Lynn Chandler Goddard Space Flight Center, Greenbelt, Md. (Phone: 301/614-5562)February 27, 2001Release No: 01-17AFRICA'S LAKE CHAD SHRINKS BY 20 TIMES DUE TO IRRIGATION DEMANDS, CLIMATECHANGEIn the 1960s, North central Africa's Lake Chad was larger than the state of Vermont but is nowsmaller than Rhode Island. NASA-funded researchers using computer models and climate datanow 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 climateand high agricultural demands for water as reasons why what was once one of Africa's largestfreshwater lakes is shrinking. "Lake Chad was about 25,000 square kilometers in surface areaback 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,"is being published today in the American Geophysical Union's Journal of Geophysical Research. Intheir paper, Coe and Foley used an integrated biosphere model (IBIS) with long time-seriesclimate data. They simulated the exchange of energy, water and carbon dioxide betweenvegetation, soil and the atmosphere, and tracked the changes in Lake Chad since 1953. Theyinput the data from the biosphere model into a hydrological model and were able to estimatechanges 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 inthe lake between 1966 and 1975. Irrigation only accounted for 5 percent of that decrease, withdrier 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 ofthe lake."NASA Landsat satellite imagery taken of the lake over the last 30 years really capture the modelconclusions and visualize them very well," the researchers noted.Lake Chad and the Chari/Logone river system, which transports 90 percent of the runoffgenerated in the area basin, are important water resources for the local population. The lake is820 feet (250 m) above sea level and is shared by Chad, Cameroon, Nigeria and Niger. Lake Chadhas 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 (25,900square km). The warming climate and increasing desertification in the surrounding Sahel regionhave dropped water levels far below the average dry season level of 4,000 square miles (10,000square km) to only 839 square miles (1,350 square km).The Northern Africa Sahel region has experienced numerous devastating droughts over the lastthree decades. "Climate data has shown a great decrease in rainfall since the early 1960's largelydue 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, Julyand August. Meanwhile, the use of water for irrigation has increased, in response to the drierclimate. Over the last 40 years, the discharge from the Chari/Logone river system at the city ofN'Djamena in Chad has decreased by almost 75 percent, drastically reducing the input into thelake. Between the increase in agricultural water use and the drier climate, there has been amassive decline in the amount of water in Lake Chad.With a drier climate and less rainfall, agricultural areas become more desperate for water toirrigate their crops, and will continue draining what is left of Lake Chad. Foley said, "The problemis expected to worsen in the coming years as population and irrigation demands continue toincrease."Regional officials have noticed the dramatic effect the shrinking lake is having on its surroundinginhabitants. In the summer of 1998, the President of Chad hosted the 10th Lake Chad summit withleaders from Nigeria, Niger, the Central African Republic, Cameroon and Sudan to discuss how toboost water levels.NASA's Earth Observing System funded the Lake Chad study. The overall goal of NASA's EarthObserving System is to advance the understanding of the entire Earth system on a global scale byimproving our knowledge of the components of the system, the interactions between them andhow the Earth system is changing.Images and additional information can be found