With excess rains in parts of the country bringing the overall deficit down to zero, the four-month southwest monsoon is inching closer to India Meteorological Department’s (IMD’s) prediction of normal rainfall.
As on Monday, the country received 681.3mm of rainfall compared to the normal of 674.7mm, recording an excess of 1%. Out of all the 36 sub-divisions, 21 have witnessed normal showers, while excess rainfall was recorded across eight sub-divisions, primarily in the western coast and parts of Rajasthan and Madhya Pradesh. Rainfall has, however, been deficient in seven remaining sub-divisions, which include parts of north-west India.
“When we issued the forecast in June, our assumption was that El Niño prevailing during that time would weaken further and the Indian Ocean Dipole (IOD) would turn positive. Both these analysis came correct and helped the monsoon to strengthen in the second half," said D.S. Pai, head, climate research and services at IMD, Pune.
In its first long-range forecast, IMD had predicted normal monsoon, which it reiterated in the second-long range forecast in June. It had said that the country would receive 96% rainfall of the long-period average (LPA) with a model error of 4%.
However, it had predicted below normal rains for June, due to the overarching influence of El Niño, which negatively affects the southwest monsoon. June indeed ended with a staggering deficit of nearly 33%.
The department had subsequently said that the rainfall scenario would improve during the second half of the season, with rains at 100% of LPA. Consistent with the forecast, rainfall improved in July with a deficit of just about 9%, before falling to zero in mid-August.
“The rainfall deficit has come down from 33% in June to +1% excess in last two months. But we still have to wait for one more month to find out if the season ends with a normal monsoon. Our forecast is 96% LPA with model error of +/-4 %," said IMD director general M. Mohapatra.
As per IMD’s prediction, the overall rainfall is likely to be 94% of LPA over north-west India, 100% of LPA over central India, 97% of LPA over south peninsula and 91% of LPA over north-east India, all with a model error of 8% at the end of September.
While central India received the maximum rainfall this season as predicted, the rains over southern peninsula were much higher than expected, at 106% of LPA. The states along the western coast experienced extremely heavy rains. An extreme rainfall event also triggered floods in Punjab and adjoining areas.
“There are always intra-seasonal variations that cannot be predicted four months in advance. This time, we witnessed strong low pressure activity. Systems forming over Bay of Bengal, which reached up to Rajasthan, brought heavy rains. They occasionally interacted with western disturbances and caused rainfall over north-western states," said Pai, adding: “This is part of monsoon variability every year."
The department’s monsoon forecast is aided by a dynamical model system, which has enabled IMD to predict low pressure systems forming over Bay of Bengal and the Arabian Sea seven days in advance. There is still one month to go, before the season comes to an end.
“The situation looks good as of now. It will not change drastically during the next month. The current forecast indicates that monsoon would be close to normal at the end of the season," said Pai.
The monsoon normally begins to withdraw from Rajasthan around 1 September, while October marks the end of the monsoon season.