Once one of Africa's largest bodies of freshwater, Lake Chad is disappearing fast, according to a new study published in this week's Journal of Geophysical Research-Atmospheres. "It's about one-twentieth of the size it was 35 years ago," co-author Michael T. Coe says. The lake has been reduced from approximately 25,000 square kilometers in 1963 to only 1,350 square kilometers today. Coe and colleague Jonathan A. Foley, both of the University of Wisconsin at Madison, found natural and man-made causes for the development.

The lake and the Chari River, which flows out of it, constitute the most important water source in the region, and massive irrigation systemsbuilt by Niger, Nigeria, Cameroon and Chad, the nations that share the lakeare seriously draining it. The researchers looked at data and observations of the lake going back 43 years. From 1953 to 1979 irrigation had only a modest impact on the ecosystem, but from 1983 to 1994 the water usage for irrigation increased fourfold. Total human water use accounts for roughly 50 percent of the decrease in lake area since the 1960s and 1970s.

The rest of the decrease is due to a shifting climate pattern over the past 40 years. The Lake Chad drainage basin depends on monsoon rains to replenish its water, and this rainfall has dropped dramatically since the early 1960s. According to Coe, the outlook for Lake Chad is gloomy: "It will be a puddle. Youll get crops and drinking water out of it, but you'll have no ecosystem left to speak of."