CONCLUSIONS
The combined study of meteorological, snowpack characteristics, piezometric levels, streamflow and streamwater isotopic values and other physical properties have permitted to deepen the understanding of the hydrological cycle of the Izas catchment during the melting period in years of contrasted snow duration and thickness. During spring, the hydrological timing and magnitude is mainly controlled by snow melting. Liquid precipitation during the melting period, however, strongly shapes the hydrographs and contributes to the highest spring peak flows. Once snow disappears from the ground, the piezometric levels quickly decline, and the streamflow values rapidly decrease. The increase of streamwater temperature, electrical conductivity and δ18O isotopic values in combination with the strong diel variability of the δ18O isotopic values during the snow cover period, which is linked to daily cycle of dominant snowmelt or baseflow in runoff generation, suggest a short transit time of the water in the catchment during snowmelt, and therefore a limited role of groundwater supply to the streamflow. Thus, the interannual variability of the snowpack has a limited role in the summer runoff evolution. Hence, snow rich years might not increase the catchment resilience to summer droughts. Streamwater isotopy has responded clearly to snow cover evolution over the catchment However, its strong interannual variability represents challenges to properly make a hydrograph separation and to infer quantitatively the contribution of snowmelt to total runoff.
ACKNOWLEDGEMENTS. This study was funded by the project HIDROIBERNIEVE (CGL2017-82216K), MARGISNOW (PID2021-124220OB-100) and SNOWDUST (TED-2021-130114B-I00), both funded by the Spanish Ministry of Science and Innovation. E. Izagirre was supported by the Consolidated Research Group IT1029-16 (Basque Country Government).