Compound marine and pluvial extremes around Anatolia: dependence structure, storm signatures and joint return periods in four semi-enclosed basins

Marine and pluvial flood drivers are usually analysed separately along the Turkish coast, yet the storms that raise offshore waves are often the same systems that deliver heavy rain. This study quantifies this dependence for the four semi-enclosed basins around Anatolia (Black Sea, Sea of Marmara, Aegean, Eastern Mediterranean) using 21 years of hourly ERA5 fields (2006–2026) reduced to paired daily series of maximum significant wave height, rainfall, runoff and GTSMv3 storm surge at 99 coastal points. ERA5 waves are first evaluated against 84,951 calibrated multi-mission altimeter observations: bias is within 0.13 m, correlation reaches 0.79–0.88 in the three open basins, and the 99th percentile is matched within 4–12%; the Sea of Marmara is noisier at instantaneous scale and is flagged accordingly. Kendall’s τ between the declustered marine and pluvial series ranges from 0.20 in the fetch-limited Sea of Marmara to 0.46 on the Eastern Mediterranean coast at basin scale (point-level medians 0.18 to 0.36), and joint exceedances of the 95th percentiles occur five to ten times more often than independence would allow. Copulas fitted to the paired block maxima (Gumbel preferred by AIC in three basins, Gaussian in the Black Sea; the two families bracket the empirical tail) put the joint return period of the event in which both drivers exceed their 99th percentiles at 1.6 to 12.8 years depending on basin and family, against 82 years under independence, and the 3 to 8 joint exceedances observed in the record confirm the few-year scale empirically. Storm surge, added from the GTSMv3-ERA5 reanalysis and checked against 15 tide gauges, is small in these microtidal basins (99th percentile of the daily maximum 0.05–0.30 m) but positively dependent on both rain and waves, and triple exceedances occur 35 to 81 times more often than under independence. Composite anomalies of the 30 strongest joint events per basin show storm signatures that are distinct between basins and internally robust, and the Arctic Oscillation emerges as the dominant large-scale modulator of joint-event frequency, acting in the Aegean (r = −0.34, p < 0.001). Storm Bettina (25–26 November 2023), the strongest wave event of the record, sits inside the fitted joint distribution: an event of its joint rank recurs every few years. These are driver-level statistics: they quantify how often the offshore ingredients of compound coastal flooding arrive together, not the flood response itself. They provide the observational basis for joint-driver screening in Türkiye and a template for other fetch-limited seas.