Context: The monsoon is over but several parts of the country are still receiving rainfall. Delhi, Kerala, Madhya Pradesh and Uttarakhand, for example, have received very high rainfall, resulting in loss of life and property in some places.
Scientists say a combination of factors — delayed monsoon and development of low-pressure areas at multiple places — have resulted in these rainfall events at several places.
Are October rains unusual?
Rain in October is not unusual.
October is considered a month for transition, during which the southwest monsoon withdraws and gives way to the northeast monsoon that largely affects southern peninsular India, mainly on the eastern side.
Western disturbances, which begin to have significant interference in local weather over the extreme northern parts of India, commonly cause either rain or snowfall.
Since second week of October, Ladakh, the higher reaches of Kashmir and Uttarakhand have reported the season’s first snowfall.
However, two low-pressure systems were active simultaneously, one each over the Arabian Sea and the Bay of Bengal regions. Collectively, these triggered severe weather events over Kerala, Tamil Nadu, Andhra Pradesh, Telangana, Delhi, Madhya Pradesh, Uttarakhand, Odisha and West Bengal.
Delayed monsoon withdrawal
The four-month southwest monsoon season normally withdraws completely by early October. During the withdrawal phase, it causes thunderstorms and localised heavy rainfall.
This year, however, the withdrawal began only on October 6 against a normal of September 17.
So far, the monsoon has withdrawn completely from the Western, Northern, Central and Eastern India regions. But it remains active over the southern peninsula. Thus, Kerala, Tamil Nadu, Telangana, Karnataka and Andhra Pradesh have had significant rainfall during the last 10 days.
Normally, by mid-October, the monsoon winds reverse their direction of flow from the southwest to the northeast.
“Even though the easterlies are beginning to replace the westerlies, the former is yet strengthen and fully establish. The easterly winds indicate the arrival of the northeast monsoon.
This year, conditions for the onset of the northeast monsoon are expected to develop around October 25.
Due to climate change, there is definitely a rising frequency in the extreme weather events round the year. But these specific occurrences of heavy to very heavy rains that we are seeing right now can be attributed to the formation of low-pressure systems.
Whenever there is a low-pressure system, depending on its strength, it results in heavy to very heavy rainfall activity. In addition, when a low-pressure system interacts with western disturbance, further intense rainfall occurs,
