Predicting Monsoon

Ajey Lele

Indians are by nature emotive. But, unfortunately they believe in overreacting. So, be it 26/11 or Swine-flu or draught like situation: mostly they react excessively. They even cannot take a loss by cricket team sportingly so naturally they are bound to start the blame game when drought is at the doorstep. What best punching bag could be than the Indian Meteorological Department (IMD)? Few intellectuals are even asking for its closure.

Forecast is anticipation of future and could go wrong. Interestingly, 9/11 was not predicted but nobody closed the Rand Corporation or CIA. 26/11 was not anticipated but RAW and IB are still functional. But, just one bad monsoon and up comes a bizarre suggestion that IMD should be closed.

Unfortunately, in India the science of weather has always remained less understood and debated. Average Indian always feels that if Americans can get the weather forecast right then why can’t we? Little did they know that they also go wrong. The other argument is that if we can manufacture cars, missiles and send satellites to space then why we can’t forecast weather correctly. However, technology transfer is not possible in regard to weather forecasting because tropical and extra tropical weather systems simply have no commonalities. Our geography is different form theirs. More importantly science of weather has neither significant commercial utility nor ‘nuisance’ value! So technocrats or economists or politicians have less interest in it. Naturally, no pressure groups or opinion makers have interest in this field. No so called glorification of achievements or also of ‘shortcomings’ of weatherman are done which otherwise found rampantly happening in various other facets of life.

It is understandable that failure of a monsoon forecast agitates the entire country. India still being a largely agriculture economy monsoon rains are important. Drinking water infrastructure of the country has such severe limitations that even one monsoon failure is not tolerable. Hence, there is a need to have a basic understanding of how monsoon forecasting is done and why it could go wrong.

Indian peninsula is a vast landmass surrounded by seas from three sides. It receives rainfall of varying intensity throughout the year. Indian summer monsoon exhibits variability on a wide variety of space and time scales. This variability is of critical importance to the agriculture sector. This intra-seasonal variability of the monsoon manifests itself as a series of wet and dry spells of weather.

The peninsula gets engulfed by monsoon current between June to September. However, the main rain bearing months of this season are July and August. During last fifteen to twenty years the monsoon has shown a normal behavior for more than a decade with years typical of drought (1987) and flood (1988) situations.

For more than a decade the monsoon prediction was done based on the “15 Parameter model”. Now, IMD is following a practice of issuing a forecast based on eight predictors for seasonal rainfall over the country as a whole. These predictors cover almost the entire land and ocean mass of the world. Like monsoon behavior is dependent upon the temperature of northwest Europe to sea surface temperature of North Atlantic to winds over North Pacific. Apart from their own model IMD also takes into account the model forecasts of other scientific organization within the country like Indian Institute of tropical meteorology, IISc etc and international organizations like World Meteorological Organization and American environmental centers. This year statistical models had suggested below normal rainfall and dynamical models had suggested above normal rainfall.

All these models have various limitations and normally the model accuracy is five to nine percent on either side. Since the monsoon season is yet to get over it would be premature to comment on the efficacy of these models. It needs to be understood that forecasting depends on the behavior of various parameters and some of them still confuse the forecaster. Few feel that there is no direct link between the El Nino and delayed monsoon but still it is an important parameter for forecasting in many other parts of the world. Other parameters like Madden-Julian Oscillation (MJO) index are useful to gauge the eastward progress of tropical rain.

IMD borne in 1875 has significant mandate beyond monsoon forecasting. It has a huge network of observatories running in few thousands all over the country, over mountains and even over oceans. It is involved in various activities from aviation foresting to ozone layer monitoring to tsunami and earthquake predictions and monitoring. It uses satellite technology, radar technology, super computers and few other state-of-art techniques for weather observations, monitoring and forecasting. Over the years it has mastered the art of cyclone prediction.

Experience this year (2009) so far, will force IMD and other organizations to have a fresh look for the efficacy of their existing models. But, at the same time it needs to be understood that the forecast could go wrong even in future too because even today we understand so little about our atmosphere. Armed-chair analysts should stop discouraging scientists with sweeping statements like ‘need to close the IMD’ just because they are not getting sufficient power to run their air conditioners!

Author Note
Ajey Lele is a New Delhi based scholar