This paper evaluates the response of stream flow and other components of the water balance to changes in climate and land use ina Pyrenean watershed. It further provides a measure of uncertainty in water resources forecasts by comparing the performance of two hydrological models: the Soil and Water Assessment Tool (SWAT) and Regional Hydro-ecological Simulation System(RHESSys). Regional climate model outputs for the 2021–2050 time frame and hypothetical (but plausible)land-use scenarios considering re-vegetation and wild fire processes were used as inputs to the models. Results indicate an overall decrease in river flows (up to 30%, depending on the combination of scenarios) when the scenarios are considered, except for the post-fire vegetation scenario, in which stream flows are simulated to increase (between 2% and 10%). However, the magnitude of these projections varies between the two models used, as SWAT tends to produce larger hydrological changes under climate change scenarios and RHESSys shows more sensitivity to changes in land cover. The final prediction will therefore depend largely on the combination of the land-use and climate scenarios and on the model used

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Abstract:We use Bayesian methods with a weights of evidence approach to model the probability of land use change over the Western part of Switzerland. This first model is followed by a cellular automata model for spatial allocation of land use classes. Our results extend and enhance current land use scenarios studies by applying Dinamica Environment for Geoprocessing Objects (Dinamica EG) to a study area comprising of the upper Rhone river basin in the Cantons of Vaud and Valais. In order to take into account the topography, we divide the study area into four regions, based on their altitude and administrative region. We show that the different regions are affected in differing ways by the same driving forces. We analyse possible outcomes in land use change in 2050 for three different scenarios: "business as usual", "liberalisation" and a "lowered agriculture production". The "business-as-usual" scenario results indicate a decrease in agriculture, mostly in extensive agriculture, with a share in the total area of 12. Gains in open land habitat with the increase of the share of extensive agriculture area under the "lowered agricultural production" scenario are expected to increase by 3.2% in 2050, while the share of intensive agriculture area is expected to decrease by 5.6%.