Don't map it all at once!

A very recent study conducted by Lebel et al (2015) evaluates the performance of In Situ Rainwater Harvesting (RWH) techniques for Maize production in Africa as an adaptation strategy to Climate Change.

Changes in rainfall due to climate change can have a detrimental effect on food production in Africa since it is the main influence on crop productivity (Muller et al 2011). Farmers in Africa rely on crop production not only as a means of income but also to survive as food for the family. Maize is the most extensively grown crop, for example it occupies 50% of harvested area in South Africa alone (Portmann et al 2010). From this alone we can tell how important this crop, amongst others, is to the livelihoods of African citizens.

In Situ RWH techniques aim to reduce the variability in crop yields, giving the farmers more security (Fox and Rockstrom 2000). They do this by reducing soil degradation from water erosion and therefore ensures a better environment for the crops to grow more successfully. Techniques such as planting pits or stone bunds allow the soil to store water in the form of soil moisture which would have otherwise been runoff, making better use of the limited water resources (Lebel et al 2015).

The study Lebel et al (2015) carried out used continental scale GCMs outputs to see which areas, in Africa, would benefit from RWH under specific changes in climatic conditions. They concluded that overall RWH is a viable solution which should be considered. It provides an alternative to irrigation from the scare water resources under current and future modelled climatic conditions in 2050. They found it could increase maize production by up to 50% in the 2050s by alleviating water deficits.

Not only can RWH be used to directly better water use efficiency by storing water, but it can also improve crop yields indirectly through improvements in soil fertility. By reducing surface runoff and the volume of water reaching the soils, it means there is less soil erosion and more nutrients remain in the soil. Breman et al (2001) found that this alone can increase water use efficiency for crops by 3-5 times.

Figure 1- The performance of RWH in different regions of Africa. Showing changes by 2050s from the 1990s. Using three GCMs as named above each map of Africa. (Lebel et al 2015).

From these results the study seems promising. It frames RWH as a go to solution for the water deficits facing Africa, but, there are still hurdles to be jumped. The study is on a continental scale- this means the details of smaller regions are ignored. This is especially alarming for a continent like Africa where the climate varies extensively, from the tropical rainforest to desert- each region receives different amounts of rainfall and so needs to be mapped in finer detail. They (Lebel et al 2015) did use GCMs, as shown in figure 1, to look at the performance of RWH techniques in different regions. For example, this compared predictive conditions in 2050 to data from the 1990s to show RWH will not work as well in countries like Zambia as oppose to Ethiopia where it works well. 

Furthermore, the implementation of these techniques requires government, NGO and community participation, again, each of which differ from one country to the next. RWH is a cheap and low skilled option compared to other technology ridden, top- down schemes but this does not erase the fact that it still requires training and financial backing.

Grouping Africa as a whole is a no go. You need tailored research and proposals for each region to get a better understanding of whether RWH is their go to or not.