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‘Normal’ monsoon with a rider

- Shadow on grain basket
Clouds gather in Guwahati on Friday. (AFP)

New Delhi, June 22: The national weather agency today predicted that India is likely to receive normal monsoon rainfall this year despite a 24 per cent rainfall deficit so far and portents of below normal rains creeping into its forecast.

India will “most likely” receive normal rainfall this year, but the northwestern grain basket states could face a rain deficit, the India Meteorological Department said in a revised, and mildly downgraded, forecast for the 2012 monsoon.

The IMD has predicted a 42 per cent probability that the monsoon rainfall would be within the normal range of 96 to 104 per cent of the long-period average, a bit lower than the 47 per cent probability it had predicted in April.

The rainfall for the country as a whole is likely to be 96 per cent of the long period average of 89 cm, the IMD said. The new forecast suggests that rains in July and August would have to make up for the deficit observed in June and one that may occur in September.

After a four-day delay in onset, the monsoon has been weak throughout June — the country has received 24 per cent lower than normal rainfall since June 1. Weather scientists had attributed the weak onset to a Pacific typhoon.

A typical monsoon-season low pressure system or depression over the northern Bay of Bengal that can deliver good rainfall over the subcontinent has not formed this year, a senior weather scientist said.

“The sea surface temperatures (SST) in the northern Bay of Bengal need to become favourable for such systems to emerge,” the scientist who requested anonymity told The Telegraph.

The northern Bay of Bengal SST needs to be slightly warmer than average and higher than the SST in the equatorial Indian Ocean region. But the northern Bay of Bengal SST last week was 0.5C lower than average, and the equatorial Indian Ocean SST was 1C above average.

The IMD has also predicted that rainfall in northwest India is likely to be below normal — 93 per cent of the long period average, while the southern peninsula, eastern India and central India are likely to receive normal rainfall.

Farmers cultivating crops such as paddy, pulses, groundnut and soyabean, among others, rely on the monsoon rainfall. The IMD has predicted near-normal 98 per cent rainfall in July and 96 per cent rainfall during August — both months crucial for agriculture.

“We expect impact on agriculture to be near normal,” Ashwani Kumar, the minister of state for earth sciences, said today, announcing IMD’s revised forecast. “All regions except the northwest are likely to receive normal rainfall — and Punjab, Haryana and western UP are irrigated."

The revised forecast predicts an 84 per cent probability of normal, below normal or above normal rainfall, but simultaneously predicts a 50 per cent probability of below normal or deficient rainfall, and a 50 per cent probability of normal, above normal, or excess rainfall. (See chart)

Although the monsoon has advanced over the southern peninsula, central and eastern India, the rainfall has been deficient in most regions. Bengal has received 39 per cent lower than normal rainfall. In Bihar the deficit is 48 per cent and in Jharkhand 59 per cent.

Weather scientists have predicted a slight warming of sea surface temperatures in the eastern Pacific Ocean — the phenomenon called El Nino — during the second half of the monsoon season. In the past, El Nino events have been associated with poor monsoon rainfall.

“Forecasts indicate a 0.5C to 0.7C warming by early September,” said Laxman Singh Rathore, the director general of the IMD. “But there is always a time lag between El Nino and an impact on the monsoon — if at all,” he said.

“The impact of El Nino, if any, is expected only during September,” said D. Sivanand Pai, the head of the long range forecasting division of the IMD, Pune.

A senior meteorologist said usually a rainfall deficit of 10 per cent or higher becomes “significant” from the point of view of agriculture and the economy. The classification of normal, below normal and above normal represents an attempt to refine the forecasting process, he said.