"Runoff farming" is identical with "Water Harvesting but for Irrigation Purposes". When the harvested runoff water from un-cropped areas is directed to a cropped area, this technique is called runoff farming. Soil profile acts as a water storage container, but storage in ponds or cisterns is also feasible. Factors affecting the capacity of soil storage are: depth of the soil profile, depth of plant roots, texture, structure, infiltration rate and the water holding capacity of the soil. The catchment-to-field ratio can range from 1:1 and from 1:many square kilometers. The higher the aridity of an area, the larger is the required catchment area in relation to the cropping area for the same water yield.
Two runoff farming water harvesting groups are generally recognized, 1. rainwater harvesting and 2. floodwater harvesting. Rainwater harvesting can be further divided into 1. microcatchment, and 2. macrocatchment runoff farming types. Floodwater harvesting can also be divided into two 1. within streambed and 2. through diversion runoff farming types. Microcatchment runoff farming is a method of collecting surface runoff from a small catchment area and storing it in the root zone of an adjacent infiltration area. Macrocatchment runoff farming (catchment area being 1,000 m 2- 200 ha) system is referred to by some authors as "runoff farming water harvesting from long slopes", as " medium-sized catchment water harvesting" or as "harvesting from external catchment systems". Runoff farming with floodwater harvesting comprises a systems with catchments being many square kilometers in size, from which runoff water flows through a major wadi (bed of an ephemeral stream or river), the water is forced to infiltrate and the wetted area can be used for agriculture or pasture improvement. Runoff farming requires relatively large labor inputs and land. Development of runoff farming is increasing specially in semi-arid and arid areas after 1950, partly due to the successful reconstruction of ancient water harvesting farms in the Negev. Low-cost efficient use of runoff farming in arid zones for food and fuel production could help to restore self sufficiency in food production for local populations in many dry regions. Countries where this method has been used include Egypt, Tunisia, Libya, and southern Algeria. Some other countries outside Africa include Isreal, Jordan, North Yemen, India, Pakistan and the Soviet Union.
There should be a global cooperation between scientists and practitioners involved in waterharvesting and runoff farming. By learning from failures and successes, a high degree of sustainability might be reached, similar to the one which apparently existed in the past thousand of years. Runoff farming has proved to be a valuable tool especially in dry marginal areas to increase crop yields and reduce cropping risk, to improve pasture growth, to boost re-afforestation, to allow a higher degree of food production, to fight soil erosion, to make best use of available water resources, to suppress soil salinity and, in a few cases and to recharge the local groundwater.