study: Classic Maya civilization collapse by rainfall

The disintegration of the Maya civilization may have been related to relatively modest reductions in rainfall, according to a study to be published Friday in the journal Science. The study was led by Professors Martin Medina-Elizalde of the Yucatan Center for Scientific Research in Mexico and Eelco Rohling of the University of Southampton in the UK. The study combines records of past climate changes from stalagmites and shallow lakes to model reductions in summer rainfall and reduced tropical storm activity over the region. The results show rather modest rainfall reductions between times when the classic Maya civilization flourished and its collapse -- between AD 800-950. 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. For more than a century, researchers have related the demise of the classic Maya civilization to climate change, and especially to drought. 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," Medina-Elizalde said in a statement. "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. The researchers said that 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.