Jim Lobe
WASHINGTON, Mar 2 2006 (IPS) – Declines in rainfall caused by global warming threaten rivers and other local sources of fresh water in densely populated areas of Africa, according to a new study published here by Science magazine Friday.
Some of these areas, particularly in southern Africa, already suffer periodic droughts, so further declines in rainfall could have devastating implications for people who depend on local water supplies, according to the two authors, Maarten de Wit and Jacek Stankiewicz of the Africa Earth Observatory Network (AEON) at the University of Capetown.
Other particularly vulnerable areas include a narrow band of territory that stretches from Senegal eastward to Sudan and crosses several important water bodies that supply populations downriver, such as the Sudd swamps in the Nile Basin and the Niger River. They also include parts of East Africa south of Somalia.
Because much of the rainwater is absorbed by soil and plants before it can reach streams and rivers, declines in rainfall in these areas translate into much steeper declines in the amount of water available for human use. A 10-percent drop in precipitation in regions that receive 600 millimetres (mms) of rainfall per year could result in a 50 percent drop in surface drainage.
Altogether, the decline in rainfall and the resulting decrease in perennial drainage rivers, lakes and other bodies of water that hold or carry surface water throughout the year will significantly affect access to water across 25 percent of Africa by the end of the century, according to the study.
The study, which is based on a number of different climate models that predict the impact of global warming on rainfall, comes amid growing indications that warming is taking place even faster than scientists had expected.
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In January, the U.S. National Aeronautics and Space Administration s (NASA) Goddard Institute of Space Studies confirmed that 2005 was the warmest year on record and the past 10 years the hottest decade by far.
According to the BBC, a report to be issued later this month by the Intergovernmental Panel on Climate Change (IPCC), a group of hundreds of scientists from around the world, will warn that given current projections of greenhouse gas emissions, global temperatures are likely to rise between two and 4.5 degrees Centigrade by the end of the century significantly higher than the IPCC s previous predictions.
A recent report that Greenland s glaciers from its massive ice sheet are melting twice as fast as previously believed along with similar reports on ice melt in the Arctic and mountain glaciers supports the notion that the Earth s climate is, as Goddard s director, James Hansen put it last December, nearing a tipping point beyond which it will be impossible to avoid climate change with far-ranging undesirable consequences .
While he was referring mainly to the impact of the rise in sea levels caused by melting ice, scientists agree that changes in the Earth s climate, including rainfall patterns, will also be dramatic.
In a study released last year, Anthony Nyong, a scientist at Nigeria s Jos University, warned that, if current trends continue, rainfall in sub-Saharan Africa will drop by 10 percent by 2050, leading to major water shortages due to the even greater loss of drainage water.
The new study builds on Nyong s work by using the latest computer models to determine how warming will affect rainfall and drainage systems in specific regions in Africa.
The study divides the continent into three regimes dry areas that will receive less than 400 mms/year of rainfall and consequently have virtually no perennial drainage; wet areas that will receive more than 800 mms/year; and intermediate, or unstable , areas that will receive 400-800 mms/year by the end of this century.
According to the study, the dry zone will cover virtually all of North Africa, the Sahel and much of the Horn of Africa, as well as the western half of South Africa extending up through Namibia and coastal Angola a total of 41 percent of the continent.
With the exception of Somalia and nearby parts of Ethiopia and Kenya, which will see an increase in rainfall of between 10 and 20 percent, most of this zone will experience a decline in rainfall, in some cases such as North and Southwestern Africa, of as much as 20 percent.
The wet areas will include Central and most of West Africa around the Gulf of Guinea extending east to parts of Sudan, Uganda, Tanzania, Mozambique and northern Madagascar. Most of these areas should see an increase in rainfall of up to 10 percent, according to the study.
The unstable, intermediate areas, comprising 25 percent of Africa, are of greatest concern to the authors, however, because declines in rainfall will have a serious impact on water supplies.
While some of these areas, especially in East Africa, are likely to see increases in rainfall of up to 10 percent, other areas, notably in West Africa and southern Africa, are likely to experience declines.
Southern Africa, in particular, will find itself in a very disturbing situation , according to the study.
Most countries in Central and Eastern Africa will fall into the unstable regime with likely declines in rainfall of around 10 percent, according to the models. Compounding the problem is the fact that most of the arid western part of the region is dependent on the Orange River, whose sources will lie in unstable areas.
While much of eastern Africa should experience increases in rainfall, most of it will still fall under the either the dry or unstable regimes. Despite major increases in rainfall forecast for Somalia, for example, most of the country will receive less than 400 mm/y.
At the same time, the unstable Upper Nile region will be very seriously affected by projected changes in rainfall patterns.
A third unstable area of concern to the authors is the east-west band that will separate the dry Sahara from wet Central Africa, precisely because it includes so many important drainage systems such as the Senegal, Niger, Volta, and Nile river systems, as well as Lake Chad on which millions of people depend for their water.
