Conflicting demands for food and water, exacerbated by increasing population, increase the risks of food insecurity, poverty and environmental damage in major river systems. Agriculture remains the predominant water user, but the linkage between water, agriculture and livelihoods is more complex than “water scarcity increases poverty”. The response of both agricultural and non-agricultural systems to increased pressure will affect livelihoods. Development will be constrained in closed basins if increased demand for irrigation deprives other users or if existing agricultural use constrains non-agricultural activities and in open basins if agriculture cannot feed an expanding or changing population or if the river system loses capacity due to degradation or over-exploitation.

Conflicting demands for food and water, exacerbated by increasing population, increase the risks of food insecurity, poverty and environmental damage in major river systems. Agriculture remains the predominant water user, but the linkage between water, agriculture and livelihoods is more complex than “water scarcity increases poverty”. The response of both agricultural and non-agricultural systems to increased pressure will affect livelihoods. Development will be constrained in closed basins if increased demand for irrigation deprives other users or if existing agricultural use constrains non-agricultural activities and in open basins if agriculture cannot feed an expanding or changing population or if the river system loses capacity due to degradation or over-exploitation.

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Alterations in climate due to increasing atmospheric concentrations of carbon dioxide and other trace gases must be viewed with concern, if not alarm, because of the risk of adverse impacts on the availability and quality of water resources. Hydrologic changes may lead to alterations in pressure on food resources in many regions of the world. This paper explores the mechanisms by which food security - defined here as the ability of a region to produce or otherwise provide food without threatening the well-being of either the population or the existing political systems - could be affected by climate-induced changes in water resources. Shifts in the timing, magnitude, or location of major hydrologic phenomena, such as runoff, soil moisture, or monsoons, are discussed, together with the important vulnerabilities of agricultural productivity to changes in water availability. Some of the concomitant political and socioeconomic implications are also presented, with suggestions for ways to enhance the reliability of food resources dependent on uncertain water supplies.