Impact assessment at the bioenergy-water nexus

Bioenergy expansion can significantly impact water resources in the region in which it occurs. Investment, policy, and resource management decisions related to bioenergy should therefore take this critical consideration into account. Water resource impacts can defy easy quantification because water consumption varies spatially and temporally, different water sources are not necessarily commensurable, and impact depends on the state of the resource base that is drawn upon. This perspective offers an assessment framework that operators and policy-makers can use in evaluating projects to avoid or mitigate detrimental effects. We adapt water footprint (WF) and life cycle assessment (LCA) techniques to the bioenergy context, describing comprehensive life cycle inventory (LCI) approaches that account for blue and green water use as well as for pollution effects, varying sources, coproduct allocation, and spatial heterogeneity. Impact assessment requires that characterization (weighting) factors be derived so that consumption values can be summed and compared across resources and locations. We recommend that characterization draw on metrics of water stress, accounting for environmental flow requirements, climatic variability, and non-linearity of water stress effects. Finally, we describe some location-specific impacts of concern that may not be revealed through common analytical approaches and may warrant closer consideration