Kenya; What is the Limit Of Up-Scaling Rainwater Harvesting In A River Basin

1. Physics and Chemistry of the Earth 28 (2003) 943–956
www.elsevier.com/locate/pce
What 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, Kenya
Abstract
The semi-arid savannah environment (SASE) of sub-Saharan Africa are characterized by low erratic rainfall which result to high
risk of droughts, intra-seasonal dry spells and frequent food insecurity. The main occupation is subsistence small-scale rainfed
agriculture and livestock production, which normally compete for the limited water resources. The main challenges to improving the
livelihoods of the small-scale farmers are how to upgrade rainfed agriculture to improve rural livelihoods and conserve nature, and
upgrade upstream landuse in balance with water needs for human and ecosystems downstream. There is an increased interest in
opportunities of improving rainfed agriculture through adoption of rainwater harvesting (RWH) technologies. However, there is
inadequate knowledge on hydrological impacts and limits of up-scaling rainwater harvesting at a river basin scale. Rainwater
harvesting 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 exploited
despite the occurrence of persistent low agricultural production and food shortage in sub-Saharan Africa. The need to quantify this
perceived potential and related hydrological impacts on a river basin led to the on-going research project titled ‘‘hydrological
impacts of up-scaling RWH on upper Ewaso Ng’iro river basin water resources management’’. It is envisaged that the study will
contribute to formulation of sustainable RWH up-scaling strategies to enhance food production and hydro-ecological balance in
semi-arid savannahs of Africa. This paper presents the preliminary findings of the study mainly focusing on assessment of the
potential of RWH technologies for improving food and water availability especially in semi-arid regions of eastern Africa. This was
achieved by evaluating six RWH case studies selected from four countries (Ethiopia, Kenya, Tanzania and Uganda). Despite the
success of a number of RWH systems, the rate of adoption is still low, hence making their impacts marginal. Nevertheless, there is a
knowledge 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 limit
of 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 scarcity
1. 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 advanced
are experiencing profound socio-economic and political for the endemic food insecurity in the SSA. Among
problems, the most dramatic being food crises and dis- these, recurring drought and unreliable rainfall are the
ruptive conflicts. The communities involved are experi- most obvious. These include: adverse weather and
encing a combination of both short-term, often acute drought; rapid population growth rates that exceed rates
food crises, and long-term or chronic food shortages. of food production; adoption of production systems
The former often translate into famine and starvation, that accelerate environmental degradation and decline
requiring 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: ngigi@gharainwater.org, gharp@warianchi.com inhabitants are pastoralists although agro-pastoral and
(S.N. Ngigi). farming communities have been slowing settling in these
1474-7065/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.pce.2003.08.015

