Kenya; What is the Limit Of Up-Scaling Rainwater Harvesting In A River Basin
Physics and Chemistry of the Earth 28 (2003) 943–956 www.elsevier.com/locate/pceWhat is the limit of up-scaling rainwater harvesting in a river basin? Stephen N. Ngigi Department of Agricultural Engineering, University of Nairobi, P.O. Box 29053, Nairobi, KenyaAbstract The semi-arid savannah environment (SASE) of sub-Saharan Africa are characterized by low erratic rainfall which result to highrisk of droughts, intra-seasonal dry spells and frequent food insecurity. The main occupation is subsistence small-scale rainfedagriculture and livestock production, which normally compete for the limited water resources. The main challenges to improving thelivelihoods of the small-scale farmers are how to upgrade rainfed agriculture to improve rural livelihoods and conserve nature, andupgrade upstream landuse in balance with water needs for human and ecosystems downstream. There is an increased interest inopportunities of improving rainfed agriculture through adoption of rainwater harvesting (RWH) technologies. However, there isinadequate knowledge on hydrological impacts and limits of up-scaling rainwater harvesting at a river basin scale. Rainwaterharvesting has a potential of addressing spatial and temporal water scarcity for domestic, crop production, livestock development,environmental management and overall water resources management is SASE. However, this potential has not been exploiteddespite the occurrence of persistent low agricultural production and food shortage in sub-Saharan Africa. The need to quantify thisperceived potential and related hydrological impacts on a river basin led to the on-going research project titled ‘‘hydrologicalimpacts of up-scaling RWH on upper Ewaso Ng’iro river basin water resources management’’. It is envisaged that the study willcontribute to formulation of sustainable RWH up-scaling strategies to enhance food production and hydro-ecological balance insemi-arid savannahs of Africa. This paper presents the preliminary ﬁndings of the study mainly focusing on assessment of thepotential of RWH technologies for improving food and water availability especially in semi-arid regions of eastern Africa. This wasachieved by evaluating six RWH case studies selected from four countries (Ethiopia, Kenya, Tanzania and Uganda). Despite thesuccess of a number of RWH systems, the rate of adoption is still low, hence making their impacts marginal. Nevertheless, there is aknowledge gap on the limits of up-scaling RWH in a river basin, which the other components of the study will address. The as-sessment of the hydrological impact of up-scaling RWH technologies is expected to provide answers to the question, what is the limitof up-scaling rainwater harvesting in a river basin?Ó 2003 Elsevier Ltd. All rights reserved.Keywords: Rainwater harvesting; River basin; Fanya juu; Fanya chini; Food production; Water scarcity1. Introduction interrelationships over longer time periods. These crises threaten the stability and existence of the aﬀected com-1.1. Background munities and economies because their systems are ob- viously failing to cope, increasing the vulnerability of the Most of the countries in sub-Saharan Africa (SSA) people. A number of explanations have been advancedare experiencing profound socio-economic and political for the endemic food insecurity in the SSA. Amongproblems, the most dramatic being food crises and dis- these, recurring drought and unreliable rainfall are theruptive conﬂicts. The communities involved are experi- most obvious. These include: adverse weather andencing a combination of both short-term, often acute drought; rapid population growth rates that exceed ratesfood crises, and long-term or chronic food shortages. of food production; adoption of production systemsThe former often translate into famine and starvation, that accelerate environmental degradation and declinerequiring emergency food aid. The latter are less obvi- in soil fertility; and retrogressive social organizations,ous, for they are characterized by negative changes in inadequate policies, legislation and institutional weak-the economic, social and ecological factors and their nesses. Over 60% of the land in the SSA falls under semi-arid savannah environments (SASE), where a majority of the E-mail addresses: firstname.lastname@example.org, email@example.com inhabitants are pastoralists although agro-pastoral and(S.N. Ngigi). farming communities have been slowing settling in these1474-7065/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.pce.2003.08.015
944 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956areas due to population pressure in the high agricultural agricultural activities. The same fact had been expressedpotential areas. SASE is predominantly characterized by by Jodha and Mascarenhas (1985) as characteristic oflow and variable rainfall, which rarely exceeds 800 mm, much of the rest of Africa. In Greater Horn of Africawith most areas receiving 200–350 mm annually. The (GHA), rainfall––amount, timing, duration and distri-water resources are limited and poorly distributed. bution––was identiﬁed by subsistence farmers as theThere are few permanent rivers, and seasonal streams dominant determining factor for food production andthat ﬂow only during the wet season and remain dry for security.the rest of the year. However, like the wetter regions, Therefore, the problems related to food security andSASE too is starting to experience land pressure re- recurrent famine need urgent solutions, especially in thesulting due to population increase within the commu- SASE, where environmental degradation has furthernities and also their livestock. This has signiﬁcantly decreased agricultural productivity, making inhabitantsraised pressure on pastures leading to overgrazing and even more susceptible to drought and other natural di-decline in vegetation cover in most of the areas. The sasters. Unless sustainable food production technologiesimpact of the frequent droughts that hit the pastoral are adopted, alleviation of poverty and food securityareas has therefore been increasing over time. Huge will remain elusive. One promising technology for rurallivestock numbers have been dying every time there is landuse systems is rainwater harvesting. This is thedrought (Kihara, 2002). Much of the pastureland has process of interception and concentration of runoﬀ andlost grass cover and is often bare. This leaves the people its subsequent storage in the soil proﬁle or in artiﬁcialhighly vulnerable. Consequently the ASALS form spe- reservoirs for crop production. The process is distin-ciﬁc pockets of poverty and food insecurity, and ensuing guished from irrigation by three key features: theconﬂicts, especially over diminishing natural resources–– catchment area is contiguous with the cropped area andmainly water and pasture. is relatively small; the application to the cropped area or Nevertheless, unreliable rainfall and low soil fertility reservoir is essentially uncontrolled; and water harvest-has continued to threaten food production in the SSA ing can be used for purposes other than crop produc-thus making food security a major concern. Currently, tion. There are many techniques being used to enhancevast areas of SSA are facing drought and the threat of crop production in the ASALs of the SSA. However, thefamine despite the fact that overall food production viability of these solutions needs to be evaluated in re-could be adequate. Relief food has on many occasions lation to environmentally sustainable factors, climaticsaved lives in the region from severe famine situations. conditions, soil characteristics, farming systems andFood relief will continue to be required as long as socio-cultural and gender perspectives in which they aretransportation facilities are poor and local food pro- practiced.duction