Climate change and surface water
From the research I have completed since starting this blog, I have figured that African water sources are vulnerable to hydro-climatic variability and therefore, it's not surprising that the IPCC expects that climate change will exacerbate existing water stress across the continent: Africa has not and will not be exempt from climate change impacts.
But as you know, I am interested in how climate change's impact on precipitation affects Africa's water scarcity. In this post, I plan to discuss specifically how surface water supplies will be altered by the impacts of climate change. Surface water is simply water on the ground surface - rivers, lakes, wetlands are all examples of surface water and offer potential potable water resources.
de Wit and Stankiewicz (2006) quantified how a change in precipitation across Africa projected by GCMs would affect the continent by the end of the century. 75 percent of countries in Africa are categorised as having an unstable intermediate rainfall regime (drainage density increases with increasing rainfall, or alternatively with decreasing rainfall there is a decrease in drainage density). By 2100, they calculated that surface water access would be significantly altered across a quarter of Africa; with a ten percent precipitation decrease in regions with 1000mm of rainfall per year, there would be a 17 percent decrease in drainage. This reduction in surface drainage would increase to 50 percent in regions with 500mm of rainfall per year. Ultimately, basins in dry areas are more vulnerable to reduced rainfall than wetter basins. Reductions in continuous flows in a river could have serious implications on water resource access, especially for countries that share water basins - for instance, the Nile Basin.
We cannot oversimplify things however: significantly, climate change across Africa will not be uniform. As I mentioned before, there are projected decreases in northern and southern parts of Africa, but alternatively there will be increases in central and eastern parts of Africa. Modelling from de Wit and Stankiewicz (2006) predict that East Africa will have a consequent increased drainage density for instance.
Additionally, Favreau et al. (2009) discovered that land clearing (from savanna to millet crop) has resulted in higher runoff in a semi-arid watershed in SW Niger, which has offset the 23 percent reduction in mean annual rainfall from 1970 to 1998. These points are both interesting since it suggests that climate change won't produce such negative impacts after all... but of course we must question whether increased drainage density and runoff equates to greater water availability. For instance, Favreau et al. (2009) also found a decreasing quality in water supply from land clearing degrading groundwater resources.
Climate change's impact on surface water supply seems to be a lot more nuanced than I first thought. There seems to be no uniform trend and other factors, such as landuse mentioned here, are expected to complicate matters further. There are also issues of data quantity and quality to help verify and validate these predictions - a reoccurring point made regularly in papers. These are all things I will like to investigate further as this blog continues. Next time, I will be looking at how groundwater sources are expected to change from climate change.
But as you know, I am interested in how climate change's impact on precipitation affects Africa's water scarcity. In this post, I plan to discuss specifically how surface water supplies will be altered by the impacts of climate change. Surface water is simply water on the ground surface - rivers, lakes, wetlands are all examples of surface water and offer potential potable water resources.
de Wit and Stankiewicz (2006) quantified how a change in precipitation across Africa projected by GCMs would affect the continent by the end of the century. 75 percent of countries in Africa are categorised as having an unstable intermediate rainfall regime (drainage density increases with increasing rainfall, or alternatively with decreasing rainfall there is a decrease in drainage density). By 2100, they calculated that surface water access would be significantly altered across a quarter of Africa; with a ten percent precipitation decrease in regions with 1000mm of rainfall per year, there would be a 17 percent decrease in drainage. This reduction in surface drainage would increase to 50 percent in regions with 500mm of rainfall per year. Ultimately, basins in dry areas are more vulnerable to reduced rainfall than wetter basins. Reductions in continuous flows in a river could have serious implications on water resource access, especially for countries that share water basins - for instance, the Nile Basin.
 |
| Results from de Witz and Stankiewicz (2006) |
We cannot oversimplify things however: significantly, climate change across Africa will not be uniform. As I mentioned before, there are projected decreases in northern and southern parts of Africa, but alternatively there will be increases in central and eastern parts of Africa. Modelling from de Wit and Stankiewicz (2006) predict that East Africa will have a consequent increased drainage density for instance.
Additionally, Favreau et al. (2009) discovered that land clearing (from savanna to millet crop) has resulted in higher runoff in a semi-arid watershed in SW Niger, which has offset the 23 percent reduction in mean annual rainfall from 1970 to 1998. These points are both interesting since it suggests that climate change won't produce such negative impacts after all... but of course we must question whether increased drainage density and runoff equates to greater water availability. For instance, Favreau et al. (2009) also found a decreasing quality in water supply from land clearing degrading groundwater resources.
Climate change's impact on surface water supply seems to be a lot more nuanced than I first thought. There seems to be no uniform trend and other factors, such as landuse mentioned here, are expected to complicate matters further. There are also issues of data quantity and quality to help verify and validate these predictions - a reoccurring point made regularly in papers. These are all things I will like to investigate further as this blog continues. Next time, I will be looking at how groundwater sources are expected to change from climate change.
Comments
Post a Comment