2. 944 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956
areas due to population pressure in the high agricultural agricultural activities. The same fact had been expressed
potential areas. SASE is predominantly characterized by by Jodha and Mascarenhas (1985) as characteristic of
low and variable rainfall, which rarely exceeds 800 mm, much of the rest of Africa. In Greater Horn of Africa
with 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 the
There are few permanent rivers, and seasonal streams dominant determining factor for food production and
that 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 and
SASE too is starting to experience land pressure re- recurrent famine need urgent solutions, especially in the
sulting due to population increase within the commu- SASE, where environmental degradation has further
nities and also their livestock. This has significantly decreased agricultural productivity, making inhabitants
raised 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 technologies
impact of the frequent droughts that hit the pastoral are adopted, alleviation of poverty and food security
areas has therefore been increasing over time. Huge will remain elusive. One promising technology for rural
livestock numbers have been dying every time there is landuse systems is rainwater harvesting. This is the
drought (Kihara, 2002). Much of the pastureland has process of interception and concentration of runoff and
lost grass cover and is often bare. This leaves the people its subsequent storage in the soil profile or in artificial
highly 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: the
conflicts, especially over diminishing natural resources–– catchment area is contiguous with the cropped area and
mainly 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 enhance
vast areas of SSA are facing drought and the threat of crop production in the ASALs of the SSA. However, the
famine 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, climatic
saved lives in the region from severe famine situations. conditions, soil characteristics, farming systems and
Food relief will continue to be required as long as socio-cultural and gender perspectives in which they are
transportation facilities are poor and local food pro- practiced.
duction in drought prone areas is inadequate. Given the Participatory evaluation is needed to determine viable
poor transportation infrastructure, emphasis on local options and adaptive strategies for sustainable food
food production appears the most logical approach to production in the ASALs. Needless to say, the solutions
improved 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 project
countries 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 to
strongly underscored that agriculture is the backbone of improve on landusers’ innovations and the applicability
these countries’ economic development and their peo- of those innovations will be a major contribution to
ple’s well being in the foreseeable future. A survey of 277 food security in this famine prone region. It is with a
societies in sub-Saharan Africa by Hunt-Davis (1986) sense of urgency that one notes the relevance of RWH
showed that approximately 86% depended primarily on technologies in certain limited but significant areas of
agriculture, 6% on animal husbandry, and animal hus- Africa, both for food production and for soil and water
bandry 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 RWH
and 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 land
on 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-Saharan
as it determines their activities geared towards earning a Africa
livelihood based on exploitation of the resources of the
land. Duckham and Masefield (1985) stated that in the The semi-arid areas of SSA are characterized by low
tropics generally, rainfall is the main determinant of annual rainfall concentrated to one or two short rainy

3. S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 945
seasons. 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 the
and 1000 mm from the dry semi-arid to the dry sub- ever increasing food demand and household income
humid zone (Rockstr€m, 2000). The length of the
o needed in SSA have to be achieved through an increase
growing period ranges from 75 to 120 and 121–179 days in biomass produced per unit land and unit water
in the semi-arid zone and dry sub-humid zone respec- (Rockstr€m, 2001). In the past, very little attention has
o
tively. Potential evaporation levels are high, ranging been paid to the development of rainfed agriculture in
from 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 the
be attributed to poor rainfall partitioning leading to need to focus on opportunities of increasing efficiency of
large proportion of non-productive water flows––not limited water in rainfed, smallholder agriculture in the
available for crop production. The nature and occur- SASE of SSA. Otherwise feeding the ever growing
rence of rainfall in SASE of SSA provides more insight population (at a rate of 2–3% per year) with diminishing
in 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
o
tensive storms, with very high intensity and spatial and current generation’s biggest challenge.
temporal variability. The result is a very high risk for
annual droughts and intra-seasonal dry spells (Rock- 1.3. Rainwater harvesting technologies and systems
str€m, 2000). From past experience, severe crop reduc-
o
tions caused by dry spells occurs 1–2 out of 5 years, Rainwater harvesting which is broadly defined as the
while total crop failure caused by annual droughts that collection and concentration of runoff for productive
occur 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 ancient
than not, leads to crop failure than absolute water roots and still forms an integral part of many farming
scarcity due to low cumulative annual rainfall. Unfor- systems worldwide (Evanari et al., 1971; Shanan and
tunately, 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, and
improving 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 water
there is a growing understanding that the major crop- conservation––to enhance soil infiltration and water
ping systems in SSA are not sustainable (Benites et al., holding capacity––dominate, while storage systems for
1998), hence the persistence low food production (food supplemental irrigation are less common, especially in
shortage) and reliance on food relief. Nevertheless, SSA (SIWI, 2001). Nevertheless, a recently concluded
majority 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 to
livelihood security (e.g., Botswana, 76%; Kenya, 85%; in situ systems, RWH for supplemental irrigation is slowly
Malawi, 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 and
drought prone SASE (UNDP/UNSO, 1997). This may stored in manually and/or mechanically dug farm ponds
explain why most of the population is poor––rely on (50–1000 m3 storage capacity). Due to the low volumes
unsustainable 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 as
culture 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 locations
agriculture 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 and
gravated by limited new land for cultivation, land and Rockstr€m, 2000) indicates a significant scope to im-
o
environmental degradation, poor infrastructure, politi- prove water productivity in rainfed agriculture through
cal and social crises, bad governance, insecure land supplemental irrigation, especially if combined with soil

