Climate impact: Northeast India's monsoon season starting earlier & getting shorter

The rainy season in northeast India is usually longer than in central India. However, if greenhouse gas emissions keep increasing, the rainy season in the northeast could become five days shorter and have more heavy rainfall.

According to the study published in Climate and Atmospheric Science, the Indian summer monsoon, which happens from June to September, brings most of the rain for the year. Scientists at Cotton University in Guwahati say that the rainy season in northeast India starts in mid-May and could last up to 155 days. This is longer than the 120-day season in central India.

A comprehensive study found that the monsoon season in Northeast India now starts as early as mid-May and lasts until the second week of October. However, over the past six decades, there has been a significant decrease in the length of the rainy season.

This change in the monsoon pattern is causing concern about the potential impact on the region’s biodiversity and its ability to cope with climate change. The El Niño and La Niña weather phenomena also play a role in this, as they can affect the duration and intensity of the monsoon.

Monsoon in Northeast starts in mid-May

The Indian Meteorological Department traditionally defines the monsoon 'Onset' in Northeast India around 5th June. However, a comprehensive study challenges this notion, suggesting that the monsoon season starts as early as mid-May, lasting until the second week of October. This discovery, backed by an objective method using tropospheric temperature gradients, contradicts existing beliefs within the Indian monsoon community.

The study also raises concerns about the exclusion of May rainfall in the calculation of the Indian Summer Monsoon Rainfall (ISMR), emphasizing its significance in understanding variability and predictability. The Northeast's extended monsoon season plays a crucial role in the region's climate, impacting local ecosystems and weather patterns.

The NEI's extended monsoon season, starting from mid-May and lasting until the second week of October, plays a crucial role in sustaining a unique biodiversity hotspot in the region. This distinct climate pattern, characterized by high rainfall, also raises concerns about its potential impact on hydrological disasters and food production.

Changing monsoon dynamics: What study reveals

The study uses a clear method to find out when the rainy season starts and ends in Northeast India. They used data from 1901 to 2015 and found that the rainy season usually starts on May 12th and ends on October 15th, lasting 157 days. But they noticed that the rainy season has been getting shorter over the last 60 years, which could affect the area’s wildlife and ability to handle climate change.

Looking at changes from year to year, the study found that the start of the rainy season is getting later and the end is getting earlier. This is making the rainy season shorter. The reason for this is a faster drop in a measure of the Indian monsoon.

The study also looked at how El Niño and La Niña affect the length of the rainy season. They found that El Niño makes the rainy season shorter and drier, while La Niña makes it longer and wetter.

The study also used CMIP6 models to predict what might happen in the future. They think that if greenhouse gas levels keep going up, the rainy season could get even shorter. Even though the models didn’t do a great job at estimating the rainy season in the past, they predict a shorter rainy season in the future.

Interestingly, even though the rainy season is getting shorter, the study found that the amount of rain during the monsoon is likely to increase in the coming years. This raises questions about what’s causing this change.

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