Projected Hydrological Alterations in the Danube River Basin under Climate Change

This work quantifies the hydrological alterations caused by climate change on 11 major basins of the Danube River. The quantification is performed using the natural discharge (i.e. without water demand and abstractions) between the years 1990 and 2020 as a reference period and the projected discharge between 2030 and 2100 for the SSP-RCP climate change scenarios SSP1-2.6, SSP3-7.0 and SSP5-8.5. Discharges for the reference period and the projections have been simulated with CWatM, a grid-based hydrological model. CWatM was calibrated and tailored for the Danube basin for this case study. The reference period was simulated using as input dataset hydrometeorological data from Multi-Source Weather (MSWX) product while the projected discharge was simulated using ISIMIP3b climate change hydrometeorological datasets for 5 global circulation models (GCM).

Past and future hydrological regimes were used to compute a set of indices from the Hydrological Nature Conservancy Indicators of Hydrologic Alteration. These indices quantify the in-stream disturbance regime and the average habitat conditions. Indices were computed using the discharge at the outlet of 11 Danube sub-basins. The differences between the reference and future hydrological regimes were assessed as percentage differences. The percentage differences were calculated for each combination of SSP-RCP—GCM, thus allowing to assess the uncertainty of the results.

The results show marked differences in the projected impacts for the different sub-basins. Overall, the basins in the lower course of the Danube are the most affected under all climate change scenarios, while those in the middle course are somehow more stable. Nevertheless, all sub-basins exhibit a moderate to strong hydrological alteration for at least two indices.