, the second one""based on six parameters""will be used to refine this prediction and project rainfall in the critical month of July, as also in the four geographical regions of the country.

Secondly, it has initiated transition from statistical models to a dynamic forecast system in vogue in many other countries. No doubt, the development of such a system is an arduous task, especially when it comes to foreseeing a highly complex phenomenon like the monsoon, but the IMD seems to be inching closer to achieving that feat. As such, it has put together an experimental forecast based on the dynamic system which has also pointed to a normal monsoon. But, this system still needs to be tested further and validated before it can be pressed into service. For that matter, the new statistical models being used this year, too, have yet to be adequately validated. After all, the previous models were also introduced with much hope in 2003 but had to be discarded because they failed to give correct predictions in two of the four years they were in use. Therefore, the IMD really needs to redouble its efforts to fine-tune the dynamic methodology to enhance the credibility of its forecasts.