in drought prone areas is inadequate. Given the Participatory evaluation is needed to determine viablepoor transportation infrastructure, emphasis on local options and adaptive strategies for sustainable foodfood production appears the most logical approach to production in the ASALs. Needless to say, the solutionsimproved food security. must be landuser-oriented, hence the need for a partic- Agriculture is the major economic activity for the ipatory technology development approach. The projectcountries of the SSA, engaging between 75% and 85% of gave special attention to RWH technologies and sys-the people of those countries. Consequently, it is tems, which are being used by land users. Any activity tostrongly underscored that agriculture is the backbone of improve on landusers’ innovations and the applicabilitythese countries’ economic development and their peo- of those innovations will be a major contribution tople’s well being in the foreseeable future. A survey of 277 food security in this famine prone region. It is with asocieties in sub-Saharan Africa by Hunt-Davis (1986) sense of urgency that one notes the relevance of RWHshowed that approximately 86% depended primarily on technologies in certain limited but signiﬁcant areas ofagriculture, 6% on animal husbandry, and animal hus- Africa, both for food production and for soil and waterbandry and agriculture are co-dominant for another 3%. conservation (Pacey and Cullis, 1986). Despite this re-Of the rest, 2% rely primarily on ﬁshing; 1% on ﬁshing alization, little practical information exists on RWHand agriculture equally, and some minorities on hunting technologies, which can be applied on site speciﬁc situ-and gathering. Thus the livelihood in this region is based ations. RWH is one of the approaches to integrated landon small-holder rural agriculture, with low levels of and water management, which could contribute to re-productivity and simple tools, making them over- covery of agricultural production in dry areas.dependent on the status of the natural environment. Sea-sonal rainfall dominates the lives of most of the people, 1.2. Food production and water scarcity in sub-Saharanas it determines their activities geared towards earning a Africalivelihood based on exploitation of the resources of theland. Duckham and Maseﬁeld (1985) stated that in the The semi-arid areas of SSA are characterized by lowtropics generally, rainfall is the main determinant of annual rainfall concentrated to one or two short rainy
S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 945seasons. The average annual rainfall varies from 400 to tenure, health/diseases outbreak, inadequate knowledge/600 mm in the semi-arid zone, and ranges between 200 capacity, and donor dependency syndrome. Thus theand 1000 mm from the dry semi-arid to the dry sub- ever increasing food demand and household incomehumid zone (Rockstr€m, 2000). The length of the o needed in SSA have to be achieved through an increasegrowing period ranges from 75 to 120 and 121–179 days in biomass produced per unit land and unit waterin the semi-arid zone and dry sub-humid zone respec- (Rockstr€m, 2001). In the past, very little attention has otively. Potential evaporation levels are high, ranging been paid to the development of rainfed agriculture infrom 5 to 8 mm/day (FAO, 1986) giving a cumulative SSA except provision of conventional irrigation pro-evapotranspiration of 600–900 mm over the growing jects. However, most of these projects have proven (e.g.period. This explains the persistence water scarcity Bura irrigation scheme in Kenya) to be unnecessary,coupled with low crop yields. Water scarcity could also costly and environmentally unsustainable. Hence thebe attributed to poor rainfall partitioning leading to need to focus on opportunities of increasing eﬃciency oflarge proportion of non-productive water ﬂows––not limited water in rainfed, smallholder agriculture in theavailable for crop production. The nature and occur- SASE of SSA. Otherwise feeding the ever growingrence of rainfall in SASE of SSA provides more insight population (at a rate of 2–3% per year) with diminishingin the food production and water scarcity situations. crop yields (oscillating around 1 ton/ha for food grains) Rainfall is highly erratic, and normally falls as in- in SSA (Rockstr€m, 1999) will remain elusive, and otensive storms, with very high intensity and spatial and current generation’s biggest challenge.temporal variability. The result is a very high risk forannual droughts and intra-seasonal dry spells (Rock- 1.3. Rainwater harvesting technologies and systemsstr€m, 2000). From past experience, severe crop reduc- otions caused by dry spells occurs 1–2 out of 5 years, Rainwater harvesting which is broadly deﬁned as thewhile total crop failure caused by annual droughts that collection and concentration of runoﬀ for productiveoccur once in every 10 years in semi-arid SSA. This purposes (crop, fodder, pasture or trees production,means that the poor distribution of rainfall, more often livestock and domestic water supply, etc.), has ancientthan not, leads to crop failure than absolute water roots and still forms an integral part of many farmingscarcity due to low cumulative annual rainfall. Unfor- systems worldwide (Evanari et al., 1971; Shanan andtunately, most dry spells occur during critical crop Tadmor, 1976; Critchley, 1987; Critchley and Siegert,growth stages (this explains frequent crop failure and/or 1991; Agarwal and Narain, 1997). It includes all meth-low yields), and hence the need of dry spell mitigation by ods of concentrating, diverting, collecting, storing, andimproving water productivity in SSA. utilizing and managing runoﬀ for productive use. From the above brief overview of rainfall patterns, However, in situ systems i.e. on-farm/cropland waterthere is a growing understanding that the major crop- conservation––to enhance soil inﬁltration and waterping systems in SSA are not sustainable (Benites et al., holding capacity––dominate, while storage systems for1998), hence the persistence low food production (food supplemental irrigation are less common, especially inshortage) and reliance on food relief. Nevertheless, SSA (SIWI, 2001). Nevertheless, a recently concludedmajority of the population in SSA make their meager evaluation of RWH in four GHA countries (i.e. Ethio-living from rainfed agriculture, and depend on to a large pia, Kenya, Tanzania and Uganda) revealed that, de-extent on smallholder, subsistence agriculture for their spite the relatively high investment costs compared tolivelihood security (e.g., Botswana, 76%; Kenya, 85%; in situ systems, RWH for supplemental irrigation is slowlyMalawi, 90%; and Zimbabwe, 70–80% of the population being adopted with high degree of success (Kihara,(Rockstr€m, 2001). Moreover, an estimated 38% of the o 2002). In this system, surface runoﬀ from small catch-population in SSA roughly 260 million people lives in ments (1–2 ha) or adjacent road runoﬀ is collected anddrought prone SASE (UNDP/UNSO, 1997). This may stored in manually and/or mechanically dug farm pondsexplain why most of the population is poor––rely on (50–1000 m3 storage capacity). Due to the low volumesunsustainable farming systems, majority living below of water stored compared with crop water requirements,the poverty limit (<US$ 1 per day). The key role of improved beneﬁts of these systems are derived by in-agriculture in Africa’s economic life is apparent––agri- corporating eﬃcient water application methods such asculture accounts for 35% of the continent’s GDP, 40% low pressure (0.5–1.5 m) drip irrigation (Ngigi et al.,of its export, 70% of its employment, and more than 2000; Ngigi, 2001).70% of the population depend for their livelihoods on Furthermore, on-farm research in semi-arid locationsagriculture and agri-business (Kijne, 2000). in Kenya (Machakos district) and Burkina Faso (Ou- The problem of low food production is further ag- agouya) during 1998–2000 (Barron et al., 1999; Fox andgravated by limited new land for cultivation, land and Rockstr€m, 2000) indicates a signiﬁcant scope to im- oenvironmental degradation, poor infrastructure, politi- prove water productivity in rainfed agriculture throughcal and social crises, bad governance, insecure land supplemental irrigation, especially if combined with soil
