Identifying regions with similar hydrology is useful for assessing water quality and quantity, especially in areas that are difficult or costly to monitor. For example, hydrologic landscapes (HLs) have been used to classify and map streamflow variability and assess the impacts of climate in Oregon, Alaska, and the Pacific Northwest. We report on using HLs to assess historic and projected climatic impacts across the Western U.S. We summarize (1) the HL classification methodology, and (2) the utility of HLs to classify the vulnerability of streams to climatic changes. During the HL classification process, we analyzed climate, seasonality, subsurface permeability, terrain, and surface permeability as the primary hydrologic drivers associated with large scale hydrologic processes (storage, conveyance, and flow of water into or out of the watershed). We derived the dominant hydrologic pathways (surface runoff or deep or shallow groundwater) from the HL classification to test our hypotheses: 1) Projected changes in climate will have greater impacts on streamflow in catchments dominated by surface runoff, and 2) Catchments historically fed by spring snowmelt will experience greater impact if winter precipitation falls as rain instead of snow under future climate projections.
Results/Conclusions
A vulnerability index was developed assuming that catchments with projections outside the historic range should be less adapted to future conditions, and therefore more vulnerable to changes in streamflow. Based upon an assessment of streamflow for historic (1901-2000) and modern (1971-2000) conditions, and based upon future climate projections (2041-2070), streams with maximum vulnerability index values had high deviations from the historic mean monthly streamflow. Our results indicate that streams dominated by surface runoff and catchments with spring seasonality are more vulnerable, therefore supporting our hypotheses. Our approach can be used to identify streams vulnerable to changes in streamflow and associated reductions in water quality, which are important for the ecological function of aquatic ecosystems. In collaboration with the Refugia Research Coalition, this research is also being used to identify climate refugia in freshwater stream ecosystems that can be used in support of regional climate adaptation strategies for threatened ecosystems.