Brooks J Renée, Johnson Henry M, Johnson Keira, Cline Steven P, Comeleo Randy, Rugh William, Trine Lisandra
U.S. Environmental Protection Agency, Office of Research and Development, Center for Public Health and Environmental Assessment, Pacific Ecological Systems Division.
College of Forestry, Forest Ecosystems and Society, Oregon State University, Corvallis, OR, USA.
Hydrol Process. 2025 May 4;39(5). doi: 10.1002/hyp.70136.
Snowpacks are an important water source for mountainous rivers, world-wide. The timing and volume of streamflow in systems reliant on snowmelt can be affected by changes in snow accumulation and melt time. In the Cascade Range (western USA), seasonal snowpacks are predicted to decrease by over 50% within the next century. During the last decade, Cascade Range snowpacks have varied between 17% and 150% of the median 1981-2023 peak snowpack values. To understand how snowpack variation could affect Willamette River streamflow, we monitored water stable isotopes over 13 years from two sites on the mainstem and 60 streams draining small catchments across the Willamette River Basin. Small catchment water stable isotope values integrated and dampened variation in precipitation isotopes, and varied with elevation, providing a marker for determining the mean elevation from which streamflow in the Willamette River was derived. During winter, while snow accumulated in the mountains, most streamflow in the Willamette River originates from rainfall at lower elevations. During summer low-flow conditions, most streamflow in the river was derived from winter snow that accumulated at elevations above 1200 m, which represents <12% of the Willamette River Basin area. Peak snow water equivalent from the previous winter was positively correlated with the proportion of Willamette River streamflow derived from >1200m during the summer low-flow period, but both high elevation (>1200m) precipitation and temperature trends explained nearly as much variance as snow water equivalent. However, after accounting for climate trends, the estimated amount of high-elevation streamflow in the Willamette River during summer low-flow has decreased over the past 13 years. Improved understanding of the origin of, and trends in, summer streamflow in the Willamette River will aid in reconciling human demands with biological instream requirements during periods of low snowpack.
在全球范围内，积雪是山区河流的重要水源。依赖融雪的水系中，河流流量的时间和总量可能会受到积雪量和融化时间变化的影响。在美国西部的喀斯喀特山脉，预计下个世纪季节性积雪将减少50%以上。在过去十年中，喀斯喀特山脉的积雪量在1981 - 2023年积雪峰值中位数的17%至150%之间波动。为了解积雪变化如何影响威拉米特河的流量，我们在13年的时间里，对威拉米特河干流上的两个地点以及该河流域内60条汇入小流域的溪流进行了水稳定同位素监测。小流域水稳定同位素值整合并减弱了降水同位素的变化，并随海拔高度而变化，为确定威拉米特河水流的平均海拔提供了一个指标。冬季，山区积雪时，威拉米特河的大部分水流源于低海拔地区的降雨。在夏季枯水期，河流的大部分水流来自于冬季在海拔1200米以上积累的积雪，而这一区域面积不到威拉米特河流域面积的12%。前一个冬季的积雪水当量峰值与夏季枯水期威拉米特河源于海拔>1200米地区的水流比例呈正相关，但高海拔（>1200米）地区的降水和温度趋势所解释的变化量与积雪水当量几乎相同。然而，在考虑了气候趋势后，过去13年中威拉米特河夏季枯水期高海拔地区的预计径流量有所下降。更好地了解威拉米特河夏季径流的来源和趋势，将有助于在积雪量较低的时期协调人类用水需求与河流生态用水需求。
