Summary (En) | Gift

The competition for limited water resources between agriculture and more highly valued domestic and industrial water uses is rapidly increasing and will likely require the transfer of water out of agriculture. This paper reviews and synthesizes the available evidence of the effects of water transfers from agricultural to urban and industrial areas on local and regional rural economies; and analyzes the potential impacts of a large reallocation on global food supply and demand. It concludes with a discussion on the potential for water policy reform and demand management to minimize adverse impacts when water is reallocated from agriculture. It is argued that comprehensive reforms are required to mitigate the potentially adverse impacts of water transfers for local communities and to sustain crop yield and output growth to meet rising food demands at the global level. Key policy reforms include the establishment of secure water rights to users; the decentralization and privatization of water management functions to appropriate levels; the use of incentives including pricing reform, especially in urban contexts, and markets in tradable property rights; and the introduction of appropriate water-saving technologies.

Global food trade entails virtual flows of agricultural resources and pollution across countries. Here we performed a global-scale assessment of impacts of international food trade on blue water use, total water use, and nitrogen (N) inputs and on N losses in maize, rice, and wheat production. We simulated baseline conditions for the year 2000 and explored the impacts of an agricultural intensification scenario, in which low-input countries increase N and irrigation inputs to a greater extent than high-input countries. We combined a crop model with the Global Trade Analysis Project model. Results show that food exports generally occurred from regions with lower water and N use intensities, defined here as water and N uses in relation to crop yields, to regions with higher resources use intensities. Globally, food trade thus conserved a large amount of water resources and N applications, and also substantially reduced N losses. The trade-related conservation in blue water use reached 85km³y⁻¹, accounting for more than half of total blue water use for producing the three crops. Food exported from the USA contributed the largest proportion of global water and N conservation as well as N loss reduction, but also led to substantial export-associated N losses in the country itself. Under the intensification scenario, the converging water and N use intensities across countries result in a more balanced world; crop trade will generally decrease, and global water resources conservation and N pollution reduction associated with the trade will reduce accordingly. The study provides useful information to understand the implications of agricultural intensification for international crop trade, crop water use and N pollution patterns in the world.