Shrinking African Lake Offers Lesson on Finite Resources
for National Geographic News
|April 26, 2001|
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
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."
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.
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.
"Vegetation has a big influence, especially in semi-arid regions, in determining weather patterns," said Foley. "The loss of vegetation in itself contributed to a drier climate."
Human and animal populations came to rely more and more on water from the lake. Massive irrigation projects to combat the drier climate diverted water from both the lake and the two main rivers that empty into it, the Chari and the Logone.
The situation is a "domino effect," the researchers say. Overgrazing reduces vegetation, which in turn reduces the ecosystem's ability to recycle moisture back into the atmosphere. That contributes to the retreat of the monsoons. The consequent drought conditions have triggered a huge increase in the use of lake water for irrigation, while the Sahara has gradually edged southward.
Lake Chad is not likely to be replenished to its former size in our lifetime, the researchers say.
The lake's decline and the climate change have had an enormous impact on the 9 million farmers, fishermen, and herders living in the region. They have experienced crop failures, dying livestock, collapsed fisheries, and the continuous draining of the lake.
"The problem is expected to worsen in the coming years as population and irrigation demands continue to increase," Foley warned. "It shows how vulnerable our water resources can be."
Coe says the situation illustrates the urgent need to better manage water resources, which are limited. "There are enough people in the world now that we need to start planning and looking at fresh water as a finite resource or we're going to be in trouble," he said. "We don't get any more."
Lake Chad was one of the largest freshwater lakes in Africa, about the size of the state of Vermont. It is 820 feet (250 meters) above sea level and is fed by the Chari and Logone river system.
Lake Chad has always undergone seasonal and inter-annual fluctuations because it is less than 23 feet (7 meters) deep.
In recent decades, the lake expands during wet periods up to 10,000 square miles (25,900 square kilometers). The warming climate and increasing desertification in the surrounding Sahel region have caused water levels to decline much below the average dry season level of 4,000 square miles (10,000 square kilometers) to only 839 square miles (1,350 square kilometers).
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