Shrinking African Lake Offers Lesson on Finite Resources
Hillary Mayell
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 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 onetwentieth 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.
"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).