Influence of El Niño-Southern Oscillation on Global Coastal Flooding

Anomalous atmosphere-ocean conditions in the tropical Pacific associated with the El Niño-Southern Oscillation (ENSO) drive interannual variations in mean and extreme sea levels. Climate change may lead to more frequent extreme ENSO events in the future. Therefore, it is important to enhance our understanding of ENSO's influence on coastal flood impacts. We assessed ENSO's influence on extreme sea levels using a global reanalysis of tides and storm surges. This allows for a full coverage of the global coastline from 1979 to 2014. A mean sea level component is added to account for steric effects. This results in a substantial improvement in the representation of the seasonal and interannual variability. Our results show significant correlations across the Pacific between ENSO and extreme sea levels (expressed as 95th annual percentiles), which is consistent with previous studies based on tide gauge observations. Average anomalies in the annual percentiles over El Niño years compared to neutral years show similar patterns. When examining total sea levels, results are largely statistically insignificant. This is because in many regions large tidal variability dominates over the other components. Combining sea levels with an inundation and impact model shows that ENSO has a significant but small effect on the number of people potentially exposed to flooding at the globally aggregated scale. Our results demonstrate that a model-based approach allows for an assessment of the influence of ENSO on coastal flood impacts and could be used to assess impacts of future changes in ENSO.