Comparative study on sea-level rise in the Yangtze River Estuary and Red River Estuary in the recent 30 years

Sea-level rise with its impacts on coastal areas has become one of the most important topics. The Yangtze River Estuary (YRE) and Red River Estuary (RRE) are the most sensitive regions to climate change but locating in temperate and subtropical regions of Asia, respectively. However, there is few comparative studies between sea level change in estuaries affected by different climatic and dynamic conditions. Using long-term satellite altimetry data combined with sea surface temperature (SST) and wind field data, this study analyzed temporal variations of sea level anomaly (SLA) and its controlling factors. The SLA in these two estuaries has shown a significant increase, with the rate in the RRE (3.6 mm/yr) being slightly higher than that in the YRE (3.4 mm/yr). Frequency spectra analysis indicated a remarkable annual, seasonal (about 4-month cycles) and about 2-month signals in the YRE. Moreover, annual and semi-annual signals were founded in the RRE. The highest SLA in these two estuaries are mostly occurring in October. SLA variations in the YRE are influenced by both SST and local wind, whereas that in the RRE are mainly affected by SST. Interestingly, the different lag time of SLA to SST in two estuaries is related to water depth. Furthermore, the maximum SLA is predicted to reach 0.47 m in the YRE and 0.41 m in the RRE for the next 10 years (2023-2032), respectively. This study aims to understand the controlling mechanism of SLA changes in estuaries in different geographical locations.