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Africa: Africa's Lakes

AfricaFocus Bulletin
Sep 10, 2006 (060910)
(Reposted from sources cited below)

Editor's Note

"For now, the future of Lake Chad does indeed look bleak. With a high population growth rate, pressures on water resources in the lake basin will invariably continue. While in the past Lake Chad has been able to rebound from low to high water levels, climate change and people's water use may now act in concert to block the natural forces of recovery." - atlas of Africa's Lakes

The new atlas of Africa's Lakes, released as a print publication and on-line by the United Nations Environmental Programme in Nairobi, contains the latest scientific research, high-quality satellite images, and policy analysis and recommendations on preserving the resources of the lakes of Africa, According to the atlas, Africa is estimated to have 30 million cubic kilometers of water in large lakes, the largest volume of any continent.

This AfricaFocus Bulletin contains excerpts from case studies on Lake Chad and Lake Victoria, from Africa's Lakes: An Atlas of Environmental Change (http://www.unep.org).

Another AfricaFocus Bulletin sent out today contains a press release on the publication of the Atlas, as well as a commentary by Achim Steiner, the new executive director of UNEP.

For an earlier AfricaFocus Bulletin on related issues, see http://www.africafocus.org/docs06/vic0602.php

++++++++++++++++++++++end editor's note+++++++++++++++++++++++

Impacts on Africa's Lakes Case Studies of Africa's Changing Lakes

United Nations Environmental Programme
http://www.unep.org

Excerpted from Africa's Lakes: An Atlas of Environmental Change

...While evidence of change is not always clearly visible on lakes, wetlands and coastal environments, human impacts on Africa's lakes can be "seen" by detecting and measuring rising water temperatures, sediment accumulation, and various chemical contaminants in their waters. Another obvious human impact is the rapid decline in fish species and numbers in many lakes. A recent 10-year study on the ecological effects of industrialised fishing in Africa's lakes found that large predatory fish species have declined by at least 20 per cent from pre-industrial levels (World Resources Institute 1994). Furthermore, the average size of surviving individuals among these species is only one-fifth to one-half of their previous size.

The composition of the Earth's atmosphere is also undergoing rapid change, with subsequent impacts on Africa's lakes. Today, increases in atmospheric concentrations of greenhouse gases are expected to cause more rapid changes in the Earth's climate than have been experienced for millennia. At least some of the global increase is due to human activity, and certainly local impacts such as urban 'heat islands' have profound effects on regional climatic conditions, which will in turn impact on Africa's lakes, wetlands and coastal environments. Lakes in Africa are major sites for water extraction and waste disposal, often with a negative impact on human health. Some contain vast amounts of CO 2, which when released can kill thousands of people. There is a need for continuing assessment and monitoring of these lakes, most of which are located in the Great Rift region, making them also susceptible to earthquakes and volcanic eruptions, which can cause flooding.

Constant evaluation and reporting on the state of Africa's lakes are critical if they and their connected wetlands are to be sustainably managed. Pressures from logging, gold-panning, hydropower and other developments are leading to the conversion of large areas of wetlands, with devastating implications for their ecological integrity. Such developments also have long-term implications for the integrity of watersheds, rivers and related coastal resources, as well as their ability to support complex biodiversity.

Several globally significant environmental trends that occurred between 1980 and 2000 may also be contributing to the pollution and degradation of Africa's lakes, including global warming, three intense El Ni¤o events, changes in cloudiness and monsoon dynamics, and a 9.3 per cent increase in atmospheric CO2. Although these factors are thought to exert their influence globally, their relative roles are still unclear and their impacts are likely to be significant for African communities whose livelihoods depend upon resources from lakes, wetlands and coastal environments.

An observed decline in freshwater fisheries is one of the more important recent challenges to African governments that depend upon the export of aquatic resources (although none of the existing surveys can accurately simulate this effect). It is known that continued reductions in fresh water, if accompanied by reduced rainfall, will have profound implications for poor communities that depend upon lake and wetlands resources for a living.

Lake Chad

Persistent droughts and the ravages of a rapidly growing human population have decimated what was once the sixth-largest lake in the world, Lake Chad straddling the borders of Nigeria, Chad and Cameroon. Over the past four decades, the lake's surface has reportedly shrunk from 22 000 km2 (8 494 square miles)to a meager 300 km2 (115 square miles). Today, it is hard to reconcile the fact that this largely dry lakebed was once the second largest wetland in Africa, supporting a rich diversity of endemic animals and plant life.

