Physical limits of sea-level rise adaptation in global river deltas

Sea-level rise threatens deltas worldwide, requiring adaptation to flood risks. Delta adaptation is typically presented as a choice between five broad strategies: advance, protect-closed, protect-open, accommodate, and retreat. However, a full assessment of the physical feasibility of these strategies across deltas remains limited. We present a first-order assessment of the physical solution space for adaptation to sea-level rise for nearly 800 deltas globally. We find that current technologies, resources, and space provide at least one physically feasible delta-wide strategy for every delta to adapt by 2100. This may increase in the future through technical innovation or collaboration between deltas. The type and number of physically feasible strategies are mostly determined by delta’s physical characteristics, whereby, large, urbanized, or frequently flooded deltas have fewer options than small, rural, or infrequently flooded deltas. Our global analysis also highlights the risk of resource limitations as deltas will need to adapt simultaneously to future flood risks.