Global estimation of storm surge seasonality and the effect of interannual variability.

Extreme storm surges exhibit significant seasonal and interannual variability influenced by large-scale climate modes. The goal of our work is to investigate the seasonality of storm surge extremes and the influence of interannual climate variability at the global scale, which to date is not fully understood due to lack of observations with long-records.   To achieve this goal, we use storm surge levels derived from the Global Tides and Surge Model (GTSM) forced with the extended ERA5 climate reanalysis data spanning 1950-2022. Our methodology consists of two main steps. First, we classify the dataset into four seasons (Winter-DJF, Spring-MAM, Summer-JJA, Autumn-SON) and compute the number of events per season. Next, we conduct extreme value analysis on selected thresholds and explore their connections with climate modes. Preliminary findings indicate that extreme surge events are more frequent and pronounced at higher latitudes during SON, with notable peaks in DJF. This is particularly significant in the North Sea and funnel-shaped coastlines such as Rio de la Plata, Arafura Sea, and Hudson Bay. In contrast, regions like the South China Sea, the Bay of Bengal, the Yellow Sea, and southern Australia experience more frequent surge extremes from JJA to SON with variations in peak season. Equatorial regions, especially around Africa, have negligible surge extremes except for occasional tropical cyclones from late DJF, with peaks in MAM in Mozambique and Madagascar. Similarly, there are occasional tropical cyclone events in parts of the Caribbean with peaks in JJA. The study findings have broader implications for understanding the global distribution and spatio-temporal variation of extreme surge events, which could help to provide guidance on the impacts of climate change in the future. Overall, the preliminary findings underpin the need to further explore what the drivers of storm surge variability are.