Impacts of external factors in salinity patterns via numerical modeling along the Scheldt Estuary, Belgium

Study region:: The Scheldt Estuary in Belgium Study focus:: Understanding the mechanisms that control salt intrusion in estuaries is crucial due to its significant impact on the ecological environment and the water resource potential of estuaries. This study utilizes the Mike11 model to perform discharge (Q), water level (WL), and salinity (S) simulations in the reference and three future scenarios with sea level (SL) rise and Q reduction. A comparative analysis is conducted to evaluate the impact of individual and combined external factors (Q and WL) in the high-risk scenario S2. New hydrological insights for the regions:: Results demonstrate that the midstream S is more sensitive to climate change compared to the upstream, leading to a transition of dominance from the freshwater zone to the mesohaline zone. The temporal evolution of S longitudinal structure exhibits significant variations throughout the year, showing increasing saltwater intrusion distance as the scenario intensify, particularly in seasonally low river flow period. It is also found that the combined effects of external factors on variable S demonstrate complex interactions, yielding varying sensitivities across different regions, rather than simply being the sum of individual factor impacts. Additionally, the correlations analysis indicates robust negative associations between upstream Q and S, and intricate and weak positive relationships between downstream WL and S.