India Met Department (IMD) appears to have premised its ‘normal monsoon’ forecast for 2017 on evolving conditions in both the Pacific and Indian Oceans.
For now, the projections depict a 38 per cent probability for near-normal monsoon, according to the the first stage forecasts issued in New Delhi on Tuesday.
The warming up of the East Pacific, or the status with respect to El Nino, has been known to influence the Indian monsoon, though not in a direct cause-effect mode. While a number of El Nino years have returned a deficit monsoon, others have either taken the Pacific phenomenon in their stride or returned normal-to-excess rainfall.
When things reverse in the Pacific (eastern part cools down and western part warms up), it’s called a La Nina, which has generally been associated with a good Indian monsoon. In the same fashion, the Indian Ocean too witnesses warming anomalies in cyclical turns — called the Indian Ocean Dipole (IOD) — with known implications for a concurrent Indian monsoon.
When the western part of the ocean warms up relative to the east, it is called the positive IOD phase, which favours the Indian monsoon (as is likely the case this year).
The reverse is called the negative IOD phase, when the eastern part of the ocean warms up more than the west. This drains away the moisture from over India and affects the monsoon.
The IMD is carefully monitoring the developments in the two oceans. It expects that more information on El Nino and IOD will be available in time for forecast updates in June.
Improved predictionsMeanwhile, it claims to have made improvement in its forecasting capabilities over the last 13 years ending in 2015 (2003-2015) over those of the same number of preceding years (1990-2012).
The average absolute error during the period 2003-2015 was 5.92 per cent of the long period average (LPA), compared to 7.94 per cent in 1990-2012.
According to information tabled in Parliament, the IMD has been carrying out monsoon prediction with ‘reasonable accuracy’. The success rate of forecasts since 1988 has been high.
During 1988-2008, the forecasts were qualitatively correct in 19 years, or 90 per cent of the time. The exception was in 2002 and 2004, both drought years.
However, in some years, the forecast error (difference between actual and forecast rainfall) was more than 10 per cent.
The 2002 drought was due to exceptionally low rainfall in July (46 per cent of LPA) caused by unexpected sudden warming of the Equatorial Pacific that started in June. The exceptionally deficient rainfall of July 2002 was not predicted by any organisation in India or abroad.
There are inherent problems in statistical models, and are being faced by forecasters worldwide, the IMD had said. Therefore, it is not feasible to expect 100 per cent success in forecasts based on statistical models.