Seen from space, the shallow Lake Chad is a circular wetland with open water in two distinct basins, divided by ancient sand dunes, which act as a swamp belt. Seated at the southern edge of the Sahara desert, where temperatures often exceed 40 C (104 F), the lake's very existence is a fascinating enigma.

Lake Chad's maximum-recorded depth, prior to the start of its decline in the 1970s, was 12 metres (39 feet). Today, the lake is far shallower, although fluctuations in volume result in substantial changes to its surface area. The lakebed itself is not flat, but lies on an ancient bed of fossilized sand dunes, many of which surface as islands when the lake level falls (Sikes 2003). Submerged dunes form hidden anchorages for floating vegetation, which covers vast areas of the lake.

About 90 per cent of Lake Chad's water comes from the Chari-Logone River, which enters the lake from the southeast, with its sources in the humid uplands of the Central African Republic. The Komadougou-Yobe River, which enters the lake in the northwest, historically has contributed about 10 per cent of its water. As well as a vital source of fresh water for local communities, Lake Chad's unique mix of terrestrial and aquatic habitats hosts biodiversity of global significance although most of its large mammal species have been hunted virtually to extinction (Nami 2002). Crocodiles and hippos were particularly important agents for maintaining a healthy wetlands ecosystem (Mockrin & Thieme 2001). Today, however, the replacement of these mammals with cattle has severely degraded the wetlands ecosystem.

Within Lake Chad itself, the major plant communities comprise floating 'sudd' weeds, permanent reed swamps, and seasonal herbaceous swamps (GEF 2002). Grasslands dominate in areas that flood, interspersed with acacia woodlands, with dryland woodlands in sandy soils further from the lake (Mockrin & Thieme 2001).

Lake Chad's level has varied greatly over time. Some 50 000 years ago, Paleo-Chad formed a freshwater inland sea covering nearly 2 million km2 (772 thousand square miles). Lake levels regressed until, between 5 000 and 2 500 years ago, the lake assumed its current level with periodic oscillations. By 1908, lake levels were so low that the lake resembled a vast swamp with small northern and southern pools (Sikes 2003). During the 1950s, levels again increased, joining the southern and northern pools, so that by 1963 the lake covered 22 902 km2 (8 842 square miles). Water levels then decreased, and by 1972 the lake covered 16 884 km2 (6 519 square miles). The most dramatic reductions occurred between 1972 and 1987, by which time the lake had shrunk to just 1 746 km2 (674 square miles). From the mid-1980s, the north basin rarely held any water at all although, since the mid-1990s, levels have once again started to rise in response to increased rainfall (FEWS 2003).

The dramatic fluctuations of Lake Chad are usually attributed to a complex interaction of climatic and human forces. Recent modelling studies have attempted to quantify the interplay of two climatic factors: variability and water use. In a nutshell, climate variability sets the parameters within which humans must operate. As the human impact upon the local landscape becomes more severe, humans are in danger of changing these parameters.

Climate

The climate around Lake Chad is hot and dry, with highly variable annual rainfall ranging from 565 mm (22 in) in 1954 to just 94 mm (4 in) in 1984 (Olivry et al. 1996). However, the lake level relies little on local precipitation, with the Chari-Logone's sources receiving an average rainfall of some 1 600 mm (63 in). Precipitation in the basin varies geographically, with much more in the south than the north. Rainfall also varies seasonally with about 90 per cent of it falling from June to September (USGS 2001). During the dry season, low humidity and high winds increase evaporation rates from the lake. Although evaporation is generally very high, salinity is not a significant issue as heavier saline water leaves the lake through fissures in its floor. Water loss through the lakebed accounts for about eight per cent of the water outflow from the lake.

In the late 1960s, the western Sahel appears to have undergone an abrupt hydro-climatic transition from a wetter to a drier rainfall state. Rainfall became intermittent at Lake Chad, culminating in two major droughts in 1972-74 and 1983-84. In the mid-1990s, rainfall again increased with several good years ensuing. Areas of the lake that once experienced a mean rainfall of 320 mm (13 in) currently receive less than 210 mm (8 in)(GEF 2002). The size of the region affected by this change and its duration are without precedent in hydro-climatic chronicles. Some authors have speculated that the change is symptomatic of a "climate rupture" (Carbonnel & Hubert 1985, in Nami 2002).

