4. Africa Needs Irrigation... particularly on small rural farms!

What is irrigation?

Irrigation is the artificial application of water to the land or soil.

Fig. 1 A classic overhead sprinkler irrigation system, common on many farms today (Source: ULS group)

When did it begin?

It an ancient technique which began around the same time as agriculture, ~ 11,000 years ago. It was the first major human modification of the natural hydrological cycle.

Why is it important?

It enabled societies to reduce their dependency upon the timing and volume of rainfall: extending and increasing the reliability of the growing season. As a global average, irrigated land produces crop yields that are almost FOUR TIMES HIGHER than unirrigated land! (FAO AQUASTAT). In fact, Wittfogel (1957) claimed that irrigation schemes were so crucial to the rise of many great civilizations, such as Ancient Egypt, that they should be referred to as “hydraulic civilizations" (Butzer, 1976).

Fig. 2 Depiction of farming life in Ancient Egypt, clearly showing the irrigation channels that were so fundamental to its development as a ‘hydraulic civilization’

Why does Africa need irrigation?
My last post highlighted that rainfall in most of Africa is hugely variable and that this variability is expected to increase due to climate change (Niang et al 2014). Therefore, rain-fed agriculture is risky and going to get riskier. Furthermore, Africa has one of the fastest growing populations in the world, meaning food demand is rapidly increasing. Irrigation increases both agricultural reliability and productivity. Clearly it is an important strategy for farms in Africa now and into the future.

What's the current extent of irrigation in Africa?

Despite the obvious benefits of irrigation, only 5% of agricultural land in Africa is currently 'equipped for irrigation' (which is generally regarded as a good proxy for the total area actually irrigated), the remaining 95% is rain-fed. Whereas in Asia, 37% of agricultural land is 'equipped for irrigation' (Siebert et al., 2010). Clearly, Africa has a lot of work to do! However, Vilholth (2013) highlights that small-scale irrigation in SSA is hard to quantify and therefore Africa’s ‘5%’ figure may be an underestimate. Nevertheless, the map below shows the 2013 estimation of the global distribution of areas equipped for irrigation in percentage of land area. The land area is divided into a grid of cells, roughly 1km x 1km in size (… not exactly because they are measured in decimal degrees, which account for the curvature of the earth, and not in meters) and the percentage coverage in that cell recorded. For the majority of countries the base year of statistics is in the period 2000 – 2008 (Siebert et al., 2013). From this map you can clearly see the concentration of irrigation in Asia and the lack of it in Africa!

Fig. 3 The map shows area equipped for irrigation in percentage of cell area (cell size = 5 minutes or 0.083333 decimal degrees). For the majority of countries the base year of statistics is in the period 2000 - 2008. (Source: Siebert et al., 2013) 

  
Rural small-scale farms:
As of 2010, the FAO reported that over half of the sub-Saharan workforce was employed in agriculture and the majority of these worked on small-scale rural farms of ~1-5ha (Gollin, 2014). Promoting expensive, centralized irrigation techniques that are only feasible on a large scale is unlikely to help expand irrigation on these small rural farms. Therefore, my next few posts will investigate how we can increase the extent of irrigated agriculture in Africa (particularly SSA), via relatively cheap, small-scale techniques to improve groundwater access and increase rainwater storage. 

3. Africa is Not Water Scarce!

In my last post I found that according to the Falkenmark's "Water Stress Index" (WSI) the majority of Africa is actually considered water sufficient. I then discussed why this may be a mis-representation of reality. The WSI may be an overestimate because the it does not account for rainfall variability or water quality, but it may also be an underestimate because it does not account for groundwater storage. In this post, I want to further examine these aspects and try to determine whether or not Africa is actually water scarce. I am not going to cover water quality in this blog (although I recognise its importance) largely because it is more relevant to water used for domestic purposes (cooking, drinking, washing) than to water used for agriculture. So lets have a look at rainwater and groundwater in Africa....

Lots of rainfall...

