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 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.
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 (arranged in order of generally increased geomorphic scale) are: (1) micro-catchment system, (2) terraced wadi system, (3) hillside conduit system, (4) liman system, (5) diversion system. 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.
Pyneham farm in Frankland, Australia, aims to achieve total control of water movement and use by performing water management activities at the catchment scale, not just within the boundaries of the individual farmer's property. The strategy is community-based and requires both co-operation and co-ordination among all farmers in the catchment area. The key factors in implementing and managing this scheme are a series of drains to control the nature and rate of water movement after rainfall events and tree planting which provides a way of utilizing deep moisture. The improved water catchment has enabled the development of a diversified approach to agriculture which has enhanced the economic viability of the farm through the improved environment and restoration of degraded lands. Livestock carrying capacity has increased and more fertile land is now available for cropping. An economic analysis of the farm has concluded that gross margins for crops are more than double the local average and for sheep almost four times the average.