Citation:

Leibowitz, S., R. Comeleo, P. Wigington, Jr., C. Weaver, P. Morefield, E. Sproles, AND Joe Ebersole. Hydrologic landscape classification evaluates streamflow vulnerability to climate change in Oregon, USA. HYDROLOGY AND EARTH SYSTEM SCIENCES. EGS, 18(9):3367-3392, (2014).

Impact/Purpose:

Hydrologic classification systems can provide a basis for broadscale assessments of the hydrologic functions of landscapes and watersheds and their responses to stressors. Such assessments could be particularly useful in determining hydrologic vulnerability from climate change. A Hydrologic Landscape (HL) classification approach developed by EPA (Wigington et al. 2013) for the State of Oregon is being used to assess streamflow vulnerability due to climate change. Statewide results of this analysis indicate a significant loss of area that currently provides spring or summer snowmelt to area characterized by winter rains and earlier runoff. The study also demonstrates how the climatic and geologic information provided by the HL approach can be applied at three case study basins. In particular, increased winter discharge and reduced summer baseflow could adversely impact winter and summer survival of threatened and non-threatened salmonids. This is especially true for basins such as the Middle Fork John Day, because of high magnitudes of changes in habitat suitability and availability during the summer months. The study serves as a proof-of-concept application that coupling of HL information with climate change projections can provide a vulnerability assessment that informs resource management.

Description:

Classification can allow assessments of the hydrologic functions of landscapes and their responses to stressors. Here we demonstrate the use of a hydrologic landscape (HL) approach to assess vulnerability to potential future climate change at statewide and basin scales. The HL classification has five components: climate, seasonality, aquifer permeability, terrain, and soil permeability. We evaluate changes when the 1971-2000 HL climate indices are recalculated using 2041-2070 simulation results from the ECHAM and PCM climate models with the A2, A1b, and B1 emission scenarios. Changes in climate class were modest (4-18%) statewide. However, there were major changes in seasonality class for five of the six realizations (excluding PCM_B1): Oregon shifts from being 13% snow-dominated to 4-6% snow-dominated under these five realizations, representing a 56-68% reduction in snowmelt-dominated area. At the basin scale, projected changes for the Siletz basin, in Oregon’s coast range, include a small switch from very wet to wet climate, with no change in seasonality. However, there is a modest increase in fall and winter water due to increased precipitation. For the Sandy basin, on the western slope of the Cascades, HL climate class does not change, but there are major changes in seasonality, especially for areas with low aquifer permeability, which experiences a 100% loss of spring seasonality. This would reduce summer baseflow, but effects could potentially be mitigated by streamflow buffering effects provided by groundwater in the high aquifer permeability portions of the upper Sandy. The Middle Fork John Day basin (MFJD), in northeastern Oregon, is snowmelt-dominated. The basin experiences a net loss of wet and moist climate area, along with an increase in dry climate area. The MFJD also experiences major shifts from spring to winter seasonality, representing a 20-60% reduction in snowmelt-dominated area. Altered seasonality and/or magnitude of seasonal streamflows could potentially affect survival, growth and reproduction of salmonids in these watersheds, with greatest effects projected for the MFJD. A major strength of the HL approach is that results can be applied to similarly classified, ungaged basins. Information resulting from such assessments can help inform management responses to climate change at regional and basin scales without requiring detailed modeling efforts

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