Sustainable water management is the key factor to countries to achieve sufficient food production. Worldwide some 17% of agricultural lands are irrigated, producing 40% of total cereal production. However, irrigation is also associated with negative economic, environmental, social and political consequences. For this reason there is a great deal of interest in meeting future food needs through rainfed agriculture as a partial substitute for irrigation.
Figure 1. Global annual precipitation and potential evapotranspiration as derived from the International Water Management Institute Global Monthly Dataset (copies available at IWMI)
An existing global climate dataset at a relatively high-resolution (Figure 1), was combined with a soil water storage capacity map derived from the FAO map of the major soil groups in the world (Figure 2). A dynamic water and crop model was developed to estimate the potential for rainfed agriculture. The methodology applied here, based on a high-resolution climate dataset, allows analyses on a global scale without losing the smaller regional scale issues.
Figure 2. Global soil water storage capacity dataset as derived from the FAO global soil map.
Result and conclusions
Figure 3 shows the potential for rainfed agriculture. The four groups in this Figure are defined somewhat arbitrarily at estimated production levels of 0-3500, 3500-7500, 7500-12500, and higher than 12500 kg ha-1 for, respectively, very low, moderate, high, and very high. The extensive areas where potential yields of purely rainfed agriculture are zero is striking.
The distribution in area of these groups indicates that on a global scale, 46% of the earth’s surface is unsuitable for rainfed agriculture due to limitations in climatic conditions. This leaves some 7 billion ha with a potential for rainfed crop production from which 4.7 billion ha is classified as moderate, high, or very high suitable. Currently about 1.5 billion ha is cropped-the remainder is presumably in forests, grasslands, wetlands and the like.
The study presented here assumed that all land would be available for agriculture, while in reality land is required for other functions. It was also assumed that other existing limitations in terms of erosion, soil fertility, and farm expertise could be overcome. The results presented here reflect therefore the upper limit of the potential for rainfed agriculture on a global scale.
Figure 3. Global potential for rainfed agriculture and details for Southern Africa and Asia.
Droogers, P., D. Seckler and I. Makin. 2001. Estimating the potential of rainfed agriculture. IWMI Working Paper 20.
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