The unexpected spell of good rainfall in the last couple of weeks, which promised to ride over predictions of a bad monsoon this year, is over and the country is entering a dry phase now, weather scientists have said.
The good rainfall this month — more than 25 per cent above normal till June 25 — was triggered by what is known as Madden Julian Oscillation (MJO). The eastward moving rain-bearing wind system along the tropics impacts monsoon systems around the world, including the southwest monsoon that brings rain over the Indian sub-continent.
“The MJO was passing through the Indian Ocean. When this happens, it usually results in good rainfall over India. But the MJO has gone past now and it is out of phase. So we will see a reduction in rainfall. In fact, rainfall has already gone down in the last few days,” D Sivananda Pai of the Indian Meteorological Department said.
Most regions in India have seen a sharp decline in rainfall after June 26, recording below normal rain. Only eastern India, particularly Bihar and eastern Uttar Pradesh, and the northeastern region have been receiving good rainfall in the past few days. These areas had been relatively dry when the rest of the country was enjoying good rainfall.
Thanks to the MJO, the monsoon covered the entire country at least two weeks in advance.
“We are entering a dry phase now. The Indian monsoon oscillates between wet and dry phases every few weeks. In a good monsoon year, there are more wet phases than dry phases, while in a drought year, the dry phases dominate over wet phases. MJO is one of the factors that influences these phases,” said J Srinivasan of the Divecha Centre for Climate Change at the Indian Institute of Science, Bangalore.
Forecast for the next few days shows that only northeastern India and some parts of eastern and central India, besides Kerala, are likely to receive widespread rains. The rest of the country is expected to receive only scattered or isolated rainfall in the coming days.
The good rainfall in the last few weeks had raised hopes that monsoon might be much better than the forecasts had showed. The IMD, in its long-range forecast last month, had predicted that the country as a whole was likely to get only 88 per cent of normal rainfall this monsoon season.
Pai said there was no need to revise the forecast after the unexpected rainfall.
“We are likely to see a greater impact of El Nino as well in the coming few weeks. El Nino has been gaining in strength and will affect the monsoon,” Pai said.
El Nino refers to an abnormal warming of sea surface temperatures in the equatorial Pacific Ocean. There is a strong correlation between an El Nino event and a weak monsoon.
In addition, there is evidence that MJO has an influence on El Nino. It can contribute to the speed of development of El Nino, and affect its overall intensity.
Pai said the impact of MJO on the monsoon rains could not be seen in earlier forecasts because long-range prediction of the system is not yet possible. “We can understand its behaviour four or five days in advance, but it is not possible to do so over a month,” he said.