In arid and semi-arid ecosystems, the efficient use of water becomes increasingly important because water is a crucial limiting factor for increased food and fibre production to supply an ever growing number of people. Rainwater harvesting agriculture (RHA) is a system that has the potential to deal with the water constraints that farmers in China's semi-arid regions face. RHA can supply limited irrigation at the key stages of crop development by using rainwater stored in containers such as tanks or cellars. A number of tests of RHA in selected experimental sites confirm its potential for significantly increasing agricultural productivity. In test plots, average yields of maize (Zea mays) and wheat (Triticum aestivum L.) increased by over 50%. This paper reviews the development and performance of RHA, based on studies of the usefulness of rainwater for agriculture, theory and practice of RHA, improvement of crop yields and water-use efficiency (WUE) and its potential role in alleviating or eliminating poverty and land degradation in semi-arid regions of Gansu province. One concept, namely harvested rainwater-use efficiency (HWUE) is put forward, and the relationship between WUE and HWUE is analysed using schematic relationships between grain yield and evapotranspiration (ET). The value of HWUE is greater than that of WUE when the compensatory harvested rainwater is supplied at critical stages for water requirements in rainfed croplands. This is the basis of RHA theory. RHA has identified a new technical system that is characterized by the combination of terracing, plastic-film cover, varieties, fertilization, water storage in cellars or tanks and micro-irrigation for increasing dryland-farming productivity. It is suggested that RHA has great potential for enhancing water availability, reducing water loss, producing more with the same amount of annual rainfall and increasing agricultural productivity in north-west China. There is no doubt that the implementation of RHA techniques will expand, and can help local farmers to solve the problem of water shortage and to achieve self-sufficiency in grain.
Spatial–Temporal Evolution Characteristics and Influencing Factors of Agricultural Water Use Efficiency in Northwest China—Based on a Super-DEA Model and a Spatial Panel Econometric Model