In terms of annual rainfall, Africa is not short of water. In fact, at a continental level Africa has enough annual rainfall to meet the demand of around 9 billion people, more than the entire global population (Mati et al., 2006)! At a national level, countries such as Kenya and Ethiopia have enough annual rainfall to supply the water needs of their current populations 6 to 7 times over (Mati et al., 2006). 

Fig. 1 During a wet November in Kenya in 2012, a passerby manages to keep dry with a wonderful classic umbrella (Source: Flora the Explorer)

... but variable
The problem is not overall supply, but the variability of this supply. Temporally, SSA has a hugely seasonal climate, characterized by infrequent by intense rainfall events that create some of the most variable river discharge in the world (McMahon et al. 2007). Climate change is expected to further increase this variability (Niang et al 2014). Spatially, rainfall also varies within and between nations, which may be hidden by continental and national-scale statistics. However, the potential to spatially re-distribute water shall not be covered in this blog.

Fig. 2 Photos from Macha, Zambia showing the contrast between the dry season in October (left) and the wet season in February (right) in 2014. The photos were taken by an American girl teaching in a local school (Source: www.emilybrowntozambia.wordpress.com)

... and lack of storage

These issues of temporal variability could largely be overcome via rainwater harvesting. Rainwater could be collected and stored during periods of excess in the wet season and used to irrigate crops during the dry season, as demonstrated in the diagram below. In fact, the Millennium Development Goals specifically highlighted the need to increase water storage capacity to adapt to future climate change (UN, 2000). Although not all rainwater can or should be harvested (some is needed to maintain healthy ecosystems), rainfall harvesting alone might have the potential to solve most of Africa’s water shortages (Mati et al., 2006). 

Fig. 3 A diagram demonstrating the variability of rainfall (y-axis = rainfall) and how dry season deficits can be overcome by storing excess rainfall from the wet season (Source: NWP, 2007)

Lots of groundwater...

Nevertheless, rain is not Africa's only potential source of water. The continent has huge perennial and good quality groundwater reserves that tend to be overlooked. The map below shows national per capita groundwater resources in m³/year. It is based on groundwater data from 1961-1990 and population data from 2000 (Döll & Fiedler, 2008). If we consider a country as water scarce if they have <1700m³ of water/person/year (see my last post), then based on groundwater ALONE many countries in SSA (those that are dark green or blue) are water sufficient. 

Fig. 4 Map showing national per capita groundwater resources in m³/year. It is based on groundwater data from 1961-1990 and population data from 2000 (Source: Döll & Fiedler, 2008)

    
Additionally, the diagram below shows the absolute volume of groundwater storage, compared to the annual renewable freshwater availability (roughly equivalent to rainfall totals) for each country in Africa. The total volume of groundwater resources in Africa is estimated to be more than 100 times the volume of annual renewable freshwater resources (MacDonald et al., 2012)!! Therefore, not including it in water supply estimates seems absurd!

Fig. 5 Diagram showing the absolute volume of groundwater storage, compared to the annual renewable freshwater availability for each country in Africa. (Source:  MacDonald et al., 2012)

...but lack of access

Unlike rainwater, groundwater is already 'stored'. Therefore, we don't necessarily need to increase 'storage capacity' but we need to increase access to these stores. At the moment, only 2% of Africa's groundwater reserves are accessed. This is primarily because most people cannot afford the technologies needed to extract water from below-ground aquifers.

Africa is not PHYSICALLY water scarce, but it is ECONOMICALLY water scarce....
With sufficient infrastructure to harvest rainwater and access groundwater, Africa would have enough water to meet the demands of its population. However, this infrastructure does not exist, mainly due to a lack of investment, and so the full potential its water supply is not being realised. Therefore, perhaps Africa should be considered 'economically' rather than 'physically' water scare (Rijsberman, 2006).

My next few posts will explore how we can increase groundwater access and rainwater harvesting to try to reduce this 'economic' scarcity. However, first I want to highlight the importance of irrigation for farms in Africa.