Vulnerability assessment of the coastal mangrove ecosystems in Guangxi, China, to sea-level rise

Sea-level rise caused by global climate change will have significant impacts on the coastal zone. On tropical and subtropical coasts, mangrove ecosystems occur in the intertidal zone and are particularly sensitive to sea-level rise. Taking the mangrove ecosystems in the coastal zone of Guangxi province, China, as a case study, the potential impacts of sea-level rise were analyzed by adopting the Intergovernmental Panel on Climate Change (IPCC) vulnerability definition. An indicator system for vulnerability assessment on coastal mangroves undergoing sea-level rise was developed, in which the rate of sea-level rise, subsidence/uplift rate, habitat elevation, mean daily inundation duration, intertidal slope and sedimentation rate were selected as the key indicators. A spatial assessment method based on a geographic information systems platform was established by quantifying each indicator, calculating the vulnerability index and grading the vulnerability. Vulnerability assessment, based on the projection of sea-level rise rates from the present trend and IPCC's A1FI scenario, was performed for three time periods: short term (2030s), medium term (2050s) and long term (2100s). The results showed that, using the present SLR rate of 0.29 cm/year, the mangrove ecosystems in the coastal zone of Guangxi would be affected only in the long-term scenario up to 2100, but not in the short-term or medium-term scenarios. In the long-term scenario of the present trend, 5.4 % of the mangroves would be within areas of low vulnerability. Under the A1FI climate change scenario, with a sea-level rise rate of 0.59 cm/year, 25.8 and 37.3 % of mangroves were within areas of low vulnerability in the scenarios of up to 2030s and the 2050s, while 23.9 and 13.4 % of mangroves were within areas of low and moderate vulnerability in the 2100s, respectively. The development of this new methodology for vulnerability assessment and the results presented in this study could assist with the objective and quantitative assessment of the vulnerability of mangrove ecosystems undergoing the impacts of sea-level rise elsewhere. Without proper mitigation options, the potential decrease and loss of mangrove habitats and ecosystem services from the Guangxi coast are inevitable. Based on the results of this study, mitigation measures should be considered for securing the future of these mangrove ecosystems, which include the management of sedimentation, control of reclamation, and methods for habitat rehabilitation.