Attributing decadal climate variability in coastal sea-level trends

Abstract. Decadal sea-level variability masks longer-term changes due to natural and anthropogenic drivers in short duration records and increases uncertainty in trend and acceleration estimates. When making regional coastal management and adaptation decisions, it is important to understand the drivers of these changes to account for periods of reduced or enhanced sea-level change. The variance in decadal sea-level trends about the global-mean is quantified and mapped around the global coastlines of the Atlantic, Pacific and Indian Oceans, from historical CMIP6 runs and a high-resolution ocean model forced by reanalysis data. We reconstruct coastal, sea-level trends via linear relationships with climate mode and oceanographic indices. Using this approach, more than one-third of the variability in decadal sea-level trends can be explained by climate indices at 24.6 % to 73.1 % of grid cells located within 25 km of a coast in the Atlantic, Pacific and Indian Oceans. At 10.9 % of the world's coastline, climate variability explains over two-thirds of the decadal sea-level trend. By investigating the steric, manometric and gravitational components of sea-level trend independently, it is apparent that much of the coastal ocean variability is dominated by the manometric signal, the consequence of the open-ocean steric signal propagating on to the continental shelf. Additionally, decadal variability in the GRD signal should not be ignored in the total. There are locations such as the Persian Gulf and African west coast where decadal sea level variability is historically small, that are susceptible to future changes in hydrology and/or ice mass changes that drive intensified regional GRD sea-level change above the global-mean. The magnitude of variance explainable by climate modes quantified in this study infers an enhanced uncertainty on projections of short- to mid-term regional sea-level trend.