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A five year view on the contribution of snowmelt to flow in the Willamette River using water stable isotopes
Citation:
Brooks, J. Renee, H. Johnson, S. Cline, AND W. Rugh. A five year view on the contribution of snowmelt to flow in the Willamette River using water stable isotopes. American Geophysical Union Annual Meeting, San Francisco, CA, December 14 - 18, 2015.
Impact/Purpose:
Much of the water that people in Western Oregon rely on come from the snowpack in the Cascade Mountains, and this snowpack is expected to decrease in coming years with climate change. This work documents recent changes in the snowpack contribution to water within the Willamette River, a primary source of water for human consumption and for endangered aquatic organisms, and highlights the coming challenges as snowpacks decrease with climate change.
Description:
Much of the water that people in Western Oregon rely on come from the snowpack in the Cascade Mountains, and this snowpack is expected to decrease in coming years with climate change. In fact, the past five 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 the 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. The proportion of water from high elevation decreased with decreasing snowpack. We combine this information with the river flow data to estimate the volume reduction related to snow pack reduction during the dry summer months. Observed reductions in the contribution of high elevation water to the Willamette River after just two years of diminished snowpack indicate the hydrologic system responds relatively rapidly to changing snowpack volume. Reconciling the demands between human consumption and off-channel water use for biological instream requirements during summer months will be challenging under climatic conditions in which winter snowpack is reduced compared to historical amounts.