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Modelling sediment dynamics at the basin scale : implications of changes in climate and hydrological regimes Tsuruta, Kai


Basin-wide sediment dynamics are closely linked to hydrological processes and landscape and therefore expected to be susceptible to climate change. Simulating sediment transport through large basins presents a challenging problem to modellers; the relationship between water flux and sediment load is complex and non-linear, and significant sediment generation can occur over small spatial and time scales. To date, most studies have employed lumped empirical models that predict annual load at the outlet of a study basin, but do not consider variability across the basin or sub-annually. In this study, we adapt a physically-based, distributed suspended sediment transport model for large-scale use. The sediment model is integrated into the Terrestrial Hydrology Model with Biochemistry (THMB) as a routine to make use of THMB’s dynamic water routing. The coupled model is applied to the 230,000 km² Fraser River Basin (FRB) in British Columbia, Canada using 1) historical hydrological input to test the model and 2) synthetic input derived from Intergovernmental Panel on Climate Change (IPCC) scenarios A1B, A2, and B1 to study potential impacts of climate change. In both cases the input data is provided by the Pacific Climate Impacts Consortium (PCIC) and comes from simulations using the Variable Infiltration Capacity (VIC) model. Simulation results using historical inputs are compared with observations at five stations using the coefficient of determination (R²), Nash-Sutcliffe coefficient of efficiency (NSE), and percent bias (PBIAS) metrics. Overall, simulated load values match well with observed values, with the monthly simulations at the station nearest the outlet scoring R² = 0.78, NSE = 0.77, and PBIAS = -20%. Simulation results using climate scenario-driven inputs are studied for potential future changes in sediment dynamics. Results re- veal a general shift in hillslope erosion and sediment yield towards larger values from autumn to spring, reduced summer values, and an overall annual increase, with hillslope generation growing 35-45% from baseline levels and yield at the basin’s outlet increasing 10-15%. These physically-based results offer unique insights into the impacts of climate change on sediment processes within a large basin and their potential implications.

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