Seasonal Forecasting Skill of Sea-Level Anomalies in a Multi-Model Prediction Framework

Coastal high water level events are increasing in frequency and severity as global sea-levels rise, and are exposing coastlines to risks of flooding. Yet, operational seasonal forecasts of sea-level anomalies are not made for most coastal regions. Advancements in forecasting climate variability using coupled ocean-atmosphere global models provide the opportunity to predict the likelihood of future high water events several months in advance. However, the skill of these models to forecast seasonal sea-level anomalies has not been fully assessed, especially in a multi-model framework. Here, we construct a 10-model ensemble of retrospective forecasts with future lead times of up to 11 months. We compare predicted sea levels from bias-corrected forecasts with 20 years of observations from satellite-based altimetry and shore-based tide gauges. Forecast skill, as measured by anomaly correlation, tends to be highest in the tropical and subtropical open oceans, whereas the skill is lower in the higher latitudes and along some continental coasts. For most locations, multi-model averaging produces forecast skill that is comparable to or better than the best performing individual model. We find that the most skillful predictions typically come from forecast systems with more accurate initializations of sea level, which is generally achieved by assimilating altimetry data. Having relatively higher horizontal resolution in the ocean is also beneficial, as such models seem to better capture dynamical processes necessary for successful forecasts. The multi-model assessment suggests that skillful seasonal sea-level forecasts are possible in many, though not all, parts of the global ocean.

Automated summary

Coastal high water level events are on the rise due to global sea-level rise, but operational seasonal forecasts of sea-level anomalies are lacking in most coastal regions. Advances in forecasting climate variability using coupled ocean-atmosphere global models provide the opportunity to predict future high water events several months in advance. Multi-model assessments show that skillful seasonal sea-level forecasts are possible in many, but not all, parts of the global ocean.