Climatic controls on the snowmelt hydrology of the Northern Rocky Mountains,

Pederson, Gregory; Gray, Stephen; Ault, Toby; Marsh, Wendy; Fagre, Daniel; Bunn, Andrew; Woodhouse, Connie; Graumlich, Lisa

This study investigates oceanic and atmospheric controls underlying changes in timing,variability, and trends documented across the entire hydroclimatic monitoring system within critical NRM watersheds. Analyses were conducted using records from 25 snow telemetry (SNOTEL) stations, 148 April 1 snowcourse records, stream gage records from 14 relatively unimpaired rivers, and 37 valley meteorological stations. Mid-elevation SNOTEL records show a tendency towards decreased regional snowpack with peak snow water equivalent (SWE) arriving and melting out earlier (c.a. 1969). Temperature records show significant seasonal and annual decreases in number of frost days (days ≤ 0°C), and changes in the spring minimum temperatures that correspond with atmospheric circulation changes and surface-albedo feedbacks in March and April. Spring temperatures coupled with increases in mean and variance of spring precipitation are associated with timing of snow melt-out, an increased number of snow-free days, and observed changes in streamflow timing and discharge. The majority of the variability in peak and total annual snowpack and streamflow, however, is explained by season dependent inter-annual to inter-decadal changes in atmospheric circulation associated with Pacific Basin SSTs. Over recent decades, increased spring precipitation appears to be buffering NRM total annual streamflow from what would otherwise be greater snow-related declines. Results have important implications for ecosystems, water resources, and long-lead forecasting capabilities.

Climatic controls on the snowmelt hydrology of the Northern Rocky Mountains,

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