Spatiotemporal Changes of the Coastal Environment in Northwestern Taiwan

Marine ecosystems, particularly in western Taiwan, where coastal and offshore areas are highly vulnerable to natural and anthropogenic pressures, face substantial challenges from global climate change. These ecosystems provide essential services, including biodiversity conservation, climate regulation, and fisheries support. This study investigates the complex coastal waters of northwestern Taiwan, covering a 95 km stretch of coastline and extending 40 km offshore (119.5°–121.5°E, 23.5°–25.5°N). The study area includes ecologically sensitive zones such as mangroves, wetlands, and coral reef ecosystems. We assessed key oceanographic parameters—Sea Surface Height (SSH), Sea Surface Temperature (SST), Sea Surface Salinity (SSS), and Sea Surface Current (SSC)—using a combination of satellite and in situ data. The Diffuse Attenuation Coefficient at 490 nm (Kd490) and chlorophyll-a (Chla) concentrations evaluated water turbidity and biological productivity. To enhance the spatial resolution of these parameters, we incorporated high-resolution data from the Second-Generation Global Imager (SGLI) on the GCOM-C satellite, alongside multi-satellite Chla and SST data. Data analysis from 1993 to 2023 revealed significant trends, with SST and SSH increasing by 0.02°C and 0.003 m per year, respectively. In contrast, SSS exhibited a declining trend of 0.006 psu annually. These changes are likely driven by increased freshwater input and altered circulation patterns, aligning with regional and global warming trends. At 8 km nearshore over the past 31 years, SSH exhibited a minimum of 0.44 m in December 1993 and a maximum of 0.7 m in September 2023. SST peaked at 31.51°C in August 2022 and exhibited a minimum of 17.49°C in January 2021. SSS recorded its highest (34.85 psu) in March 1993 and its lowest value (31.82 psu) in September 2014. Kd490 and Chla concentrations displayed seasonal climatology fluctuations from 2003 to 2023, with lower values in July (0.06 m⁻¹, 0.45 mg m⁻³) at 8 km offshore and higher values in May and July (0.29 m⁻¹, 3.79 mg m⁻³) at 4 km nearshore. These findings, reflecting changes in nutrient availability and oceanographic conditions driven by seasonal currents and highlighting the dynamic nature of the region's coastal ecosystems and their sensitivity to both climatic and oceanographic influences, pose significant risks to Taiwan's marine ecosystems. This research offers a comprehensive analysis of the coastal environment in northwestern Taiwan, providing a scientific basis for climate change adaptation strategies. By identifying the need to balance development and conservation, the study emphasizes the importance of implementing algal reef protection, coastal forest restoration, marine protected area establishment, and coastal development regulations.