A team of scientists at NYU Abu Dhabi have published a paper arguing that monsoon winds that provide rain to the west coast of India may shift northward in the future, leaving southern areas of the country drier than they are now. The work was led by Ajaya Ravindran, senior scientist at the Center for Prototype Climate Modeling (CPCM), and was published in the journal Climate Dynamics.
The CPCM works to improve computer models that are used to forecast future climate. "In this particular case, we wanted to know how the regional climate is responding to climate change, specifically the monsoon," said Sandeep Sukumaran, an author on the paper and a postdoctoral associate at the CPCM. "We found that in the historical period and in our simulations of future climate, the monsoon circulation is gradually shifting northward."
As the monsoon winds move east across the Arabian Sea, they meet the Indian landmass. Clouds are forced to a higher elevation when they collide with the Western Ghats, a mountain range that runs along India's west coast. Rising, the clouds cool and condense at higher elevations, dropping rain on the windward slope.
"We've found that consistent with the shift of these strong winds to the north, the rainfall pattern is also shifting," Sukumaran said. "The pattern has been shifting for about the last 30 years. And by the end of the century, we expect that it would shift by 1.5 to 3 degrees north, or about 165 to 330 kilometers."
Interestingly, Sukumaran noted that the shift in their observational data is happening faster than it occurs in their model: "the model is underestimating the shift."
The evolving monsoon will impact the Arabian Sea differently than it will India. "There is strong upwelling in the Arabian Sea during the monsoons due to the winds, and the pattern of upwelling seems to be changing," Sukumaran noted. (Upwelling is a phenomenon caused by wind moving parallel to the coast. This wind action on the sea causes cooler, deeper water to rise to the surface near the coast in a current perpendicular to the wind direction.)
Upwelling is important for fisheries, as the cooler water brings with it to the surface nutrients that are depleted at higher ocean temperatures. "But we need to do more experiments to know exactly how to understand how this shift in winds is changing coastal upwelling," Sukumaran added.
In time, changes like these could have consequences for the fishing industry in the Arabian Sea, and the wider region.