Journal of Tropical Oceanography ›› 2025, Vol. 44 ›› Issue (2): 157-177.doi: 10.11978/2024099CSTR: 32234.14.2024099

• Marine Geomorphology • Previous Articles     Next Articles

Spatiotemporal changes of lime-sand islands in the Xisha Islands under the impacts of typhoons

XIAO Haiting1(), HUANG Rongyong2,3,4(), LIU Yi1, YU Kefu2,3,4   

  1. 1. School of Earth System Science, Tianjin University, Tianjin 300072, China
    2. Guangxi Laboratory on the Study of Coral Reefs in South China Sea, Guangxi University, Nanning 530004, China
    3. Coral Reef Research Centre of China, Guangxi University, Nanning 530004, China
    4. School of Marine Sciences, Guangxi University, Nanning 530004, China
  • Received:2024-04-30 Revised:2024-06-12 Online:2025-03-10 Published:2025-04-11
  • Contact: HUANG Rongyong
  • Supported by:
    National Natural Science Foundation of China(4192200195); National Natural Science Foundation of China(42030502); National Natural Science Foundation of China(42090041)

Abstract:

In this study, we explored the changing characteristics of spatial patterns of lime-sand islands in the Xisha Islands under the impacts of typhoons and their driving factors, which are of great significance to the ecological protection and sustainable development of lime-sand islands in the South China Sea (SCS). First, to determine the area of the BeiDao, ZhongDao and Nandao islands of the Xisha Islands and their beaches, the toe of beach line (ToB) and the boundary of vegetation were extracted using the gradient vector flow-snake (GVF-snake) model based on Sentinel-2 remote sensing images. The monthly average area of the study islands from 2016 to 2022 was examined using the change point detection method, and the typhoon events that had caused significant changes in the size of the study islands were identified. Finally, the spatial and temporal characteristics of the islands affected by typhoons were analyzed based on the changes in lime-sand islands area, vegetation area, beach area and normalized difference vegetation index (NDVI) during typhoon events. The results are shown as follows. 1) The vegetation of the islands was mainly slightly stressed by the typhoons, and the severely stressed areas were mainly located along the shorelines. The typhoons caused a significant retreat of the vegetation boundary of the islands, and the sediments were stripped off with the damaged vegetation and washed to the beach with the wind and waves, resulting in the seaward advancement of the ToB line. The windward coasts were the first to be impacted by the direction of the typhoon path, and the vegetation along the windward side of the islands was heavily damaged, resulting in more significant changes in vegetation, vegetation boundary, and the ToB line on the windward side. 2) As the vegetation along the lime-sand islands was damaged, the retreat of the vegetation boundary line and the seaward advancement of the ToB line resulted in the expansion of the beach area, whereas after the typhoon, due to the loss of vegetation fixation, the loose sediment accumulated on the beach was transported away from the islands to the reef flats by the wind and wave action, resulting in the reduction of the beach area. Therefore, coastal vegetation that buffers and fixes the sand is critical to the stability of lime-sand islands. 3) Increased typhoon wind speeds and shorter distances between typhoon paths and the islands, as well as increased surface currents during the typhoon, made the islands exposed to extreme wave and storm currents, which led to an increase in the area of severely damaged vegetation on the islands, resulting in greater shoreline movement and changes in beach area. In addition, typhoons can cause sediment transport between the lime-sand islands and their surroundings, which can directly change the beach area and morphology of the lime-sand islands. The loss of large amounts of unconsolidated sediments on the lime-sand islands after the typhoon, which led to an abrupt decrease in the size of the islands, together with the decrease in the rate of biogenic carbonate production due to global warming and the insufficient supply of sediments from the surrounding environment, may be the reasons for the long-term decreasing trend in the size of the lime-sand islands in the Xisha Islands.

Key words: lime-sand island, typhoon, remote sensing, Xisha Islands

CLC Number: 

  • P737.13