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Climate Impacts on Source Contributions and Evaporation to Flow in the Snake River Basin Using Surface Water Isoscapes (δ2H and δ18O)
Citation:
Windler, G., J. Renee Brooks, H. Johnson, R. Comeleo, R. Coulombe, AND G. Bowen. Climate Impacts on Source Contributions and Evaporation to Flow in the Snake River Basin Using Surface Water Isoscapes (δ2H and δ18O). WATER RESOURCES RESEARCH. American Geophysical Union, Washington, DC, 57(7):e2020WR029157, (2021). https://doi.org/10.1029/2020WR029157
Impact/Purpose:
Climate fluctuation affect the timing, magnitude and spatial distribution of precipitation and streamflow across the continent, and monitoring tools are needed to help managers understand these changes. Stable isotopes are a conservative tracer of hydrologic flows, and integrate spatial information about the water’s origin. Stable isotopes of precipitation vary spatially, allowing for the creation of isoscapes: a map of the spatial signatures of precipitation. This tracer 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. We created an isoscape of the Snake River Basin to help understand how and when water sources are changing across the basin to identify hydrologically important parts of the landscape. Longitude and elevation were the dominant drivers of isotopic variation across the basin. The stable isotopes revealed that water originated from a very small eastern mountains section of the basin most of the time, but particularly during low flows. High snowpack years with high flows shifted the origin of water to include more of the basin contributing to flow. This work reveals the vulnerability of the Snake River Basin to expected changes in mountain snowpacks.
Description:
Rising global temperatures are expected to decrease the precipitation amount that falls as snow, causing greater risk of water scarcity, groundwater overdraft, and fire in areas that rely on mountain snowpack for their water supply. Streamflow in large river basins varies with the amount, timing, and type of precipitation, evapotranspiration, and geologically mediated drainage properties of watersheds; however, these controls vary in time and space making it difficult to identify the areas contributing most to flow and when. In this study, we address this problem by separating the evaporative influences from source values of water isotopes from the Snake River Basin in the western United States (US) to relate source area to flow dynamics. We developed isoscapes (δ2H and δ18O) for the Snake Basin and found that surface water isotopes of small watersheds are primarily controlled by longitude and elevation via Rayleigh distillation. To examine temporal variability in source contribution to flow, we present a six-year record of water isotopes from King Hill, Idaho with evaporative influences removed. During periods of low flow, source water values were isotopically lighter and evaporation exerted greater influence, indicating longer surface transport times and restriction of flow-contributing areas to the highest elevation, far eastern fringe of the basin. Our findings present a potential tool for identifying watersheds that are vulnerable to warming temperatures and a framework for understanding flow contributions in other continental-interior basins of the western US where river evaporation may obscure source water isotopic signatures.
URLs/Downloads:
DOI: Climate Impacts on Source Contributions and Evaporation to Flow in the Snake River Basin Using Surface Water Isoscapes (δ2H and δ18O)