Planetary-scale sea-level variability in the Adriatic Sea under present and future climate conditions

Abstract

Sea-level variability on planetary time scales (10–100 d) is a prominent feature of the Adriatic Sea and an important preconditioner of coastal flooding. We characterized its properties in the present climate using the nearly century-long Bakar tide-gauge record (1929–2021) and mean sea-level pressure from ERA5 reanalysis, and assessed projected changes using three regional climate model simulations (ALADIN, CCLM, and RACMO). High coherence between sea level and mean sea-level pressure in the 10–100 d band justified using mean sea-level pressure as a proxy for planetary-scale sea level in future climate. Extreme planetary-scale episodes were defined as sea-level anomalies ≥ +19 cm and mean sea-level pressure ≤ -13.5 hPa, separated by at least ten days. In the past period, extreme sea-level episodes peaked in the cold season, occurred typically once or twice per year, lasted three to six days, and showed no significant century-scale trend in intensity, frequency, or duration. Evaluation of regional climate models for the period 1971–2000 showed that all models reproduced the observed seasonal cycle and episode intensity, while the CCLM and especially RACMO models tended to overestimate frequency and duration. Future projections (2039–2068, 2069–2098) under RCP4.5 and RCP8.5 indicated no robust changes in episode intensity, duration, or frequency suggesting that planetary-scale atmospheric forcing over the northern Adriatic is unlikely to change substantially in warmer climates. Consequently, future flood risk will be governed primarily by mean sea-level rise and its superposition with tides and storm surges, rather than by strengthened planetary-scale anomalies.