946 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956fertility management. The results were more promising ability and management for downstream and naturalon soils with higher water holding capacity on which ecosystems like wetlands and swamps, due to reducedcrops seem to cope better with intra-seasonal dry spells. catchment water yields. Therefore, even though RWHHowever, incremental water productivity improvements practices can be eﬃcient in increasing the soil moistureare only achieved during rainy seasons with severe dry for crops (principle objective) in water scarce areas, eachspells, while rainy seasons with adequately distributed technique has a limited scope due to hydrological andrainfall the incremental value can be negative (Rock- socio-economic limitations. Rockstr€m (2000) high- ostr€m et al., 2001). o lighted the major hydro-climatic hazards in SASE Runoﬀ is collected mainly from ground catchments as farming aswell as ephemeral streams (ﬂood water harvesting) androad/footpath drainage. The storage is either in diﬀerent • Poor rainfall partitioning, where only a small fractionstructures (tanks, reservoirs, dams, water pans, etc.), of rainfall reaches the root zone, coupled with within-mainly for supplemental irrigation systems, or soil ﬁeld crop competition for soil water;proﬁle (for in situ and ﬂood irrigation). RWH can be • The high risk of periods of below optimal cumulativeconsidered as a rudimentary form of irrigation (Fentaw soil water availability during the growth season (i.e.et al., 2002). The diﬀerence is that with RWH the farmer not necessarily dry spells, but rather situations whenhas no control over timing, as runoﬀ can only be har- soil water availability is below crop water require-vested when it rains. In regions where crops are entirely ments for optimal yields due to low cumulative rain-rainfed, a reduction of 50% in the seasonal rainfall, for fall levels); andexample, may result in a total crop failure (Critchley and • The high risk of intermittent droughts, or dry spells,Siegert, 1991). However, if the available rain can be occurring during critical crop growth stages (i.e. notconcentrated on a smaller area, reasonable yields will necessarily a lack of cumulative soil availability, butstill be received. Fig. 1 shows the principle of RWH, rather periodic water stress due to poor rainfall distri-which is common for diﬀerent classiﬁcations, except bution.in situ (no runoﬀ) systems which capture rainfall whereit falls. Classiﬁcation of runoﬀ-based RWH technologiesdepends: 2. Rainwater harvesting technologies and systems in SSA• Source of runoﬀ (external) or within-ﬁeld catchments; This section brieﬂy presents the diﬀerent RWH• Methods of managing the water (maximizing inﬁltra- technologies and systems found in SSA, focusing on tion in the soil, storing water in reservoirs and inun- their classiﬁcations, and their opportunities and limita- dating cropland with ﬂoods); and tions for improving rainfed agriculture in SASE. The• Use of water (domestic, livestock, crop production, term RWH is used in diﬀerent ways and thus no uni- gully rehabilitation, etc.). versal classiﬁcation has been adopted. However, ac- cording to Oweis et al. (1999) the following are amongRWH systems operate at diﬀerent scales (household, its characteristics: RWH is practiced in ASALs whereﬁeld and catchment/basin), and can aﬀect water avail- surface runoﬀ is intermittent; and is based on the utili- zation of runoﬀ and requires a runoﬀ producing area (catchment) and a runoﬀ receiving area (cropped area and/or storage structures). Therefore, each RWH sys- tem, except in situ water conservation (as shown in Fig. Catchment 1 above) should have the following components: runoﬀ (natural surfaces, roads/footpaths, gullies, rills ephemeral streams, croplands, pasture, producing catchment, runoﬀ collection (diversion and hillslopes) control) structures, and runoﬀ storage facility (either soil proﬁle in cropland or distinct structure (farm ponds, tanks, water pans, earthdams, sand dams, sub-surface Runoff dams, etc.). Conveyance To avoid further confusion, and facilitate the pre- and/or sentation of various types of RWH technologies and “Storage systems, the classiﬁcation shown in Fig. 2 below is based on runoﬀ generation process, type of storage/use and Cropland size of catchments is adopted. The runoﬀ generation (water applied directly or through criteria yields two categories––runoﬀ farming (where irrigation for storage systems) runoﬀ is generated i.e. runoﬀ-based systems) and in situ water conservation (rainfall conserved where it falls).Fig. 1. The principle of runoﬀ-based rainwater harvesting technology. The runoﬀ storage criteria also yields two categories––
S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 947 RWH SYSTEMS In-situ Water Conservation Runoff-based Systems (Tillage and cultural practices) (Catchment and/or storage) Direct Application Systems Storage Systems (Runoff diversion into (Distinct storage structures cropland where soil profile for supplemental irrigation provide moisture storage) and other uses) Micro-Catchment Systems Small Catchment Systems Macro-Catchment Systems (Within field/internal (Runoff generated from small (Flood diversion and catchments systems) external catchments and spreading i.e. spate diverted to cropland/pasture) irrigation) Fig. 2. Adopted classiﬁcation of rainwater harvesting technologies and systems in sub-Saharan Africa.soil proﬁle storage (direct runoﬀ application) and dis- district also incorporate runoﬀ spreading from smalltinct storage structures for supplemental irrigation, external catchments such as road/footpath drainage andlivestock, domestic or commercial use). Whilst the size adjacent ﬁelds. It is also common to ﬁnd runoﬀ fromof catchment criteria yields three categories––macro- external catchment being directed into cropland withcatchments (ﬂood diversion and spreading i.e. spate farm ponds for supplemental irrigation. In situ waterirrigation), small external catchments (road runoﬀ, ad- conservation is also combined with runoﬀ farming onjacent ﬁelds, etc.), and micro (within ﬁeld)-catchments farms with terraces, in which the terrace channel (mainly(e.g. Negarims, pitting, small bunds, tied ridges, etc.). fanya juu and contour ridges/bunds) collects and stores Moreover, runoﬀ storage structures capture runoﬀ runoﬀ from small external catchments while the crop-mainly from small catchments especially for smallscale land between the channels harvest and conserve directlandusers, but macro-catchments with large storage rainfall. However, excess runoﬀ that may be generatedstructures could also be used for large-scale or com- from the cropland between the terrace channels wouldmunity-based projects. In situ water conservation could be collected at the channel.also be considered under soil proﬁle storage systems, The following sub-sections highlight some of theonly that in that case direct rainfall is stored, but not RWH technologies and systems that have been tried,surface runoﬀ. However, the classiﬁcation is further experimented and practiced in diﬀerent parts of sub-complicated by the fact that a number of RWH tech- Saharan Africa, in addition to those identiﬁed andnologies are integrated or combined by landusers, for evaluated as part of the GHARP case studies in parts ofexample, ﬁelds under conservation tillage in Laikipia Ethiopia, Kenya, Uganda and Tanzania.
