Lake Chad (in French: Lac Tchad)
is a large, shallow lake in Africa. It is economically very important, providing
water to more than 20 million people living in the four countries which surround
it — Chad, Cameroon, Niger and Nigeria. It is located mainly in the far west
of Chad, bordering on northeastern Nigeria. The Chari River is its largest
source of water, providing over 90% of Lake Chad's water. The lake possesses
many small islands and mudbanks, and its shorelines are largely composed of
marshes. Because it is very shallow — only 10.5 metres (34 ft) at its deepest
— its area is particularly sensitive to small changes in average depth, and it
consequently also shows seasonal fluctuations in size. Lake Chad has no apparent
outlet, but its waters percolate into the Soro and Bodélé depressions.
Lake Chad gave its name to the
country of Chad. The name Chad is a local word meaning "large expanse of
water," in others words simply "lake."
According to fossil evidence,
Lake Chad has probably dried out half a dozen times in the past 1,000 years.
Scientists attribute the latest shrinkage to droughts and increased irrigation.
NEWS Release No: 01-17
Space Flight Center--EOS Project Science Office
once one of the African continent's largest bodies of fresh water, has
dramatically decreased in size due to climate change and human demand for water.
Once a great lake close in surface area to North America's Lake Erie, Lake Chad
is now a ghost of its former self. According to a study by University of
Wisconsin- Madison researchers, working with NASA's Earth Observing System
program, the lake is now 1/20th of the size it was 35 years ago. Found at the
intersection of four different countries in West Africa (Chad, Niger, Nigeria
and Cameroon,) Lake Chad has been the source of water for massive irrigation
projects. In addition, the region has suffered from an increasingly dry climate,
experiencing a significant decline in rainfall since the early 1960's.The most
dramatic decrease in the size of the lake is shown in the fifteen years between
January 1973 and January 1987. Beginning in 1983 the amount of water used for
irrigation began to increase. Ultimately, between 1983 and 1994, the amount of
water diverted for purposes of irrigation quadrupled from the amount used in the
previous 25 years. The red color denotes vegetation on the lake bed and the
ripples on the western edge of the lake denote sand dunes formed by the wind.
Goddard Flight Center Photographs
In the 1960s,
North central Africa's Lake Chad was larger than the state of Vermont
but is now smaller than Rhode Island.
Chad as seen from Apollo-7 in 1968
NASA-funded researchers using
computer models and climate data now understand why Africa's freshwater
Lake Chad has been disappearing over the last 30 years. Michael T. Coe
and Jonathan A. Foley of the University of Wisconsin-Madison cite a
drier climate and high agricultural demands for water as reasons why
what was once one of Africa's largest freshwater lakes is shrinking.
"Lake Chad was about 25,000 square kilometers in surface area back
in 1963," Foley noted. Now the lake is about one-twentieth the size
it was in the mid 1960s. Their paper titled "Human and Natural
Impacts on the Water Resources of the Lake Chad Basin," was published
in the American Geophysical Union's Journal of
Geophysical Research. In their paper, Coe and Foley used an integrated
biosphere model (IBIS) with long time-series climate data. They
simulated the exchange of energy, water and carbon dioxide between
vegetation, soil and the atmosphere, and tracked the changes in Lake
Chad since 1953. They input the data from the biosphere model into a
hydrological model and were able to estimate changes in river discharge,
the amount of water in wetlands and in Lake Chad. Using model and
climate data, Coe and Foley calculate that a 30 percent decrease took
place in the lake between 1966 and 1975. Irrigation only accounted for 5
percent of that decrease, with drier conditions accounting for the
remainder. They noticed that irrigation demands increased four-fold
between 1983 and 1994, accounting for 50 percent 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 and the Chari/Logone river system, which transports 90 percent
of the runoff generated in the area basin, are important water resources
for the local population. The lake is 820 feet (250 m) above sea level
and is shared by Chad, Cameroon, Nigeria and Niger. Lake Chad has always
undergone seasonal and inter-annual fluctuations because it is less than
23 feet (7 m) deep. In recent decades, during wet periods the lake
expands up to 10,000 square miles (25,900 square km). The warming
climate and increasing desertification in the surrounding Sahel region
have dropped water levels far below the average dry season level of
4,000 square miles (10,000 square km) to only 839 square miles (1,350
square km). The Northern Africa Sahel region has experienced numerous
devastating droughts over the last three decades. "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. Lake
Chad's primary source of water comes from the monsoon rains that
typically fall in June, July and August. Meanwhile, the use of water for
irrigation has increased, in response to the drier climate. Over the
last 40 years, the discharge from the Chari/Logone river system at the
city of N'Djamena in Chad has decreased by almost 75 percent,
drastically reducing the input into the lake. Between the increase in
agricultural water use and the drier climate, there has been a massive
decline in the amount of water in Lake Chad. 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. Foley said, "The problem is expected to worsen in the coming
years as population and irrigation demands continue to increase."
Regional officials have noticed the dramatic effect the shrinking lake
is having on its surrounding inhabitants.
NASA UNEP ,ESA
compiled from The British Antarctic Study, NASA, Environment Canada,
UNEP, EPA and other sources as stated and credited Researched by Charles
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