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Low Flow

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YG00G2K - Streamflow in the Western United States during the 2015 Drought and the vulnerability of streams to climate change

Problem - Given the hydrologic conditions in 2015, watersheds where snowmelt is the primary source of groundwater recharge and streamflow recedes rapidly over the summer are likely more vulnerable to low streamflow. Region wide low streamflow conditions have significant implications for surface water supplies, endangered species, and agriculture and municipal water users. Water users and managers need have information to assess the vulnerability of their groundwater and surface water resources in the context of This information will be use to evaluate whether some types of systems are more vulnerable than others to variability in precipitation and snowpack.

Objectives - This project has three main objectives:

  1. Document streamflow conditions during the late summer in WY 2015 in in California, Idaho, Nevada, Oregon, Utah, and Washington. Include sites in basins with near-normal and below-normal precipitation.
  2. Assess how the change in the dominant form of precipitation from snow to rain in WY 2015 affects low flows in western rivers and streams. Identify types of streams where low flows are most vulnerable and least vulnerable to this type of change in precipitation.
  3. Evaluate whether WY 2015 can serve as a model for potential climate change impacts on late summer water availability in unregulated rivers and streams (no large reservoirs) and alluvial aquifers. Identify uncertainty in using WY 2015 as an analog for climate change.

Relevance and Benefits - This project will document streamflow conditions in the Western U.S. under extreme weather patterns. It will contribute to our understanding of river and stream vulnerability to climate change in the western U.S. by characterizing the sensitivity of base flow to variation in precipitation amount and snowpack. The results will improve the capability of resource managers to anticipate when and where streamflow is likely to reach critically low levels, which can be used to target drought relief efforts.

The proposed low-flow data collection networks included in this multi-State study will support USGS Water Mission Area Strategic Directions Goal 1, Objective 1: to provide society with the information it needs regarding the amount and quality of water in all components of the water cycle at high temporal and spatial resolution, nationwide through the advancement of hydrologic monitoring networks and techniques. The assessment of stream vulnerability to variation in precipitation and snowpack supports Goa1 2, Objective 2: to advance the understanding of processes that determine water availability through the comprehensive understanding of the effects of climate variation on water availability at multiple spatial and temporal scales.

This coordinated regional effort to document and analyze low flows includes significant portion of the United States serving many different communities. Drought is long-standing issue of great socio-economic and ecological interest in the West that is often neglected when other more immediate, short-term events capture people's attention. The usefulness of this data collection effort reaches far beyond this project. It will be important for model development, ecological investigations, and state and local water resource management strategies such as conjunctive use of surface and groundwater.

Approach - The USGS will collect streamflow information across a range of hydrologic systems with respect to WY 2015 precipitation and snowpack, groundwater interactions (discharge to streams), and groundwater recharge sources (hillslope/fluvial, rainfall/snowmelt). The proposed project has two components: extensive synoptic streamflow and water-quality measurements made throughout California, Idaho, Nevada, Oregon, Utah, and Washington during August and September 2015; and the analysis of those measurements and available streamflow records in 2016. A minimum of about 60 measurements in each state is anticipated but will depend on the location of sites and travel time between sites. Additional measurements would be made if additional funding is available. Water temperature will be collected at all sites and specific conductance when possible, depending on meter availability, to provide additional information about sources of base flow.

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Page Last Modified: Thursday, 15-Dec-2016 13:17:00 EST