948 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–9562.1. In situ rainwater conservation ing, where runoﬀ is impended and soil water is stored in the crop root zone (Rockstr€m et al., 1999). o In situ rainwater conservation technologies are dis- Unlike the conventional tillage systems, based on soiltinct from runoﬀ farming systems in that they do not inversion which impedes soil inﬁltration and root pene-include a runoﬀ generation area, but instead aims at tration, conservation tillage covers a spectrum of non-conserving the rainfall where it falls in the cropped area inversion practices from zero-tillage to reduced tillageor pasture. The most common technology is conserva- which aim to maximize soil inﬁltration and productivity,tion tillage which aims to maximize the amount of soil by minimizing water losses (evaporation and surfacemoisture within the root zone. A number of cultural runoﬀ) while conserving energy and labour. Kiharamoisture practices such as mulching, ridging, addition of (2002) revealed the successes of conservation tillage inmanure, etc. could fall under this category. Small ﬁeld/ harnessing rainwater and improving yields. Field visitsfarm structures such as tied ridges/bunds within cropped in Machakos revealed that, during the recent belowarea that conserve direct rainfall without Ôexternal’–– average short rains (2001/2002), farms where conserva-outside cropland boundary, i.e. no distinct catchment tion tillage was practiced had good harvest whilearea, except overﬂow from upstream sections also falls neighbouring farms without convention tillage had lit-under this category. Within cropland or pasture contour erally no harvest––conspicuous contrast.bunds/ridges, bench terraces, and sweet potatoes ridges Conservation tillage has several attractive eﬀects onpracticed in Rakai district of Uganda could also fall water productivity (Rockstr€m et al., 2001) compared to ounder this category. traditional soil and water conservation systems such as In situ rainwater conservation technology is one of fanya juu terracing in Machakos district. In addition tothe simplest and cheapest and can be practiced in almost enhancing inﬁltration and moisture conservation, it en-all the landuse systems. In situ water conservation sys- ables improved timing of tillage operations, which istems are by far the most common (Rockstr€m, 2000) o crucial in semi-arid rainfed farming. It can also be ap-and are based on indigenous/traditional systems (Reij plicable on most farmlands compared say to storageet al., 1996; LEISA, 1998). The primary objective has RWH systems for supplemental irrigation. Promotionbeen to control soil erosion and hence manage the of animal drawn conservation tillage tools such as rip-negative side-eﬀects of runoﬀ––soil and water conser- pers, ridgers and sub-soilers among smallholder farmersvation measures, i.e. ensures minimal runoﬀ is gener- in semi-arid Machakos and Laikipia districts (Kenya)ated. The positive eﬀect of in situ water conservation has resulted in signiﬁcant water productivity and croptechniques is to concentrate within-ﬁeld rainfall to the yields (Kihara, 2002; Muni, 2002). There are manycropped area. In a semi-arid context, especially with documented examples of successful conservation tillagecoarse-textured soil (especially sandy soils common in practices in ESA, where crop yields have been increasedthe ASALs) with high hydraulic conductivity, this through the conservation of soil water and nutrientsmeans that in situ conservation may oﬀer little or no and/or draught power needs have been reduced (Rock-protection against the poor rainfall distribution. In such str€m et al., 1999). ocases, the farmers will continue to live at the mercy of The ﬁndings of the case studies in Laikipia andthe rain. In eﬀect, the risk of crop failure is only slightly Machakos districts of Kenya reveals that conservationlower than that without any measures. However, soil tillage (sub-soiling and ridging) have improved yields byimprovements such as addition of manure would en- more than 50% (Kihara, 2002; Muni, 2002). The po-hance realization of better yields. tential of conservation tillage is tremendous especially with communities already using animal drawn imple-2.1.1. Conservation tillage ments for their tillage operations. This is because con- Conservation tillage is deﬁned as any tillage sequence servation tillage implements are compatible with thehaving the objective to minimize the loss of soil and conventional tools. On large scale farming systems inwater, and having an operational threshold of leaving at Laikipia district, tractor drawn conservation tillage im-least 30% mulch or crop residue cover on the surface plements have improved wheat yields. Pastoral com-throughout the year (Rockstr€m, 2000). However, with o munities are also not being left behind, as groundrespect to small-scale farmers in SASE, conservation scratching using animal or tractor drawn tools havetillage is deﬁned as any tillage system that conserves improved pasture development in Laikipia district. Inwater and soil while saving labour and traction needs. Dodoma, Tanzania, trench cultivation, a form of con-Conservation tillage aims at reversing a persistent trend servation tillage have been developed by innovativein farming systems of reduced inﬁltration due to com- farmers, where shallow trenches are dug, ﬁlled with or-paction and crust formation and reduced water holding ganic materials then covered by soil to form ridges oncapacity due to oxidation of organic materials (due to which crops are planted (Lameck, 2002). The Ôorganic’excessive turning of the soil). From this perspective, furrows between the ridges capture water, which seepsconservation tillage qualify as a form of water harvest- into the covered trenches and is slowly extracted by the
S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 949crops. The organic material improves soil fertility and may be beyond the reach of many farmers. Farmers arewater holding capacity. This seems to be an improve- still experimenting with various seepage control meth-ment of the furrow and ridge systems as used in Kitui ods, among them, plastic lining (found not durable),and Machakos. The furrows and ridges are made using butimen lining, clay lining and even goats trampling.animal drawn mould board ploughs. Seeds are planted Nevertheless, seepage control still remains a majorin the furrow, which collects water between the ridges. challenge.After seedlings develop, weeding operation (using ani- Other storage systems used by smallscale farmers inmal drawn ridgers) ensures that the furrows and ridges semi-arid districts of eastern Kenya are rock catch-alternate––the crops grow on the ridges while the fur- ments/dams, sand dams and sub-surface dams (Gouldrows captures and concentrates the rainwater. In trench and Petersen, 1991; Pacey and Cullis, 1986). Sand damscultivation, the ridges and furrows are rotated after and sub-surface dams are barriers constructed alongeach growing season and have enhanced crop yields in sandy riverbeds––a common phenomenon in most semi-otherwise low yielding areas. arid environments in GHA––to retain water within the trapped sand upstream. These systems have provided2.2. Runoﬀ farming water for decades especially in Machakos and also in some parts of Kitui district. They have also been in- The runoﬀ farming systems, which entail runoﬀ gen- troduced in the Dodoma area of Tanzania but theireration either within ﬁeld or from external catchments potential has however, not been realized. They provideand subsequent