Rainy October

Subject – Geography

Context – The monsoon is over but several parts of the country are still receiving rainfall.

Concept –

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 in the last few days, resulting in loss of life and property in some places.
- Delhi has just had one of its wettest 24-hour periods in several decades.
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.
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 late last week, Ladakh, the higher reaches of Kashmir and Uttarakhand have reported the season’s first snowfall.
Last week, 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 So far, the monsoon has withdrawn completely from the Western, Northern, Central and Eastern India regions.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.
When a low-pressure system interacts with western disturbance, further intense rainfall occurs.
The Western Ghats, northeast and central India are known as high-rainfall receiving regions. However, in recent years, it has been noted that intense spells during a short time span are increasingly becoming frequent.

Extreme rainfall in Kerala

A low-pressure system that formed in the east-central Arabian Sea moved and sustained over Kerala between October 15 and17.
Simultaneously, another low-pressure system prevailed over the north Andhra Pradesh coast and southern Odisha.
The interaction between them strengthened the southwest winds which brought extreme rainfall over central and southern Kerala during the last weekend.