Global warming dominating monsoon dynamics in India, monsoons to be more chaotic: Study

For every degree Celsius of warming, monsoon rainfalls will likely increase by about 5%, according to a new study

A new research paper titled, ‘Robust increase of Indian monsoon rainfall and its variability under future warming in CMIP6 models’ has warned that summer monsoons in India will become stronger and more erratic unless tight reins are put on global warming.

The research, conducted by a team of German researchers, analysed long-term trends of the Indian summer monsoon and its variability based on 32 models of the latest climate model generation(CMIP6). CMIP6 comprises the results from around 100 different climate models being produced across 49 different modelling groups.

Some parts of India will receive more rainfall

According to the study, a majority of the climate models (28 out of 32) estimated that the increase in precipitation will be more prominent in the Himalayan region, northeast of the Bay of Bengal and in the Western Ghats. However individual models suggest decreasing rainfall along the southwest coast of India and around Myanmar, it said.

It pointed out that these regions already receive good amounts of rainfall as per the existing rainfall pattern leading to a “wet-regions-get-wetter” pattern during June-to-September (JJAS) monsoon rainfall. The projected increase in rainfall is 0.33 mm per day per kelvin of global warming, it said.

Difference in Indian summer monsoon mean rainfall (mm/day) for the period 2070–2100 under SSP 5-8.5 in comparison to average rainfall levels from 1985–2015.

Reasons behind the intensification of rainfall

The study highlights that human behaviour is behind the intensification of rainfall. Starting in the 1950s, human-made forcings have begun to overtake slow natural changes occurring over many millennia

At first, high sun-light blocking aerosol loadings led to subdued warming and thus a decline in rainfall, but since then, from 1980 onwards, greenhouse gas-induced warming has become the deciding driver for stronger and more erratic monsoon seasons, it said.

Linear dependence of rainfall on global mean temperature

The study also analyzed the dependence of rainfall on global mean temperature (GMT). It revealed that rainfall has a linear dependence on GMT. 

“We have found robust evidence for an exponential dependence: For every degree Celsius of warming, monsoon rainfalls will likely increase by about 5%,” says lead author Anja Katzenberger from the Potsdam Institute for Climate Impact Research (PIK) and Ludwig-Maximilian University in Munich, Germany (LMU). 

The study is also able to confirm the results of previous studies, she said. But global warming is increasing monsoon rainfall in India even more than previously thought and it is dominating monsoon dynamics in the 21st century, she added.

Crops sensitivity to rainfall variability 

Indian monsoon plays a significant role in the livelihood of people.  Over 60% of Indian farmers depend on rainfed agriculture and the crop yields (especially rice) are highly sensitive to the monsoon rainfall variability. More rainfall is not necessarily a good thing for the farming sector in India, the study noted.

According to co-author Julia Pongratz from Ludwig Maximilian University, Germany, “Crops need water especially in the initial growing period, but too much rainfall during other growing states can harm plants – including rice on which the majority of India’s population is dependent for sustenance. This makes the Indian economy and food system highly sensitive to volatile monsoon patterns.”

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