4. 946 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956
fertility management. The results were more promising ability and management for downstream and natural
on soils with higher water holding capacity on which ecosystems like wetlands and swamps, due to reduced
crops seem to cope better with intra-seasonal dry spells. catchment water yields. Therefore, even though RWH
However, incremental water productivity improvements practices can be efficient in increasing the soil moisture
are only achieved during rainy seasons with severe dry for crops (principle objective) in water scarce areas, each
spells, while rainy seasons with adequately distributed technique has a limited scope due to hydrological and
rainfall the incremental value can be negative (Rock- socio-economic limitations. Rockstr€m (2000) high-
o
str€m et al., 2001).
o lighted the major hydro-climatic hazards in SASE
Runoff is collected mainly from ground catchments as farming as
well as ephemeral streams (flood water harvesting) and
road/footpath drainage. The storage is either in different • Poor rainfall partitioning, where only a small fraction
structures (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 cumulative
considered 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 when
has 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); and
example, 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. not
concentrated on a smaller area, reasonable yields will necessarily a lack of cumulative soil availability, but
still 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 where
it falls. Classification of runoff-based RWH technologies
depends: 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 among
RWH systems operate at different scales (household, its characteristics: RWH is practiced in ASALs where
field 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––

5. 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 small
tinct storage structures for supplemental irrigation, external catchments such as road/footpath drainage and
livestock, domestic or commercial use). Whilst the size adjacent fields. It is also common to find runoff from
of catchment criteria yields three categories––macro- external catchment being directed into cropland with
catchments (flood diversion and spreading i.e. spate farm ponds for supplemental irrigation. In situ water
irrigation), small external catchments (road runoff, ad- conservation is also combined with runoff farming on
jacent 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 direct
landusers, but macro-catchments with large storage rainfall. However, excess runoff that may be generated
structures could also be used for large-scale or com- from the cropland between the terrace channels would
munity-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 the
only 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 and
nologies are integrated or combined by landusers, for evaluated as part of the GHARP case studies in parts of
example, fields under conservation tillage in Laikipia Ethiopia, Kenya, Uganda and Tanzania.

6. 948 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956
2.1. 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 soil
tinct 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 tillage
or 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 surface
moisture within the root zone. A number of cultural runoff) while conserving energy and labour. Kihara
moisture practices such as mulching, ridging, addition of (2002) revealed the successes of conservation tillage in
manure, etc. could fall under this category. Small field/ harnessing rainwater and improving yields. Field visits
farm structures such as tied ridges/bunds within cropped in Machakos revealed that, during the recent below
area 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 while
area, 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 on
practiced in Rakai district of Uganda could also fall water productivity (Rockstr€m et al., 2001) compared to
o
under 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 to
the 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 is
tems 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 storage
et al., 1996; LEISA, 1998). The primary objective has RWH systems for supplemental irrigation. Promotion
been 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 farmers
vation 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 crop
techniques is to concentrate within-field rainfall to the yields (Kihara, 2002; Muni, 2002). There are many
cropped area. In a semi-arid context, especially with documented examples of successful conservation tillage
coarse-textured soil (especially sandy soils common in practices in ESA, where crop yields have been increased
the ASALs) with high hydraulic conductivity, this through the conservation of soil water and nutrients
means 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).
o
cases, the farmers will continue to live at the mercy of The findings of the case studies in Laikipia and
the rain. In effect, the risk of crop failure is only slightly Machakos districts of Kenya reveals that conservation
lower than that without any measures. However, soil tillage (sub-soiling and ridging) have improved yields by
improvements 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 the
having the objective to minimize the loss of soil and conventional tools. On large scale farming systems in
water, 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 ground
respect to small-scale farmers in SASE, conservation scratching using animal or tractor drawn tools have
tillage is defined as any tillage system that conserves improved pasture development in Laikipia district. In
water 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 innovative
in 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 on
capacity 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 seeps
conservation tillage qualify as a form of water harvest- into the covered trenches and is slowly extracted by the

