Assessment of Ecological and Hydro-Geomorphological Alterations under Climate Change Using SWAT and IAHRIS in the Eo River in Northern Spain

Magnitude and temporal variability of streamflow is essential for natural biodiversity and the stability of aquatic environments. In this study, a comparative analysis between historical data (1971-2013) and future climate change scenarios (2010-2039, 2040-2069 and 2070-2099) of the hydrological regime in the Eo river, in the north of Spain, is carried out in order to assess the ecological and hydro-geomorphological risks over the short-, medium- and long-term. The Soil and Water Assessment Tool (SWAT) model was applied on a daily basis to assess climate-induced hydrological changes in the river under five general circulation models and two representative concentration pathways. Statistical results, both in calibration (Nash-Sutcliffe efficiency coefficient (NSE): 0.73, percent bias (PBIAS): 3.52, R-2: 0.74) and validation (NSE: 0.62, PBIAS: 6.62, R-2: 0.65), are indicative of the SWAT model's good performance. The ten climate scenarios pointed out a reduction in rainfall (up to -22%) and an increase in temperatures, both maximum (from +1 to +7 degrees C) and minimum ones (from +1 to +4 degrees C). Predicted flow rates resulted in an incrementally greater decrease the longer the term is, varying between -5% (in short-term) and -53% (in long-term). The free software IAHRIS (Indicators of Hydrologic Alteration in Rivers) determined that alteration for usual values remains between excellent and good status and from good to moderate in drought values, but flood values showed a deficient regime in most scenarios, which implies an instability of river morphology, a progressive reduction in the section of the river and an advance of aging of riparian habitat, endangering the renewal of the species.