Agricultural uses, primarily irrigation, account for 70 per cent of global water withdrawals (FAO 2016). Irrigated land, which accounted for 25 per cent of total cropland in 2012 (FAO 2016), nevertheless represented half of global crop production (FAO 2016). Climate change effects on temperature and rainfall patterns may drive additional irrigation demands, with water scarcity in many parts possibly limiting crop yields by 2070 (Elliott et al. 2014). Efforts are under way worldwide to address predicted hydrologic changes, including shifts to more waterefficient irrigation technologies, while trade of agricultural products provides opportunities for improving food security and adjusting to water scarcity through food imports (United Nations 2017).
The quality and availability of irrigation water and irrigated land are projected to decrease concomitantly, with potential negative effects on food security and human health. About 34.2 million ha of irrigated area has been affected by salinization (Mateo-Sagasta and Burke 2012), representing 10 per cent of total irrigated area globally (324 million ha) (FAO 2017). About 60 per cent of irrigation water does not reach crops due to leakage, spillage and evaporation (FAO 2017), with losses being especially high in developing countries with poor irrigation infrastructure. Improved irrigation efficiency could make a substantial difference. The Mediterranean region could save 35 per cent of its irrigation water through efficiency improvements (Fader et al. 2016).
Food security and associated water demands are and will be further stressed by a growing population (FAO 2016). Changing food preferences with rising incomes also increases water demands, with livestock products being more water-intensive than crops. Global meat and dairy consumption are projected to increase by 89 per cent and 81 per cent, respectively, during 2002-2050, with higher growth rates in developing countries (Thornton 2010). However, use of drought-tolerant or floodtolerant crops will be critical to improving the productivity of the agricultural industry with changing water supply conditions (Zandalinas et al. 2018).
The virtual water trade concept (i.e. water embedded in traded products ranging from crops to manufactured goods) illustrates the comparative advantages of certain water uses, including agriculture and energy, in particular regions (Gilmont et al. 2018). If water is appropriately priced and allocated, market forces can lead to overall efficiency by capitalizing on these advantages, with virtual water trade redistributing water efficiently, and partially helping to address the disconnect between consumption and production impacts (Mekonnen and Hoekstra 2011; Vörösmarty et al. 2015). However, water is not always priced and valued appropriately: water embedded in food commodities is controlled by supply chain corporations and international trade that neither account for ecosystem services nor costs of watershed degradation. The problem lies in the lack of accounting systems for water stewardship in market systems and the practice of subsidies and taxes to keep food prices low (Allan et al. 2015; Allan and Matthews 2016). Farmers are faced with the resulting pressures on food prices, further disempowering them from managing and sustaining water and ecosystems (Allan and Matthews 2016).
