In a candid admission, India Meteorological Department (IMD) has said that its forecasts for the just-concluded South-West monsoon have been ‘mostly' off the mark.
An end-of-the-season report put out by the IMD seemed to blame the repeat La Nina in the east equatorial Pacific for the sudden surge in rainfall, especially during the second half of the monsoon.
A La Nina has been known to bring about normal to above-normal monsoon in India, though without a direct cause-effect relationship. A typical play-out of the scenario was on show during the 2010 monsoon as well.
La Nina effect
But, according to a leading meteorologist who wished not to be named, IMD should also have taken into account the fact that La Nina events have had a tendency to repeat themselves, though not always to the same levels of intensity.
This was not done until it was too late, and this could have made a big difference in the ultimate analysis, the meteorologist told Business Line , even as he admitted that long-range monsoon forecasts are proving beyond the number-crunching abilities of the best weather models.
The main reason for the underestimation of the forecasts, particularly those issued for the second half of the monsoon season ( August to September), was due to the increased rainfall activity in the second half of the season in association with the sudden re-emergence of the La Nina conditions over equatorial Pacific, the IMD report added.
It was only in Peninsular India that the forecast rainfall amount fell within the model error margin that the IMD has allowed for itself (see graphic).
Considering the three other broad geographic regions of the country, the seasonal rainfall was expected to be 97 per cent of the LPA (long period average) over north-west India, 95 per cent over central India and 95 per cent over north-east India, all with a model error of eight per cent on either side. But actual rainfall overshot the forecast amount in two cases, and was under par in the north-east.