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Tuesday, January 25, 2022

How south India recorded its wettest November this year

The number of very heavy rain events jumped from 26 to 168 in the last five years, whereas extremely heavy rains recorded in November 2021 were 11 as opposed to just one in 2017, indicating over a ten-fold increase. 

Written by Anjali Marar | Pune |
Updated: December 5, 2021 2:17:55 pm
Commuters wade through a waterlogged street after heavy rain in Thiruvananthapuram (PTI Photo)

An active northeast monsoon season, which uncharacteristically saw five consecutive low-pressure systems develop in the North Indian Ocean Region, triggered heavy rains across southern India in recent weeks. In October, Kerala alone received record rainfall of 589.9 mm (94 per cent surplus), its highest in 122 years. Rains have continued over southern India since August and more showers are in store in December.

Wettest November since 1901

This year, most of south India has not seen a break from rainfall activity since August. The southern peninsula has witnessed an extended monsoon season with the last four months seeing little respite. Between October 1 and November 30, Kerala has received the most surplus rainfall at 115 per cent, followed by Puducherry (106%), Karnataka (103%), Tamil Nadu (83%) and Andhra Pradesh (47%).

This is due to the delayed exit of the southwest monsoon in October, immediately followed by the commencement of the northeast monsoon on October 27. The continuing rainfall activity nearly peaked in November over Tamil Nadu, Kerala, Puducherry and coastal Andhra Pradesh, as a result of which south India experienced its wettest November since 1901, officials of the India Meteorological Department (IMD) said.

This November, Andhra Pradesh, Tamil Nadu, Puducherry, Kerala and south interior Karnataka collectively received 316.2 mm, which is 149 per cent higher than the Long Period Average (LPA) of 117.5mm in November.

Rise in heavy, very heavy rainfall events

Even though the northeast monsoon brings rainfall over southern India, November has seen an unprecedented number of heavy rainfall events.

Chennai rains, Tamil nadu rains, Tamil Nadu floods, Chennai flood, Stalin, MK stalin, Chennai, tamil nadu, Chennai rainfall, Tamil nadu rainfall, Indian express, indian express news, chennai news, tamil nadu news The rainfall over south India was mainly triggered by strong and moist easterly winds and consecutive low-pressure systems formed mostly in the Bay of Bengal.

The number of heavy rainfall events increased four-fold between 2017 and 2021. The number of very heavy rain events jumped from 26 to 168 in the last five years, whereas extremely heavy rains recorded in November 2021 were 11 as opposed to just one in 2017, indicating over a ten-fold increase.

“There has been a significant rise in the number of heavy and very heavy rainfall events. In November this year, most of these were concentrated in south India, mostly Tamil Nadu and coastal Andhra Pradesh,” said Mrutyunjay Mohapatra, Director General, IMD.

BOX : Rainfall events in November

Year Rainfall category
Heavy (64.5 to 115.5mm in 24 hrs) Very heavy (115.6 to 204.4mm in 24 hours) Extremely heavy (above 204.5mm in 24 hours)
2021 645 168 11
2020 247 98 11
2019 116 24 00
2018 135 36 04
2017 139 26 01

Source: IMD

What caused the rains
The rainfall over south India was mainly triggered by strong and moist easterly winds and consecutive low-pressure systems formed mostly in the Bay of Bengal. Last month, five low pressure systems developed in the North Indian Ocean region (Bay of Bengal and Arabian Sea together). Of these, two intensified into depressions.

“The climatological normal for the number of low-pressure systems is anywhere between 2.8 to 3 in November,” said RK Jenamani, senior official at IMD’s National Weather Forecasting Centre, New Delhi. But 2021 is the third year since 1990 when more than five low-pressure systems have developed in the North Indian Ocean region during November, the other two years being 1994 and 2015.

In its forecast for December, the Met department has said that the monsoon will be ‘good’ over south India and more rains are in store throughout the month.

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