Sea-level change in coastal areas of China: Status in 2021

The sea level in coastal areas of China reached the second highest in 2021, just after that recorded in 2022. External force and dynamic analyses based on tide gauges, satellite observations, reanalysis data and regional numerical outputs were conducted to understand these abnormally high sea levels and determine their possible causes. Results show that the coastal sea level of China had increased at an annual rate of 3.4 ± 0.3 mm during 1980–2021, with an acceleration of 0.06 ± 0.02 mm per year². The superposition of significant oscillations of quasi-2, 3–7, quasi-9, quasi-11, quasi-19 and 20–30 years contributed to the anomalously high sea levels. The negative-phased El Niño/Southern Oscillation was correlated with the anomalously high sea level and the north‒south anti-phase pattern of the coastal sea level in 2021. Meanwhile, phase lags of 1–4 months occurred with the sea-level response. On a decadal timescale, the Pacific Decadal Oscillation (PDO) was negatively correlated with the anomalous mean sea level (MSL), and the negative-phased PDO contributed to the anomalous sea-level change in 2021. Particularly, the monthly MSL peaked in April and July, and the contribution of wind stress to the anomalously high sea level was 38.5% in the south of the Taiwan Strait in April and 30% along the coast of China in July. These results were consistent with the tide gauge and satellite data. Close agreement was also observed between the coastal sea-level fingerprint and the air and sea surface temperatures.