Water water everywhere... But not a drop to drink!

Water Variability... The factors behinds it.

Last week we figured out that Africa actually has enough water available, and cannot be considered water scarce. But it's the variability of water throughout the season and between regions that present us with the challenge of managing African water reserves. Today I will be discussing the natural/ physical drivers of water resources in Africa by focusing on two key articles presented by Conway et al 2009 and Taylor (2004).

Physical Setting 

An important element of East and South Africa is that it lies on an altitude of around 1000 meters above sea level, compared to 400-600 meters in North/ West Africa. This formation of the East African Rift System due to swelling of the Earth's crust in the Oligocene eras has a predominant effect on climate and rainfall distribution. The mountain uplift creates a rain shadow effect that reduces moisture availability on the Rift Valley mountain side, producing strong aridification (Maslin 2014)

Tectonics also largely characterize patterns of surface drainage. Large lakes have formed in troughs throughout the East African Rift Valley. Warping of the land surface has also created surface flows I.e.  Lake Victoria and Kyoga, as well as being a major determinant in the formation of river basins (up warping of the rift  on the western side of Lake Albert divides the basins of the River Nile and River Congo). 

Climatic Setting 
Seasonal climate in Africa is controlled by global atmospheric circulation trends. Atmospheric circulation forms as a result of unequal heating of the Earth's surface. At the equator heated air expands, rises and moves towards the pole regions, where it then cools and sinks at approximately 30 degrees North and South, A fraction of it returns back to low latitudes thus completing a cycle, known as a Hadley Cycle. The area near the equator where the moisture rich flows meet is the Inter Tropical Convergence Zone (ITCZ). The ITCZ is not static but moves as a result of changes in solar radiation, which is the main driver of seasonal rainfall variability across much of Africa.

Figure 1 below illustrates the movement of the ITCZ across Africa between January and August. In December the ITCZ reaches the southernmost latitudes, where it brings moisture to before moving north and bringing heavy rainfall to northern latitudes up to July. This annual cycle creates a uni modal distribution of rainfall for countries in South and North Africa. However places near the equator at lower latitudes have a bimodal rainfall cycle, as the ITCZ passes twice throughout the year. Thus as Taylor (2004) correctly noted, this means that regions at the periphery of the ITCZ receive comparatively little rainfall i.e.  Namib Desert in Northern Africa, compared to those at latitudes of 10 degrees N/S.

 Figure 1: Movement of ITCZ across Africa (Ziegler et al 2013)

This has profound impacts on water use due to the high seasonal water variations. Regions are having to adapt their water use depending on the season, in sectors like agriculture which heavily depends on rain for irrigation especially for small hold farmers, their planting seasons take into consideration this rainfall variability , timing it to the arrival of water. 

As we can see water in Africa comes with a large uncertainty and variability, which presents a challenge to adapting to these unreliable water sources. I think concerns over irrigation should address these issues and present a sustainable solution that can tackle large variability of rainfall as well as looking at other sources.