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 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 separate the evaporative influences from source values of water isotopes from the Snake River basin in the western United States to relate source area to flow dynamics. We developed isoscapes (δ²H and δ¹⁸O) for the basin and found that isotopic composition of surface water in small watersheds is primarily controlled by longitude, latitude, and elevation. To examine temporal variability in source contributions to flow, we present a 6-years record of Snake River water isotopes from King Hill, Idaho, after removing evaporative influences. During periods of low flow, source water values were isotopically lighter indicating a larger contribution to flow from surface waters in the highest elevation, eastern portion of the basin. River evaporation increases were evident during summer likely reflecting climate, changing water availability, and management strategies within the basin. Our findings present a potential tool for identifying critical portions of basins contributing to river flow as climate fluctuations alter flow dynamics. This tool can be applied in other continental-interior basins where evaporation may obscure source water isotopic signatures.

中文翻译：

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使用地表水等值景观（δ2H 和 δ18O）对 Snake 河流域流量的源贡献和蒸发的气候影响

全球气温上升预计将减少以降雪形式出现的降水量，从而在依赖山区积雪供水的地区造成更大的缺水、地下水超采和火灾风险。大河流域的流量随流域降水量、时间和类型、蒸发量和排水特性而变化；然而，这些控制在时间和空间上有所不同，因此很难确定对流动贡献最大的区域和时间。在这项研究中，我们将蒸发影响与来自美国西部蛇河流域的水同位素源值分开，以将源区与流动动力学联系起来。我们开发了 isoscapes（δ ² H 和 δ ¹⁸O) 为盆地，发现小流域地表水的同位素组成主要受经度、纬度和高程控制。为了检查水源对流量的贡献的时间变化，我们提供了爱达荷州 King Hill Snake River 水同位素在去除蒸发影响后的 6 年记录。在低流量期间，源水的同位素值较轻，表明盆地东部最高海拔的地表水对流量的贡献更大。夏季河流蒸发量增加很明显，这可能反映了气候、不断变化的水资源可用性和流域内的管理策略。我们的研究结果提供了一种潜在的工具，用于确定随着气候波动改变流动动态而导致河流流动的流域关键部分。