7. S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 949
crops. The organic material improves soil fertility and may be beyond the reach of many farmers. Farmers are
water 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 major
in the furrow, which collects water between the ridges. challenge.
After seedlings develop, weeding operation (using ani- Other storage systems used by smallscale farmers in
mal 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 (Gould
rows captures and concentrates the rainwater. In trench and Petersen, 1991; Pacey and Cullis, 1986). Sand dams
cultivation, the ridges and furrows are rotated after and sub-surface dams are barriers constructed along
each 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 provided
2.2. 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 their
eration either within field or from external catchments potential has however, not been realized. They provide
and subsequent application either directly into the soil water for all purposes and could lead to environmental
profile or through periodic storage for supplemental ir- improvement, for example in Utooni in Machakos and
rigation, are classified according to two criteria (as some parts of central Kitui. The impacts of sand dams
shown 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 irrigation
2.2.1. 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 can
also been introduced in Ethiopia (near Nazareth) on also be used for kitchen gardening, for example in Kitui
experimental 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 for
and other places around Africa (Fentaw et al., 2002). water stress control––dry spell mitigation. They reduce
Initial results from RWH experiments in Machakos risks of crop failures, but their level of investment is high
district, 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 extent
encouraging (Rockstr€m et al., 2001). The main chal-
o depend on rainfall distribution. During extreme drought
lenge 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 no
that could permit gravity-fed irrigation to reduce the runoff producing rainfall have fallen during early growth
cost 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 worthy
underground 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 storage
surfaces 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 the
iron sheet), minimizes evaporation. However, similar crops. However, it would be more prudent to locate the
initiative in Kitui district was discouraging as most of reservoir upstream of the cropland to take advantage of
the mortar sealed underground tanks ended up cracking gravity to deliver the water (Rockstr€m, 2000).
o
and hence being abandoned (Ngure, 2002). In Laikipia, Runoff is collected from grazing land, uncultivated
loss of water through seepage has been identified as a land, cultivated land and road drainage and directed
major 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 gardening
adoption could be hampered if simple seepage control and establishment of orchards. This technology was
measures are not devised. Concrete sealing seem to work introduced in Laikipia district Kenya in the late 1980s
well in Ng’arua division of Laikipia district, but the cost by the Anglican Church of Kenya and has shown

8. 950 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956
promising results. It has been promoted by Dutch-sup- Extensive flood irrigation of paddy rice in cultivation
ported ASAL and SARDEP progammes with limited basins (commonly referred to as ‘‘majaluba’’) created
success 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 and
mum 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 where
lifting and application technologies such as treadle RWH is practiced. Similar techniques have been used
pump 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 terrain
to store large quantities of water, especially for live- and diversion into leveled basins in the arid lowlands
stock and small-scale irrigation. These water pans and croplands. In Kobo Wereda (south of Tigray), spate
earth 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 contour
settlers while the water pans have been traditional bunds to enhance uniform water application. A series of
sources of water e.g. hafirs (water pans) in northeastern main canals for different group of farmers are normally
province 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 in
tanks (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 their
rated from the main herds) in Somaliland (Pwani, 2002). farms. These system have sustained livelihoods that
would otherwise be impossible in that dry part of the
2.2.2. 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 in
runoff 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 in
storage reservoir. This technology is further classified, Turkana district, Kenya for sorghum production and
according to size of catchments: macro-catchments parts of Sudan (Cullis and Pacey, 1992). In western
systems––large external catchments producing massive Sudan, terraces and dykes are used for spreading runoff
runoff (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 and
irrigation; 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 collection
cropland; 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 reasonably
2.2.3. Flood diversion and spreading (spate irrigation) good rainfall distribution. The farmers still live under
systems 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. This
refers 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 and
distributed through a network of canals/ditches or wild 2.2.4. Small external catchment systems
flooding 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 or
denuded highlands to cropped land well prepared to pasture through a series of contour bunds or into terrace
distribute 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 Kenya
period through seasonal waterways. Worse still the (Machakos and Laikipia), in which flood water from
number of rainstorms are normally limited within the road/footpath drainage is diverted either into storage for
short rainy seasons. supplemental irrigation or into croplands (wild flooding,

