Abstracts Geography

Spatial accumulation patterns of snow water equivalent in the southern Rocky Mountains

by Thaden Benjamin Von

Only several point measurements may be taken within a given watershed to estimate snow water equivalent (SWE) due to cost limitations, which necessitates basin-scale estimation of SWE. Modeling often assumes consistency in the spatial distribution of SWE, which may not be correct. Identifying patterns and variability in the spatial distribution of SWE can improve snow hydrology models and result in more accurate modeling. Most previous snow distribution studies focused on small domains, less than 10 km. This study examined SWE distribution at a domain of 757 km. This study used variogram analysis for SWE data from 90 long-term SNOTEL stations to determine if a physical distance exists at which snow accumulation patterns across the southern Rocky Mountains vary abruptly. The concurrent accumulation period from SNOTEL stations were paired one-by-one until all 90 stations were compared among each other for all years on record. This comparison generated a relative accumulation slope (relative to the accumulation slope of all other 89 SNOTEL stations from the period of record) and along with physical distance between station pairs, variograms were computed using the semi-variance of the relative accumulation slopes. A physical divide (a break in high-elevation terrain) exists in the topography of the study region that runs East-West about the parallel 38°45’N. Two subset variograms were computed, one by dividing station pairs by their location relative the parallel 38°45’N into a north zone and a south zone, and the second by the pair’s land cover type, specifically evergreen, non-evergreen, or mixed. From the variogram analyses two physical distances were determined (100 and 340 km) at which snow accumulation patterns in the southern Rocky Mountains vary abruptly. There was more variance in snow accumulation south of the 38°45’N parallel, as the zone north of the 38°45’N parallel experiences storm tracks different from the storm tracks that dominate the zone south of this dividing parallel. Land cover was shown to have little effect on snow accumulation patterns. The amount of variability in individual day SWE was found to be correlated to the magnitude of the average SWE among all SNOTEL stations, such that the greater the average SWE, the larger the variability in SWE across the southern Rock Mountains. Advisors/Committee Members: Fassnacht, Steven R. (advisor), Stednick, John D. (committee member), Butters, Gregory (committee member).