Water crisis looming for Africa
Mar 19, 2006
GLOBAL warming is expected to lead to broad changes in average rainfall across Africa. A recent study published in Science shows that the impact of those changes on rivers and lakes in Africa should be a major cause for concern.
By Jennifer Austin
GLOBAL warming is expected to lead to broad changes in average rainfall across Africa. A recent study published in Science shows that the impact of those changes on rivers and lakes in Africa should be a major cause for concern.
Expected changes in annual rainfall will have an amplified effect on surface water across much of the continent.
In extreme cases, a decrease in annual rainfall of just 10% is expected to bring drainage density to zero. Drainage density is defined in the study as perennial stream length per unit area and essentially indicates the availability of surface water.
Drainage will be most seriously affected in areas in the ‘intermediate, unstable regime’ defined as areas receiving between 400 and 1000mm of rainfall per year.
A 10% reduction in rainfall in an area usually receiving 1000mm per annum will lead to a 17% decrease in surface water, whereas the same drop in rainfall over an area receiving just 500mm per year will lead to a 50% drop in surface water. Areas with between 400 and 500mm per year are expected to lose more than half, if not all, of the already miniscule drainage density they have.
Land classified as intermediate and unstable covers 25% of the African continent falling into 75% of the countries.
Most of southern Africa lies in the unstable to dry regime and is at high risk of losing much of the drainage it has.
Western South Africa is already facing the biggest drought in 100 years and is expected to see a continued decline in rainfall, leading to even larger declines in surface water.
The east-west band stretching from Senegal to Sudan, also an unstable region expected to see decreases in rainfall and drainage, includes a number of important water catchment areas, including parts of the Nile Basin, Lake Chad (which has already shrunk to 10% of its former size) and the Niger River.
East Africa is expected to see an increase in rainfall in some places enough to change its classification from intermediate to a ‘wet’ regime area.
The largest increases in rainfall and drainage are expected over Somalia, but the area will still be ‘dry’ because even 10 times the current drainage is still very small.
The study warns that while cities may be able to cope by re-engineering water provision systems, rural areas that are directly dependent on rain-fed streams for water and agriculture will be hard hit and do not have much ability to adjust.
Because of the importance and scarcity of water across the continent, the political and social implications of these changes in surface water availability are huge. All major African rivers cross international boundaries and almost 40% of these borders are marked by rivers.
The expected movement of people in search of water could lead to political tensions, as these so called ‘water refugees’ crowd the areas where water remains.
To make these calculations, scientists combined data from climate change models predicting expected changes in rainfall, with detailed studies of how changes in rainfall affect drainage density.
Rainfall predictions in the study were taken from the Climate System Analysis Group based in Cape Town, South Africa, which has made detailed rainfall predictions for specific regions in Africa based on results from six Global Circulation Models (GCMs).
The study used these results as well as a ‘composite ensemble of African precipitation models for the period 2070-2099, derived from 21 fully-coupled ocean-atmosphere GCMs listed by the Intergovernmental Panel on Climate Change (IPCC).’
The IPCC is the body established by the World Meteorological Organisation and the UN Environmental Programme to monitor and assess scientific information related to climate change.
Climate change models are based on the expected climate effects of different levels of greenhouse gas emissions.
Future emissions are of course dependent upon what actions are taken by governments and agencies to curb emissions. This study looked at “a relatively optimistic model that includes the assumption of a timely and effective development of non-fossil energy supply†named the B1 marker-scenario by climate change scientists.
Ends
GLOBAL warming is expected to lead to broad changes in average rainfall across Africa. A recent study published in Science shows that the impact of those changes on rivers and lakes in Africa should be a major cause for concern.
Expected changes in annual rainfall will have an amplified effect on surface water across much of the continent.
In extreme cases, a decrease in annual rainfall of just 10% is expected to bring drainage density to zero. Drainage density is defined in the study as perennial stream length per unit area and essentially indicates the availability of surface water.
Drainage will be most seriously affected in areas in the ‘intermediate, unstable regime’ defined as areas receiving between 400 and 1000mm of rainfall per year.
A 10% reduction in rainfall in an area usually receiving 1000mm per annum will lead to a 17% decrease in surface water, whereas the same drop in rainfall over an area receiving just 500mm per year will lead to a 50% drop in surface water. Areas with between 400 and 500mm per year are expected to lose more than half, if not all, of the already miniscule drainage density they have.
Land classified as intermediate and unstable covers 25% of the African continent falling into 75% of the countries.
Most of southern Africa lies in the unstable to dry regime and is at high risk of losing much of the drainage it has.
Western South Africa is already facing the biggest drought in 100 years and is expected to see a continued decline in rainfall, leading to even larger declines in surface water.
The east-west band stretching from Senegal to Sudan, also an unstable region expected to see decreases in rainfall and drainage, includes a number of important water catchment areas, including parts of the Nile Basin, Lake Chad (which has already shrunk to 10% of its former size) and the Niger River.
East Africa is expected to see an increase in rainfall in some places enough to change its classification from intermediate to a ‘wet’ regime area.
The largest increases in rainfall and drainage are expected over Somalia, but the area will still be ‘dry’ because even 10 times the current drainage is still very small.
The study warns that while cities may be able to cope by re-engineering water provision systems, rural areas that are directly dependent on rain-fed streams for water and agriculture will be hard hit and do not have much ability to adjust.
Because of the importance and scarcity of water across the continent, the political and social implications of these changes in surface water availability are huge. All major African rivers cross international boundaries and almost 40% of these borders are marked by rivers.
The expected movement of people in search of water could lead to political tensions, as these so called ‘water refugees’ crowd the areas where water remains.
To make these calculations, scientists combined data from climate change models predicting expected changes in rainfall, with detailed studies of how changes in rainfall affect drainage density.
Rainfall predictions in the study were taken from the Climate System Analysis Group based in Cape Town, South Africa, which has made detailed rainfall predictions for specific regions in Africa based on results from six Global Circulation Models (GCMs).
The study used these results as well as a ‘composite ensemble of African precipitation models for the period 2070-2099, derived from 21 fully-coupled ocean-atmosphere GCMs listed by the Intergovernmental Panel on Climate Change (IPCC).’
The IPCC is the body established by the World Meteorological Organisation and the UN Environmental Programme to monitor and assess scientific information related to climate change.
Climate change models are based on the expected climate effects of different levels of greenhouse gas emissions.
Future emissions are of course dependent upon what actions are taken by governments and agencies to curb emissions. This study looked at “a relatively optimistic model that includes the assumption of a timely and effective development of non-fossil energy supply†named the B1 marker-scenario by climate change scientists.
Ends