Attribution of glacier runoff to river streamflow in the Danube Basin

Glaciers in the Danube Basin are projected to disappear almost entirely by 2100. This study quantifies both the trajectory of glacier loss and its hydrological consequences across the basin.

The Open Global Glacier Model (OGGM) is employed, driven by downscaled and bias-corrected meteorological forcing from multiple CMIP6 General Circulation Models to simulate the evolution of 800 glaciers from the Randolph Glacier Inventory 6.0 across three SSP-RCP scenarios. Results indicate substantial glacier loss across all scenarios, with most of the glaciated area disappearing by 2060. Even under the optimistic SSP1-2.6 pathway, only a minor fraction of glacier area and volume persists through 2100.

To assess the hydrological consequences of glacier retreat, the hydrological model Community Water Model (CWatM) is used. CWatM is calibrated for the entire Danube basin at 645 discharge stations, with daily temporal and one arcminute spatial resolution, incorporating glacier runoff contributions derived from OGGM. Paired simulations are conducted with and without glacier runoff to quantify the contribution of glacier runoff to river streamflow using historical meteorological forcing (1990–2020).  Additionally, an attribution analysis is performed comparing the hydrological regime under glacier runoff with that under non-glaciated conditions in presently glaciated areas.

This study reveals the spatial and temporal patterns of glacier decline and demonstrates how glacier runoff contribution and attribution evolve along the Inn, Drau, and Danube rivers from headwaters to the river mouth, providing insights into the changing water balance of the Danube.