Towards forecasting the retreat of California’s coastal cliffs during the 21st century

In California, sea-level rise during the 21^st century threatens to accelerate coastal cliff recession rates. To forecast such changes for managers and policymakers, models must play a key role. In this paper, we extend a ~70-year long dataset of measured historic sea cliff retreat rates in Southern California into the 21^st century using a suite of simple analytical and empirical models. Ensemble results suggest that coastal cliff recession rates could increase on average by 0.09-0.22 m yr^-1 for a 0.5-1.0 m rise in sea level by 2100, 27-67% faster than historical rates. The basic models used herein will serve as a baseline against which more complex, process-based and statistical (Bayesian) forecasts will be compared. The application of different models, with varying levels of detail, to the same geomorphic problem will provide a comprehensive forecast and address the question of how to reduce model complexity while minimizing uncertainty.