India Meteorological Department (IMD) has blamed the sudden emergence of La Nina weather phenomenon over the Pacific ocean for its 2011 monsoon forecast going haywire, but also accepted that its Long Range Forecast for the year’s southwest monsoon underestimated actual rains.
“Particularly bad” is how the country’s premier weather forecaster described its forecast issued for the past two months of the June-September season. The total actual rainfall in the country during the entire season this year was around 101 per cent of long period average (LPA), while the Met department’s second forecast said rains this year could be “slightly below normal” at 95 per cent of the LPA — with a model error of plus, minus four.
Actually, the second forecast was issued on June 21, when the monsoon had already entered the mainland.
The actual rains were around two per cent more than the error limits mentioned in the second forecast. Interestingly, the IMD’s first-stage forecast issued on April 19 ended up to be more accurate than the second one, as rains actually turned out to be within the range given in the first forecast.
“Most of the operational long-range forecasts issued for 2011 southwest monsoon season were underestimating actual rainfall situation, and therefore not very accurate,” the Met department said in its end of-season report for 2011 southwest monsoon. It wasn’t just the overall prediction; even the Met’s month-wise and region-wise forecasts were way off the mark.
In some cases, they not even within the error limits.
It said rainfall in July, August and September would be 93 per cent, 94 per cent and 90 per cent of the LPA, with the model errors ranging from plus-minus 9 for July and August to plus-minus 15 for September. But in reality, the actual rains in July was 85 per cent of the LPA, while in August and September it was 110 per cent and 106 per cent of the LPA, respectively. In short, the Met overestimated July rains and grossly underestimated August and September rains.
Region-wise, the Pune-headquartered Met said its forecast was two per cent over the error limit in Northwest India and one per cent below in Northeast India.
However, in the central state of Madhya Pradesh and the west’s Maharashtra, actual rainfall was a staggering seven per cent more than the error limit mentioned in the forecast. Only rains in southern India were within the IMD’s forecast limits.
