The Sea-Level Changes in Hong Kong from Tide-Gauge Records and Remote Sensing Observations over the Last Seven Decades

The importance of studying the sea-level change (SLC) in Hong Kong (HK) is emphasized by factors related to high population density, intensive urban, and industrial development, particularly along the coast that involves a considerable landreclamation. To address this issue, we investigate the spatiotemporal characteristics of SLC in the HK territories by analyzing tide-gauge (TG) records collected from 1954 to 2019 and satellite-altimetry (SA) data from 1993 to 2019. The application of the ocean-tide and inverted barometer corrections to TG data substantially decreased uncertaintie by achieving a submillimeter accuracy. The SLC rates detected at six TG stations vary significantly even within this relatively small coastline. According to our estimates, the annual rates vary between 0.32 ± 0.51 and 4.19 ± 0.46 mm/yr from 1997 to 2019. These large differences are related to different patterns of ocean currents and the freshwater discharge in the Pearl River Estuary. The empirical orthogonal function analysis confirms the expected increasing rising in SLC with two anomalous periods during 2002-2003 and 2015-2016 that are likely attributed to the El Niño-Southern Oscillation (ENSO). SLCs are positively correlated with the ENSO index and ENSO precedes several months (normally 5 months) the interannual SLC. The analysis of the GPS trends reveals a prevailing subsidence in the HK territories, which aggravates the relative SLC estimates. Between 1997 and 2019, the absolute sea level raised at the annual rate of 3.17 ± 1.56 mm/yr (when using the GPS+TG) and 2.88 ± 0.59 mm/yr (when using SA observations).