FEATURE ARTICLE
Climate and the Collapse of Maya Civilization
A series of multi-year droughts helped to doom an ancient culture
Larry Peterson, Gerald Haug
Rainforest Crunch
Given the common image of lost Maya cities buried beneath tangles of jungle vegetation, it may come as a surprise to discover that the Yucatán is, in fact, a seasonal desert. The lush landscape depends heavily on summer rains for nourishment, rains that vary considerably across the peninsula. Annual precipitation ranges from as little as 500 millimeters along the northern coast to as high as 4,000 millimeters in parts of the south. As much as 90 percent of this moisture falls between June and September, and a pronounced winter dry season runs from January to May.
This wet-dry contrast results from the seasonal migration of moisture associated with the intertropical convergence zone, an atmospheric feature that is sometimes known as the "meteorological equator." In this zone, the easterly trade winds of the northern and southern tropics converge, forcing air to rise and bringing on cloudiness and abundant rainfall. During the winter months, the intertropical convergence zone shifts far to the south, and dry conditions prevail over both the Yucatán Peninsula and northern South America. Then, with the coming of summer, this zone migrates north again, bringing life-giving rain to the Yucatán and southern Caribbean region.
The Maya had to deal with this seasonal contrast and, in particular, had to cope with a long dry season each year. This feature of their environment had special significance, because surface waters tend to dissolve the limestone bedrock of the Yucatán, forming caves and underground rivers but leaving little opportunity for water to flow over land. So the Maya could not simply locate their settlements along major watercourses. Even important regional centers—such as Tikal, Caracol and Calakmul—developed in places that were without permanent rivers or lakes. The lack of surface water for four or five months of the year in such areas spurred the construction of large-scale water-collection systems.
Many cities were designed to catch rainfall and channel it into quarries, excavations and natural depressions that had been specially prepared to retain the captured water without letting it seep into the ground. Tikal, for example, had numerous reservoirs, which together were capable of holding enough water to meet the drinking needs of roughly 10,000 people for about 18 months. The Maya also built reservoirs on the tops of hills, using gravity to distribute the water through canals into complex irrigation systems. Despite the sophistication of their hydrological engineering, the Maya ultimately depended on the seasonal rains to replenish their water supplies, natural groundwater being inaccessible over a considerable portion of their realm.
In his fascinating book, The Great Maya Droughts, independent archaeologist Richardson B. Gill persuasively argues that a lack of water was a major factor in the terminal Classic collapse. Gill pulls together an enormous amount of information on modern weather and climate, draws on the record of historical droughts and famines, and heaps on evidence from archaeology and from geological studies of ancient climates. To demonstrate the importance of the porous limestone bedrock, for example, he quotes Diego de Landa, Bishop of Yucatán, who in 1566 wrote: "Nature worked so differently in this country in the matter of rivers and springs, which in all the rest of the world run on top of the land, that here in this country all run and flow through secret passages under it."
Gill builds an impressive case. When his work was first published (five years ago), the most compelling evidence for drought came from sediment cores that David A. Hodell, Jason H. Curtis, Mark Brenner and other geologists at the University of Florida had collected from a number of Yucatán lakes. Their measurements of these ancient deposits indicate that the driest interval of the last 7,000 years fell between 800 and 1000 A.D.—coincident with the collapse of Classic Maya civilization. Later work by these same investigators found evidence for a recurrent pattern of drought, which seems also to explain other, less dramatic breaks in Maya cultural evolution.
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