Irrigation in Kenya

Coefficient of Variation (c.v)

In last week's post i mentioned the C.V in order to describe the seasonal variability of rainfall in regards to Maize Farming.  

C.V is the formal definition of intra-annual or seasonal variability defined through 'normalised' spread of average rainfall over the year.  The CV is the average of 12 monthly rainfall values for a country (k) defined as CVMk = σ(Pj,k)/μ(Pj,k); i.e. as the ratio of standard deviation of calendar month (j) average rainfall to its grand mean across all calendar months (Brown, 2006).

Climate change is increasing rainfall variability, and is therefore making conditions for agriculture and economic development very difficult (Brown, 2006). Greater rainfall variability highlights a greater need for irrigation. It brings to attention the areas that may need supplementary irrigation to 'regularise' crop yields (Challinor, 2006). CV therefore enables solutions to increase reliance to these changes to be put in place, and therefore mitigate some of the expected impacts of climate change (Brown, 2006).

Irrigation in Kenya

Agriculture is the leading sector in the Kenyan economy, contributing to 24% of GDP, and is the largest contributor to employment (with > 70% of the labour force based in rural areas), and accounts for about 50% of principal export earnings (Kabubo- Mariaria, 2007).

In Kenya, traditional irrigation dates back 400 years, which is longer than most countries in Eastern and southern Africa. According to the Fao, in terms of utilising low- cost technologies (including rainwater harvesting, bucket irrigation, gravity fed sprinkles and drip, treadle and pedal pumps, rope and washer, mortised pumps, wind power and construction of small earthen dams), Kenya is well ahead of other countries in the sub- region.

Irrigated lands are up to 2.5 times more productive in comparison to rain-fed agriculture. They play an important role in the agricultural sector in SSA, and are often favoured by governments and donor agencies for their high return rate.

Models predict that global warming will lead to increased temperatures ~4℃ and rainfall variability up to 20% by 2100. Using Ricardian analysis, a study on the economic impact of climate change on Kenyan Agriculture, shows that climate does affect agricultural activity. They show that adaptation to climate change in Kenya is important, if households want to counter the impacts of long- term climate change. Results of perceptions and adaptation of farmers to climate change showed that Kenyan's are aware of both the long and short term changes in climate and have implemented various adaptation mechanisms. They do show that coping strategies must be tailored specifically to different factors including physical, economic and sociocultural. They found that irrigation is adopted in the drier regions, but not the areas that have a high potential for evaporation, in which the most common adaptation measure is diversification.

Some of the types of irrigated agriculture found in Kenya are:

• Large- scale surface irrigation schemes by the Government, in which smallholder farmers play a very small role in management.
• Smallholder irrigation, either by individuals or small groups, that have been able to exploit water in streams and irrigate small areas in valley floors. This is mainly subsistence, but also cash crops for local markets.
• Agro-industrial irrigation of high- value crops, finance and developed by private corporations or individuals. These rely heavily on pump- based technologies in conjunction with drip or sprinkler irrigation.

Irrigation potential 

However, Kenya is still heavily dependent on rain-fed agriculture. With 17% of the land considered to have medium to high potential for irrigation, less than 10% is utilised, which amounts to only 2% of total arable land in Kenya (FAO, 2005).

A study on the potential for irrigation in Kenya, has showed that there is high potential for the expansion of both dam-based (water stored in large reservoirs) and small- scale irrigation (surface runoff based) in Kenya. The analysis of the potential investment for Small- scale irrigation project expansion in Kenya ranges from 54,000 ha to 241, 000 ha, with an internal return rate of 17-32%. For the dam- based investment analysis, under low- cost assumption, 58/ 73 damn are profitable. At high cost level, 32 of these dams are economically feasible.

Irrigation does not come without its environmental problems. For example, development of irrigation systems can increase the salinity of cultivated land in the area- this affects 29% of irrigated land in Kenya (FA0, 1997). The main challenges however facing irrigation expansion in Kenya is the cost of implementing projects. Kenya's agriculture sector (75%) is dominated by small- scale farmers, who do not have the capacity to invest in gravity- led or pump- fed irrigation canals (You, 2014). The problem found with large scale irrigation projects, is that often government and donor interests come first before smaller famers. The capacity for governments to manage these systems effectively has often collapsed.

Concluding thoughts

There is potential for both small and large scale irrigation schemes. However, for this to be effective, there needs to be better management and incentives to small scale farmers like subsidies, so that they can invest in technology.

Increasing variability in rainfall, is seeing exceptional high rates of precipitation, which may lead to groundwater recharge which can be harnessed during dry periods. However, the decrease/ lack of precipitation in the dry periods and increased demand may not only lead to decreases in runoff and streamflow downstream, but may also deplete groundwater supplies. As this post never explored groundwater as a source of water for irrigation, next week's post will look closely at the Groundwater potential in East Africa.