Why Lake Chad is shrinking

Posted: 4 April 2001

Satellite imagery has helped researchers to understand why one of Africa's largest freshwater lakes has been disappearing over the last 30 years.

Michael Coe and Jonathan Foley of the University of Wisconsin-Madison have found that a drier climate and high agricultural demands have caused the water of Lake Chad to shrink. Their research was funded by the National Aeronautics and Space Administration (NASA).

"Lake Chad was about 25,000 square kilometres in surface area back in 1963," Foley says. Now the lake is about one-twentieth the size it was in the mid-1960s. Using model and climate data, Coe and Foley calculate that a 30 per cent decrease took place in the lake between 1966 and 1975. Irrigation accounted for five per cent of that, with drier conditions accounting for the rest.

They say that irrigation demands increased four fold between 1983 and 1994, accounting for 50 per cent of the additional decrease in the size of the lake.

"NASA Landsat satellite imagery taken of the lake over the last 30 years really capture the model conclusions and visualize them very well," the researchers noted. Lake Chad 1973Lake Chad, 1973© NASA
The satellite image taken in January 1973 stands in sharp contrast to that taken in 2001, which shows the dramatic decrease in size of the lake. Present day Lake Chad occupies a fraction of its former lake bed, (shown in green, indicating vegetation).
Lake Chad 2001Lake Chad, 2001© NASA
The warming climate and increasing desertification in the surrounding region have lowered water levels far below the average dry season level of 4,000 square miles (10,000 square kilometres) to only 839 square miles (1,350 square kilometres). "Climate data has shown a great decrease in rainfall since the early 1960's largely due to a decrease in the number of large rainfall events," Coe said.

With a drier climate and less rainfall, agricultural areas become more desperate for water to irrigate their crops, and will continue draining what is left of Lake Chad. "The problem is expected to worsen in the coming years as population and irrigation demands continue to increase," warns Foley.

Source: Environment News Service (ENS), February 28, 2001.

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