Climate crisis in North East India: Why are rainfall patterns changing?

Synopsis: Climate change is causing increased variability and unpredictability of rainfall in the North East region of India.

Introduction

The climate of North East India is changing: Rainfall patterns over the region in the last century have considerably changed, resulting in its overall drying up. The India Meteorological Department’s September forecast stated that normal to below-normal rainfall was most likely to continue over many areas of northwest and northeast India.

Why is the rainfall pattern changing? 

Climate change causing drying up of land: An aspect of warming that influences rainfall is drying of the land, which increases the frequency and intensity of dry periods and droughts. An increase in moisture and the drying up together change the rainfall patterns in unpredictable ways.

Increased snowfall in the Eurasian region also impacts monsoon rainfall in North East India. Excessive snowfall in Eurasia causes cooling of the atmosphere of the region, which triggers events eventually leading to a weak summer monsoon season there.

Sea surface temperatures: A study has also attributed a decrease in rainfall to sea surface temperatures over the subtropical Pacific Ocean, which vary in a cycle and each phase of which lasts a decade. The peak comes every 20 years and is known as the Pacific Decadal Oscillation (PDO). As per a study, PDO is being influenced by global warming as it decreases the difference of temperatures among the layers of the ocean. The peak of PDO will change from 20 to 12 years, which may have an impact on the monsoon rainfall in North East India.

These factors may be at play in the north-eastern region of India.

Also, one cannot be sure about the exact impact of climate change on the rainfall in the region for the lack of data and credible long-term research on the same. This is because there is no data collection infrastructure.

What is the future climate scenario for the North East region?

The future climate scenarios look bleak for the region.

Inc in temp and rainfall: They show an increase in temperatures and in rainfall, in contrast with the evidence of a decrease in rainfall over the past century. Environment Ministry has projected that temperatures in the region will rise by 1.8-2.1 degrees Celsius by the end 2030. Annual mean rainfall can rise by 0.3-3 per cent in the same period.

In Assam, the Indian state most vulnerable to climate change, models predict an increase in temperature of 1.7-2.0 degree Celsius between 2021-2050.

What are the implications of a changing rainfall pattern?

A changing rainfall pattern, especially during the monsoon season, has the following impacts:

-Affects the flow of rivers: There is some evidence of the changing course of rivers from several districts in Assam such as Lakhimpur and Dhemaji, where the Subansiri, Dibang (tributaries of Brahmaputra) and Brahmaputra rivers are changing courses in unexpected ways. In Arunachal Pradesh, the Papum Pare district has also been affected by the changing course of the Dikrong river.

Extreme rainfall events being caused by global warming trigger a cascade of events such as accelerated soil erosion along the hill slopes devoid of forest cover. This increases the surface run-off of rivers and changes their course.

The new courses taken by the rivers are often the ancient paleo-channels that it has abandoned for centuries and where people have settled to avoid flooding.

-Extent of snow cover and

-Health of mountain springs

All this, in turn, has an impact on livelihoods, especially agriculture and fishing, forest flora growth, animal and bird habitat (and behaviour), and other ecosystem aspects.

Source: This post is based on the article “Climate crisis in North East India: Why are rainfall patterns changing?” published in Down to Earth on 6^th Sep 2021.