Wetlands are globally important ecosystems that provide critical services for natural communities and human society, such as water storage and filtration, wildlife habitat, agriculture, recreation, nutrient cycling, and carbon sequestration. They are also considered to be among the most sensitive ecosystems to climate change, which will exacerbate the already threatened nature of wetlands due to changes in land-use. In montane regions, wetlands are expected to be particularly susceptible to climate-induced changes, but tools to assess the impacts of climate change are severely limited relative to other ecosystem types. To address the need for quantitative assessment tools we developed projections of climate-induced hydrologic changes for a group of montane wetlands in Washington, Oregon, and California based on existing macro-scale hydrologic simulations for the western U.S. The approach relates soil moisture simulated by the hydrologic model to wetland water levels using site-specific regression models fitted to observed wetland data. We then used these models to a) simulate the historical wetland behavior associated with observed climate variability from 1916-2006, and b) assess the impacts of projected climate change on wetlands for the 2040s and 2080s. To better understand landscape scale impacts, we used observed relationships between simulated soil moisture thresholds and drying in summer to construct spatially explicit estimates of probability of drying for intermediate wetlands in the Pacific Northwest for both historical and projected future conditions. Our results show that warmer and drier summers and reduced snowpack associated with climate change are likely to cause earlier wetland drawdown, a more rapid rate of drying, reduced water levels, increased probability of drying, and shortened hydroperiod in montane wetlands, with greatest impacts to biologically productive intermediate hydroperiod wetlands. By the 2080s widespread conversion of intermediate wetlands to ephemeral wetlands is projected in mountain areas in WA.
