Climatic and anthropogenic changes in Western Switzerland: Impacts on water stress

Recent observed hydro-climatic changes in mountainous areas are preoccupying as they may directly affect the capacity to fulfill water needs. The canton of Vaud is representative of this context as it underwent local water shortage episodes during the past decade. Based on an integrated modeling framework, this study explores how hydro-climatic conditions and water needs could evolve in mountain environments and assesses their potential impacts on water stress by the 2060 horizon. Flows were simulated based on a daily semi-distributed hydrological model. Future changes were derived from Swiss climate scenarios based on two regional climate models. Regarding water needs, the authorities of the canton of Vaud provided a population growth scenario while irrigation and breeding trends followed a business-as-usual scenario. Currently, the canton of Vaud experiences moderate water stress from June to August, except in its alpine area where no stress is noted. In the 2060 horizon, water needs could exceed 80% of the rivers' available resources in low- to mid- altitude environments in mid-summer. This should be due to the combination of drier and warmer climate enhancing longer and more severe low flows, and increasing urban (+40%) and irrigation (+25%) water needs. Highlighting regional differences supports the development of sustainable development pathways to reduce water tensions. Based on a quantitative assessment, this study also calls for broader impact studies including water quality issues