Modelling Austria’s water future: A transboundary national-scale distributed hydrological model for climate change impact assessment

Austria has set an ambitious goal to produce 100% of its electricity from renewable sources by 2030. To support this transition and to enable informed energy planning and optimized resource use in the future a detailed national-wide distributed hydrological model of Austria was set up to assess the changes in water balance in more than 50000 river profiles. The model operates on a daily time step and simulates the hydrological processes on a 2x2 km grid in cells that are aggregated into sub-basins of a mean area of 115 km² and routed along the pre-defined river network. The meteorological inputs for the model comprised high-resolution grids interpolated from station datasets for areas with available observations and low-resolution EOBS grids for small areas outside of Austria with small coverage of available station data.

To account for anthropogenic influences, reservoir operation and water transfer modules were incorporated, significantly improving model performance in affected regions. The model was calibrated and validated using a newly proposed step-wise iterative procedure within the 1991-2020 period, focusing on the interannual flow regime and the monthly water balance. Significant improvements in the robustness of the model were achieved by incorporating remote sensing products of snow cover and soil depth reducing the number of free parameters. The model achieved a median Nash-Sutcliffe efficiency of 0.9 across 532 Austrian profiles, calculated for the interannual regime.

Future water balance changes were projected for 2066–2075 using the MPI-M-MPI-ESM-LR_r1i1p1_SMHI-RCA4 climate model under RCP 4.5 and RCP 8.5 scenarios. A delta-change approach was used to adjust historical air temperature and rainfall records, minimizing biases associated with climate model projections. Results indicate increased mean monthly river discharges during winter and little to no change or slight decreases during summer in most river profiles. These changes are more pronounced in smaller mountainous catchments, where rising air temperatures lead to reduced snowpack accumulation and shorter snow cover durations.