A recent SciDev.net article Improve water efficiency in farming, urges report describes an International Water Management Insitute (IMWI) report – Beyond More Crop per Drop prepared for the 4th World Water Forum in Mexico (March 2006).
The article quotes IWMI director general, Frank Rijsberman, who justifies the need to increase water use efficiency by the statement that it takes “70 times more water to grow the food we eat every day than we need for drinking, cooking, bathing and other domestic needs.”
The report describes how water management usually focuses on runoff, blue water, which is only 40% of rainfall. The other 60% is green water that replenishes soil moisture and evaporates from the soil or is transpired by plants. The report states that three quarters of the world’s poor depend upon rainfed agriculture (90% in sub-Saharan Africa), meaning that improving green water productivity has the potential to improve the well-being of the world’s poor.
The report writes:
Increasing the productivity of green water used in rainfed agriculture has great potential to reduce the area needed for agriculture. Agricultural production of staple crops in Africa, has, over the last 40 years, increased almost exclusively by area expansion, at the cost of large areas of natural ecosystems. To enable sustainable increases in food production in Africa, agricultural intensification is absolutely necessary. Increasing the productivity of green water used in rainfed agriculture – particularly by adding a limited amount of blue water (from rivers or aquifers) through supplemental irrigation has great potential.
The report recommends using rainwater harvesting, supplemental and micro irrigation, and using land and water conservation to increasee infiltration and reduce runoff, to increase green water efficiency. It suggests that using these known techniques could double crop yields.
See also, my previous post on agricultural modification of green water flows.