Aldenderfer said scientists are still working out the exact nature of the shift—for example, whether bouts of rainfall became harder but shorter, or whether it didn't rain at all.
Morrill's research does not distinguish between those scenarios. "All I can say is that overall it became drier in India and Tibet," she said.
Either way, the change would have altered the way springs channel water off the Tibetan plateau, according to Aldenderfer.
"This has an effect on the irrigation systems," he added, explaining that the springs were the primary means for watering crops in the region.
And whatever the exact changes entailed, Aldenderfer continued, his Tibet project is beginning to reveal how the culture high up on the plateau responded.
For example, Guge, an ancient kingdom in western Tibet, shifted inland at about the time of the suggested shift in the monsoon, he noted.
He and his colleagues also have some evidence of large-scale abandonment of agricultural fields.
The team will return to Tibet this summer to continue their investigations.
Lessons for the Future
While climate experts are just now figuring out what will happen to the Asian monsoon as a result of global warming, Aldenderfer said intensity is likely to increase and thus cause more erosion.
(Learn about the causes and effects of global warming.)
"That would make planting of agricultural fields really a very chancy thing," he said.
The Tibetan plateau, like all mountainous areas, is also likely to experience earlier snowmelt. As a result, people who rely on snowmelt for irrigation will be forced to plant their crops earlier, before the start of the traditional growing season.
"There's going to be some serious issues with agricultural shortfalls," Aldenderfer said.
He added that governments must prepare now to regulate access to water.
"Water conflicts are likely to increase in the future as problems of this kind worsen," he noted.
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