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Popular Archaeology Episodic periods of fewer and weaker summer storms cited as a reason. 
Along with runaway slash-and-burn agriculture and mismanagement of resources, climate change has long been suggested by scientists as a cause for the mysterious 200-year decline of the Maya civilization. The suspect was drought, but there has been no solid data to explain the timing and gravity of any such drought period(s). Now, new research has produced results that give us some specifics about how this could have happened. According to a study led by Martín Medina-Elizalde of the Yucatan Center for Scientific Research in Mexico and Eelco Rohling of the University of Southampton in the UK, the decline of the Classic Maya civilization was concurrent with an approximate 25 to 40 percent reduction in annual rainfall. The researchers determined this by combining highly detailed records and data taken from three lakes and one stalagmite. They found that precipitation in the region decreased episodically for periods as long as a decade at a time by up to 40 percent. Moreover, they suggest that it was due to fewer and weaker summer storms in that part of the world. Although 40 percent is considered significant, it is not considered extreme. However, the difference could explain how the balance between rates of evaporation and rainfall could disrupt and deplete critical water supplies or reservoirs needed to sustain certain levels of human occupation. Says Professor Rohling: "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." The researchers further warn that the ancient Maya drought model reconstructed for this study also has implications for the future. They note that, although there are differences, the climate projections for this same region for the near future are very similar. "......The warning is clear," says Professor Medina-Elizalde. "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." The research was funded by the Natural Environment Research Council of the UK. The detailed research paper appears in the 24 February 2012 issue of Science, published by the AAAS, the nonprofit science society.
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