IMD predicts normal monsoon this year

El-Nino could emerge later but drought unlikely

 
By Dinsa Sachan
Last Updated: Saturday 04 July 2015

Despite the current spell of fluctuating weather, the monsoons this year would not be affected. This is good news for farmers because 60 per cent of agriculture in the country is rainfed.

“India will experience a normal monsoon,” Union minister of earth sciences Vilasrao Deshmuksh announced during a briefing of the India Meteorological Department (IMD) on April 26.

D Sivanand Pai, head of long-range forecasting at IMD, said there is a 47 per cent probability of the country receiving normal rainfall. This means rainfall will be 99 per cent of the long period average (LPA) — average of monsoon rainfall of 50 years. The LPA of seasonal rainfall over the country for the period between 1951 and 2000 is 89 cm. Since the prediction model is not perfect, there is a chance of an error of up to 5 per cent and rainfall may fluctuate between 94 and 104 per cent of LPA. Pai added there was a close to a quarter (24 per cent) chance of below normal rainfall. This is quite a high probability.

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Pai said La Nina was neutral this year and there is no probability of it affecting the monsoons. La Nina—an ocean-atmospheric phenomenon signified by a decrease of 3-5 degree in sea surface temperature across the Equatorial Pacific Ocean—is favourable for monsoon. El Nino, which is La Nina’s counter phenomenon, and is often accompanied by drought, could emerge later in the season, Pai said. But there is low probability of that, too, he added.

El-Nino effect

Over the years, research has shown there is an association between El-Nino and deficient rainfall. However, all El-Nino years are not deficient in rainfall. Pai says 1997 saw the strongest El-Nino phenomenon in the last century, but the monsoon rainfall that year was 101 per cent of LPA, which means it was marginally more than 89 cm. The five major droughts of the last 20 years—1982, 1987, 2002, 2004 and 2009—were accompanied by El-Nino. A research analysis between 1880 and 2004 by Krishna Kumar at Indian Institute of Tropical Meteorology (IITM) shows that in 13 instances of El-Nino occurrence, India experienced normal monsoon rainfall, while in 10 instances rainfall was below normal.

While this year’s forecast was based on a statistical model, the experimental dynamic model by IMD-IITM was also taken into account. Pai said it will be integrated for operational forecast in a phased manner.

IMD will issue the date of onset in mid-May. Another forecast in June will give a month-wise break-up of rainfall over the four-month period. Monsoon outlook for four broad geographical areas in India will also be provided.

The April forecast is based on five parameters, which include sea surface temperature over North Atlantic Sea between December and January, South Indian Ocean Sea around the Equator region, sea level pressure over East Asia, air temperature over north western Europe and volume of warm water over Pacific Ocean. Pai said, “Out of these, three factors were neutral, one favourable and one unfavourable for a normal monsoon.”



 

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