Snowmelt rate and continuity determine the intra-annual variability and
magnitude of streamflow in three alpine watersheds in the western U.S.
In semiarid to arid regions of the western U. S., the availability and
variability of river flow are highly subject to shifts in snow
accumulation and ablation in alpine watersheds. This study aims to
examine how shifts in snowmelt rate (SMR) and snow continuity, an
indicator of the consistent existence of snow on the ground, affect
snow-driven streamflow dynamics in three alpine watersheds in the U.S.
Great Basin. To achieve this end, the coupled hydro-ecological
simulation system (CHESS) is used to simulate river flow dynamics and
multiple snow metrics are calculated to quantify the variation of
snowmelt rate and snow continuity, the latter of which is measured,
respectively, by snow persistence (SP), snow residence time (SRT) and
snow season length (SSL). Then, a new approach is proposed to partition
streamflow into snow-driven and rain-driven streamflow. The statistical
analyses indicate that the three alpine watersheds experienced a
downward trend in SP, SRT, SSL and SMR during the study period of
1990-2016 due to regional warming. As a result, the decrease in SMR and
the decline in snow continuity shifted the day of 25% and 50% of the
snow-driven cumulative discharge as well as peak discharge toward an
earlier occurrence. Besides, the magnitudes of snow-driven annual
streamflow, summer baseflow and peak discharge also decreased due to the
declined snow continuity and the reduced snowmelt rate. Overall, by
using multiple snow and flow metrics as well as by partitioning
streamflow into snow-driven and rain-driven flow via the newly proposed
approach, we found that snowmelt rate and snow continuity determine the
streamflow hydrographs and magnitudes in the three alpine watersheds.
This has important implications for water resource management in the
snow-dominated region facing future climate warming given that warming
can significantly affect snow dynamics in alpine watersheds in semiarid
to arid regions.