Non-linear interaction modulates global extreme sea levels, coastal flood exposure, and impacts

We introduce a novel approach to statistically assess the non-linear interaction of tide and non-tidal residual (NTR) to quantify its contribution to extreme sea levels and its role in modulating coastal protection levels globally. We demonstrate that extreme sea levels are up to 30% (or 70 cm) higher if non-linear interactions are not accounted for (e.g., by independently adding astronomical and non-astronomical components). These overestimates are similar to recent sea-level rise projections to 2100 at some locations. We further find evidence for changes in this non-linear interaction over time, which has the potential for counteracting increasing flood risk associated with sea-level rise and tidal and/or meteorological changes alone. Finally, we show how accounting for non-linearity in coastal impact assessment modulates coastal exposure, reducing recent estimates of global coastal flood costs by 16% and population affected by 8%.

Arne Arns, Thomas Wahl, Claudia Wolff, Athanasios T. Vafeidis, Ivan D. Haigh, Philip Woodworth, Sebastian Niehüser, Jürgen Jensen