Improving rain use efficiency can reduce climate vagaries in ASALs

Bus stuck in floodwaters after River Dawa busts its banks in Mandera on May 2, 2018. [Feisal Abdirahman, Standard]

This year's long rain season is with us, and it is a welcome relief. The reality is that, the rain will either be used rewardingly or disappear into the wilderness. The agriculture sector uses the largest amount of water - about 80-90 per cent of physical water resources. This is mainly through irrigation systems. However, rain-fed agriculture is today still the most common food production system.

About 95 per cent of agricultural land in sub Saharan Africa (SSA) is under rain-fed system. Irrigated food production system covers only a small portion. Furthermore, rain-fed agriculture feeds over 60 per cent of population in SSA. The rain-fed agriculture in SSA will remain an important source of food and fodder, now and beyond. Yet it operates under continuously variable rainfall pattern.

In Kenya, there is a bimodal rainfall pattern. A wet season with two rainfall peaks, separated by at least one dry month, is bimodal. The long rains start in March/April and ends in June/July, while the short rains start around October/November and ends in December.

The long-rain season in Kenya plays an important role in food and fodder production. Though, the start, duration and end of the rain season cannot be precisely predicted due to high climate variability, this variability is more pronounced in Arid and Semi-Arid Lands (ASALs) of northern Kenya.

Livestock production in ASALs is vulnerable to the spatial and temporal variability of rainfall. The need to know whether each drop of rain is being put into productive use is gaining importance, especially in ASAL areas. That is where Rain Use Efficiency (RUE) comes in. RUE entails putting a portion of rain into productive use.

It is the ratio of above-ground net primary productivity to seasonal or annual rainfall. Some 75 per cent of Kenya's landmass is either arid or semi-arid, and animal agriculture is the backbone of the economy in the ASALs.

Over 90 per cent of human population in the ASALs practice livestock production. They depend on seasonal rainfall for production of feed biomass. Therefore, March/April rainfall plays a significant role in food security of Asals. The vagaries of weather in ASALs necessitates that each drop of rain is put into beneficial use. The quantity of pasture biomass produced per rainy season has direct influence on survival of livestock during drought.

Although drought may lead to low yields of biomass in northern Kenya, the minimal portion of rain put into beneficial use is the major impedement. So far, the RUE in arid and semi-arid Kenya oscillates around 10 per cent. This means that only about 10 per cent of rain that falls to the ground goes into productive use.

Sadly, about 70-80 per cent of rain that falls in arid and semi-arid areas is lost. Some 30-50 per cent of this rain evaporates, 10-25 per cent is lost through surface run-off and 10-30 per cent goes down through deep percolation.

There is worrying vanishing of rain into vast rangelands of northern Kenya. Evidence shows that there is significant disappearance of rain into expansive rangelands of Odha and Balesa in Marsabit County.

This loss of rain has been the trend season after season. The good news is that all is not lost; an opportunity exists to improve through RUE. In Saku Constituency of Marsabit County, the average annual rainfall for the last 50 years is 727.0 mm.

If all this water is utilised, one millimetre of rainfall can produce at least 7.9 kg/ha dry matter forage biomass. But, of this annual rainfall, the amount put into productive use is dispiriting. Computation of probability of exceedance has revealed that the probability that any annual rainfall can be equal to 600 mm is 58 per cent.

In fact, Saku Constituency receives 300 - 598 mm of rainfall during normal long rain season. A wet season in this area can translate into dry matter forage biomass of 6,317 kg/ha. Therefore, the quantity of rain is not the most pressing problem.

The predicament lies in dichotomy between disappearance of rain into vast rangelands vis-a-vis utilisation of collectable rainfall. Putting each drop of rain into good use is strategy against climate change. There are various proven technologies for improving RUE. These include both in-situ and ex-situ water conservation technologies.

Specifically, rainwater harvesting for supplemental irrigation, damming, increased land cover through range re-seeding, and crop or fodder production under flood irrigation, among others.

The bottom line is that low RUE in ASAL areas presents an opportunity to put more rain into productive use of biomass production. Increased forage biomass boosts livestock productivity, thereby enhancing food security in ASAL areas.