This paper evaluates the response of streamflow and other components of the water balance to changes in climate and land use in a 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 wildfire 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 streamflows 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. Copyright © 2014 John Wiley & Sons, Ltd.