Rainwater-harvesting agriculture is an ingenious method of rainfed agriculture in dry regions where normal dry farming is unreliable or out of the question. The method should be considered in regions where annual rainfall has decreased during the last decade and normal rainfed farming has become a very hazardous venture.
Runoff farming does not necessarily depend on high technology, although it does require expertise, primarily for evaluating site suitability and in designing the system. Some arid-region experts estimate that up to 5 percent of the worlds arid zones could be cultivated using rain-water harvesting. Such an area is comparable to the amount of land which can be cultivated with conventional irrigation technologies from surface or subsurface water sources. Unfortunately, the majority of dry regions simply do not contain easy-access to such water sources, especially higher quality water suitable for irrigation.
More efficient and intelligent use of rainwater in arid zones for food and fuel production is the essence of rain-water harvesting agriculture. These low-cost systems could help to restore self sufficiency in food production for local populations in many African dry-land regions.Countries where this method has been used historically include Egypt, Tunisia, Libya, and southern Algeria. Some other countries outside Africa where rain-water harvesting agriculture has been practiced successfully include Isreal, Jordan, North Yemen, India, and the Soviet Union.
In North America, rain-water harvesting agriculture was practiced in a variety of techniques by the Anasazi people nearly 1000 years ago. These consisted of dams in seasonal streams (or washes), earth and stone coutour terraces and enclosed gardens with stone retaining walls. The main crops produced were maize, kidney beans, tepary beans and squash. Today, the Hopi people of northeastern Arizona use similar runoff farming systems which probably date back to the 13th century.
Structures built by ancient cultures for collecting runoff were sometimes highly complex and very large. One Mexican system, the extensive Purron Dam Complex, operated for 900 years.
1) The landscape surface or soil conditions must be able to produce runoff.
2) The landscape surface must include variations in elevation so that runoff water created during rains will flow into and be collected by cultivated areas.
3) Collection areas must have adequately deep soil horizon of a suitable structure to store sufficient runoff for crop production.
Just as there are many different kinds of irrigation methods, rainwater harvesting can be accomplished using a broad range of technologies, from very simple and very small structures to very extensive and complex ones. Scientists with the Ben Gurion University of the Negev, Institute for Desert Research have divided the technology into five categories, including Micro-catchment systems, Terraced wadi (stream-bed) systems, Hillside conduit systems, 'Liman' systems and Large-scale diversion systems.
Runoff farming has recently been introduced to the area of Tahoua, about 650 kn northwest of Niamey. Average annual rainfall is about 400mm. Tahoua is on the boarder of the desert steppe with very sparse vegetation. Crescent shaped micro-catchments spaced 4m apart with a 4m diameter and 40cm depth have been constructed. Within this area sorghum is planted and has given yields of up to 300 kg ha. The particular size and shape of the plots enables construction by one person, who can dig the half circle and easily throw soil from the inside of the catchment onto the low runoff-retaining walls.
Initial testing of the method was done on a 4 hectare area protected by fencing. Millet, sorghum, beans and local herbs were planted. Interest among the local people in this technique has grown rapidly, resulting in the creatio of over 15,000 similar microcatchments.
Turkana District, Kenya
Low-cost rain-water harvesting projects, where practical, offer inhabitants of semi-arid zones an alternative to the growing dependence on emergency relief. Such an effort was inisiated in the remote and drought prone Turkana district of northern Kenya. Since the late 1970's a Salvation Army project, centered around a training polytechnic, has been testing and teaching the use of Nabatean-style water-harvesting systems. The project objectives were "to attempt to utilize runoff water from rainstorms to grow drought-resistant food crops in small catchments of fertile deep soil to which this water had been diverted. it was hoped that, given favorable results, this method of using small amounts of rainfall to gain some sort of food crop might be taken up by the turkana people and adapted to their nomadic way of life."
Five sites averaging .5 hectares were prepared as demonstration sites under a food-for-work program. In years of good rainfall (annual totals range from less than 200mm to about 600mm) a local 'marille' variety and improved strains of grain sorghum have been grown successfully. Cowpeas have also performed well under variable moisture conditions. The combination of selecting drought-hardy crops with increased soil organic matter (through addition of livestock manure) has often resulted in a successful harvest where none was possible before. Several species of indigenous/leguminous trees, including Prosopis chilensis, Acacia tortilis and Salvadora persica were also planted along the perimeter of catchment areas as sources of fuelwood, fodder and fencing material.
Although herding livestock has been the key to survival for the Turkana, it is not their sole economic pursuit. Raising some form of food crop has become an increasingly vital part of the survival strategy of many family groups. Runoff farming is already contributing to the viability of many Turkana households, and with continued refinement and expansion may alleviate some of the pressure on the districts limited pastoral resources.