Analysis of historical extreme coastal water level and its contributors along the South American Pacific coast

Uncertainty in Extreme Coastal Water Levels (ECWL) remains high globally. Along the South American Pacific Coast (SAPC), limited studies hinder effective coastal planning and hazard assessment. This study presents a regional ECWL analysis, including extreme value characterization, their top 5%, and trends for 1993–2019. Results show a median 95th-percentile ECWL of 2.58 m with a standard deviation of 0.92 m, reaching over 5 m in some mid-latitude sectors. ECWL trends exhibit a mean increase of 2.26 mm/yr, primarily driven by regional sea level anomaly variability. Among ECWL components, the upper 2% of wave run-up exerts the strongest influence. Multivariable correlations reveal that large-scale climate oscillations, such as the El Niño Southern Oscillation and the Pacific Decadal Oscillation, explain up to 85% of sea level anomaly variance near the Equator, decreasing to 30% toward southern latitudes. Along the Chilean coast, vertical land motion derived from tide gauges and satellite altimetry indicates uplift rates comparable to or exceeding ECWL trends at co-located sites. These findings demonstrate the combined influence of oceanic variability and crustal motion on ECWL dynamics, underscoring the importance of incorporating both processes into regional hazard evaluation and coastal management strategies.