9. S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 951
contour bunds, deep trenches with check-dams to im- (e.g. maize, sorghum etc) in case of chololo pits in
prove crop yields. Similar system is practiced in south- Dodoma, Tanzania. Pitting techniques, where shallow
western Uganda, where runoff from gullies, grazing planting holes (<25 cm deep) are dug for concentration
land, or road drainage is diverted into banana planta- of surface runoff and crop residue/manure, are found in
tions (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 pits
harvesting. They are modified by constructing planting (Kenya). Moisture retention terraces and ditches are
pits 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 are
provided to discharge excess runoff, which is normally • Fanya juu terraces, which are made by digging a
diverted 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 very
district. 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 for
adequate moisture for crops grown between the terrace RWH by incorporating tied ridges in the channel
channels. 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 dry
Agroforestry (for firewood and fodder) is also incorpo- areas of southern Kenya and retention ditches and
rated, 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 bunds
tremendously 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 <50
trenches have also been adopted to improve pasture in cm deep, are often constructed along the retention
southern 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 in
land 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 and
thrown upward (fanya juu) or downwards (fanya chini) small basins have been reported to improve maize
and 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 in
ches (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 and
harvesting 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 the
on 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 upstream
field and subsequent concentration on either a single wings and 40m at the base) have been tried in arid
crop 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 the
systems 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).

10. 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. Thus
improving 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 water
techniques especially for irrigation have been tested and harvesting has not been fully assessed, this potential is
proven successful but majority, which are mainly land- probably quite large in the Greater Horn of Africa where
users’ 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-Saharan
participation, however novel they may be, has not been Africa, probably as a result of increasing pressure on
successful. One such project is the multi-million Bura land, which forces more and more people into dry areas
irrigation 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 and
challenge now is to evaluate landusers innovations and changing environments forcing people to adopt new
traditional systems to determine their appropriateness in survival strategies. Therefore, water harvesting has a
solving the recurrent food crisis in the region. Clearly the high potential for improving food security and reducing
development 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 be
major challenge is how to utilize the available water––the identified for particular areas within the region. The case
most 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 tested
marshal financial resources to enable bulk water trans- and approved, and look into ways of improving the
fers (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 for
forward is in the development of least-cost small-scale improving the livelihoods of many inhabitants of the
rainwater harvesting technologies by the communities vast dry regions of the world. RWH can be viable in
and 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 more
improvise 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 not
digenous 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 the
through technical improvements of the existing water Negev desert of Israel with meagre annual rainfall of
harvesting 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 receives
used 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 to
need 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 for
sources of water. Water management, however, can supplemental irrigation, the deficit is maintained by
never 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 method
to protect and improve the land users’ situation (LEISA, of agricultural production in the ASAL (Pacey and
1998). 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 the
users would benefit from low-cost techniques more sui- perceived low rates of financial investments, especially in

