Climate change threatens Indian monsoon

The Indian monsoon – on which more than a billion people depend for food crops – could fail frequently and catastrophically over the next 200 years as a result of global warming.

The researchers define monsoon failure as a drop of between 40 and 70 percent in rainfall, compared with normal levels – something that’s never happened in the 140 years of measurements by the India Meteorological Department.

But by 2150, says the Potsdam Institute for Climate Impact Research and Potsdam University team, the rains could be failing every fifth year. India’s economy relies heavily on the monsoon season to bring fresh water to farmlands.

“Our study points to the possibility of even more severe changes to monsoon rainfall caused by climatic shifts that may take place later this century and beyond,” says lead author Jacob Schewe.

The changes, say the team, would be triggered by increasing temperatures and a change in strength of the Pacific Walker circulation in spring.

The Walker circulation usually brings areas of high pressure to the western Indian Ocean. However, in years when El Niño occurs, this pattern gets shifted eastward, bringing high pressure over India and suppressing the monsoon, especially as it begins to develop in spring.

But the researchers’ simulations showed that as temperatures increase in the future, the Walker circulation will bring more high pressure over India – even if El Niño doesn’t occur any more often.

The findings may be controversial, as most models conclude that global warming is more likely to increase monsoon rainfall, rather than decrease it.