This project extends the study Transition énergétique et Multiusage de l’eau (2024–2025) by expanding it to five municipalities on the adret (sun-facing slope) of central Valais, across the catchments of the Morge, the Sionne and the Lienne (Arbaz, Grimisuat, Ayent, Savièse, Sion). In a region where small karstic basins, water transfers via bisses and pipelines, and municipal boundaries do not coincide, classic “by catchment” management reaches its limits. The objective is to quantify resources and uses (drinking water, irrigation, hydroelectric and thermal energy, tourism, heritage), to add a governance component, and to propose a regional management concept based on a functional area combining the catchment, use basins and municipal boundaries.

Duration: 05.2025–05.2026

Results

Evolution of resources

The future resource was assessed for each sub-catchment using the Hydro-CH2018 grid data (RCP 8.5, 2085 horizon). On the Sionne catchment, where a FOEN flow measurement exists and where anthropogenic uses could be estimated (see the Transition énergétique et Multiusage de l’eau project), this calculation was supplemented by a detailed hydrological model (using the RS MINERVE software) calibrated on the naturalised flows of 2021 (see Figure 1). In the absence of equivalent data elsewhere, the resource for the other sub-catchments relies on Hydro-CH2018 alone.

The projection results are consistent across sub-catchments, with a winter increase, a sharp summer decrease (on the order of −60% in July), and a low-flow period that shifts from winter to late summer. The headwater catchments are the most affected, in particular the upper Morge (up to −70% in July) due to the disappearance of the Tsanfleuron glacier, and the karstic springs of the Lienne fed by the Plaine Morte and Wildhorn glaciers. On the Sionne, where the 30-year averages of Hydro-CH2018 smooth out the signal (see Table 1), RS MINERVE shows that the low flows at the end of the century could potentially be more severe than those of 2003 and 2022, with a substantial spring snowmelt peak not being enough to avoid an extreme summer drought (see Figure 2).