11. S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956 953
runoff 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 of
tion such as competition for water between various uses the community and management of conflicts over use of
and 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 and
tegrated with many land use system, hence it is appro- land, have been politicized in the SSA. According to
priate 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-scale
optimal use of available rainfall (LEISA, 1998). horticultural farming by wealthy local and international
concerns on the slopes of the Aberdares and Mt. Kenya
3.2. 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 also
dowed with water resources. This scarcity is aggravated contributed to water conflicts by abstracting water, in
by 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 administration
country has adequate water resources for rainfed agri- normally intervenes by banning water abstraction for
culture. In the vast dry areas, the main challenge is, irrigation. Otherwise downstream users would organize
therefore, 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 as
the 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 has
flicts 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 the
the pastoral communities, in the ASAL have been en- affected communities to storm horticultural farms over
gaged 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 producers
conflicts leading to severe clashes have also occurred to raise funds to construct and maintain reservoirs to
over control of natural resources. Notwithstanding ex- harness flood waters. Hence RWH could play a major
isting traditional institutions, that to some extent have role in conflict resolutions, especially in drier areas of
promoted 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 to
Hence, 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 rainy
proach has apparently worked well in northeastern season over limited runoff on shared road/footpath
Kenya, especially in Wajir district, where a local NGO drainage. This is becoming common in Ng’arua division
has 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 to
case where low technology––water harvesting––has their farms, especially those with farm ponds for storing
proved 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 kind
technology has led to improved food security and living of conflicts could be addressed through improved
standards through provision of water for domestic, management systems at community level.
livestock and agricultural purposes. This technology has
also created employment besides being easily replicable.
Similar cases will be articulated in the proposed project 4. Hydrological impacts: limits of up-scaling rainwater
and hence ways of dealing with the twin problem of food harvesting
security and conflicts over natural resources which is
prevalent 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

12. 954 S.N. Ngigi / Physics and Chemistry of the Earth 28 (2003) 943–956
withdrawals 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 sustainable
made 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 unexpected
The on-going PhD study aims at assessing downstream– downstream effects, both negative and positive, in terms
upstream interaction related to increased adoption of water quality and quantity (Vertessy et al., 1996). In
rate––retaining more water in the watershed––in the general though, increasing the residence time of runoff
water scarce Ewaso Ngi’ro river basin in Kenya. Up- flow in a watershed, e.g., through RWH may have
grading 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
o
management at river basin scale, rather than conven- hydrological impacts at watershed/river basin level of
tional 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 proposed
needed 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 on
where surface runoff from upstream watershed entering water availability to sustain hydro-ecological ecosystem
a farm will no longer be seen as a threat to be disposed services. The expected shifts in water flows in the water
of or diverted away, but as a resource to be harnessed balance would affect both nature and economic sectors
and utilized to improve rainfed agriculture. Such depending on direct water withdrawals (Rockstr€m o
transformation is complex, especially among smallscale et al., 2001). Upgrading rainfed agriculture through
farmers, since even a runoff from a small catchment will RWH that enables dry spells mitigation, would involve
involve multiple landusers. Presently there is little at- the addition of water, through storage of runoff, to the
tention given to ownership and management of locally rainfed system. The cumulative effect of RWH may have
produced runoff, but this is expected to become a par- an impact on downstream water availability within a
amount issue if runoff is to be optimally managed on a river basin scale. The effects are bound to be site specific
larger scale for local production purposes. In Laikipia and need to be studied further (Rockstr€m et al., 2001).
o
district of Kenya, conflict over runoff diversion and The potential of developing small farm ponds and
utilization 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
o
for resource-poor smallscale farmers, who depend solely practiced farming systems, population pressure, formal
on 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 to
for irrigation) are very common particularly during the analyze the downstream effects on water availability, for
dry periods. The rainfed farmers are also in the course of example for household and livestock needs, as well as
entering the conflict, among each other and with the heath and environmental impacts, before introducing a
downstream landusers––both farmers and pastoralists in technology which retains water upstream, an possibly
this water-scarce river basin. The Indian experience on reducing river flows.
communal rainwater management may provide useful
background in an attempt to develop sustainable RWH
up-scaling strategies in SSA.
In the view of ensuing competition and conflicts over References
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