New research suggests that the rate of failure in Indian summer monsoon will increase over the next two centuries, due to global warming [1].
The Indian farmers rely on the monsoons to disperse freshwater on agricultural land. Failure of the summer monsoons could be very detrimental to India’s economy.
Walker Circulation
The Walker circulation is a vast loop of winds that influences climate across much of the globe, including the Indian summer monsoons.
Image courtesy of NOAA
Walker circulation describes the air flow in the tropics in the lower atmosphere. The Walker circulation is generated by the pressure gradient that results from a high pressure system over the eastern Pacific ocean, and a low pressure system over Indonesia.
El Niño
The Southern Oscillation is the natural variation in the temperature of the surface of the tropical eastern Pacific Ocean and the surface air pressure. This occurs across the tropical Pacific Ocean roughly every five years. The extremes of this climate pattern’s oscillations, El Niño (warm) and La Niña (cool), cause extreme weather events across many regions of the world.
The Walker circulation brings areas of high pressure to the western Indian Ocean, bringing the monsoons. However, in years when El Niño occurs, the winds get shifted eastward, bringing high pressure over India and the effect is to suppress the monsoons.
The predictions
Jacob Schewe and Anders Levermann simulations suggest that as temperatures increase in the future, the Walker circulation, will on average bring more high pressure over India; even though the occurrence of El Niño doesn’t increase.
The effect of this will be an increase in the occurrence of monsoons failing to form and an increase in drought across India.
Reference
Jacob Schewe and Anders Levermann (2012), A statistically predictive model for future monsoon failure in India, Environ. Res. Lett. 7 044023
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