Forecast Flaws

Spot-on monsoon predictions leave out details that can hinder crop prospects

In the last week of March, private weather forecasting agency Skymet Weather Services predicted that rainfall this monsoon would be below normal. In early April, India Meteorological Department ( IMD), the country’s 142-yearold national weather bureau, came up with its assessment – rainfall would be normal.

In a country where about 54 per cent of the gross cropped area is rain- fed, and agriculture and allied sectors contribute 17 per cent of its gross value added or GVA (`20.93 lakh crore at current prices during 2015/16), any comment on the monsoon calls for an instant response.

Right after the Skymet prediction, Ritesh Kumar Sahu, an analyst with Angel Commodities Broking, pointed out a surge in guar gum futures prices, attributing it to the “anticipation that monsoon may be weak on account of El Nino, coupled with growing export demand from the country”.

Understandably, the IMD forecast was greeted with relief. Industry chambers said it would mean modest food inflation and vibrancy in India’s economic growth. Buoyed by the official forecast, Radha Mohan Singh, Union Minister for Agriculture and Farmers Welfare, announced a food grain production target of 273 million tonne ( MT) for 2017/18.

A closer look suggests that the difference between the two predictions is not much. While Skymet has predicted that the Southwest Monsoon 2017 is likely to be below normal at 95 per cent of the long period average ( LPA) of 887 mm, the IMD says it is likely to be 96 per cent of the LPA. Both agencies have given a standard error margin of +/-5 per cent.

So, how reliable are these predictions?

In 2016, the cumulative monsoon rainfall during June-September was 3 per cent lower than the LPA, and it was well within the predictions. But here is a more detailed account of rainfall in the four broad geographical divisions during the period: Rainfall was 6 per cent higher than the LPA in Central India, 11 per cent lower than the LPA in East and Northeast, 8 per cent lower in South Peninsula and 5 per cent lower in North West India.

Out of the 629 districts, 111 (18 per cent) had excess rainfall, 314 (50 per cent) saw normal rainfall, 189 (30 per cent) received deficient rainfall and 15 (2 per cent) districts had scanty rainfall during the period. During the post-monsoon season ( October 1- December 31, 2016), the cumulative rainfall, as a whole, was 45 per cent lower than the LPA, which explains the drought relief demands from some states.

It shows that the long-term predictions, even if accurate, do not foresee distribution patterns. However, a lot depends on when, where and with what intensity the rain will fall. Late arrival of monsoon, early withdrawal, intensity as well as the distribution pattern can affect the overall growth of agriculture and allied sectors. Therefore, in spite of the IMD’s positive predictions, the ministry of agriculture is busy readying district-level contingency plans to minimise the impact of a bad monsoon.

THE IMD also provides weather-based agriculture advisories to farmers. Such efforts are laudable, but it should be done at a sub-district level. The closer you are to the farm, the better the analysis. ~