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Africa News afrol News
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Africa News afrol News
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afrol News, 25 April - Because of unrelenting human demand for water, Africa's Lake Chad, once one of the continent's largest bodies of fresh water "has shrivelled to a ghost of a great lake," write University of Wisconsin-Madison scientists Michael T. Coe and Jonathan A. Foley. Lake Chad now is "about one-twentieth of the size it was 35 years ago," says Coe, who led the NASA-supported study by the UW-Madison Center for Sustainability and the Global Environment. "It's a huge change" from 25,000 square kilometres of surface area in 1963 to 1,350 square kilometres today. While Lake Chad has been subject to large fluctuations in size before, this is the first time it is due to human influence, the study shows. "The human need for water, mostly through massive irrigation projects, and the competing demands of the four nations that share the lake, account for almost 30 percent of the observed decrease in lake area since the early 1960s," say Coe and Foley. Bad as that is, the problem is expected to worsen as climate change forces an even heavier reliance on irrigated agriculture. A similar environmental disaster has earlier been experienced in Lake Aral in the former Soviet Union. The once important fresh water and fisheries resource Lake Aral has turned into a uninhabitable salt desert after the feeding rivers were overexploited for irrigation. By merging historical data of climate and water use in a computer model, the Wisconsin team now charted the impact of a shifting pattern of climate on Lake Chad over the past 40 years and the rapid growth of human consumption of water from Lake Chad and the rivers that flow into it. The Lake Chad drainage basin, which is similar in size to the US Mississippi River basin, is a closed system that depends on monsoon rains to replenish the water. But the region is extremely sensitive to climate fluctuations and has experienced a significant decline in rainfall since the early 1960s. The amount of water diverted to nearby fields over the past 40 years has affected the lake's equilibrium. "Add poverty, political instability and national rivalries over a scarce resource to the mix, and a recipe for ecological disaster results," Coe says.
The impact is felt by the local populations. One major problem they face is invasive carpets of grass which now cover up to half of the lake's surface, making navigation impossible and threatening the fisheries. Unsustainable water management, including dyke-building and the lack of proper irrigation systems and resulting salt accumulation in the soil, exacerbate this problem. Until about 1979, irrigation had a modest impact on the hydrology of the region. But between 1983 and 1994, the amount of water diverted for irrigation quadrupled over water used for the previous 25 years. In addition to the radically reduced lake surface area, the flow of water from the primary river system that feeds it has decreased by almost 75 percent over the past 40 years. Because Lake Chad is shallow, it responds rapidly to changes in precipitation and runoff. A shifting climate, with fewer large rainfall events, will place the lake in serious jeopardy, threatening the well being of the humans who depend on it and undermining lake and related ecosystems, Coe and Foley say. - The study illustrates the importance of considering human activities on water resources, even in very large hydrologic systems, the Wisconsin climate researchers say. Moreover, the case of a shrinking Lake Chad, Coe and Foley report, demonstrates how human activities exacerbate problems caused by a decline in precipitation. "The take-home message," Coe says, "is that humans have a big impact on these systems and now, through the use of computer simulations, we have some predictive abilities for what humans can do to them." Lake Chad however has experienced great changes in size in history, due to fluctuations in climatic conditions. In the early Holocene (between about 10,000 and 5,000 years ago), when rainfall in Africa was much higher than now, one speaks of a Megachad lake that overflowed to the Atlantic through the Benue River. The Megachad had an extension up to 15 times greater than Lake Chad 35 years ago, and slowly dried in with the dryer climate.
In pre-colonial times, Lake Chad was mostly used as a fisheries resource, while the freshwater resource mostly was exploited through the high groundwater levels in the areas close to the lake. European colonialists however saw the potential in the fresh water source in the middle of the Sahelian zone. Thus, French, British and German colonialists made sure to get access to the resource, a fact that can still be observed by the many international borders leading up to the lake. The colonial powers however did not manage to exploit the lake's fresh water resources at a larger scale, something first achieved by the independent African states surrounding the lake from the 1980's. This, coupled with reduced rainfall in the Sahel in the same period, now clearly shows its environmental consequences, the new study reveals. In addition to the importance Lake Chad plays for the human settlement in the region, it is also "the continent's most endangered wetland," according to the conservation organization WWF. The future of Lake Chad, Coe says, is gloomy: "It will be a puddle. It will be completely managed. You'll get crops and drinking water out of it, but you'll have no ecosystem left to speak of."
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