Climate changes threaten SADC

The internationally respected journal “Science” has warned that streams and rivers in southern Africa could dry up, leading to a surge in migration as people lose access to their water supply. The report warns that unless there is increased regional co-operation the danger of water conflict will grow. The study shows that relatively small changes in rainfall can leave rivers dry, and points out that “water is essential to human survival, and changes in its supply from overland flow can potentially have devastating implications, particularly in Africa, where much of the population relies on local rivers for water”. The report is clear that “future climate change poses one of the greatest threats to poverty eradication on this continent, and related changes in surface water supply will exacerbate this”. One of the report’s authors, Maarten de Wit, of the University of Cape Town, told AIM that the effects of any change in water supply would hit women hardest. He pointed out that “many African rural women in particular spend much of their day-time walking great distances to fetch water: in future such distances are going to increase substantially, so that it may become more efficient for people to vote with their feet and move, joining millions of other African water refugees in a battle to survive”. He predicted that this could become the century of “water wars”, warning that “water, like all resources, can be a source of conflict. River channels and basin watersheds very often mark international boundaries – in Africa they make up almost 40 percent. “In southern Africa disputes seem inevitable if rainfall decreases”, he said. “For example, storing water in Lake Kariba for Zambia and Zimbabwe would have a serious effect in Mozambique. These issues need to be addressed by countries sharing river basins. Being able to estimate the future water supply, like this study does, is an essential factor in any African water basin management scheme”. The article is based on a study by the Africa Earth Observatory Network, in Cape Town, which used databases of all rivers and lakes in Africa to model how changes in rainfall patterns might affect river flows. It found that there is not a simple relationship, rather that in areas that receive rain within the range of 400-1 000 mm per year small changes in rainfall can have larger changes in the total length of perennial rivers (rivers that flow throughout the year). The study is based on predictions of future rainfall patterns determined by the 21 best climate change models for the last 30 years of the 21st Century. The researchers predict that areas near Cape Town will suffer very badly, losing more than half of their perennial river water supply. Also badly hit will be the Orange River, which runs through South Africa and Namibia, with western South Africa currently experiencing its worst drought in over a century. It also warns that Angola will be badly hit. The study points out that those living in rural areas will be the worst affected. While water storage and management systems in most large cities can be restructured to cope with changes in river levels, this is not true in rural areas where people rely on streams and small rivers – some of which might dry up completely. Global warming, caused by greenhouse gasses released by human activity, will not have a uniform effect throughout Africa, and the study’s authors use a climate change assessment made by the Climate System Analysis Group, which is also based in Cape Town, along with research by other respected scientific groups. This predicts that most of southern Africa will have a drop in rainfall, with central and eastern Africa having an increase in rainfall. This is broadly in line with another study, published recently in “Nature” magazine, which warned that it is likely that rivers in southern Africa will shrink by up to a third. That study looked at a dozen climate models to predict the complex relationship between temperature increase and rainfall, and found that while countries in southern Africa are projected to have a decrease in precipitation of between 10 and 30 percent, in eastern equatorial Africa there is a projected increase of between 10 and 40 percent. The author of the “Nature” report, Chris Milly of the United States Geological Survey’s “continental water, climate and earth-system dynamics project”, said that “warmer air can hold more water. This is a large effect. For every degree Celsius of warming, air can hold seven percent more water vapour”. The key to predicting rainfall is to identify where this moist air will turn to rain. One explanation given by Milly is that rainfall occurs where moist air cools as it rises. This causes the moisture to condense, leading to rain. This process is the dominant pattern in equatorial regions, and Milly argues that “any increases in atmospheric humidity are likely to lead to increases in precipitation in such regions”. The “Science” study gives the shock finding that a 10 percent drop in rainfall can result in much larger drops in river levels. Thus, a 10 percent drop in rainfall in eastern Zambia is predicted to result in a 19 percent drop in water levels. A 20 percent drop in rainfall would lead to a 38 percent drop in water levels. Southern Africa therefore has a challenge to make proper plans to serve the region from drying up.

April 2006
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