Climate warming risk assessment for underwater cultural heritage: Quantifying environmental parameters on historic shipwrecks in the Taiwan Strait

Underwater Cultural Heritage (UCH) represents invaluable records of past maritime activity, yet it faces growing threats from climate change and associated environmental extremes. This study develops a climate-induced risk assessment framework to evaluate the vulnerability of UCH in the Taiwan Strait, with case studies of two representative shipwrecks in the Penghu region: General No.1, an 18th–19th century wooden trade vessel, and the Warship Guang Bing, a late 19th century ironclad. Using multi-scale dynamic and empirical downscaling of Coupled Model Intercomparison Project Phase 6 (CMIP6) climate projections (historical: 1985–2014; SSP2-4.5: 2040–2069), we analyzed three critical environmental stressors: temperature, current velocity, and seawater acidity (pH). The results show that climate-driven extremes in temperature and pH will substantially increase in frequency and intensity, which will amplify the risk of corrosion, biological degradation, and material fragility. Meanwhile, changes in current velocity will remain relatively minor. Probabilistic risk analyses reveal that acidification poses the fastest-growing hazard, especially for metal-rich sites like Warship Guang Bing. Meanwhile, increasing temperatures significantly endanger organic and composite materials, such as wood, at General No. 1. Integrating empirical modeling with archaeological vulnerability assessments, this study identifies priority areas for adaptive conservation strategies and highlights key environmental stressors. These findings lay the methodological groundwork for linking climate science with cultural heritage management and highlight the urgency of incorporating climate adaptation into UCH preservation policies.