DNA Explainer: Why it's raining so much in October - Isn't monsoon over yet?

India Meteorological Department (IMD) says India's monsoon season is over but is it? Several parts of the country are reeling under heavy rainfall in October which is considered a month for transition.

In October, the southwest monsoon withdraws completely from most of north India and gives way to the northeast monsoon that largely affects southern peninsular India, mainly on the eastern side.

This is the second-most delayed withdrawal of the southwest monsoon since 1960. The four-month southwest monsoon season normally withdraws completely by early October. In 2019 it started on October 9. 

But despite this, October has emerged as the wettest month for Delhi since 1960. States like Kerala, Uttarakhand and Madhya Pradesh have received very heavy rainfall in the last few days which is unusual.

In Uttarakhand, nearly 50 people have died due to landslides triggered by heavy rainfall, which also blocked key highways. However, the heavy to very heavy rains are not due to the monsoon retreat.

So what is the reason behind this sudden downpour? According to IMD, an unusual western disturbance swept across the northern plains and slammed into the Himalayan ranges triggering heavy rainfall.

Reasons behind offseason rainfall

An unusual western disturbance that originates in the Mediterranean region swept across the northern plains and slammed into the Himalayan ranges.

Scientists say that a combination of delayed monsoon and the development of low-pressure areas at multiple places is causing rainfalls at several places.

The rains are the result of a unique weather phenomenon developed over North-West India due to a low-pressure area created in the Bay of Bengal.

The heavy to very heavy rainfall in the month of October results from an interaction of western disturbances that bring rainfall and snow in North-West India.

The western disturbances result in a low-pressure area created over the Bay of Bengal bringing moisture-laden air to the North-West region of the country.

The interaction of these two phenomena has led to heavy rainfall in parts of North India.

The four-month southwest monsoon season normally withdraws completely by early October. During this phase, it causes thunderstorms and heavy rainfall.

This year, however, the southwest monsoon withdrawal began only on October 6 against a normal of September 17. 

Conditions for the onset of the northeast monsoon are expected to develop around October 25 this year.

Last week at least two low-pressure systems remained active along the east and west coasts and over central India, bringing rains over large parts of the country.

Climate change has also impacted the weather. Climate change has increased the moisture-holding capacity of the atmosphere all around the world.