Water use

Since the 1960s, human demands for water near Lake Chad have grown rapidly. Between 1960 and 1990, the number of people living in the lake's catchment area has doubled from 13 million to 26 million (UNEP 1999). With agriculture providing the main livelihood in 60 per cent of the lake basin, demand for water for irrigation is estimated to have quadrupled between 1983 and 1994 (GEF 2002). At present, some 135 000 hectares of land are irrigated in the lake basin. The most extensive irrigation projects, totaling over 100 000 ha, have been developed in Nigeria, where the Southern Chad Irrigation Project alone had the goal of irrigating 67 000 ha of land with an average cropping intensity of 130 per cent, and resettling about 55 000 families onto the irrigated land (Sikes 2003). Unfortunately, since the droughts of the early 1970s, the water level of Lake Chad has not been high enough to reach the intake canals of the irrigation system (Sarch & Birkett 2000).

In addition to irrigation, dams have influenced the rivers that feed Lake Chad. In the Kano and Hadejia basins, there are believed to be about 23 earth dams. The Komadougou-Yobe river system provides an example of the dramatic impact of human diversion. The upper basin used to contribute approximately 7 km3/yr (4 cubic miles/yr) to Lake Chad. Today, the bulk of this water is impounded in reservoirs within Kano province in northern Nigeria, and the system provides just 0.45 km3/yr (0.23 cubic mile/yr). Nor is there any likelihood of increasing discharge down the Komadougou-Yobe, as demands for water for irrigation in the densely populated upper basin near Kano will never decrease.

Although the contribution from the Komadougou-Yobe drainage system was only 10 per cent of the total contribution to Lake Chad, once the lake divided into a north and a south basin its loss to the north basin became critical, as good pasture for livestock became harder to find (Sikes 2003). The loss of water behind dams has been further compounded by an increase in irrigation from wells and boreholes since the 1960s, resulting in reduced groundwater regeneration.

Research by Oyebande (2001) suggests that dam construction in the upper Komadugu-Yobe system is largely to blame for the change in the flow regime. He suggests that the river course was heavily influenced by the spring flooding prior to the dams' construction, and that the leveling out of the flow would result in less water reaching downstream provinces and Lake Chad, even if the flow volume was increased. By contrast, decreasing input from the Chari-Logone river system, where human consumptive use has been estimated at less than five per cent of the basin yield, is attributed mainly to lower rainfall (Olivry et al. 1996).

Using an integrated biosphere model, run with and then without extraction for irrigation, Coe and Foley (2001) concluded that water-level fluctuations in Lake Chad over the past 35 years have been caused by both climate variability and water use. From 1956 to 1975, decreases in the lake's level and surface area resulted primarily from long-term climate change, with only five per cent of the lake level decrease attributed to water management practices. Since the 1970s, however, with marked population increases, human activities have begun to play a more significant role in accelerating lake-level declines. The onset of dry climatic conditions in the early 1970s induced people to dramatically increase their irrigation activities, almost doubling water loss from Lake Chad (Coe & Foley 2001). The balance between the lake and its wetlands has always been precarious, as inputs balance losses to groundwater and evaporation. However, increased irrigation, which would be modest for many river systems, is particularly critical to the fate of the carefully balanced climatic-ecological system of Lake Chad.

Traditionally, fishing and farming near the lake have followed its rise and fall, both seasonally and through the years. During dry seasons and years, farmers move to the rich soils of the newly exposed lake bottom, and then fish during floods (Sarch & Birkett 2000). However, as lake levels recede, the danger increases that the lake will not reach villages during the annual floods. The cost of exporting surplus crops has also increased as cheap water transportation across the open lake is increasingly being replaced by transport via road or maintained canals. The introduction of irrigation and the movement of people to the lake, who only know the lake in its present state, shift the perspective from water use to water management. In fact, a danger exists that, if the water were to rise again to 1960 levels, the long-time inhabitants of the basin may no longer be able to retreat from its rising waters, as the land behind them is increasingly exploited for irrigated agriculture.

The Future

As Lake Chad continues to shrink, its future as Africa's second largest wetland is increasingly uncertain. Plants that require water, or are adapted to changing water levels, are becoming more disadvantaged than those adapted to water stress. With little fresh water entering the north basin from the Komadougou-Yobe, the basin will become more saline if it is isolated for long periods (Dumont 1992). As annual grasses replace productive perennial grasslands, biodiversity is also declining (Verhoeye 2001). Declines in vegetation associated with the lake ecosystem may result in increased erosion, and ultimately in desertification. The IPCC has predicted reduced rainfall and run-off, and increased desertifi cation, in the Sahelian belt near Lake Chad (IPCC 2001).

