Lack of green water in Sub- Saharan Africa? Let's savour what we can

A recent paper by Rockstrom and Falkenmark (2015) begins by painting the harsh but realistic truth; one fifth of the current 1 billion people in Sub- Saharan Africa face water shortages (Rockstrom and Falkenmark 2015). The population of Sub- Saharan Africa is set to double by 2050 to almost 2.5 billion (Gerland et al 2014). That is a staggering 150% larger than current numbers. If so many are facing water problems now, what kind of picture will be painted then?

Due to these water shortages prospects of agriculture are limited.

The arid desert and semi- arid savannahs receive too little surface runoff to grow staple crops such as maize, rice, corn millet etc (figure 1). These kinds of crops need around 400mm of water annually but the region receives just under 100mm (Rockstrom andFalkenmark 2015).

 

 Figure 1- Rainfall and runoff in Sub- Saharan Africa is inadequate for growing staple food crops (Rockstrom andFalkenmark 2015).

Green Water is precipitation that is held in the soil and 95% of Sub- Saharan Africa depends it. Future rainfall could drop by 25% in many semi- arid regions (Schewe et al 2013).  Thus, management of green water, in my opinion, is essential. Aside from reductions in rainfall, precipitation is likely to be unpredictable and varied. We are already seeing signs of this inconsistency. In 2000 Kenya experienced an early onset of rain followed by 6-9 weeks of no rain. This prevented staple crops growing and caused 4 million people across the country to experience food shortages (Rockstrom andFalkenmark 2015). As can be seen these inconsistencies, variability and altogether lack of rainfall has detrimental effects on the agriculture of the region.

So what can be done? I think Rockstrom and Falkenmark (2015) make a good suggestion: water harvesting. It is small- scale, cheap and arguably practical for many subsistence farmers across Sub- Sahran Africa so keep a look out for the next post!