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 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. Here, we show that current technologies, resources, and space provide at least one physically feasible delta-wide strategy for every delta to adapt by 2100. This number 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 analysis highlights the risk of resource limitations as global deltas will need to adapt simultaneously to future flood risks.