Seasonal prediction of the Indian monsoon - A paper from Current Science

This paper published in Current Science presents the results of the national project on ‘Seasonal Prediction of the Indian Monsoon’ (SPIM), which involved a comparison of the skill of the atmospheric models used in the country for prediction of the summer monsoon, in simulation of the year-to-year variation of the summer monsoon rainfall over the Indian region for 1985–2004.

The article argues of the importance and relevance of presenting the results of this first national project on simulation of the Indian summer monsoon by atmospheric models, in the context of the decision by the Ministry of Earth Sciences, Government of India to launch a national ‘Monsoon mission’ for improving the forecasts with dynamical models, which can be said to be a logical follow-up of the SPIM project.

SPIM was conceived in response to the need for an objective assessment of the skill of the atmospheric models in the country, in the simulation and prediction of the Indian summer monsoon rainfall (ISMR). In this study, simulation of interannual variation of ISMR, by five AGCMs at different institutions in the country was assessed. In addition, an attempt was made to understand the possible cause of the errors in these models. Two sets of runs were made for this purpose.

In the first set, AGCMs were forced by the observed SST for May–September for 1985–2004. In the second set, runs were made for 1987, 1988, 1994, 1997 and 2002 forced by SST which was obtained by assuming that the April anomalies persist during May–September. The results of the first set of runs showed that, as expected from earlier studies, none of the models were able to simulate the correct sign of the anomaly of ISMR for every year.

However, amongst the five models, PUM simulated the correct sign in the maximum number of years. It was found that the SFM model had the maximum skill in the simulation of the extremes (i.e. droughts or excess rainfall seasons). The basic results of this study helped to develop some insight into the ‘how and why’ of the simulation of the interannual variation of monsoon rainfall by these models. Such an understanding is a necessary prerequisite for improvement of the models, argues the article.

The article ends by arguing that, in the past few years, there has been a remarkable increase in computational resources and network connectivity in India. At present, in the country as a whole, there is considerable expertise in modelling as well. The national Monsoon Mission, which envisages harnessing of all these resources, would be a far more ambitious effort than SPIM.

While SPIM involved assessment of the performance of some AGCMs in the simulation of monsoon variability, the Monsoon Mission envisages research and development of both atmospheric and coupled ocean– atmosphere models for improvement in the accuracy and reliability of prediction of the monsoon. Given the enormous impact of monsoon on our agriculture and economy, it is important to address this challenging problem and make the mission successful.

Download the paper here.