53productivity to land, provide drinking water to both humans and animals, minimize
risk in drought-prone areas, increase groundwater recharge and reduce storm water
discharge (Rainwater Harvesting 2006 ). Today, WH is used for crop irrigation,
groundwater recharge and water storage for future use in drought-prone areas.
WH works by concentrating rainwater from a large catchment area to a small
target area. It can significantly increase plant production in drought-prone areas by
concentrating rainfall/runoff in parts of the total area (Prinz 1996 ; Oweis et al. 1999 ;
Rockström 2002 ). WH collects water from (1) sources where water is widely dis-
persed and quickly changes location or form and becomes unavailable or (2) where
it occurs in quantities and at locations where it is unusable unless intervention can
gather the water to locations where it provides benefits (Pereira et al. 2002 ).
WH has been defined in several ways, with more general definitions being (1) the
collection of runoff for its productive use (Critchley et al. 1991 ) and (2) the process
of collecting and concentrating water from runoff into a run-on area where it is
either directly applied to the cropping area and stored in the soil profile for immedi-
ate use by the crop (Prinz and Singh 2000 ). Here, we consider it in the broadest
sense, as an umbrella term covering a wide range of techniques and methodologies
to collect and conserve various forms of runoff water, originating from ephemeral
water flows generated during rainstorms. In this sense, we adopt a similar approach
to the definition by Critchley et al. ( 1991 ) of water harvesting as “the collection of
water for its productive use”. WH focuses on improving the productive use of rain-
water on the local scale (field to subcatchment scale) before the runoff water leaves
the geographical unit in question. The aim is to mitigate the effects of temporal
water shortages to cover both domestic and agricultural needs. In terms of upgrad-
ing rainfed agriculture, WH can be categorized into three broad objectives
(Rockström 2002 ): the systems that (i) improve infiltration of rainwater into the soil,
(ii) prolong the duration of soil water availability in the soil and (iii) store surface
and subsurface runoff for later use.
WH incorporates a broad set of techniques and methodologies that can be
grouped into three main domains (Rockström 2002 ; Prinz 2002 ):
- In situ water conservation (soil and water conservation)
- Concentration of runoff to crops in the field, at a field (runoff farming) or catch-
ment (floodwater harvesting) scale - Collection and storage of runoff water into different structures (soil, ponds,
dams, tanks etc.) for supplemental irrigation.
This simple categorization is useful in terms of water management as it distin-
guishes between three distinctly-different hydrological situations in a farmer’s field.
In situ soil water conservation aims to make the best use of the rain that falls on the
field, i.e., maximize rainfall infiltration into the soil and its storage in the root zone
of the crop. The crop still lives at the mercy of the rainfall. Runoff concentration
systems add surface water from outside the cultivated land at two scales, either from
local sheet, rill and small gully runoff (i.e., runoff generated immediately adjacent
up to several hundred meters from the land) or from gully flow at catchment scale
Water Harvesting in Dry Environments