Snow Accumulation and Melt Timing at High Elevations in Northwest Montana
The sensitivity of snowmelt driven water supply to climate variability and change is difficult to assess in the mountain west, where strong climatic gradients coupled with complex topography are sampled by sparse ground measurements. We developed a snowmelt model, which ingests daily satellite imagery and meteorological data and is suitable for application to areas greater than 1000 km2, yet captures important spatial variability in steep mountain terrain. We applied the model to the Middle Fork of the Flathead Basin, a 2900 km2 snowmelt-dominated watershed in northwest Montana. Time integration of the melt model yielded a history of snow water equivalent distribution for the years 2000-2008. We found that over 25% of the total annual snow falls above the highest measurement station in the basin, and over 70% falls above the mean elevation of the nine nearest SNOTEL stations. Furthermore, elevation lapse rates in snow water equivalent are variable from year-to-year and are not described by the poorly distributed ground measurements. Consequently, scaling point measurements of snow water equivalent to describe basin conditions leads to significant misrepresentation. Numerical melt simulations performed on the basins peak snow accumulation elucidated the control of temperature variability on snowmelt timing under modern climate and future climate projected by downscaled GCMs. Natural temperature variability affects snowmelt timing on the order of 4 weeks, and plays an even larger role in a warmer climate. Timing of melt in a large snowpack year was found to be more susceptible to natural temperature variability than in a small snowpack year. On average, snowmelt timing occurs 24 days earlier in our projected future climate, but the range of variability is such that an overlap of todays conditions occurs as often as 50% of the time.
Advisor:Joel T. Harper; Johnnie N. Moore; Scott W. Woods
School:The University of Montana
School Location:USA - Montana
Source Type:Master's Thesis
Date of Publication:01/15/2009