The Physical Distribution of Water Across Africa

In this post, we will discuss the physical distribution of water resources across the continent.

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Global Climate Dynamics

It is far too often when one picture the African continent to immediately reduce it to an extensive piece of land that is eternally dry and water-scarce. In reality, high variability in precipitation and hydrology results in a myriad of different landscapes and ecosystems at different times of the year.

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Precipitation across Africa is controlled by global patterns of atmospheric circulation and the Intercontinental Convergence Zone (ITCZ). The ITCZ is formed at the equatorial trough where deflected moisture-rich northeastern and southeastern trade winds converges after the completion of the Hadley circulation cell. The ITCZ migrates both north and south according to the axial tilt of Earth's orbit as shown in the figure below. This migration controls both intra-annual variability (seasonality) and spatial variability of rainfall across Africa (Taylor, 2004)

Geology and Elevation

Water is distributed across Africa as lakes, wetlands, rivers, swamped forests or reservoirs (Rebelo et.al. 2010). While the regulation of global atmospheric circulation determines precipitation and runoff patterns, the spatial distribution of water resources as lakes or wetlands is primarily determined by local geology and elevation. On the one hand, areas with a rise in elevation would induce orographic rainfall effects with increased precipitation in mountainous regions relative to low-lying adjacent regions. On the other hand, extensive low-lying, low relief surfaces favours ponding and the formation of lakes (eg. Lake Victoria) or widespread floodplains and the formation of wetlands.

Importance

In one of the most recent comprehensive study on the distribution of wetlands and rivers across sub-Saharan Africa, Rebelo et.al. (2010) concluded that lakes, wetlands, rivers and reservoirs is the dominant source of freshwater with a cumulative area of 1,448,771 km2, covering 6% of the African continent. 143 sites in sub-Saharan Africa are designated as Wetlands of International Importance at the RAMSAR Convention. One of the most alarming statistics taken from this publication is that >90% of the listed RAMSAR sites in the region are used for agricultural or fisheries purposes but >70% of which are threatened because of supporting agricultural or fisheries uses. This fully highlights the importance of an ecosystem services approach in which the quantification of monetary value of wetland systems and economic costs of wetland degradation is urgently needed.  

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Owing to global atmospheric circulation, surface geology and elevation, water resources across Africa is highly diverse and plentiful. However, due to seasonal and spatial variability, the distribution of water resources and thus the ecosystem services they provide are not evenly distributed across the continent. This means that different types and levels of access to ecosystems services exists across local regions. Power relations and problems of access will no doubt influence the valuation and economic incentive of ecosystem services which may lead to trade-offs which are detrimental to complex ecosystem functions or other ecosystem resources (Ryan et.al. 2016). 

The following questions will be addressed in the upcoming series of blogs:

1) What are the current status of provision of and access to freshwater ecosystem services in sub-Saharan Africa?

2) How will the provision of ecosystem services change according to changes to people's access of    ecosystems?

3) How does poverty alleviation, agricultural expansion and global environmental change impact the provision of and access to ecosystem services?

4) Is payment for ecosystem services and the economic valuation of ecosystem services the future for sub-Saharan Africa?