Minimizing Urban Floodplain Management Regrets under Deeply Uncertain Climate Change

Optimization modeling can reveal promising multiperiod schedules for adapting to deeply uncertain changes in flooding. We contribute a parsimonious optimization model (mixed integer program) that adjusts the efficacy of property-scale adaptation measures (first-floor elevation, wet floodproofing, permanent retreat, insurance) for different floodwall investments and insurance incentives. After minimizing expected flood-control and damage costs for individual scenarios, we identified adaptation portfolios that minimize underdesign and overdesign regrets under a deeply uncertain future. A near-optimal solutions algorithm also identified diverse solutions with different multistakeholder tradeoffs. A stylized example showed that, when mild damage is tolerated, portfolios combining smaller floodwalls, wet floodproofing of basements, and moderately elevated manufactured (mobile) homes can be more robust to climate uncertainty than larger floodwalls alone. Yet, near-optimal solutions demonstrated that larger floodwalls without any property-scale measures are also feasible. Insurance incentives targeting property-scale measures (elevation, wet floodproofing) suited for permanent homes discourage municipal floodwall investments and force owners of manufactured homes to retreat. The results motivate further research on wet floodproofing, retreat financing, and insurance-based adaptation incentives.