Climate Change–Driven Hydrological Extremes and Indirect Impacts on Socio-Economic Vulnerability and Resilience in the Danube Basin

Climate change impacts on human systems increasingly emerge through hydrological extremes that generate complex socio-economic vulnerabilities across sectors. However, traditional risk assessments often emphasize physical hazards rather than how climate-driven hydrological changes cascade through ecosystem services to affect livelihoods, infrastructure, and adaptive capacity. To translate climatic scenarios into river discharge projections for the Lower Danube, we employed the Europe-HYPE (E-HYPE) hydrological model. This semi-distributed, process-based model simulates water balance components and river flow across hydrological response units. E-HYPE has been configured for pan-European applications and evaluated against observed flows across multiple basins. For the historical reference period (1971–2000), we used the HYPE reanalysis dataset at the Brăila gauge to characterise the baseline hydrological regime. Daily meteorological forcings in the reanalysis reflect observed and interpolated inputs that drive hydrological processes (e.g., rainfall, temperature). For future discharge projections (2001–2100), we constructed an E-HYPE ensemble of eight members by forcing the model with bias-adjusted meteorological inputs derived from multiple regional climate models under two Representative Concentration Pathways (RCP4.5 and RCP8.5). These forcings provide consistent daily temperature and precipitation inputs that reflect alternative greenhouse gas concentration trajectories through to 2100. The ensemble captures structural and forcing uncertainty in the projected hydrological response.

IWe used a hydrological impact dataset providing water-related Essential Climate Variables (ECVs) and Climate Impact Indicators (CIIs), derived from bias-adjusted regional climate simulations from the EURO-CORDEX. The dataset includes daily mean river discharge produced using a multi-model hydrological setup based on the E-HYPEcatch model at a pan-European scale, available at the catchment level and on a 5 km × 5 km grid. We have extracted the simulated daily discharge at the Brăila station, for two climate scenarios (RCP4.5 and RCP8.5) and then was analysed across near-term (2021–2050), mid-century (2051–2080), and late-century (2081–2100) horizons to evaluate changes in the frequency and magnitude of hydrological extremes (e.g., >10 000 m³/s and >15 000 m³/s for floods; <3 000 m³/s for low flows) and seasonality patterns relative to the historical baseline (1971-2006). Sectoral context for interpretation was drawn from ICPDR, UNECE, and national data for the Lower Danube / Brăila region. Results show that climate change amplifies hydrological variability rather than uniformly shifting mean discharge. By mid-century, the frequency of high-flow events (>10 000 m³/s) increases by ~50 – 75 %, and extreme floods (>15 000 m³/s), historically rare, become recurrent under both scenarios. Concurrently, exposure to navigation-critical low flows (<3 000 m³/s) rises substantially, with up to ~80 days per year below this threshold by the late century under RCP8.5. Seasonal reorganisations are pronounced: flood peaks shift toward winter, while critical low flows concentrate in summer and early autumn.

Interpreted through an ecosystem services and socio-economic vulnerability framework, these hydrological changes weaken regulating services (natural flood mitigation), strain supporting services (habitat integrity and resilience), and constrain provisioning services such as water for agriculture and inland navigation. The co-occurrence of altered extremes and seasonality underscores cascading risks that extend beyond physical hazard zones, affecting agricultural productivity, transport reliability, and community adaptive capacity.