Katherine Anarde, Laura J Moore , Brad Murray, Ian R B Reeves

Developed barrier systems (barrier islands and spits) are lowering and narrowing with sea-level rise (SLR) such that habitation will eventually become infeasible or prohibitively expensive in its current form. Before reaching this state, communities will make choices to modify the natural and built environment to reduce relatively short-term risk. Using a new coupled modeling framework, we simulate how, over decades to centuries, defensive measures to protect development (roadways and communities) alter the physical characteristics, and therefore habitability, of barrier systems. We find that the pathway toward uninhabitability (via roadway drowning or community narrowing) and future system states (drowning or rebound) depends largely on dune management – which influences overwash delivery to the barrier interior – but also on exogenous conditions (SLR and storminess), initial conditions (barrier elevation and width), and alongshore connectivity of management strategies. The timing and occurrence of barrier drowning depends on the rate of SLR and on stochasticity in the timing and intensity of storms and dune recovery processes. We find that negative feedbacks involving storms can allow barriers that do not drown to rebound toward steady-state geometries within decades after management practices cease. In the case of partial, early abandonment of roadway management (i.e., decades before the road is deemed untenable), we find that system-wide transitions to less vulnerable states are possible, even under accelerated SLR and increased storminess.