Cities and the sea level

Construction on low elevation coastal zones is risky for both residents and taxpayers who bail them out. To investigate this construction, we analyze spatially disaggregated data covering the entire US Atlantic and Gulf coasts. We find that the 1990 housing stock reflects historical avoidance of locations prone to sea level rise (SLR) and flooding, but net new construction from 1990–2010 was similar in SLR-prone locations and safer ones; and within densely built coastal areas, net new construction was higher in SLR-prone locations. These findings are difficult to rationalize as mere products of moral hazard or imperfect information, suggesting that people build on risky locations to benefit from nearby urban agglomerations. To explain our findings, we develop a simple model of a monocentric coastal city, which we use to explore the consequences of sea level rise. This model helps explain cities’ role in expanding flood risks, and how future sea level rise may reshape coastal cities, creating significant challenges for policymakers.