Managed Retreat Threshold Simulator

Coastal communities facing sea-level rise usually pick one of three strategies: protect the shoreline, accommodate the water, or retreat inland — and the "right" choice is really an economic threshold, not a fixed answer. This simulator runs a small coastal town year by year: sea level climbs at the rate you set, a Gumbel extreme-value model turns that into an annual probability of the seawall being overtopped by storm surge, and every flood year adds expected damage to a running protect-cost line. Compare that line against the flat, one-time cost of buying out and relocating every household, and watch for the exact year the two lines cross — the point at which continuing to defend the coast costs more than simply leaving it.