The India Meteorological Department on Friday forecast normal rainfall — at 98 per cent of the long period average (LPA) of 89 cm, with a model error of plus or minus five per cent — during the coming south west monsoon season. The forecast is for the country as a whole and for the entire season, which is from June to September.
Announcing it at a press conference here, Union Science and Technology Minister Jaipal Reddy said monsoon forecast models showed that there was 46 per cent probability for the monsoon rainfall to be between 96 per cent and 104 per cent, and 27 per cent probability for it to be between 90 per cent and 96 per cent.
The probability of the monsoon being deficient (below 90 per cent of LPA), above normal (104 to 110 per cent of LPA) or excessive (over 110 per cent of LPA) was very small, he said, and added: “It is most likely to be between 96 and 104 per cent.”
Asked whether a negative Indian Ocean Dipole event, which could have an adverse impact on the monsoon, could develop in coming months, Ministry of Earth Sciences secretary Shailesh Nayak said international models forecast it would only be a weak event, reaching its maximum peak only in Autumn, and therefore was unlikely to affect monsoon.
In any case the IMD, he said, would keep a close watch on the situation so that the government could take timely remedial measures just in case conditions hinting at a strong IOD event developed.
. As regards the phenomenon of El Nino, which could also disrupt the monsoon, Mr. Nayak said borderline El Nino conditions were observed between July and September. Subsequently, the situation returned to normal and was remaining so. Latest forecasts for various models show that the conditions are expected to remain normal in the coming months too till the end of the monsoon season.
The monsoon forecast issued on Friday is based on a statistical model constructed with five parameters that have been historically found to have a bearing on Indian monsoon. The parameters are: sea surface temperatures over the North Atlantic Sea during December and January, and over equatorial south Indian Ocean Sea during February and March, the mean sea level pressure over East Asia during February and March, surface air temperature over north-west Europe in January and the volume of warm water over equatorial pacific during February and March.
It has, among other things, taken into account experimental forecasts prepared by several national institutions, including Indian Institute of Science, ISRO’s Space Applications Centre, CSIR’s Centre for Mathematical Modelling and Computer Simulation, and Centre for Development of Advanced Computing, Pune.
In addition, forecasts prepared by several international agencies such as National Centres for Environmental Prediction, USA, Meteorological Office, UK, Meteo France, and World Meteorological Organisations, the leading centre for long range forecast multi-model ensemble, were consulted.
Asked why the IMD was still basing its forecast on a statistical model, when developed countries were using dynamic models, Mr. Nayak said an experimental forecast was also generated using a dynamic model being developed under the Monsoon Mission launched by the Ministry recently.
The model has forecast higher rainfall at 104 per cent of LPA, with model error of plus or five per cent.
But, the IMD, he pointed out, was not going by that forecast as it was more confident of the statistical model’s forecast. “The dynamic model is under development. Hopefully, we should be able to improve its confidence level to be better than that of the statistical model over the next four to five years.”
