for National Geographic News
Lake Chad, once one of Africa's largest freshwater lakes, has shrunk
dramatically in the last 40 years. Two researchers from the University
of Wisconsin, Madison, have been working to determine the
causes.
In a report published in the Journal of Geophysical
Research, they conclude that human activities are to blame for the
shrinking of Lake Chad.
The question of interest to Jonathon A. Foley and Michael T. Coe is applicable to many other natural phenomena as well, such as melting ice caps, retreating glaciers and warming oceans: Are the dramatic changes we are now witnessing the result of natural variation over millennia, or more or less a direct function of human activities?
The lake's decline probably has nothing to do with global warming, report the two scientists, who based their findings on computer models and satellite imagery made available by NASA. They attribute the situation instead to human actions related to climate variation, compounded by the ever increasing demands of an expanding population.
"Humans in the system are the big actors here," says Coe, a hydrologist. "What has happened to Lake Chad may be an illustration of where we're heading."
Lowest Level
Lake Chad is in the Sahel, a vast savanna bordered by the rain forests of the west coast of Africa on one side and the Sahara desert to the north. Chad, Niger, Nigeria, and Cameroon are neighboring countries.
The lake is probably at least 20,000 years old and has shrunk and expanded over thousands of years, Coe said. But the recent decline is by far the greatest, he explained. Said his colleague Foley: "The lake has shrunk quite a bit before, but never to this degree. This is an unprecedented low."
In 1963, the lake covered about 9,700 square miles (25,000 square kilometers). Today it is one-twentieth of that size.
Historically, Lake Chad received most of its water from the monsoon rains that fell annually from June to August. But beginning in the late 1960s, the region experienced a series of devastating droughts. As the rains increasingly failed to come, the region began undergoing desertification. At the same time, local people became more and more dependent on the lake as a source of water to replace the water they had previously obtained from the monsoons.
"Domino Effect"
Overgrazing of the savanna is one of the biggest factors in the shrinking of the lake, according to Coe and Foley. As the climate became drier, the vegetation that supported grazing livestock began to disappear.
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