ABSTRACT
Eighty per cent of the world’s agricultural land area is rainfed and generates 58% of the world’s staple foods (SIWI, 2001). The importance of rainfed agriculture varies regionally, but produces most food for poor communities in developing countries. In sub-Saharan Africa (SSA)more than 95%of the farmed land is rainfed, while the corresponding figure for Latin America is almost 90%, for South Asia about 60%, for East Asia 65% and for Near East and North Africa 75%. Farming systems in sub-Saharan Africa and Latin America are almost exclusively rainfed, while a predominant blue water dependence in irrigation is concentrated in the West Asian (>80% dependence) and North African regions (>60% dependence) (Rockström, 2003). In South and East Asia the picture is mixed, with countries depending in varying degrees on both rainfed and irrigated agriculture (e.g., India where 60% of water use in agriculture are estimated to originate from directly infiltrated rainfall, while 40% originates from extraction of river and groundwater for irrigation). A survey of “irrigation schemes’’ in Tanzania has shown that over 80% of them are supplementary irrigated systems where the bulk of water for crops is supplied by direct rainfall (MAFS, Tanzania Ministry of Agriculture, 2003).
