Evaluating and mitigating ecosystem impacts under future extreme sea-level events: The case of Hong Kong

Global climate change accelerates sea level rise. Hong Kong, with its coastal location and low-lying terrain, is one of the cities most vulnerable to extreme sea-level (ESL) rise. Previous studies have primarily focused on impacts on urban areas, leaving the effects on ecosystems and their service values unexplored. This study evaluates the expected extent of impacts on ecosystems and their service values from ESL events in Hong Kong under two Representative Concentration Pathways (RCP4.5 and RCP8.5) scenarios. Results reveal that under RCP4.5, 6.79% and 7.98% of Hong Kong's land area will be inundated in 2050 and 2100, respectively, whereas under RCP8.5, the inundation extent will increase to 7.52% and 9.55%. Urban ecosystems are the most impacted in terms of area, while mangrove ecosystems experience the greatest percentage loss and reduction in ecosystem service value. The ecosystem service loss is estimated to be at least $167.86 million per year under the RCP4.5 in 2050, which will increase to $186.95 million per year under the RCP8.5 in 2100. These findings suggest that the stricter greenhouse gas controls (limiting temperature rise to 1.5 °C) in the Paris Agreement would be more beneficial to Hong Kong. Additionally, the study highlights the need to prioritize protecting the Ramsar Site and Deep Bay Wetland, while old trees should be safeguarded based on impact urgency. The study highlights the importance of addressing climate change impacts and offers insights into protecting ecosystems from ESL events in coastal cities.