Indonesia and perhaps Australia risk more droughts because of shifts in Indian Ocean temperatures and stronger monsoons widely linked to global warming, scientists say.
They said studies of 6,500-year-old fossil corals had helped to reveal unexpected links between monsoons, droughts and periodic cooling of the eastern Indian Ocean known as the Indian Ocean Dipole (IOD).
A trend towards stronger monsoons in Asia “will probably serve to prolong IOD-related droughts in western Indonesia, and possibly also southern Australia”, the scientists wrote in the journal Nature.
More droughts could disrupt agriculture, slow an Indonesian drive to end poverty, lead to more wildfires that cause both smog and deforestation, threaten wildlife habitats and disrupt hydropower generation.
The scientists said recent stronger monsoons had been widely linked by scientists to a global warming blamed on human burning of fossil fuels. But most studies of monsoon have focused on the likelihood of more rains in India and other parts of Asia.
“Our findings suggest that the some of the knock-on effects will cause more widespread consequences … than previously thought,” said Nerilie Abram of the Australian National University of the report in the journal Nature.
She said that the Dipole oscillation of the Indian Ocean, reversing usual winds and disrupting ocean temperatures, was similar to the better-known El Nino shifts in the Pacific Ocean.
“With a Dipole we get very cold temperatures off the coast of western Indonesia,” she told Reuters of a report written with colleagues in China, the United States and Indonesia.
“Those cold temperatures reduce the amounts of rainfall so you end up with intense droughts in western Indonesia and then you don’t get the cloud bands forming there that travel across to parts of Australia,” Abram said.
The last Dipole peaked in October-November 2006, following monsoon rains that typically last from May-September. The previous Dipole was in 1997-98.
A current El Nino event in the Pacific also tends to draw rainfall eastwards from Indonesia, aggravating droughts.
“If the consensus holds true that the Asian monsoon will intensify with climate warming, Indonesia can expect more frequent and longer droughts,” Jonathan Overpeck and Julia Cole, both of the University of Arizona, wrote in a separate commentary in Nature.
“Rural livelihoods and natural resources will thus be at greater risk as drought undercuts regional food supplies and stokes wildfires that also generate exceedingly poor air quality in the region.”