Coupling snowpack and groundwater dynamics to interpret historical streamflow trends in the western United States

Abstract

A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. During the last century in the western United States, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter and a decline in the summer. Previous work has identified elevation as it relates to snowpack dynamics as the primary control on streamflow sensitivity to warming. But along with changes in the timing of snowpack accumulation and melt, summer streamflows are also sensitive to intrinsic, geologically mediated differences in the efficiency of landscapes in transforming recharge (either as rain or snow) into discharge; we term this latter factor drainage efficiency. Here we explore the conjunction of drainage efficiency and snowpack dynamics in interpreting retrospective trends in summer streamflow during 1950–2010 using daily streamflow from 81 watersheds across the western United States. The recession constant (k) and fraction of precipitation falling as snow (Sf) were used as metrics of deep groundwater and overall precipitation regime (rain and/or snow), respectively. This conjunctive analysis indicates that summer streamflows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. During the spring, however, watersheds that drain rapidly and receive precipitation as snow are most sensitive to climate warming. Our results indicate that not all trends in western United States are associated with changes in snowpack dynamics; we observe declining streamflow in late fall and winter in rain‐dominated watersheds as well. These empirical findings support both theory and hydrologic modelling and have implications for how streamflow sensitivity to warming is interpreted across broad regions. Copyright © 2012 John Wiley & Sons, Ltd.

Watershed Response to Climate Change and Fire-Burns in the Upper Umatilla River Basin, USA

“…SWE/P substantially decreases with each time period, indicating a hydrologic regime shift from a snow-rain-dominated to a rain-dominated basin. This is consistent with predictions in the Pacific Northwest [5,14,[64][65][66][67][68]. Vynee et al [65] predicted SWE to decrease more than 50% by the 2080s in the URB.…”

“…This could be due to varying energy balances at the land and atmosphere interface, including radiative fluxes and changes in albedo, which can significantly influence the melting snow rate and the intensity of reflection by snow cover. Albedo was observed to be higher after a forest fire and lower after afforestation [68]. Further analysis of montane snowpacks that store winter precipitation and provide water for the rest of the year is required for climate adaptation planning in dam water releases and flood control [27].…”

Parameterizing sub-surface drainage with geology to improve modeling streamflow responses to climate in data limited environments

“…Using only the end-member drainage parameters from the WC for the SF watershed resulted in greater and more variable estimates of the reductions in spring fraction of flow with warming relative to estimates using only HC drainage parameters, suggesting that greater drainage rates associated with WC geology enhance the sensitivity of the spring fraction of flow to warming. These results are consistent with our earlier model-based analysis which demonstrated that greater subsurface drainage rates in snow dominated catchments in the Western US tended to increase spring sensitivity to warming and decrease summer streamflow sensitivity (Tague and Grant, 2009;Safeeq et al, 2012). We note that differences in SF response across drainage parameters are solely due to the effect of subsurface effective conductivity/drainage rates since all other factors, including topography and changes in snow accumulation and melt, are held constant across the warming scenarios (Fig.…”

A hydrogeologic framework for characterizing summer streamflow sensitivity to climate warming in the Pacific Northwest, USA

“…Historical streamflow analysis across the western US underscores the importance of both climatic and geologic controls on streamflow response to climate change (Safeeq et al, 2013). Accordingly, approaches that capture both climatic and geologic controls are needed to identify landscape-level streamflow vulnerability to changing climate.…”

“…Climate change will intensify this water scarcity by reducing summer streamflows (Safeeq et al, 2013). Declines have the potential to be acute, due to a combination of observed and predicted shifts in precipitation phases from snow to rain, earlier onset and faster rates of snowmelt, and increased summer evapotranspiration (Mote et al, 2005;Stewart et al, 2005;Nolin and Daly, 2006;Das et al, 2011).…”