Multi-Model Climate Projections of Hydrological and Sediment Change in the Ebro River Basin Using SWAT+

ABSTRACT: Rural depopulation and urban expansion have driven widespread natural revegetation in mountainous areas, resulting in substantial land-use changes. Combined with recent climate variability, these processes affect hydrological behavior and sediment dynamics by altering runoff generation, infiltration, and sediment transport. However, their integrated impacts remain poorly quantified at large spatial scales in mountain regions.

This study assesses changes in water and sediment fluxes in the northern sector of the Ebro Basin using the SWAT+ model, a semi-distributed hydrological model operating at a daily time step. The study area was divided into twelve sub-basins, each represented by an individual model. Model calibration and validation were conducted sequentially. Streamflow was first calibrated using observations from more than 30 gauging stations, and performance was evaluated using the Nash–Sutcliffe Efficiency (NSE). Sediment calibration was subsequently performed using reservoir bathymetry data and published sediment yield estimates. The final models achieved NSE values between 0.53 and 0.95, with a basin-wide mean of 0.75, indicating good model performance.

Future hydrological and sediment responses were simulated using climate projections from the NEX-GDDP-CMIP6 dataset. Seventeen climate models were processed at a daily scale and statistically downscaled. Bias correction was applied using Empirical Quantile Mapping (EQM), calibrated over the 2015–2020 period and applied from 2021 onwards. Extreme values were further corrected using a Generalized Pareto Distribution with a Peak-Over-Threshold (GPD/POT) approach, followed by a delta-change adjustment to better match observed conditions.

The overall objective is to compare the impacts of the 17 climate models across the 12 sub-basins. Preliminary results from one sub-basin indicate a consistent decrease in future streamflow, highlighting potential implications for water availability in mountainous Mediterranean basins.

ACKNOWLEDGMENTS: This work is funded by the European Research Council (ERC) through the Horizon Europe 2021 Starting Grant program under REA grant agreement number 101039181 - SEDAHEAD.