Rain hopes

New Delhi, April 18: South Asia is likely to receive normal monsoon rainfall this year, but parts of India’s north-west grain belt and the Northeast may have to contend with below normal rain, a group of international weather scientists has said.

India’s national weather agency plans to deliver its long-range forecast of the monsoon on Tuesday, but a consultation exercise by scientists from India and nine other countries has generated independent predictions for the South Asian monsoon in 2011.

Their consensus statement has said the monsoon rainfall over South Asia as a whole is likely to be within the normal range — within 10 per cent of the long-period average — despite portents of sea surface temperature anomalies in the Indian Ocean that tend to weaken the monsoon. It has predicted “an enhanced likelihood of below normal rainfall conditions over the northwesten parts and some northeastern parts of South Asia”.

The assessment has assigned a 45 per cent probability that India’s southern peninsula, Sri Lanka and the Andaman and Nicobar islands will receive above normal rainfall — a quantum of rain greater than 110 per cent of the long-period average.

A vast territory across central, eastern and western India has been assigned a 40 per cent probability of receiving normal rainfall. The assessment involved weather forecasters from India and other South Asian countries, as well as France, Japan, Korea and the US.

Their statement says current weather observations indicate that sea surface temperature anomalies linked to a phenomenon called Indian Ocean Dipole are likely to form during the second half of 2011.

These anticipated changes tend to weaken the monsoon. However, since they are likely to evolve only towards the close of the monsoon season, they may not have much impact on the monsoon circulation, at least during the early part of the monsoon season.

A senior India Meteorological Department (IMD) scientist said this exercise is “completely independent” of the process that goes into developing its own long-range forecast of the monsoon which is due tomorrow. “This gives us a broad picture for South Asia. But the (IMD) forecast may not differ too much from this picture,” the scientist who requested anonymity told The Telegraph.

The South Asian monsoon consultations — the second since they began in 2010 — are intended to bring the best forecasting brains involved in studying monsoons, a meteorologist at IMD, Pune, said.

The scientists have cautioned that there is a “large uncertainty” in the forecasting information, partly because of a weakening of the weather phenomenon called La Nina — the cooling of sea surface temperatures in the Pacific Ocean. In the past, a strong La Nina has been linked to a good monsoon over India. But the weakening this year is expected to occur only towards the close of the monsoon season.

Another source of uncertainty is a higher-than-normal snow cover in the northern hemisphere between October 2010 and March 2011. “This may result in reduced land-sea heat contrast in the Asian monsoon region and thus may slightly weaken the monsoon circulation,” the consensus statement said.

India had experienced a normal monsoon last year — 102 per cent of the long period average — with significant regional variations. The northwestern region and the southern peninsula had both received above normal rainfall — 112 per cent and 118 per cent. But the Northeast had received below normal 82 per cent.