Impacts of Climate Change on Riverine Ecosystems: Alterations of Ecologically Relevant Flow Dynamics in the Danube River and Its Major Tributaries

Abstract

River flow dynamics play an important role for aquatic and riparian ecosystems. Climate change is projected to significantly alter river flow regimes in Europe and worldwide. In this study, we evaluate future river flow alterations in the entire Danube River basin by means of ecologically relevant river flow indicators under different climate warming scenarios (Representative Concentration Pathway (RCP) 2.6, RCP 4.5, and RCP 8.5). The process-based watershed model SWIM was applied for 1124 sub-catchments to simulate daily time series of river discharge for the Danube River and its tributaries under future scenario conditions. The derived hydrological data series were then statistically analyzed using eight eco-hydrological indicators to distinguish intra-year variations in the streamflow regime. The results are used to: (a) analyze the possible impacts of climate change on the ecologically relevant flow regime components; and (b) identify regions at the highest risk of climate change-driven flow alterations. Our results indicate that climate change will distinctively alter the recent ecological flow regime of the Danube River and, in particular, the tributaries of the Middle and Lower Danube basin. While for the RCP 2.6 scenario the projected flow alterations might still be considered moderate for many rivers, the impacts might strongly accelerate if global mean temperatures rise more than 2 • C compared to pre-industrial times. Under RCP 4.5 and RCP 8.5 warming scenarios, the recent ecological flow regime might be highly altered, posing a serious threat to river and floodplain ecosystems.

Temporal Hydrologic Alterations Coupled with Climate Variability and Drought for Transboundary River Basins

“…Yet, most of the recent research has focused on the streamflow alteration from an ecological point of view (Suen 2008;Doll and Zhang 2010;Kim et al 2011;Lee et al 2014;Mittal et al 2014;Stagl and Hattermann 2016) and not from a hydrological one. In addition, they did not consider to incorporate anthropogenic interventions, CC and drought event impacts within a comprehensive study.…”

The role of floods and droughts on riverine ecosystems under a changing climate

“…The majority of model-based climate change impact studies address biological consequences by defining changes in 'ecologically relevant' flow regimes (Dhungel, Tarboton, Jin, & Hawkins, 2016;Döll & Zhang, 2010;Laizé et al, 2013;Morales-Marin, Rokaya, Sanyal, Sereda, & Lindenschmidt, 2019;O'Keeffe et al, 2018;Piniewski, Laize, Acreman, Okruszko, & Schneider, 2014;Stagl & Hattermann, 2016;Vigiak et al, 2018;Van Vliet et al, 2013). Ecological relevance in this case is usually assessed based on available literature.…”

“…Ecological relevance in this case is usually assessed based on available literature. This approach is better suited for large-scale analyses: from global (Döll & Zhang, 2010), through continental (Laizé et al, 2013;Van Vliet et al, 2013), to national (Dhungel et al, 2016) and large river basin scale (O'Keeffe et al, 2018;Stagl & Hattermann, 2016). Predicted effects of climate change on riverine biota are only implicit in such studies.…”

Development of a procedure for assessing the environmental risk of the surface water status deterioration

“…It has been shown in [4] that climate change will significantly change river runoff regimes in Europe and throughout the world. Based on SWIM forecasting models, estimation of future changes in river runoff throughout the Danube River basin was made using environmentally relevant river flow indicators under different climate change scenarios.…”