Rainwater-harvesting agriculture for food production in arid zones: the challenge of the African famine

Rainwater-harvesting agriculture is a specialized form of rainfed farming that has a significant potential to increase food production in the arid zones of our planet. Runoff farming and rainwater-harvesting agriculture are considered synonymous terms, defined here as ‘farming in dry regions by means of runoff rainwater from whatever type of catchment or ephemeral stream’. There are indications that runoff rainwater was already used for farming during the Neolithic. Remnants of ancient rainwater-harvesting agricultural systems have been found in many dry regions of Asia, Africa and America. Today, rain is still the cheapest and often only available source of water for agricultural purposes, albeit not always reliable. In many dry regions of the world there is no alternative but a better and more effective use of rain to increase food production. This is the essence and potential significance of runoff farming in a hungry world. A geomorphic classification of runoff farming systems is presented, as suitability of an arid region for rainwater-harvesting agriculture depends upon the landscape as much as upon the climate. Hyper-arid zones are usually too dry for runoff farming. Five major types of runoff farming are distinguished, arranged in order of generally increasing geomorphic scale: (1) micro-catchment system, (2) terraced wadi system, (3) hillside conduit system, (4) liman system, (5) diversion system. The introduction and use of runoff farming in arid zones of a number of African countries is reported. As arid regions are characterized by large yearly fluctuations in the amount of runoff-producing rainfall, droughts have to be taken into account in proper runoff farming management. The forming of reserve buffer stockpiles of water and food during the good years for drought periods are considered essential in this respect.