Science Question of the Week - 29 March 2001

Let's stay in Africa but move north to Chad. What has been happening to Lake Chad in recent years and why?

Many of us probably think back to the election when we hear the word "chad." We had to deal with hanging chads, dimpled chads, pregnant chads, and even missing chads. Unfortunately for Lake Chad, it also may be soon missing - missing form atlases.

Lake Chad, in north central Africa, has suffered a stunning loss of water during the last several decades. This vanishing inland lake was first observed by the Landsat satellite in 1973, when it was still one of the largest, fresh water inland lakes in Africa. Recent Landsat images have shown that Lake Chad has shrunk to 1/20 of its dimensions of 35 years ago, when it was the size of Lake Erie! It's fading faster than the ratings of the XFL.

Geography, especially political geography, has worked against Lake Chad. In the shallow depression where the lake lies, the boundaries of four different countries, Cameroon, Niger, Nigeria, and Chad, come together. With the exception of Cameroon, these countries, like many African nations, have experienced nearly constant conflict between warring internal factions and frequent changes in government during the past 30 years. Though the region is blessed with rich reserves of oil and uranium, the people are poor, and the land has been prone to drought. Very little of the land is arable, and irrigation from Lake Chad and its feeder rivers is needed for growing crops such as cotton, peanuts, cereal grains and sugar cane.

Overgrazing of domestic animals, using water to irrigate crops, cutting the few remaining stands of scrub forests, and lack of expected precipitation have led to desertification - the desert has been expanding for three decades across Africa's sub Sahara region. It's encroaching on areas that were formerly semiarid or savanna.

Lake Chad sits in the Sahel or the southern rim of the Sahara Desert. It's situated between the belt of subtropical anticyclonic flow to the north and equatorial convergence to the south. In this part of Africa, the climate tends to be rather uniform from west to east, and precipitation varies from about 25 inches a year to the south of Lake Chad to about 5 inches a year in northern Chad. Lake Chad itself receives about 15 inches of rain a year. Most of the precipitation occurs from mid summer through early fall.

Temperatures can exceed 100 degrees F on many days during the spring and early summer season. In fact, within the past week, a town in Cameroon recorded the world's highest daily temperature - 108 degrees F. High temperatures, plus fairly high average daily wind speeds, plus low rainfall, equals high evaporation rates. Approximately 90% of the rainfall evaporates - less than 10% penetrates into the soil or runs off into streams and rivers. By the end of the dry season, the soil moisture is almost completely exhausted around Lake Chad.

Niger and Chad are landlocked nations. A portion of the Niger River flows through southeastern Niger, but otherwise, both Chad and Niger have no reliable source of surface water except for Lake Chad and the handful of non ephemeral streams feeding it. However, because numerous wells have been punched into aquifers that help supply Lake Chad with water, the lake is not receiving as much subterranean water as in the past, and due to sporadic rainfall, the aquifers are not being adequately replenished.

Although Nigeria and Cameroon both border the Atlantic Ocean and have more humid climates than Niger and Chad, and consequently rivers which flow throughout the year, they also much have larger populations to support than Niger or Chad - Nigeria is Africa's most populous nation.

Too many people live near and depend on a body of water for subsistence that, because of variable precipitation, has been known to fluctuate in size over the years. If dry periods persist, and as more water is being withdrawn from the lake for irrigation purposes, Lake Chad will continue to dry up, the desert will advance, and yet another wave of famine will creep across the Sahel.

The current drying has been especially obvious since the early 1980s. Between about 1983 and 1995, the volume of water diverted from Lake Chad for irrigation projects quadrupled over the volume used in the preceding 25 years. With little input from rainfall, the lake is shriveling. Sand dunes now prosper where water once lapped at the lake's western shore.

Lake Chad is basically losing its water because of lack of rain and corresponding reduced flows from rivers which feed it and increased irrigation use. It joins the Aral Sea in central Asia as another sad example of what can happen to our water supply when Mother Nature doesn't come through with expected amounts of precipitation and controls on irrigation projects and land use are unbridled.

The Sahara Desert has expanded and contracted on a periodic basis. It's thought that perhaps 20,000 years ago, the Sahara Desert extended 300 miles south of it's current position. Like the desert, Lake Chad has also waxed and waned. It was once part of a much larger ancient inland sea. Natural climatic shifts are largely responsible for the long term displacement of the desert and the fluctuation of lake levels. The fact that the lake is smaller now is unrelated to the relatively recent global warming.

However, human impact has contributed to short term changes, on the order of decades. A human presence has certainly accelerated the rapid desertification of the Lake Chad area and the shrinking of the lake itself. And the fact that the four national governments having an interest in conserving the lake have been unsuccessful in implementing a "reasonable use" policy and enforcing it, is a pretty clear indication that, without the help of Mother Nature, the once healthy lake could in a few more decades be a swampy depression on the desert floor.

For more about this see the August 1987 issue of National Geographic Magazine and


29 March 2001