Climate change will make summer monsoon rainfall in India stronger and more erratic, according to a study that predicts extremely wet years in the future, with potentially grave consequences for over a billion people's well-being, economy, food systems, and agriculture.
The study, published in the journal Earth System Dynamics, compared more than 30 state-of-the-art climate models from all around the world.
''We have found robust evidence for an exponential dependence: For every degree Celsius of warming, monsoon rainfalls will likely increase by about 5 percent,'' said study lead author Anja Katzenberger from the Potsdam Institute for Climate Impact Research (PIK) in Germany.
''Hereby we were also able to confirm previous studies but find that global warming is increasing monsoon rainfall in India even more than previously thought. It is dominating monsoon dynamics in the 21st century,'' Katzenberger said.
The researchers noted that more rainfall is not necessarily a good thing for the farming sector in India and its neighboring countries.
''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 depending for sustenance,'' said study co-author Julia Pongratz from Ludwig-Maximilian University (LMU) in Germany.
''This makes the Indian economy and food system highly sensitive to volatile monsoon patterns,'' said Pongratz.
A look into the past underlines that human behavior is behind the intensification of rainfall, according to the researchers.
Starting in the 1950s, human-made forcings have begun to overtake slow natural changes occurring over many millennia, they said.
At first, high sun-light blocking aerosol loadings led to subdued warming and thus a decline in rainfall.
However, from 1980 onwards, greenhouse gas-induced warming has become the deciding driver for stronger and more erratic Monsoon seasons.
''We see more and more that climate change is about unpredictable weather extremes and their serious consequences,'' said group leader and co-author Anders Levermann from PIK and Columbia University in the US.
''Because what is really on the line is the socio-economic well-being of the Indian subcontinent," Levermann said.
He explained that a more chaotic monsoon season poses a threat to the agriculture and economy in the region and should be a wake-up call for policymakers to drastically cut greenhouse gas emissions worldwide.