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Africa's great shrinking Lake Chad

Satellite images of Lake Chad taken in 1973, top, and 1997, below, show how dramatically the body of water has shrunk  

MADISON, Wisconsin (CNN) -- One of the world's biggest lakes is shrinking dramatically and a report released Tuesday blames humans and nature.

In the 1960s, North central Africa's Lake Chad was larger than the state of Vermont but is now smaller than Rhode Island.

Using NASA satellite images, two researchers at the University of Wisconsin-Madison measured the surface area of the freshwater lake at 10,000 square miles (25,000 square km) in 1963, compared with 839 square miles (1,350 square km) today.

The said the lake's disappearing act was being caused by the combination of a drier climate and growing human demand for water. Their paper, "Human and Natural Impacts on the Water Resources of the Lake Chad Basin," appears in the American Geophysical Union's Journal of Geophysical Research.

Lake Chad is shallow -- less than 23 feet deep -- and its primary water source is seasonal monsoon rains. But over the past few decades the region has experienced a series of devastating droughts.

"Climate data has shown a great decrease in rainfall since the early 1960s, largely due to a decrease in the number of large rainfall events," said researcher Michael T. Coe.

At the same time, the need for water for irrigation in the four countries that share the lake has increased about fourfold, further draining the lake.

"The problem is expected to worsen in the coming years as population and irrigation demands continue to increase," said Jonathan A. Foley, the other researcher.

"The take-home message," Coe said, "is that humans have a big impact on these systems and now, through the use of computer simulations, we have some predictive abilities for what humans can do to them."

The future of Lake Chad, Coe said, is gloomy: "It will be a puddle. It will be completely managed. You'll get crops and drinking water out of it, but you'll have no ecosystem left to speak of."

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4:30pm ET, 4/16

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