Abstract
As drinking water supply systems worldwide face increasing challenges, there is concern of future drinking water shortage. This paper proposes an innovative participatory modelling framework to fill the lack of tools to assess future demand-supply imbalances under global changes in large interdependent drinking water supply systems for which collective planning is needed. The framework is usable in contexts where there is no history of centralized management and stakeholders are not used to working together. It makes it possible to i) quantitatively assess the magnitude, location and duration of future drinking water supply shortfalls under various medium-long term scenarios, ii) identify the blocking points in the supply scheme that explain why the shortfalls occur and evaluate the need for securing measures, iii) build a shared diagnosis between stakeholders. The development and use of the modelling tool is illustrated through two contrasting case studies in France, facing quality and quantity issues. The importance of the tool is demonstrated by the future supply shortfalls diagnosed in the two case studies. It is crucial to anticipate and quantitatively assess them to adequately invest and adapt for future drinking water security. Results in the two case studies exhibit both differences (e.g. main blocking points identified) and similarities (e.g. importance of demand-side management measures). They also both highlight the interdependencies between the different management units and the importance of collective planning. Results demonstrate that the framework is adaptable to different contexts and issues. The framework is replicable where such a tool is needed.