|LUCE, CHARLES - Us Forest Service (FS)|
|WENGER, SETH - University Of Georgia|
|BERGHUIJS, WOUTER - University Of Bristol|
Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2016
Publication Date: 7/2/2016
Citation: Kormos, P.R., Luce, C.H., Wenger, S.J., Berghuijs, W.R. 2016. Trends and sensitivities of low streamflow extremes to discharge timing and magnitude in pacific northwest mountain streams. Water Resources Research. doi:10.1002/2015WR018125.
Interpretive Summary: Historical stream flow data from the Pacific Northwest shows that low flows have been more sensitive to precipitation amounts than to air temperatures. This is important for planning because models of future precipitation and air temperature are often skillful at predicting temperature but not at predicting precipitation in the Pacific Northwest. Low stream flows from the majority of catchments in this study have declined from 1948 to 2013, which may significantly affect ecosystems, water resource management, and wild fire behavior. Trends in mean annual stream flow have declined and the timing of the stream flow has occurred earlier in response to snow melting earlier. We quantify the relative influences of total precipitation and air temperature on the annual low stream flows from 42 stream gauges using mean annual stream flow to represent precipitation amount effects and stream flow center of timing to represent temperature effects on low flows, including 7q10 summer, mean August, mean September, mean summer, 7q10 winter, and mean winter flow metrics. Winter low flow metrics are not very sensitive to mean annual stream flow or center of timing.
Technical Abstract: Historical streamflow data from the Pacific Northwest indicate that the precipitation amount has been the dominant control on the magnitude of low streamflow extremes compared to the air temperature-affected timing of snowmelt runoff. The relative sensitivities of low streamflow to precipitation and temperature changes have important implications for adaptation planning because global circulation models produce relatively robust estimates of air temperature changes but have large uncertainties in projected precipitation amounts in the Pacific Northwest. Low streamflow extremes from the majority of catchments in this study have declined from 1948 to 2013, which may significantly affect terrestrial and aquatic ecosystems, water resource management, and wild fire behavior. Trends in the 25th percentile of mean annual streamflow have declined and the center of timing has occurred earlier. We quantify the relative influences of total precipitation and air temperature on the annual low streamflow extremes from 42 stream gauges using mean annual streamflow as a proxy for precipitation amount effects and streamflow center of timing as a proxy for temperature effects on low flow metrics, including 7q10 summer, mean August, mean September, mean summer, 7q10 winter, and mean winter flow metrics. Winter low flow metrics are weakly tied to both mean annual streamflow and center of timing.