Assessment of the diverse responses of water resources to climate change and high concentrations of CO2 is crucial for the appropriate management of natural ecosystems. Despite numerous studies on the impact of climate change on different regions, it is still necessary to evaluate the impact of these changes at the local scale. In this study, the Soil and Water Assessment Tool (SWAT) model was used to evaluate the potential impact of changes in temperature, rainfall and CO2 concentration on water resources in a rural catchment in NW Spain for the periods 2031-2060 and 2069-2098, using 1981-2010 as a reference period. For the simulations we used compiled regional climate models of the ENSEMBLES project for future climate input data and two CO2 concentration scenarios (550 and 660 ppm). The results showed that changes in the concentration of CO2 and climate had a significant effect on water resources. Overall, the results suggest a decrease in streamflow of 16% for the period 2031-2060 (intermediate future) and 35% by the end of the 21st century as a consequence of decreasing rainfall (2031-2060: −6%; 2069-2098: −15%) and increasing temperature

Soil losses and the subsequent sediment delivery constitute significant environmental threats. Climate change is likely to have an impact on the availability of water and therefore on sediment yield in catchments. In this context, quantifying the sediment response to an increased atmospheric CO 2 concentration and climate change is of utmost importance to the proper management of rural catchments. However, quantitative assessment of climate change impact remains a complex task. In this study, the potential medium (2031-2060) and long-term (2069-2098) impacts of projected changes of temperature, rainfall and CO 2 concentration on sediment yield in a small rural catchment located in NW Spain were evaluated using the Soil and Water Assessment Tool (SWAT) model. Climate change scenarios were created using future climate data projected by regional climate models from the ENSEMBLES project and two CO 2 concentration scenarios (550 and 660 ppm). The results showed that climate change would have a noticeable impact on suspended sediment if the forecast temperature, rainfall and CO 2 concentration changes included in this study were met. Overall, suspended sediment is expected to decrease (2031-2060: −11%, 2069-2098: −8%) compared to the baseline period , mainly due to decreased streamflow. However, an increase in sediment transport in winter is predicted, possibly associated with increased erosion in cultivated areas (11%-17%), suggesting that, at this time of the year, the effect of soil detachment prevails over sediment transport capacity. Consequently, management practices aimed at reducing soil erosion in cultivated areas should be carried out, because these are the main source of sediment in the study area.

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The nutrient flow dynamics in rural landscapes are among the basic characteristics of landscape functioning. In this study, the ecohydrological model SW"T Soil and Water "ssessment Tool was applied in a small rural catchment in northwest NW Spain to evaluate the contribution of land use on nitrate losses and to assess the relative importance of different pathways by which nitrate is delivered to the drainage network. The model was first calibrated and validated at a monthly time step. The SW"T model performance was satisfactory R > . Nash-Sutcliffe efficiency NSE > . and percent bias P"I"S < % during both the calibration and validation periods, indicating that SW"T predicted the nitrate discharge accurately. Using the calibrated SW"T model, this study showed that agricultural lands, even though they represent only % of the catchment, were main contributor to the nitrate losses accounting for about % of the total nitrate yield. The model results also indicated that, irrespective of the land use, groundwater flow is the main pathway for nitrate losses % therefore, appropriate management practices aimed at decreasing nitrate leaching will be key factors in reducing nitrate yield in the study catchment.