Snowmelt rate dictates streamflow

Abstract

Declining mountain snowpack and earlier snowmelt across the western United States has implications for downstream communities. We present a possible mechanism linking snowmelt rate and streamflow generation using a gridded implementation of the Budyko framework. We computed an ensemble of Budyko streamflow anomalies (BSAs) using Variable Infiltration Capacity model‐simulated evapotranspiration, potential evapotranspiration, and estimated precipitation at 1/16° resolution from 1950 to 2013. BSA was correlated with simulated baseflow efficiency (r2 = 0.64) and simulated snowmelt rate (r2 = 0.42). The strong correlation between snowmelt rate and baseflow efficiency (r2 = 0.73) links these relationships and supports a possible streamflow generation mechanism wherein greater snowmelt rates increase subsurface flow. Rapid snowmelt may thus bring the soil to field capacity, facilitating below‐root zone percolation, streamflow, and a positive BSA. Previous works have shown that future increases in regional air temperature may lead to earlier, slower snowmelt and hence decreased streamflow production via the mechanism proposed by this work.

Snowmelt response to simulated warming across a large elevation gradient, southern Sierra Nevada, California

“…The results confirm previous findings in the US Pacific Northwest that the current observing network design may be insufficient in a warmer world (Gleason et al, 2017;Sproles et al, 2017). Warmer temperatures and earlier melt timing (Stewart et al, 2004) also influence the rate of meltwater production (Musselman et al, 2017), a critical determinant of streamflow (Barnhart et al, 2016), forest carbon uptake (Winchell et al, 2016), and flood hazard (Hamlet and Lettenmaier, 2007). Despite a strong negative relationship between temperature and elevation, we show a positive relationship between elevation and seasonal snowmelt rates.…”

“…Snowmelt rates have been mechanistically linked to streamflow production (Barnhart et al, 2016), but less understood are the potential implications of climate-induced changes in snowmelt rates on subsurface water storage, evapotranspiration, and streamflow response. For example, recent empirical evidence that a precipitation shift from snow towards rain will lead to a decrease in streamflow (Berghuijs et al, 2014) lacks definitive causation.…”

“…The 15 mm day −1 threshold was selected as a compromise between the 12.5 mm day −1 threshold above which positive streamflow anomalies were reported by Barnhart et al (2016) and a 20 mm day −1 classification of very heavy rainfall (Klein Tank et al, 2009) used by Musselman et al (2017). To examine how daily snowmelt rates respond to simulated warming, we present a quantile analysis of the 25th, 50th, 75th, 90th, 95th, and 99th percentiles of daily snowmelt rates ≥ 1 mm day −1 from the warmer scenarios compared to those from the nominal case.…”

“…Rapid and prolonged spring snowmelt is unique to these mountain environments (Trujillo and Molotch, 2014). This efficient runoff generation mechanism (Barnhart et al, 2016) produces water resources of vast economic importance (Sturm et al, 2017). Improved understanding of regional elevation-dependent snowmelt response to warming is a key step toward better predicting and interpreting model estimates of basin-wide runoff.…”

Now You See It Now You Don’t: A Case Study of Ephemeral Snowpacks in the Great Basin U.S.A.

“…In addition to stressing local vegetation, ephemeral snowmelt may reduce groundwater recharge and streamflow. For example, baseflow contributions 5 to streamflow and overall water yield declined when snowmelt rates were smaller (Barnhart et al, 2016;Earman et al, 2006;Trujillo and Molotch, 2014), and overall water yields were lower in basins receiving more rain and less snow (Berghuijs et al, 2014). Changes in percolation patterns also affect the distribution of more shallow rooting plants versus deeper rooting plants that need long duration moisture pulses to grow and reproduce (Schwinning and Sala, 2004).…”