application either directly into the soil water for all purposes and could lead to environmentalproﬁle or through periodic storage for supplemental ir- improvement, for example in Utooni in Machakos andrigation, are classiﬁed according to two criteria (as some parts of central Kitui. The impacts of sand damsshown in Fig. 2 above): runoﬀ storage and/or applica- on food security have been highlighted by Isika et al.tion, and size of catchments. (2002). They are mainly used for domestic purposes, but in several cases also used for smallscale irrigation2.2.1. Storage RWH systems (Rockstr€m, 2000). Rock catchment dams are masonry o RWH systems with storage for supplemental irriga- dams, for capturing runoﬀ from rock surfaces/catch-tion are becoming popular in semi-arid districts of ments, with storage capacities ranging from 20–4000 m3 .Kenya (e.g., Machakos, Laikipia, and Kitui). They have They are generally used for domestic purposes, but canalso been introduced in Ethiopia (near Nazareth) on also be used for kitchen gardening, for example in Kituiexperimental basis by RELMA. Moreover, small stor- district (Ngure, 2002).age systems are all over parts of Ethiopia (e.g. Tigray), RWH storage systems oﬀers the landuser a tool forand other places around Africa (Fentaw et al., 2002). water stress control––dry spell mitigation. They reduceInitial results from RWH experiments in Machakos risks of crop failures, but their level of investment is highdistrict, which focused on the feasibility of using earth- and requires some know-how especially on water man-dams for supplemental irrigation of maize have been agement. However, these systems also to some extentencouraging (Rockstr€m et al., 2001). The main chal- o depend on rainfall distribution. During extreme droughtlenge with this initiative is to assess whether it is possible years, very little can be done to bridge a dry spell oc-to design simple and cheap earthdams or farm ponds curring during the vegetative crop growth stage if nothat could permit gravity-fed irrigation to reduce the runoﬀ producing rainfall have fallen during early growthcost of lifting water. stages. Under normal intra-seasonal droughts, the farmer In the semi-arid parts of Laikipia district (Kenya), will be assured of a better harvest and hence it is worthyunderground water tanks (50–100 m3 capacity) have any investment to improve crop production in the semi-been promoted mainly for kitchen gardening. The tank arid tropics of SSA. Nevertheless, location of the storagesurfaces are usually sealed with polythene lining, mor- structure with respect to cropland needs to be addressed.tar, rubble stones or clay to reduce seepage losses while Conventionally, the reservoirs are located downstream,covering the tanks, with either local material (thatch or thus requiring extra energy to deliver the water to theiron sheet), minimizes evaporation. However, similar crops. However, it would be more prudent to locate theinitiative in Kitui district was discouraging as most of reservoir upstream of the cropland to take advantage ofthe mortar sealed underground tanks ended up cracking gravity to deliver the water (Rockstr€m, 2000). oand hence being abandoned (Ngure, 2002). In Laikipia, Runoﬀ is collected from grazing land, uncultivatedloss of water through seepage has been identiﬁed as a land, cultivated land and road drainage and directedmajor drawback (Kihara, 2002). Thus despite the posi- into small manually constructed reservoirs (50–200 m3 ).tive impact realized by this technology, its widespread The stored water is mainly utilized for kitchen gardeningadoption could be hampered if simple seepage control and establishment of orchards. This technology wasmeasures are not devised. Concrete sealing seem to work introduced in Laikipia district Kenya in the late 1980swell in Ng’arua division of Laikipia district, but the cost by the Anglican Church of Kenya and has shown
950 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956promising results. It has been promoted by Dutch-sup- Extensive ﬂood irrigation of paddy rice in cultivationported ASAL and SARDEP progammes with limited basins (commonly referred to as ‘‘majaluba’’) createdsuccess due to seepage related problems. Various reme- from 25–100 cm high earth bunds, is practiced in semi-dies are being tried to reduce seepage to realize maxi- arid central parts of Tanzania (Dodoma, Singida andmum beneﬁts from this technology. In Kenya, it has also Shinyanga) (Mwakalia and Hatibu, 1992; Hatibu et al.,been introduced in Machakos district by RELMA. 2000; Lameck, 2002). It is estimated that 32% of Tan-Optimal beneﬁts could be realized if appropriate water zania’s rice production originate from cropland wherelifting and application technologies such as treadle RWH is practiced. Similar techniques have been usedpump and drip irrigation are incorporated. Farm ponds for maize and sorghum in Tanzania.have also been used for watering livestock. At commu- Spate irrigation in northern Ethiopia and Eritrea,nity level, earth dams or water pans are constructed involve capturing of storm ﬂoods from the hilly terrainto store large quantities of water, especially for live- and diversion into leveled basins in the arid lowlandsstock and small-scale irrigation. These water pans and croplands. In Kobo Wereda (south of Tigray), spateearth dams are the lifeline for livestock in the ASAL of irrigation is well developed with main diversion canals,Kenya, Somalia and parts of Uganda (southern and secondary/branch, tertiary and farm ditches which dis-northeastern). The earth dams were introduced by white tribute ﬂood water into cultivation basins with contoursettlers while the water pans have been traditional bunds to enhance uniform water application. A series ofsources of water e.g. haﬁrs (water pans) in northeastern main canals for diﬀerent group of farmers are normallyprovince of Kenya, parts of Somalia and western Sudan constructed together to reduce destruction by ﬂoods(Critchley, 1987). Concrete/mortar lined underground (Fentaw et al., 2002). Farmers in Kobo plains intanks (100–300 m3 ) are used for domestic and some northern Ethiopia have developed a traditional irriga-livestock (milking cows, calves or weak animals, sepa- tion system that diverts part of such ﬂoods to theirrated from the main herds) in Somaliland (Pwani, 2002). farms. These system have sustained livelihoods that would otherwise be impossible in that dry part of the2.2.2. Direct runoﬀ application systems country. These systems are similar in principle to those This category of RWH technology is characterized by developed by the early settlers of the Negev Desert inrunoﬀ generation, diversion and spreading within the Israel. The system has also been tried in Konso, south-cropland, where the soil proﬁle acts as the moisture ern Ethiopia. This technology has also been practiced instorage reservoir. This technology is further classiﬁed, Turkana district, Kenya for sorghum production andaccording to size of catchments: macro-catchments parts of Sudan (Cullis and Pacey, 1992). In westernsystems––large external catchments producing massive Sudan, terraces and dykes are used for spreading runoﬀrunoﬀ (ﬂoods) which is diverted from gullies and from wadis onto vertisols (Critchley, 1987). The poten-ephemeral streams and spread into cropland, i.e. spate tial of these systems are enormous and if improved andirrigation; small external catchments (e.g. road drainage, promoted could lead to food security.adjacent ﬁelds, etc.) from which runoﬀ is diverted into The use of external catchments for runoﬀ collectioncropland; and micro-catchments normally within crop- immediately adds water to the ﬁeld scale water balance.land which generate small quantities of runoﬀ for single With ﬂood irrigation systems in the SASE where abso-crops, group of crops or row crops. lute crop water scarcity is common, crop yields can be improved substantially during years with reasonably2.2.3. Flood diversion and spreading (spate irrigation) good rainfall distribution. The farmers still live undersystems the mercy of the rains, but when it rains, the supply of Flood diversion and spreading (i.e. spate irrigation) water to the root zone exceeds rainfall depths. Thisrefers to RWH system where surface runoﬀ from macro- disparity can be addressed by introducing storage fa-catchments concentrating on gullies and ephemeral cilities.streams/water courses is diverted into cropped area anddistributed through a network of canals/ditches or wild 2.2.4. Small external catchment systemsﬂooding and subsequently retained in the ﬁeld by bunds/ These include a form of smallscale ﬂood/runoﬀ di-ridges. It entails controlled diversion of ﬂash ﬂoods from version and spreading either directly into cropland ordenuded highlands to cropped land well prepared to pasture through a series of contour bunds or into terracedistribute and conserve the moisture within the plants channels and other forms of water retention structures.rootzone. The rainfall characteristics in the semi-arid The runoﬀ is either conveyed through natural water-savannah environment occurs as high intensity storms ways, road drainage or diversion/cutoﬀ drains. Road/that generate massive runoﬀ that disppear within a short footpath runoﬀ harvesting is practiced in parts of Kenyaperiod through seasonal waterways. Worse still the (Machakos and Laikipia), in which ﬂood water fromnumber of rainstorms are normally limited within the road/footpath drainage is diverted either into storage forshort rainy seasons. supplemental irrigation or into croplands (wild ﬂooding,
S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 951contour bunds, deep trenches with check-dams to im- (e.g. maize, sorghum etc) in case of chololo pits inprove crop yields. Similar system is practiced in south- Dodoma, Tanzania. Pitting techniques, where shallowwestern Uganda, where runoﬀ from gullies, grazing planting holes (<25 cm deep) are dug for concentrationland, or road drainage is diverted into banana planta- of surface runoﬀ and crop residue/manure, are found intions (Kiggundu, 2002). many farming systems throughout SSA. They come in Fanya juu terraces which were previously used with many names and include zai pits (Burkina Faso), mat-diversion/cutoﬀ drains for soil conservation especially in engo pits (southern highlands of Tanzania) and tum-Machakos and Kitui have been adopted for rainwater bukiza for napier grass and banana or pawpaw pitsharvesting. They are modiﬁed by constructing planting (Kenya). Moisture retention terraces and ditches arepits mainly for bananas and tied ridges (check dams) for other micro-catchment techniques promoted and adop-controlling the runoﬀ. The outlet is blocked to ensure as ted in SESA. The following are more examples:much runoﬀ as possible is retained while spillways areprovided to discharge excess runoﬀ, which is normally • Fanya juu terraces, which are made by digging adiverted into the lower terraces. Runoﬀ spreading has trench along the contour, and throwing the soil up-also been accomplished by contour bunds in Laikipia slope to form an embankment. They have made a verydistrict. They collect and store runoﬀ from various signiﬁcant impact in reducing soil erosion in semi-catchments including footpaths and road drainage. The arid areas with relatively steep slopes (Thomas,stored runoﬀ seeps slowly into lower terraces ensuring 1997; Tiﬀen et al., 1994). They have been used foradequate moisture for crops grown between the terrace RWH by incorporating tied ridges in the channelchannels. In southern Uganda, a similar system has been with closed outlets.adopted, in which contour ridges/bunds, (shallow fanya • Fanya chini, in which the soil is thrown downslope in-juu terraces) tied at regular intervals are used in banana stead of upslope, was developed in Arusha region,plantations. The runoﬀ from hilly grazing lands is dis- Tanzania.tributed into the banana plantations by contour ridges. • Contour bunds, e.g. stone bunds and trashlines in dryAgroforestry (for ﬁrewood and fodder) is also incorpo- areas of southern Kenya and retention ditches andrated, where trees planted on the lower side and Napier stone terraces in Ethiopia. Yields of sorghum are re-or giant Tanzania grass along the ridges. This system has portedly increased by up to 80% using contour bundstremendously improved the yield of the bananas and has in northwestern Somalia (Critchley, 1987).enhanced zero grazing. Contour ridges and inﬁltration • Micro-basins, which are roughly 1.0 m long and <50trenches have also been adopted to improve pasture in cm deep, are often constructed along the retentionsouthern Uganda (Kiggundu, 2002). The inﬁltration ditches for tree planting (e.g., northern Tigray, Ethi-trenches are dug at speciﬁed intervals according to the opia) (Lundgren, 1993). Sweet potato ridges/bunds inland slope and tied at regularly intervals to allow water southern Uganda fall under this category (Kiggundu,retention and subsequent inﬁltration. The soil is either 2002). In Kwale districts of Kenya, tied ridges andthrown upward (fanya juu) or downwards (fanya chini) small basins have been reported to improve maizeand stabilizing grass or fodder crops. Runoﬀ from uphill yields by more than 70%.catchments is normally diverted into these contour dit- • Semi-circular earth bunds (demi-lunes) are found inches (inﬁltration trenches) to increase soil moisture. ASALs for both rangeland rehabilitation and for an- In eastern part of Sudan, a traditional system of nual crops on gently sloping lands (e.g. Baringo andharvesting rainwater in ‘‘terraces’’ is widely practiced Kitui districts) (Thomas, 1997). Semi-circular bunds(Critchley, 1987). It consists of earthen bunds with wing adopted for establishment of tree seedlings in de-walls which impound water to depths of at least 50 cm nuded hilly areas in southern Uganda applies theon which sorghum is planted. Within the main bund same principle (Kiggundu, 2002).there may be smaller similar bunds which impound less • Negarims micro-catchment are regular square earth-runoﬀ on which planting can be done earlier. dams turned 45° from the contour to concentrate sur- face runoﬀ at the lowest corner of the square (Hai,2.2.5. Micro-catchment systems 1998) are found in eastern province of Kenya. This involve runoﬀ generation within the farmer’s • Large trapezoidal bunds (120 m between upstreamﬁeld and subsequent concentration on either a single wings and 40m at the base) have been tried in aridcrop especially fruit trees, a group of crops or row crops areas of Turkana district, northern Kenya for sor-with alternating catchment and cropped area mainly ghum, trees and grass (Thomas, 1997).along the contours. A number of within-ﬁeld RWH • Inﬁltration trenches/ditches, which are dug along thesystems fall under this technology, in which crop land is contour, at speciﬁed intervals according to the slope,subdivided into micro-catchments that supply runoﬀ for retaining runoﬀ in banana plantations in south-either to single plants (e.g. pawpaw or oranges) for ex- western Uganda, Mbarara and Rakai districts (Kigg-ample Negarims in Kitui, Kenya or a number of plants undu, 2002).
