Citation:

Jones, C., S. Leibowitz, K. Sawicz, R. Comeleo, L. Stratton, AND P. Wigington. Using hydrologic landscape classification to assess streamflow vulnerability to changes in climate. 7th Annual Northwest Climate Conference, Stevenson, Washington, November 14 - 16, 2016.

Impact/Purpose:

Hydrologic landscape (HL) classification is an active area of research on regional and national scales in the United States. EPA’s Western Ecology Division continues to expand a framework for defining areas of the landscape that are hypothesized to have similar hydrologic responses. The concept has been or is being used to make spatially distributed assessments of variability in streamflow and climatic response in Oregon, Alaska, and the Pacific Northwest (PNW), and is currently being applied to the Southwestern U.S (SW). In our research, we are analyzing historic climate models and future climate projections to assess how changes in climate affect hydrologic processes and their associated impacts (e.g. water resource availability, ecological impacts, etc.) across the PNW and the SW. The HL classification process analyzes the primary drivers (climate, seasonality, aquifer permeability, terrain, and soil permeability) that are associated with large scale hydrologic processes (storage, conveyance, and flow of water into or out of the watershed). In this analysis, we summarize (1) the HL classification methodology and (2) the utility of using HLs as a tool to classify the vulnerability of streams to climatic changes in the Western U.S. This conference will allow us to present the Hydrologic Landscapes methodology to an audience that is specifically interested in multidisciplinary implications of this research and will provide feedback our modeling approach and the Hydrologic Landscapes methodology. This work helps address the issue of vulnerability of hydrologic landscapes and streamflow to climate change under ACE Task MA-1 249 by expanding utility of the hydrologic landscape classification tool.

Description:

Identifying regions with similar hydrology is useful for assessing water quality and quantity across the U.S., especially areas that are difficult or costly to monitor. For example, hydrologic landscapes (HLs) have been used to map streamflow variability and assess the spatial distribution of climatic response in Oregon, Alaska, and the Pacific Northwest. HLs have also been applied to assess historic and projected climatic impacts across the Western U.S. In this project, we summarized (1) the HL classification methodology and (2) the utility of using HLs as a tool to classify the vulnerability of streams to climatic changes in the Western U.S. During the HL classification process, we analyzed climate, seasonality, aquifer permeability, terrain, and soil permeability as the primary hydrologic drivers (and precipitation intensity as a secondary driver) associated with large scale hydrologic processes (storage, conveyance, and flow of water into or out of the watershed) in the West. We derived the dominant hydrologic pathways (surface runoff or deep or shallow groundwater) from the HL classification of different catchments to test our hypotheses: 1) Changes in climate will have greater impacts on streamflow in catchments dominated by surface runoff. 2) Catchments historically fed by surface runoff from winter snowmelt in the spring will experience greater impact if precipitation falls as rain instead of snow. We calculated S* (precipitation surplus, which includes snowmelt runoff) as a proxy for streamflow for watersheds across the landscape under historic (1901-2000), modern (1971-2000), and future climate projections (2041-2070) to determine whether future projections of S* fall outside of the range of historic S*. Catchments with projections outside the historic range may be more vulnerable to changes in streamflow. Our results indicate that streams dominated by surface runoff and catchments with spring seasonality are more vulnerable to climatic changes. This approach can be used to identify streams that are vulnerable to changes in streamflow and associated reductions is water quality, which are of important for the ecological function of aquatic ecosystems throughout the U.S.

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