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Climate impacts on connectivity of snowmelt to flow in the Willamette River using water stable isotopes
Citation:
Brooks, J. Renee, H. Johnson, S. Cline, AND W. Rugh. Climate impacts on connectivity of snowmelt to flow in the Willamette River using water stable isotopes. American Water Resources Association¿s 2017 Spring Specialty Conference, Snowbird, Utah, April 30 - May 03, 2017.
Impact/Purpose:
Much of the water that people in Western Oregon rely on comes from snowpack in the Cascade Range, and this snowpack is expected to decrease in coming years with climate change. We have developed an isotopic technique for monitoring the contribution of snowmelt to the Willamette River. The range of variation in snowpack over the last 6 years has informed us as to what to expect in the future when the Cascade snowpack is greatly diminished. This abstract contributes to ACE 249.
Description:
Much of the water that people in Western Oregon rely on comes from snowpack in the Cascade Range, and this snowpack is expected to decrease in coming years with climate change. In fact, the past 6 years have shown dramatic variation in snowpack, from a high of 174% of normal in 2010-11 to a low of 11% for 2014-15, one of the lowest on record. During this timeframe, we have monitored the stable isotopes of water within the Willamette River twice monthly, and mapped the spatial variation of water isotopes across the basin. Within the Willamette Basin, stable isotopes of water in precipitation vary strongly with elevation and provide a marker for determining the mean elevation from which water in the Willamette River is derived. In winter, when snow accumulates in the mountains, low elevation precipitation (primarily rain) contributes the largest proportion of water to the Willamette River. During summer, when rainfall is scarce and demand for water is the greatest, water in the Willamette River is mainly derived from high elevation snowmelt. Our data indicate that the proportion of water from high elevation decreased with decreasing snowpack. We combine this information with river flow data to estimate the volume reduction related to snowpack reduction during the dry summer. Observed reductions in the contribution of high elevation water to the Willamette River after just 2 years of diminished snowpack indicate that the hydrologic system responds relatively rapidly to changing snowpack volume. Reconciling the demands between human use and biological instream requirements during summer will be challenging under climatic conditions in which winter snowpack is reduced compared to historical amounts.