Climate change impacts on the streamflow in Spanish basins monitored under near-natural conditions

Abstract Study region This study is focused on 12 basins in mainland Spain where monthly series longer than 30 years of near-natural streamflow measurements are available. It covers areas with different climate conditions. Study focus The potential impact of future climate change scenarios on water resources in the Spanish basins is studied. It takes into account uncertainties in the estimation of local climate conditions, and the propagation of the impact due to the structural uncertainties related with the adopted conceptual-numerical approach. Local climate scenarios are derived from available Regional Climate Model (RCM) simulations after statistical downscaling. The future scenarios have been generated assuming two hypotheses of future warming for two basins in mainland Spain: 1.5 oC and 3 oC. In each of these basins, the local climate scenarios have been propagated by using 4 hydrological models, with sufficient capacity to reproduce the historical dynamic, providing values of above 5 in a 0–9 range for the grading method used. New hydrological insights The results show a significant spatial heterogeneity of the impact of climate change on the mean streamflow in Spanish basins. The highest reductions of flow appear in the wetter northern basins. The seasonality of the impact is also significant, with the highest reductions during autumn, and the smallest changes in the summer months. Finally, the highest uncertainties in this climate change impact assessment are due to the RCM projections, with the influence of the hydrological models being significantly smaller.