LAUSR

Significance Deltaic land is valuable and at risk of drowning due to relative sea-level rise. Forecasts for the next century suggest sediment deposition by rivers can help counteract land loss, but estimates have yet to account for deposition patterns as rivers change course over time. We present a model and a laboratory experiment that resolve these patterns. Results show deltaic land is in more danger than previously anticipated. Repeated changes in river course temporarily build land that later drowns for decades to centuries. This process leaves less of the river’s sediment supply available to sustain persistently dry and habitable land. Revised forecasts suggest deltas worldwide will require more sediment—or frequent engineered river diversions—to sustain land through the coming century.