The biodiversity of fish and birds in the Lake Chad region is also under threat. The drying up of water basins and ponds both directly and indirectly increases fish mortality. The Alestes naremoze, a species that once contributed up to 80 per cent of the local catch, is becoming rare due to the disappearance of its natural spawning beds. Migratory birds like the European white stork, which depend upon Lake Chad as a key resting place on their migrations across the Sahara, may no longer be able to complete this vital part of their annual lifecycle.

Diminishing water resources and continued ecosystem decline also have severe health and economic implications for the people living around Lake Chad. The northern states of Nigeria and Cameroon are among the poorest in these two countries (World Bank 1995b). Sarch and Birkett (2000) report a rapidly shrinking average annual fish catch in the Lake Chad Basin, from 243 000 tonnes in 1970-77 to 56 000 tonnes in 1986-89. As fish decline, economic losses may also lead to cultural losses particularly among the Yedina, a unique fishing people that occupies the lake's islands and swamps (Sikes 2003). Around the lake, domestic plant and animal production may become untenable due to increasing soil erosion and desertifi cation. In the lower Yobe, dunes and layers of sand are already invading date palm plantations (Nami 2002). And finally, health problems also appear to be increasing, with less potable water leading to cases of diarrhea, cholera and typhoid fever throughout the basin (GIWA 2004).

For now, the future of Lake Chad does indeed look bleak. With a high population growth rate, pressures on water resources in the lake basin will invariably continue. While in the past Lake Chad has been able to rebound from low to high water levels, climate change and people's water use may now act in concert to block the natural forces of recovery. While renewed rainfall has recently returned to the region, it is clear that the lake's future continues to hang in the balance and will require very careful planning and multilateral management commitments in order to prevent one of Africa's greatest life-forces from becoming yet another extinct species.

Lake Victoria

The largest freshwater lake in Africa and the second largest in the world, Lake Victoria occupies a total catchment of about 250 000 km2, of which 68 870 km2 is the actual lake surface (URT 2001). Located in the upper reaches of the Nile River Basin, the lake waters are shared by the three East African countries of Kenya, Uganda and Tanzania. The lake draws 20 per cent of its water from the Kagera, Mara, Simiyu, Grumeti, Yala, Nyando, Migori and Sondu-Miru rivers, while the remaining 80 per cent comes from rainfall. Mountains surround the catchment area on all sides except for the north.

Lake Victoria supports one of the densest and poorest rural populations in the world, with densities of up to 1 200 persons per square kilometre in parts of Kenya (Hoekstra and Corbett 1995). An average annual population growth rate of three per cent is exerting increasing pressures on the lake's natural resources. In all of the riparian countries, the people living around the lake have become increasingly vulnerable to environmental change over the past two decades, due to natural processes and inappropriate human actions (Birch-Thomsen et al. 2001).

Water erosion is extensive in many parts of the Lake Victoria Basin, with approximately 45 per cent of the land prone to such erosion. Increased siltation of the lake and increased risk of flooding in estuaries are the direct effects of soil erosion and other degradation forces in the basin. The near annual flash floods on the Lake Victoria plains have been linked to such forces emanating from point and non-point processes (Gichuki 2003).

The eutrophication of Lake Victoria is clearly linked to land-use changes and rapid population growth in the lake catchments, with impacts clearly affecting the lake from about 1930. Only a small proportion of land around the lake has favourable agro-ecological conditions for agricultural development, and these tend to be the most overpopulated areas. Most of the land has fragile ecosystems that need to be protected, soils with low fertility and poor texture, biotic constraints such as tsetse fly, and areas prone to flooding. Despite these unfavourable conditions, however, major population increases have resulted in the widespread cultivation of these fragile pockets of land accelerating the degradation of the entire lake ecosystem.

The infestation of Lake Victoria by water hyacinth in the 1990s disrupted transportation and fishing, clogged municipal water pipes, and created a habitat for disease-causing insects. This led to the initiation of the Lake Victoria Environmental Management Project in 1994, which prioritised the removal of hyacinth infestations, particularly from the severely affected bays of Uganda.

The urgent need to rapidly transform land use in the Lake Victoria Basin is underscored by the fact that the region's anticipated population growth will not only reduce the availability of land per capita, but will accelerate the rate of its degradation. Dwindling land resources in the basin present its inhabitants and their development partners with monumental paradoxes, from the mounting freshwater demands of some 30 million people, to growing industrialisation and urbanisation, increasing agricultural pollution, the loss of freshwater biodiversity, and the overexploitation of fishery resources.


AfricaFocus Bulletin is an independent electronic publication providing reposted commentary and analysis on African issues, with a particular focus on U.S. and international policies. AfricaFocus Bulletin is edited by William Minter.

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