Projected Hydrological Changes and Trends in the Romanian district of the Lower Danube River Basin under Climate Change

The Danube River Basin is one of the most complex hydrological systems in the world, collecting waters from 19 countries and covering an area of over 800,000 km². In the context of ongoing climate change, the Danube River faces increasing challenges in achieving effective water resource management.

Projected hydrological changes and trends in the Lower Danube River Basin were assessed using simulated river discharge for 1985–2100, forced by downscaled and bias-corrected meteorological inputs derived from 11 General Circulation Models (GCMs) within the ISIMIP3b (5 models) and RESTORE4LIFE (6 models) datasets. The reference period was selected as 1985–2014, consistent with the CMIP6 historical simulations. The projected periods are 2031–2060 (mid-century) and 2071–2100 (late-century), simulated using the CMIP6 climate change scenarios SSP2–4.5 (Middle of the Road) and SSP5-8.5 (Fossil-fuelled development). Within the framework of the Danube Water Balance project, a hydrological water balance model is being developed for the entire Danube River Basin, using the Community Water Model (CWatM), which was specifically configured, calibrated, and validated for this basin.

This study focuses on the major tributaries draining Romanian territory that contribute to the flow regime of the Lower Danube River. The results indicate significant changes and decreasing trends in discharges of the analysed rivers, particularly under SSP5–8.5. Under SSP2–4.5, generally a stationary trendline has been highlighted. However, inter-model spread across the 11 GCMs combined with the SSP–RCP scenarios contributes to notable uncertainty in the projections. Additionally, significant differences are observed among the analysed river basins regarding how future discharge will evolve.

Understanding how river discharge may evolve in the future could support the timely implementation of measures and policies for the sustainable management of the analysed Danube tributaries and the Lower Danube River as a whole.

Acknowledgment 
This work/paper was supported as part of DANUBE WATER BALANCE – DRP0200156, an Interreg Danube Region Programme project co-funded by the European Union.