“We are looking to capture these recent changes in our new analysis. A committee is studying these changes so that we can review the dates. If required, we will do it from next year," said M. Mohapatra, director general of meteorology at IMD, New Delhi.
The southwest monsoon normally makes an onset over the southern coast of Kerala around 1 June, marking the beginning the four-month rainy season that accounts for more than 75% of India’s annual rainfall. The monsoon usually begins to withdraw on 1 September, according to the normal dates assigned in the 1960s.
For the last few years, its withdrawal is beginning later than usual. Except for 2015, when it started withdrawing on 4 September, the retreat of the monsoon is starting towards the end of September. This year, the monsoon began retreating on 8 October.
“If the monsoon withdraws late, it means the rainfall is continuing till October and winter could set in suddenly. If the monsoon season is indeed becoming longer, farmers will have to judiciously utilize that period," said Mohapatra.
The withdrawal of the southwest monsoon is normally completed by 15 October, after which the arrival of the northeast monsoon, or the winter monsoon, begins. However, this year the withdrawal of the southwest monsoon was completed on 16 October with the simultaneous arrival of the northeast monsoon.
Scientists are trying to determine whether the shift is a permanent trend. “Apparently, 2010 onwards, the shift is clearly visible. We need to see how significant this is in a statistical sense to come to a conclusion," said K.J. Ramesh, a former chief of IMD.
There are concerns that an extended monsoon could lead to late harvest and delay in the sowing of rabi crops. “Late cessation of rain will improve soil moisture, which favours rabi crops, especially wheat. However, yield of crops such as mustard could go down as it grows well if sown early and needs more time," said Ranbir Singh Rana, agronomist at the Himachal Pradesh Agricultural University, Palampur.
The reduced transition time between the monsoon and winter could especially affect agriculture in hilly areas, where winter could set in early and a sudden drop in temperature could hurt farming.
“Rabi crops need a temperature of 16-20°C for plantation. If winter sets in early, there could be changes," added Rana.