India's Monsoon Season Could Be Drastically Affected By Climate Change

From Mother Nature Network's John Platt:

More than a billion people in India currently depend on the rainy monsoon season for the water necessary to grow crops such as rice and wheat, but those annual rains could be less predictable in the future, according to a new study published Nov. 5 in the journal Environmental Research Letters.

The study, by Jacob Schewe and Anders Levermann of the Potsdam Institute for Climate Impact Research in Germany, looked at climate change models for the next 200 years and concluded that monsoons could begin to "fail" late in the next century, threatening food production ever five years.

The researchers defined a monsoon failure as a season in which rains were between 40-70 percent below normal levels. They say that this could occur every five years between 2150 and 2200. To put that in context, this year's monsoon season produced rains at just 12 percent below normal, causing widespread crop failures due to lack of agricultural waters.

Although there have been a few years with below-average rainfall in India recently, Levermann told Reuters that the monsoon season has been stable for the past century. The team's paper does mention that the annual number of extreme rain events is increasing.

The researchers compared several climate-change models, including models from the Intergovernmental Panel on Climate Change (IPCC), which showed both an increase in global temperatures and a change in strength in the Pacific Walker circulation, the tropical air flow patterns that are caused by heat distribution between land masses and the world's oceans. According to a press release issued by the Institute of Physics, the publisher of Environmental Research Letters, the Walker circulation "usually brings areas of high pressure to the western Indian Ocean but, in years when El Niño occurs, this pattern gets shifted eastward, bringing high pressure over India and suppressing the monsoon, especially in spring when the monsoon begins to develop."

Although this study looks at changes that could occur more than a century in the future, the authors write that developing reliable projections for rainfall in India will be vital to maintaining the safety of food production for a large share of the world's population.