Natural Endowment

Natural endowment – Prosperous for some but a source of downfall for others: 

Naturally favourable traits are no exception when it comes to countries and their geographic location (Ndikumana et al, 2010). It is common to instantly connect natural endowment to countries that have benefited greatly from their natural characteristics. For example, the countries of OPEC who found themselves living on top of the most in demand energy source of the 20th century. However, countries with less favourable natural characteristics are less commonly thought of in these contexts. This is no exception for the continent of Africa and its relationship with food and water. This is epitomised as just 4% of crop land in Sub-Saharan Africa is irrigated (Siebert et al, 2010) and withdrawals of freshwater in the majority of countries in Africa are below Malin Falkenmark’s definition of requisite water availability (Falkenmark, 1989). I am therefore dedicating this post to the physical geographies of food and water in Africa. 

The haunting of the ITCZ:

The Intertropical Convergence Zone (ITCZ) occurs where two Hadley cells converge causing warmer air to rise and create low pressure (Yongyun et al, 2007). As air rises it expands, cools and in turn creates rain. However, as this air moves poleward it begins to warm and descend, creating areas of high pressure which characteristically have little precipitation. This is the reason for the dry areas to the north and south of Africa such as the Sahara and Kalahari deserts. 

The ITCZ thus explains the latitudinal symmetry seen in Figure 2, and why the magnitude of rainfall generally declines the further north or south of the equator you move. But, it doesn’t end there! The ITCZ changes locations throughout the different months of the year which in turn creates a seasonality in precipitation (Schneider et al, 2014). This can be seen in Figure 3 which shows a rainy season in July for the southern hemisphere and vice versa for the northern hemisphere whose rainy season is in January. 

Figure 2:(a) depicts the amount of annual average total rainfall from 1998 to 2012 (mm) (b) depicts annual average total rainfall frequency of rainy days observed from 1998 to 2012 (Kaptué et al, 2015)

 

Figure 3:Depicts variability in rainfall across Africa – (a) January (b) August. This depicts the impact the ITCZ has on the distribution of rain across Africa (Ziegler et al, 2013)

Hang on a second, we just said that Africa has problems with growing its crops due to its low irrigation percentages, it seems from the above diagrams that there is enough water, what’s going on? Well, there are two factors which we will now consider:

•        What happens to the rain water after it hits the ground
•       The distribution of this water across Africa

Perhaps these factors will solve our confusion!

Geology plays an incredibly important role when it comes to the supply and storage of groundwater (MacDonald et al, 2012). Unfortunately for Sub-Saharan Africa, over 40% is underlain by weathered and fractured rock aquifers that have a low bulk transmissivity which can lead to low well yields. A low bulk transmissivity can also prevent intense water pumping as the characteristics of the geology will prevent such stores from delivering water to the desired location in adequate time and quantities. In addition, strengthened seasonality in rainfall may lead to more frequent ephemeral river conditions rather than perennial (Arnold et al, 2016). This is epitomised as river flow in Southern Africa is the most variable in the world as most rivers within this region are ephemeral. It is estimated that a 10% decrease in rainfall reduces river discharge within these regions of Africa by 17 to 50% (de Wit, 2006). Furthermore, the warmth of countries on and around the Equator means that potential evapotranspiration in the tropics are extremely high and due to become higher as global warming intensifies thus leading to poor retention rates of surface water. 

We now have a background understanding of the physical characteristics which manipulate water and its distribution across Africa and how this helps us to understand why just 4% of crop land in Sub-Saharan Africa is irrigated. Next week we will explore how global warming is going to change these patterns and their relative impacts on food in Africa.