PIAHS Proceedings of the International Association of Hydrological Sciences PIAHS Proc. IAHS 2199-899X Copernicus Publications Göttingen, Germany 10.5194/piahs-366-86-2015 What part of natural flow can be considered a "water resource"? Andréassian V. 1 Margat J. 2 Thirel G. 1 Hubert P. 3 Irstea, Hydrosystems and Bioprocesses Research Unit (HBAN), Antony, France BRGM, Orléans, France Sorbonne Universités, UPMC Univ. Paris 06, UMR 7619 METIS, 75005, Paris, France 10 04 2015 366 86 92 Copyright: © 2015 V. Andréassian et al. 2015 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://piahs.copernicus.org/articles/366/86/2015/piahs-366-86-2015.html The full text article is available as a PDF file from https://piahs.copernicus.org/articles/366/86/2015/piahs-366-86-2015.pdf

In this paper, we discuss an unfortunate semantic shortcut – the use of the expression "water resources" as a synonym for "river/groundwater flow" – which causes great confusion in all Water Security-related discussions. We show that only a part of the flow can be considered a resource, and that the efficiency of the flow-to-resource conversion is a complex function of: (i) the hydrologic regime, (ii) environmental constraints (in-stream reserved flows), (iii) the type of water demand, and (iv) the existence of artificial reservoirs. Last, we illustrate how the flow-to-resource conversion can be affected by future climatic changes. Hydrologic data and climate change simulations for three French rivers (the rivers Vilaine, Durance and Garonne) are used to illustrate this discussion.