Impacts of Global Change on hydrologic and sedimentologic dynamics in the Northern Ebro Basin

ABSTRACT: The shift from rural to urban living has resulted in natural revegetation of abandoned rural areas located in mountainous regions. These land-use changes, combined with recent temperature and precipitation trends, affect water resources and sediment yields. Consequently, surface runoff, water infiltration, and sediment production/transport are impacted. Studies of this impact in mountainous areas are limited and partial, restricted to small basins. Therefore, this study examines the changes in both water and sediment fluxes in the northern draining region of the Ebro Basin. For the study, the SWAT+ hydrological model was employed. SWAT+ is a semi-distributed, deterministic, continuous basin model that operates on a daily time step. The model requires several inputs: a Digital Elevation Model (DEM), reservoir locations, land use map and index, soil type map and properties, as well as climatic data. The Ebro basin was divided into eight sub-basins and a hydrological model was developed for each. Calibration and validation processes were conducted in two steps: firstly, hydrological calibration and validation was performed and afterwards the process was repeated for the sediments. Firstly, hydrological calibration and validation were conducted at available and relevant gauging stations within the sub-basins. In total, over 30 stations were used as control points. The precision of the calibration and validation was evaluated using the Nash-Sutcliffe Efficiency (NSE). Secondly, sediment calibration was conducted using available reservoir bathymetry data or sediment yield estimates from scientific literature. The sediment calibration aimed to reproduce values of the same order of magnitude as those derived from bathymetry or literature data. The resulting hydrologic and sedimentologic model was re-run and NSE, maintaining or improving the NSE values obtained from the hydrological calibration. NSE values, thus, ranged from 0.53 to 0.95 depending on the gauging station. The mean NSE for the entire basin under study was 0.75, indicating that a well-established hydrologic and sedimentologic model was achieved. Future work will involve, firstly, applying climate change scenarios from CMIP6 and comparing the current results to observe the response to climate change. Secondly, generating downscaled land-use change maps to accurately represent the evolution of land-use change in each sub-basin. This approach will allow for the analysis of the impacts of climate change alone and in combination with land-use change.

 

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.