952 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956• Circular depressions (3–4 m in diameter and <1.0 m ted to their conditions and needs, and which also ensure deep) where a variety of crops are inter-cropped an increase in water use eﬃciency and conservation. It is and literally allows no runoﬀ from the ﬁelds are prac- encouraging that land users have developed many low- ticed in southern Ethiopia. cost water saving techniques. Unfortunately, although most of these innovations remain unrecognized, many of them are within the reach of the land users. Therefore,3. Role of rainwater harvesting technologies according to LEISA (1998), water scarcity can be chal- lenged!3.1. Potential for improving food production Traditional water harvesting systems are characterized by ﬂexibility and endurance and are strongly associated There are a number of promising interventions for with the people who live in marginal environments. Thusimproving water availability either for crop production diﬀerent areas will have diﬀerent techniques for harvest-or other uses in the dry parts of the SSA region. A few ing and applying water. Although the potential for watertechniques especially for irrigation have been tested and harvesting has not been fully assessed, this potential isproven successful but majority, which are mainly land- probably quite large in the Greater Horn of Africa whereusers’ innovations remain unproven. It is evident that the food security is a major concern. Recently, renewed in-introduction of new technologies without landusers terest has been shown in water harvesting in sub-Saharanparticipation, however novel they may be, has not been Africa, probably as a result of increasing pressure onsuccessful. One such project is the multi-million Bura land, which forces more and more people into dry areasirrigation scheme in Kenya. On the other hand, the (Oweis et al., 1999). This new trend could also be at-landusers’ ingenuity has certainly paid dividends. The tributed to failure of more conventional methods andchallenge now is to evaluate landusers innovations and changing environments forcing people to adopt newtraditional systems to determine their appropriateness in survival strategies. Therefore, water harvesting has asolving the recurrent food crisis in the region. Clearly the high potential for improving food security and reducingdevelopment of the ASAL represents the highest poten- over-dependency on food aid. However, for this poten-tial for further economic advancement in the region. The tial to be realized, appropriate techniques need to bemajor challenge is how to utilize the available water––the identiﬁed for particular areas within the region. The casemost limiting factor to economic activity in the dry areas. studies will contribute towards identifying diﬀerent Currently, most countries in the region are not able to techniques land users in the region have already testedmarshal ﬁnancial resources to enable bulk water trans- and approved, and look into ways of improving thefers (e.g. inter-basin transfers), or dam and reservoir adopted technologies.construction for most of the ASAL. The pragmatic way Rainwater harvesting is a promising technology forforward is in the development of least-cost small-scale improving the livelihoods of many inhabitants of therainwater harvesting technologies by the communities vast dry regions of the world. RWH can be viable inand individuals who live within these areas. Mere sur- areas with as low as 300 mm of annual rainfall (Kutch,vival instinct has led many land users in the ASAL to 1982). However, Pacey and Cullis (1986) gave a moreimprovise various indigenous runoﬀ-farming systems. conservative range of annual rainfall, 500–600 mm. But,However, due to limited technical resources, these in- Kutch (1982) further stated that annual rainfall is notdigenous runoﬀ-farming systems are poorly designed the most important criterion. Nevertheless, the tech-and operated. Therefore, a great beneﬁt can be realized nology has been used to sustain food production in thethrough technical improvements of the existing water Negev desert of Israel with meagre annual rainfall ofharvesting initiatives. This can be accomplished by ﬁrst about 100 mm (Shanan and Tadmor, 1976). Ironically,understanding and evaluating the various systems being most of the famine stricken areas of Africa receivesused in the region and comparing their performance much more than 100 mm of rainfall.vis--vis the prevailing local conditions. a Thus many parts of the SSA could tremendously As water becomes more and more scarce, there is a improve food security through RWH, which aim toneed for an integrated approach to water management supply the deﬁcit between rainfall and evapotranspira-that encompasses all water users, types of water uses and tion during the growing season. In case of RWH forsources of water. Water management, however, can supplemental irrigation, the deﬁcit is maintained bynever be an aim in itself, it is an integral part of farm supplying water to the crops during the critical periods.and land husbandry and its objective should always be Some experts regard irrigation as the only viable methodto protect and improve the land users’ situation (LEISA, of agricultural production in the ASAL (Pacey and1998). Nevertheless, high-external-input techniques may Cullis, 1986). But history has proved otherwise espe-be too expensive for smallholders or are inappropriate cially for small scale farming systems. Therefore, pro-to local biophysical and social conditions. Many land motion of RWH should take into consideration theusers would beneﬁt from low-cost techniques more sui- perceived low rates of ﬁnancial investments, especially in
S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 953runoﬀ farming, compared to irrigated agriculture. RWH tainable environmental management strategies and tra-minimizes some of the problems associated with irriga- ditional institutions that are involved in the well being oftion such as competition for water between various uses the community and management of conﬂicts over use ofand users, low water use eﬃciency, and environmental natural resources. Many of the conﬂicts, especially inter-degradation. It is a simple, cheap and environmentally clan conﬂicts, are normally aggravated by food insecu-friendly technology, which can be easily managed with rity and competition over scarce natural resources.limited technical skills. The technology can also be in- Conﬂicts over natural resources, especially water andtegrated with many land use system, hence it is appro- land, have been politicized in the SSA. According topriate for local socio-cultural, economic and biophysical Mathenge (2002), the issue of water is of equal impor-conditions. Furthermore, there are many traditional tance on the political scene as security in Laikipia Dis-water management techniques still being used to make trict in upper Ewaso Ng’iro river basin. Large-scaleoptimal use of available rainfall (LEISA, 1998). horticultural farming by wealthy local and international concerns on the slopes of the Aberdares and Mt. Kenya3.2. Reduction of conﬂicts over water resources has depleted the mountain streams that used to be the main sources of water leading to upstream–downstream Extensive areas of the SSA countries are not well en- conﬂicts. Smallscale farmers along the streams have alsodowed with water resources. This scarcity is aggravated contributed to water conﬂicts by abstracting water, inby poor distribution of water resources in most coun- most case (more than 70%) illegally, for irrigation.tries. For instance, in Kenya, less than 20% of the During extreme dry spells, the provincial administrationcountry has adequate water resources for rainfed agri- normally intervenes by banning water abstraction forculture. In the vast dry areas, the main challenge is, irrigation. Otherwise downstream users would organizetherefore, to increase water supply through more eﬃcient themselves and destroy