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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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