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The number of rainy days and the amount of rainfall the islands receive during the dry winter season have dropped in recent years, according to data from 1949-2014 compiled by scientists at the India Meteorological Department and the Central Island Agricultural Research Institute.
In these islands, said Ayyam Velmurugan, a soil scientist with the institute, two weeks of sunshine can suck the soil dry, turning a flood quickly into a drought.
Farmers on India's mainland can sometimes dig for groundwater to make up for a lack of rain, but coastal Andaman soil isn't deep enough to hold much water, and digging into the coral soil of the Nicobar islands can flood a field with saltwater, scientists say.
All this is creating challenges for the 380,000 people who live on the archipelago, more than a quarter of them in the capital, Port Blair, according to data from the last nationwide census in 2011.
RAIN WOES
One of the problems facing the drying Andaman islands is that the deepest soil - that good at soaking up rain - lies in the interior regions that are largely mountainous, forested and undeveloped, Velmurugan said.
Moving water from inland areas to the coast is too costly, he said.
In total, rainfall over the Andaman and Nicobar Islands still hovers near its historical average, Velmurugan said - but now more of it comes during the monsoon, often in heavy cloudbursts. The Indian Ocean has warmed more consistently than the Atlantic and Pacific, according to Roxy Koll, an Indian Ocean warming expert at the Indian Institute of Tropical Meteorology who is currently a visiting scientist at the U.S. National Oceanic and Atmospheric Administration.
The warming waters increase evaporation and cause bursts of rain that can erode away soil, scientists say.
This is a constant problem on the Andaman and Nicobar Islands, where morning droplets of rain can flow out to sea by afternoon,
As warming continues, "you can expect this over most of the islands over the Indian Ocean," Koll warned. "It will only add to the agriculture woes."
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