Evaluation of water use for bioenergy at different scales

This perspective reviews water metrics for accounting total water demand to produce bioenergy at various spatial scales. Volumes of water abstracted, consumed, and altered are estimated to assess water requirements of a bioenergy product, providing useful tools for water resource management and planning at local, regional, and global scale. Blue-water use accounting, integrated over time and space, provides the most direct measurements of the effects of bioenergy production on freshwater allocation among various end-users, and on human and ecosystem health and well-being. Measurement of total water demand for crop evapotranspiration, which includes both blue and green water, communicates vital information of how land and water productivity supports/constrains bioenergy expansion, and helps identify potential areas to increase the productivity of agriculture through improved soil and water conservation, changes in crop choice, and improved crop management. Life-cycle water use accounting provides a useful comparison of water required for production and conversion of feedstock to various forms of energy, and opportunities to improve water use efficiency throughout the supply chain. In addition, life-cycle water use may be used to account for water use avoided as a result of displacement of products by coproducts of biofuel production; though these applications must be interpreted with caution. Local or regional conditions and the objective of the analysis at hand determine which water accounting metrics are most relevant and the relative importance of water use impact compared to other impacts, such as impacts to soil quality and biodiversity.