Shift in balance between precipitation and rainfall was enough to reduce sources of accessible water
By Summit Voice
SUMMIT COUNTY — Relatively minor changes in summer rainfall patterns may have been a big factor in the collapse of the Central American Maya civilization.
The new study relied on sediment data in shallow lakes and moisture records in cave formations reconstruct past climate in the region, finding that the drop in rainfall occurred around the same time the Maya abandoned their cities.
The results serve as a warning for other regions that exist in a delicate balance of climate and water availability, the researchers said.
“Our results show rather modest rainfall reductions between times when the Classic Maya Civilization flourished and its collapse – between AD 800-950,” said Professor Martín Medina-Elizalde, of the Yucatan Center for Scientific Research, one of the primary researchers.
“These reductions amount to only 25 to 40 percent in annual rainfall. But they were large enough for evaporation to become dominant over rainfall, and open water availability was rapidly reduced. The data suggest that the main cause was a decrease in summer storm activity,” he said.
In related research, NASA climatologists recently suggested the Maya may have contributed to the reduction in rainfall by clearing the rainforest around their cities, thus changing the amount of water vapor available for condensation in the lower atmosphere.
The study combines records of past climate changes from stalagmites and shallow lakes to model 40 per cent reductions in summer rainfall and reduced tropical storm activity over the region.
“For more than a century, researchers have related the demise of the Classic Maya civilization to climate change, and especially to drought,” said Eelco Rohling, of the University of Southampton in the UK. “No sound estimates had been made about the severity of this drought, but some have suggested extreme scenarios. New data made it possible to finally get detailed estimates. To do this, we developed a model that coherently explains changes in critical datasets of change in the region’s balance between evaporation and rainfall.”
“Summer was the main season for cultivation and replenishment of Mayan freshwater storage systems and there are no rivers in the Yucatan lowlands.Societal disruptions and abandonment of cities are likely consequences of critical water shortages, especially because there seems to have been a rapid repetition of multi-year droughts,” said Rohling, explaining why such modest rainfall reductions would cause the disintegration of a well-established civilisation.
The scientists also said the reconstructed droughts during the demise of the Classic Maya Civilization were of similar severity as those projected by the IPCC for the near future in the same region.
“There are differences too, but the warning is clear,” Medina-Elizalde said. What seems like a minor reduction in water availability may lead to important, long-lasting problems. This problem is not unique to the Yucatan Peninsula, but applies to all regions in similar settings where evaporation is high. Today, we have the benefit of awareness, and we should act accordingly.”