Assessing climate impacts on river water sources using basin-specific isoscapes: A PNW perspective
On this page:
Climate fluctuation affects the timing, magnitude, and spatial distribution of precipitation and streamflow across continents. Stable isotopes of water are a conservative tracer of hydrologic flows and integrate spatial information about water’s origin. Stable isotopes of precipitation vary spatially, allowing for the creation of isoscapes, maps of the spatial signatures of precipitation. Isoscapes can be used to understand which regions of a watershed are contributing water to larger integrated rivers, and how those water sources are changing over time with climate. We used isoscapes to help understand how and when water sources are changing within major river basins in the Pacific Northwest to identify hydrologically important parts of the landscape. Across the Pacific Northwest, stable isotopes of water in small headwater streams vary strongly with elevation and provide a fingerprint for determining the mean elevation from which water in rivers is derived. Much of the water that people in the Pacific Northwest rely on comes from snowpack in the Cascade Range or other nearby mountain ranges, and their snowpacks are expected to decrease in coming years. Using isoscapes, we explore temporal trends in water originating from high elevation snowpack areas across river basins in Oregon, Idaho, Washington, and Alaska to understand the impact of diminishing snowpack for the region and find not all basins are created equal and that underlying geology plays a strong role in determining watershed vulnerability to snowpack variation. Reconciling the demands between human water-use and biological instream requirements during summer will be challenging under decreasing winter snowpack conditions, emphasizing the need to understand the dynamics of critical water sources that will aid managers in balancing water resource needs.