Fall of Mayan cities blamed on long dry spell
A long dry period punctuated by three intense droughts probably played a major role in the mysterious collapse of Mayan civilisation in Mexico, according to a new study.
The severe droughts, each lasting between three and nine years, may have the been the final straws for a civilisation already on the verge of collapse, says a report published today in the journal Science.
"Between about 750 and 950 AD, the Maya experienced a demographic disaster as profound as any other in human history," said the report, by an international research team led by Dr Gerald Haug of the Swiss Federal Institute of Technology in Zürich.
The Mayan were so successful that at their so-called Classic Maya peak, around 750 AD, the civilisation supported a population of between three and 13 million people, the researchers said. But then it progressively collapsed and by the early 9th century, many of its cities and towns had been permanently abandoned.
The study details new evidence that the three droughts occurred around 810, 860, and 910 AD - corresponding to the three phases of Mayan collapse suggested by archaeological evidence.
The researchers also found that a more subtle but long-term drying trend was ongoing during the collapse. The droughts may have been what specifically "pushed Mayan society over the edge," they said.
The findings are based on an analysis of long-term climate records as revealed in pristine undisturbed sediments from the Cariaco Basin, off northern Venezuela. The distinctly layered sediments, washed out from land by rivers, show up as pairs of light and dark bands that correspond to annual wet and dry seasons.
Within them, the team identified yearly variations in titanium levels, which reflect the amount of rainfall each year. They correlate well with palaeoclimate data obtained elsewhere from sources such as ice cores and tree rings.
Until now, however, climate records from the time had not been precise enough to test the relationship between drought and the Maya's downfall during the 9th and 10th centuries, the report said.
The Mayans began cultivating maize in the region about 2000 BC, using dryland farming techniques that depended on fallowing to rest the soil and needed relatively little labour. Like other Native Americans, they went on to develop sophisticated ways of intensively cultivating fertile soils associated with seasonal and permanent wetlands, on which multiple crops could be grown year after year.
Living in the Yucatan lowlands of Mexico and depending mainly on an inconsistent rainfall cycle, the Maya developed labour-intense networks of raised fields as well as canals, reservoirs and other systems for storing and gravity-powered distribution of rainwater.
The Mayans had abandoned their major cities once before - between about 150 and 250 AD - an incident that may also be due to drought. But their population constantly recovered, cities were reoccupied and their culture blossomed.
"The control of artificial water reservoirs by Maya rulers may also have played a role in both the florescence and the collapse of Maya civilisation," the researchers wrote.
Other scientists have suggested that drought may have undermined the institution of Mayan ruling class when existing ceremonies and technologies failed to provide sufficient water.
The Mayans were an ancient people whose high civilisation flourished in what is today Mexico, Honduras and Guatemala. They created monuments as impressive as those in ancient Egypt, were proficient in mathematics and astronomy and invented a unique written language.