LAKE ALJOJUCA
The maar lake Aljojuca, 20 miles south of Cantona, yielded sediments that recorded a lengthy series of droughts between AD 500 and 1150.Tripti Bhattacharya, UCB

The abandonment of Cantona, a once-fortified Mexican city, has been traced to a centuries-long period of droughts, resulting most probably from climate change.

The Mesoamerican metropolis dried up about 1,000 years ago following below-average rainfall from about AD 500 to about AD 1150, believed to be part of a period of droughts in modern-day Mexico's highlands that lasted from about 200 BC until AD 1300.

"The decline of Cantona occurred during this dry interval, and we conclude that climate change probably played a role, at least towards the end of the city's existence," said lead researcher Tripti Bhattacharya, a graduate student of geography at the University of California, Berkeley.

Initially, the population of Cantona increased during the dry period, probably due to political upheaval elsewhere, she said. Teotihuacan, to the west for instance, was in decline at the time.

The findings were published in the journal Proceedings of the National Academy of Sciences.

The team studied sediment cores and samples from lake Aljojuca, 32 km from the city. Most of the lakes in the region are created by magma explosions. They are deep and contain undisturbed and regularly layered sediments which provide insight into the various time periods.

Oxygen isotope ratios in carbonate sediments were correlated with the ratio of precipitation to evaporation. Organic material in the sediments was used for carbon-14 dating. The data showed the area had dry summers.

While the average weather showed wet summers and dry winters, it was seen that the regular monsoon season was disturbed by frequent long-term droughts. This affected crops and water supply, the researchers said.

Moreover, the long period of droughts worsened the situation.

Cantona, located in a dry volcanic basin, was once a flourishing city housing 90,000 people.

It has been established that monsoons are not only governed by topography but also influenced by global climate.

Studies have shown that air pollution caused by humans and resulting in high concentration of aerosols in the atmosphere affected the annual monsoon rainfall in the northern hemisphere in the last 50 years.

Alterations to summer monsoon rainfall affect the lives of billions of people, mostly those living in India, South East Asia and parts of Africa where agriculture is critically dependent on these seasonal rains.

Recent droughts in unlikely places like California have raised the spectre of the Dust Bowl events of the last century, when agricultural patterns contributed to the worst drought in North America.