water diversion structures up-utilization of rainfall. It is evident that water scarcity is stream.one of the main drawbacks to substantial development of Insecurity too has contributed to the problem asthe ASAL. This scarcity has led to persistent conﬂicts many farmers have abandoned livestock rearing––over use and access to existing water supply. The con- attractive to cattle rustlers––to try out farming. This hasﬂicts involve diﬀerent water users and uses. increased conﬂicts over water rights and food insecurity. More often than not, diﬀerent clans especially within The politicians in the area have threatened to lead thethe pastoral communities, in the ASAL have been en- aﬀected communities to storm horticultural farms overgaged in increasing conﬂicts over the control and use of water conﬂicts, while others have proposed that gov-communal water sources and grazing land. Cross border ernment impose levies on major horticultural producersconﬂicts leading to severe clashes have also occurred to raise funds to construct and maintain reservoirs toover control of natural resources. Notwithstanding ex- harness ﬂood waters. Hence RWH could play a majoristing traditional institutions, that to some extent have role in conﬂict resolutions, especially in drier areas ofpromoted peaceful coexistence, the conﬂicts seem to get GHA. Some large-scale horticultural farmers have al-worse by the day as water resources become scarcer. ready adopted RWH by constructing large earthdams toHence, one of the logical ways to contain the situation is harvest runoﬀ to supplement limited water for irriga-to provide adequate water and food supply. This ap- tion. Another form of conﬂict occurs during the rainyproach has apparently worked well in northeastern season over limited runoﬀ on shared road/footpathKenya, especially in Wajir district, where a local NGO drainage. This is becoming common in Ng’arua divisionhas assisted in the construction of water pans to store of Laikipia District where neighbouring farmers com-rainwater for diﬀerent clans (Githinji, 1999). This is a pete and some times ﬁght over diversion of runoﬀ tocase where low technology––water harvesting––has their farms, especially those with farm ponds for storingproved itself, not only as a water supply system, but also water for use during inter-seasonal droughts––to miti-as a conﬂict resolution mechanism. In addition, the gate water stress during critical growth stages. This kindtechnology has led to improved food security and living of conﬂicts could be addressed through improvedstandards through provision of water for domestic, management systems at community level.livestock and agricultural purposes. This technology hasalso created employment besides being easily replicable.Similar cases will be articulated in the proposed project 4. Hydrological impacts: limits of up-scaling rainwaterand hence ways of dealing with the twin problem of food harvestingsecurity and conﬂicts over natural resources which isprevalent in the GHA region. Rainwater harvesting involves abstraction of water Moreover, the case studies considered interrelated in the catchment upstream and may have hydrologi-environmental governance and gender issues aﬀecting cal impacts on downstream water availability. Down-food security and water availability. These include sus- stream access to water as a result of increased water
954 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956withdrawals upstream is an issue of concern, but it is There is need for research to provide information to as-assumed that there are overall gains and synergies to be sist decision and policy makers formulate sustainablemade by maximizing the eﬃcient use of rainwater at river basin water resources management strategies.farm level (Rockstr€m, 1999). However, up-scaling of o As shown by several hydrological studies at water-RWH––increasing adoption––could have hydrological shed and basin, upstream shifts in water ﬂow parti-impacts on river basin water resources management. tioning may result in complex and unexpectedThe on-going PhD study aims at assessing downstream– downstream eﬀects, both negative and positive, in termsupstream interaction related to increased adoption of water quality and quantity (Vertessy et al., 1996). Inrate––retaining more water in the watershed––in the general though, increasing the residence time of runoﬀwater scarce Ewaso Ngi’ro river basin in Kenya. Up- ﬂow in a watershed, e.g., through RWH may havegrading rainfed agriculture, through the promotion of positive environmental as well as hydrological implica-RWH in the ASALs, require proper planning of land tions/impacts downstream (Rockstr€m et al., 2001). The omanagement at river basin scale, rather than conven- hydrological impacts at watershed/river basin level oftional focus on farm level. up-scaling system innovations, such as RWH, are still In the past, runoﬀ has been as being destructive and unknown and require further research. The proposedneeded to be diverted from agricultural lands as wit- study aims to shed some light on this issue.nessed by over 30 years of soil conservation practices in Increased withdrawals of water in rainfed and irri-Kenya. However, radical transformation are required, gated agriculture may have negative implications onwhere surface runoﬀ from upstream watershed entering water availability to sustain hydro-ecological ecosystema farm will no longer be seen as a threat to be disposed services. The expected shifts in water ﬂows in the waterof or diverted away, but as a resource to be harnessed balance would aﬀect both nature and economic sectorsand utilized to improve rainfed agriculture. Such depending on direct water withdrawals (Rockstr€m otransformation is complex, especially among smallscale et al., 2001). Upgrading rainfed agriculture throughfarmers, since even a runoﬀ from a small catchment will RWH that enables dry spells mitigation, would involveinvolve multiple landusers. Presently there is little at- the addition of water, through storage of runoﬀ, to thetention given to ownership and management of locally rainfed system. The cumulative eﬀect of RWH may haveproduced runoﬀ, but this is expected to become a par- an impact on downstream water availability within aamount issue if runoﬀ is to be optimally managed on a river basin scale. The eﬀects are bound to be site speciﬁclarger scale for local production purposes. In Laikipia and need to be studied further (Rockstr€m et al., 2001). odistrict of Kenya, conﬂict over runoﬀ diversion and The potential of developing small farm ponds andutilization for crop production is a reality (Kihara, earthdams for supplemental irrigation in SSA, is deter-2002). The situation may become much worse with the mined by a set of site speciﬁc biophysical and socio-growing realization of the beneﬁts of RWH especially economic factors (Rockstr€m, 2001), which include ofor resource-poor smallscale farmers, who depend solely practiced farming systems, population pressure, formalon rainfed agriculture. Already even with limited RWH and informal institutions, land tenure, economic envi-systems, downstream–upstream conﬂicts between pas- ronment and social structures. Thus hydrological im-toralists and farmers (who divert meager stream water pacts cannot be assessed in isolation. It is important tofor irrigation) are very common particularly during the analyze the downstream eﬀects on water availability, fordry periods. The rainfed farmers are also in the course of example for household and livestock needs, as well asentering the conﬂict, among each other and with the heath and environmental impacts, before introducing adownstream landusers––both farmers and pastoralists in technology which retains water upstream, an possiblythis water-scarce river basin. The Indian experience on reducing river ﬂows.communal rainwater management may provide usefulbackground in an attempt to develop sustainable RWHup-scaling strategies in SSA. 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