| Summary: | Deltas are important climate change hot spots that provide critical locations for human populations, agriculture, and aquaculture, as well as ecosystems and the services they provide. However, they are vulnerable systems as the sediment inputs which have historically oset relative sea level rise in undisturbed deltas appear to be threatened by anthropogenic activities. This thesis contributes to the understanding of future delta sustainability by projecting sediment delivery to a set of 47 signicant deltas worldwide. This is the rst study of future sediment uxes to such a large group of major deltas, and for some of these individual deltas the projection of future sediment ux has never been done before. The hydrological model WBMsed was chosen after a review of possible models to project uvial sediment delivery to each delta annually up to the year 2100. The model was forced by scenarios of climate change (RCPs 2.6, 4.5, 6.0, and 8.5), socioeconomic change (population and GDP data derived from SSPs 1, 2, and 3), and projected dam construction. On average, across all 47 deltas, uvial sediment delivery is predicted to decrease by 36-41%, dependent on scenario, during the 21st century. The largest overall contributor to decreasing sediment delivery is reservoir construction. However, for some individual deltas socioeconomic changes can cause a larger decline in the supply of uvial sediment than dam construction. In comparison, climate changes have a much smaller eect than both dam construction and socioeconomic changes, but the inuence of climate change is generally of opposing sign (for 39 of 47 rivers), thereby increasing future sediment supply. There are large dierences between the sediment ux changes projected between individual deltas, with some increases, but the majority of deltas (32 of 47) display decreases in sediment ux on average. The signicance of the sediment delivery changes for each river was assessed by developing a new Sediment Starvation Risk Index (SSRI), which considers absolute sediment ux change versus delta area. The SSRI highlights those deltas most at risk from sediment delivery losses over the 21st century and also shows a correlation between the dominant drivers of sediment ux change for each delta and the degree of sediment starvation risk. Those deltas with sediment ux changes driven by socioeconomic change are likely to be at greater risk of sediment starvation, whereas those driven by climate change are likely to be at less risk. This research assesses projected changes in sediment load to deltas, the key drivers of these changes, and the potential signicance of these changes for individual deltas using globally consistent methods. The research suggests widespread challenges for delta management and sustainability due to reduced sediment inputs over the 21st century.
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