Validating Multidecadal Fluvial Sediment Flux Projections to Major Deltas Under Environmental Change Scenarios
Summary
This thesis critically evaluates the pioneering work of Dunn et al. (2019) in projecting decadal sediment fluxes for major global deltas using the WBMsed model. It assesses the model's performance in accurately projecting sediment flux scenarios and its potential as a 'missing link' in delta sustainability research, particularly in projecting relative sea level changes for individual deltas. Recognizing the capabilities and limitations of substituting empirical data with a model is crucial for establishing its projection accuracy, reliability, and applicability to other global deltas, addressing knowledge gaps in accurately projecting future challenges faced by deltaic systems.
Through a comprehensive operational validity study, insights into how well the WBMsed model captures real-world patterns and behaviors are provided. The model's performance is evaluated against recent and reliable validation data, revealing significant challenges and areas for improvement. While mean annual sediment flux projections generally perform acceptably, with 37 out of 43 rivers falling within one order of magnitude of validation data, the model struggles to accurately capture yearly increase or decrease fluctuations for 21 rivers, failing to represent natural delta system morphology behavior. Extreme inter-annual fluctuations dominate sediment flux trends, emphasizing the need for model refinement to enhance short-term variation projections.
Regarding sediment flux magnitudes, the WBMsed model tends to overpredict, with also fluvial water discharges overestimated up to +1700%, contrasting with underpredictions of -54% in certain rivers. Furthermore, while projections suggest 16 deltas would experience increased pressure on their ability to withstand relative sea level rise due to decreasing fluvial sediment flux, observations show that 26 deltas actually experienced increased pressure.
The research concludes that while the WBMsed model shows promising accuracy in average annual sediment flux predictions for many rivers worldwide, addressing identified challenges such as overprediction, unnatural inter-annual variability, and the exclusion of variables influencing fluvial sediment fluxes in reality is crucial for its broader applicability to global deltas and reliable use in delta sustainability projections.