Oregon Sea Grant

Climate change impacts on extreme water levels (WLs) at two United States Pacific Northwest estuaries are investigated using a multicomponent process-based modeling framework. The integrated impact of climate change on estuarine forcing is considered using a series of sub-models that track changes to oceanic, atmospheric, and hydrologic controls on hydrodynamics. This modeling framework is run at decadal scales for historic (1979–1999) and future (2041–2070) periods with changes to extreme WLs quantified across the two study sites. It is found that there is spatial variability in extreme WLs at both study sites with all recurrence interval events increasing with further distance into the estuary. This spatial variability is found to increase for the 100-year event moving into the future. It is found that the full effect of sea-level rise is mitigated by a decrease in forcing. Short-recurrence-interval events are less buffered and therefore more impacted by sea-level rise than higher-return interval events. Finally, results show that annual extremes at the study sites are defined by compound events with a variety of forcing contributing to high WLs.