National scale assessments of global water scarcity predict that by 2050 as much as 66% of the world's future population will experience some water stress and that water requirements for food production will be a major issue. However, practical planning and management of water resources requires models with greater spatial and temporal resolution. Such models give improved (higher) estimates of the number of people at risk and how these might change as the population grows. Further improvements to these models require local/basin scale water resource data and, ultimately, the integration of relevant social, economic, institutional and legal information. An example of how progress might be made with this complex task of integration is given in the paper.¶ Although the above models are important for the identification and management of water resources issues, the crux of the food production issue lies in improving the efficiency with which food is produced from existing water and land resources. Water use efficiency1 can be increased in irrigated and rainfed systems using both physical and non-physical means. Substantial improvements are possible by maximizing transpiration and/or increasing the yield per unit of water transpired. The former is most practicable in systems with low water use efficiency and can be achieved mainly via managerial and/or institutional improvements, while the latter is more appropriate in systems with higher water use efficiency, via introducing agronomic and/or other technical improvements.¶There is also scope for improving water use efficiency and food production by considering larger catchment scales, where water can be recycled within irrigation schemes or moved between different rainfed parts of the landscape. This holistic approach to catchment water management allows the upstream/downstream impacts of improvements in agricultural water use efficiency to be taken into account and further emphasises the need for integration of both physical information and socio-economic factors if truly sustainable solutions are to be achieved. Future global change research, in both the physical and social sciences, has a major role to play in addressing this real and immediate challenge.¶¶ 1 Defined here as yield per unit area/water used to produce yield.
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