Sensitivity of montane grassland water fluxes to warming and elevated CO2 from local to catchment scale: A case study from the Austrian Alps

Study region: Montane grassland within the Gulling catchment, Austrian Alps. Study focus: A climate-change experiment in a grassland ecosystem used lysimeters and HYDRUS-1D models to quantify changes in evapotranspiration (ET) and groundwater recharge (GWR) due to warming (＋3 °C) and elevated ${\mathrm{CO}}_2$ concentrations ($\Delta {\mathrm{CO}}_2$; ＋300 ppm). Findings at the plot-scale were generalized and transferred to the surrounding catchment, half comprised of grassland, using three lumped rainfall–runoff models and two spatially-distributed Community Water Models, differing in soil hydraulic properties.

New hydrological insights for the region: Warming increased ET and decreased GWR and river discharge compared to ambient conditions. $\Delta {\mathrm{CO}}_2$ increased stomatal resistance, which partially offset warming effects. In scenarios combining warming and $\Delta {\mathrm{CO}}_2$, the impact of warming was higher than $\Delta {\mathrm{CO}}_2$ effect. Elevation influenced the sensitivity of ET to warming, which was greater at the catchment scale than at the plot scale, while GWR was more sensitive to warming at the plot scale. Under dry conditions, GWR and discharge exhibited increased sensitivity to warming at both scales. HYDRUS-1D successfully reproduced lysimeter experiment results and their sensitivity to warming and $\Delta {\mathrm{CO}}_2$. Despite model agreement on water flux sensitivity to climate changes, the varying response magnitudes highlight the need for a multi-model approach in climate impact assessments. This study provides insights into how climate change might impact hydrological dynamics of montane grassland systems across the Central European Alps.