The forecast by India Meteorological Department (IMD) on June 2 of a deficient monsoon has set off fears of a drought for the second successive year. The stock market has panicked amid fears of distress in agriculture, a drop in farm incomes and higher inflation.

But how reliable is the IMD forecast? A study of IMD data on annual forecasts and actual rainfall in the last 25 years shows that the agency has been right (tolerance of +/- 4 per cent) on only eight occasions.

Over the last 10 years, beginning 2005, IMD has been particularly conservative in its estimates and has tended to err on the side of caution.

Not once in the last 10 years has the IMD forecast rainfall in excess of 100 per cent of the Long Period Average (LPA) — but there were four occasions when that actually happened: 2007, 2010, 2011 and 2013.

There were just three occasions in the last 10 years when actual rainfall was lower than the IMD forecast. Two of these — 2009 and 2014 — were drought years, when the actual precipitation was just 88 per cent of LPA.

Among the four meteorological regions, northwest and central are the most important from the perspective of agricultural production. A study of the spatial distribution of rainfall shows that the northwest region has recorded excess rainfall in July — the key month for kharif sowing — only in two of the last 10 years: 2005 and 2010. The region, comprising Rajasthan, Punjab, Haryana, Himachal Pradesh, Delhi and Uttarakhand, has recorded a rainfall deficit for 80 per cent of the period under study but yet output of foodgrain has not suffered.

Interestingly, the northwest region, important for rice in the kharif season, recorded deficient July rainfall even when there was an overall excess in the country. This happened in 2007, 2011 and 2013. It appears that agriculture in this important region is resilient to the monsoon thanks to good irrigation facilities.

The central region, comprising Madhya Pradesh, Gujarat, Maharashtra, Chhattisgarh and Odisha, which is important for pulses, oilseeds and coarse cereals, has fared even better than the northwest, recording excess July rainfall even in the drought years of 2009 and 2014. The central region states have seen excess rainfall in six out of the last 10 years.

On Friday, the IMD declared the onset of the monsoon over Kerala, with rains arriving in the southern state four days late.

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