Innovating on Hydrological Modelling Calibration Towards a Realistic Simulation of Climate Change Impacts on Water Resources

The plausible impacts of climate change threat water resources sustainability in Mediterranean regions, where they are already under pressure. Hydrological modelling might aid assessing this threat, but realistic models are needed to guarantee accurate simulations. This work presents a hydrological model for the Guajaraz River basin (central Spain) using SWAT+. This basin contains the homonym reservoir and supplies the historic city of Toledo. An innovative calibration procedure, "inverse calibration", was designed towards achieving a model that simulates the hydrological processes realistically rather than just providing satisfactory metrics: hard calibration results were filtered by two soft indices, the runoff coefficient and the groundwater contribution, to constrain parameter values. The methodology was successful, solved model structural problems (i.e. equifinality) and yielded a realistic model to simulate climate change. Then, five out of sixteen climate models were selected after calculating a suitability index, and they were simulated under two emissions scenarios (mid and high) and two time horizons (mid and long term). As expected, results foresee more severe hydrological impacts for the high emissions scenario and towards the end of the 21st century, with an average decrease in reservoir inflow up to 28% (or even up to 35% when analysing median values). Results also reveal that quickflow will be more affected than baseflow. These insights might aid on decision-making towards sustainable water management in a region where studies of this kind are scarce.