In many areas of the world, particularly arid and semi-arid areas, unregulated overland flow originating from desert storms and seasonal rains means a loss of scarce water. With rainwater harvesting this water can be used. Techniques for rainwater harvesting vary from simple micro-catchments consisting of runoff areas and basin depressions in which trees are planted, to roadside collection from surfaced highways, rooftop collection off houses and agricultural greenhouses, to whole hillside management plans with terracing and contour management. The technology involved in applying rainwater harvesting in the field is not complicated and can be adapted to the local environmental conditions of arid zones.
It has been concluded from various studies that extremely arid zones with less than 100mm of winter rainfall are too dry for micro-catchments, and in zones with 200mm, each tree requires aproximately 40 square metres of basin area and 60 square metres of runoff area.