Trade-off between environmental flow and water availability: A mesoscale analysis for Europe

Environmental flow allocation is one of the key aspects of environmental policy regarding water management. Traditionally, water allocation decisions were mainly based on water productivity, accounting for the benefits obtained from using water for urban supply, agriculture, hydropower and other economic activities. In some basins, this approach caused excessive water abstraction and environmental degradation. Increasing social awareness of environmental problems led to a new paradigm for water resources management where the central objective is good ecological status of water bodies (Pahl-Wostl 2007). Water allocation is now subject to the pre-requisite of meeting environmental flow requirements (EFRs). However, the practical application of this principle is controversial due to the competing interests of affected stakeholders. A wide range of methods has been proposed to determine EFRs: hydrologic, hydraulic, habitat simulation and holistic methodologies provide an array of usually divergent values that challenge water allocation decisions (Arthington et al. 2018). The choice of a single method or value for EFR may lead to sub-optimal or inequitable allocation decisions, which would produce direct economic impacts on affected stakeholders. The main objective of this work is to conduct a regional assessment in Europe of the trade-off between water allocation to environmental flow and to other productive uses. In this assessment we account for local conditions that determine the influence of environmental flow allocation on water availability as a function of hydrologic regime and available regulation storage.