The India Meteorological Department (IMD) has forecast ‘below normal' rainfall for the country during the second half (August-September) of the current south-west monsoon season.

This comes even as the first half (June-July) has turned out to be not so bad, with the monsoon showers being reasonably well spread, both in spatial as well as temporal terms.

According to the IMD, rainfall for the country as a whole during August-September is likely to be 90 per cent of the ‘normal' or long period average (LPA) of 435 millimetres (mm) for these two months. That makes it ‘below normal', technically defined to be between 86 and 94 per cent of the LPA.

Moreover, there is a 27 per cent likelihood of the monsoon even being ‘deficient' (below 85 per cent of the LPA) during the second half. The corresponding probabilities for ‘below normal' (86-94 per cent of LPA), ‘near normal' (95-105 per cent), ‘above normal' (106-115 per cent) and ‘excess' (above 115 per cent) are pegged at 46 per cent, 24 per cent, three per cent and zero respectively.

The IMD's quantitative rainfall forecast at 90 per cent of LPA for August-September – with a model error of plus or minus 8 per cent – would suggest a weakening of monsoon activity during the second half of the season.

Good first half

The first half had seen the country receive an area-weighted rainfall of 429.2 mm, which was 94.87 per cent of the LPA of 452.4 mm for June-July. Within that, rainfall was surplus (111.31 per cent of LPA) in June and deficient (85.57 per cent) in July.

If the IMD's 90 per cent of LPA rainfall prediction for August-September – based on its Long Range Forecast Outlook released on Monday – comes true, the 2011 monsoon season would return an overall shortfall of about 7.5 per cent (92.5 per cent of LPA).

But these overall percentages, by themselves, may not hold much meaning. For agriculture, what matters is not aggregate numbers as much as their distribution across space and time. By that yardstick, this year's monsoon has so far been quite satisfactory.

As the accompanying table shows, most of the areas that received very little rains in June – the contiguous stretch covering Gujarat, Maharashtra, North Interior Karnataka, Andhra Pradesh and Tamil Nadu – saw a revival of monsoon activity during July. As a result, there has been a considerable lowering of sowing acreage deficit for most kharif crops over the last couple of weeks.

The converse of this, however, has been that much of the North and East, which were hugely rainfall surplus in June, recorded sub-par precipitation in July. In other words, a balancing of sorts has taken place, with no region (barring maybe, Assam) going entirely dry over the two months.

No reason for pessimism

The other sliver lining is that the IMD itself does not give any specific reason for its pessimistic prognosis for August-September. The Department has, in fact, virtually ruled out the emergence of any ‘El Nino' conditions associated with monsoon failure.

According to it, the latest global forecasts “from a majority of dynamical and statistical models indicate high probability (about 80 per cent) for the present ENSO-neutral conditions (i.e. neither El Nino nor La Nina) to continue during the remaining part of the 2011 south-west monsoon season.”

That perhaps indicates the IMD's preference to err on the side of caution.

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