The Counteracting Effects of Snowmelt Rate and Timing on Runoff

Abstract

The declining mountain snowpack is expected to melt earlier and more slowly with climate warming. Previous work indicates that lower snowmelt rates are associated with decreased runoff. However, earlier snowmelt could increase runoff via lower vegetation water use in early spring. The relative importance of these factors with regard to runoff is linked to site‐specific conditions such as plant available water storage (PAWS) and energy availability. To disentangle the effects of snowmelt rate and timing on runoff production, we conducted a hydrologic modeling experiment at sites in Colorado (NR1) and California (P301) that controlled for snowmelt rate and timing multicollinearity. We tested the sensitivity of snowmelt season potential runoff (R), changes in subsurface storage (ΔS), and other water budget components to snowmelt rate (smr) and timing (smt) using multiple linear regression and global sensitivity analysis (GSA). Regression results confirmed that R was governed by the competing influence of smr and smt. At both sites, ΔS was more sensitive to smt than smr while R was more sensitive to smr at P301 and to smt at NR1, reflecting energy limitation at NR1. GSA analyses mirrored the regressions for R, confirming that smt was more important at NR1 than P301. This work suggests that runoff increases from earlier snowmelt may counteract runoff losses due to slower snowmelt and that this process is mediated by PAWS and energy availability. These results suggest that R will be more susceptible to future changes in smr and smt at sites with greater PAWS and available energy.

Future land cover and climate may drive decreases in snow wind‐scour and transpiration, increasing streamflow at a Colorado, USA headwater catchment

“…This pattern fits in part with Jeton et al (1996) where increased streamflow was associated with earlier water availability because vegetation may not be able to utilize water inputs early in the season due to phenological limitations. Barnhart et al (2020) also found that runoff from this site was more sensitive to changes in snowmelt timing than to changes in snowmelt rate and that earlier snowmelt resulted in increased runoff. The increase in streamflow by 2100 observed in Como Creek may be partially attributable to this process as we observed a 5 and 10 mm decrease in ET by 2100 under MP and LP scenarios, respectively, and an increase in streamflow (Table 3).…”

Spatial and Temporal Shifts in Historic and Future Temperature and Precipitation Patterns Related to Snow Accumulation and Melt Regimes in Alberta, Canada

“…Annual streamflow is positively related to the percentage of total precipitation that falls as snow [83,84]; therefore, a decrease in snowfall fraction is expected to elicit a nonlinear hydrologic response. Additionally, an earlier onset of spring temperatures may not result in a detectably earlier spring freshet as energy limitations during late winter and early spring attenuate snowmelt rates [22,25] or weaken relationships between snowpack and spring hydrology [26,27]. Spring runoff should be monitored and evaluated for changes in magnitude and climatehydrologic coupling.…”

“…Although several studies have detected an earlier spring freshet [23,24], there is not a simple linear relationship between rising temperatures, snowmelt, and hydrologic responses. Due to solar energy limitations during winter and early spring, rising temperatures and an earlier onset of above-freezing temperatures result in a slower rate of snowmelt [22,25], effectively weakening relationships between snowpack regimes and spring hydrology [26,27].…”

Efficiency of the Summer Monsoon in Generating Streamflow Within a Snow‐Dominated Headwater Basin of the Colorado River

“…For example, competing processes of canopy interception and sheltering from winds and solar radiation suggest forests with intermediate tree density promote greater snow accumulation and a later peak SWE (Broxton et al, 2015; Musselman et al, 2008). In turn, snow persistence has been found to produce more rapid snowmelt to induce soil saturation (Trujillo & Molotch, 2014), after which water can move vertically as recharge or laterally through the soil zone as interflow to promote more streamflow (Barnhard et al, 2020; Barnhart et al, 2016). Lateral movement of water is largely a function of soil storage and water holding capacity (Xiao et al, 2019) and initial soil moisture content, such that soil moisture observations can improve streamflow forecasts (Crow et al, 2018; Mahanama et al, 2012; Shahrban et al, 2018).…”