Predicting water resources at Swiss national scale: the more models the better?

Hydro-climatic diversity is a key challenge for national-scale water governance. Switzerland represents, with this respect, an extremely interesting case study: This small (40’000 km²) country encloses a wide range of hydro-climatic regimes (with precipitation ranging from 300 mm/year to > 2500 mm/year) and provides water to several large European rivers (Rhône, Rhine, Danube, Po). Over the years, an impressive number of hydrological models have been specifically developed or implemented for this country by national or regional authorities and by academia. The purpose of the models ranges from water resources and energy assessment to natural hazard management and real-time forecasting. Most existing models focus on the individual catchment scale, with few models extending to the regional and country scale. For real-time flood forecasting, there is a recent effort from the authorities to reduce the number of models; for national drought forecasting, a single model is used at the national scale, but for selected catchments, the simulations of 11 hydrological models are available for stakeholders. Existing climate change impact and water availability predictions (mostly developed at research institutes and universities) rely on collections of models applied at the individual catchment scale, with divergent results. Accordingly, despite the impressive amount of models being developed and implemented in this country, a coherent, national-scale strategy for hydrological modelling is missing; there is no general agreement on best practices among (academic) hydrologic modellers and the access of stakeholders to modelling results or modelling resources is heterogeneous. In this presentation, we discuss what we learned from the past, future challenges for national-scale hydrological modelling and possible ways forward.