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A climatological study of snow covered areas in the western United States




Moore, Cara, author
Kampf, Stephanie K., advisor
Fassnacht, Steven R., committee member
Sibold, Jason S., committee member

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Snow accumulation and timing of melt affect the availability of water resources for the Western United States. Climate warming can significantly impact the hydrology of this region by decreasing the amount of precipitation falling as snow and altering the timing of snowmelt and associated runoff. Therefore, it is essential to characterize how regional climatology affects snow accumulation and ablation and to identify areas that may be especially sensitive to climate warming. This can help resource managers plan appropriately for hydrologic changes. This study utilizes 11-year average (2000 - 2010) MODIS Snow Cover Area (SCA) and Land Surface Temperature (LST) data and annual PRISM precipitation to determine how elevation, slope orientation, latitude, and continentality influence regional characteristics of SCA and LST for early April, early May, early June, and early July in four focus regions: the Colorado Rockies, the Sierra Nevada, the Washington Cascades, and the Montana Rockies. Then, using monthly averages of the 11-year MODIS SCA for January to June, we examine the spatiotemporal evolution of the snowpack and LST throughout the Western U.S. We use threshold values of January to July 11-year average SCA to determine the duration of snow persistence and delineate zones of intermittent, transitional, persistent and seasonal snow. Within the transitional and persistent snow zones, we use 11-year average LST data for January-February-March (LSTJFM) to categorize five different snow sensitivity zones. Areas with the highest winter average land surface temperatures are assumed to be most sensitive to climate warming, whereas areas with the lowest land surface temperature are assumed to be least sensitive. Results show that snow cover tends to increase with increasing elevation, and the elevation of snow cover is lower in higher latitudes, maritime environments, and most western slopes. Land surface temperature tends to decrease with increasing elevation, increasing latitude, and tends to be colder on most western slope sites. The largest divergence between eastern and western slope SCA and LST characteristics is observed in the Sierra Nevada, while little divergence is observed in the Colorado Rockies. Snow cover in the Western U.S. is observed predominantly along two main axes: from north to south along the Cascades and the Sierra Nevada, and from northwest to southeast along the axis of the Rocky Mountain Cordillera. The snow line is lowest in the Washington Cascades and highest in the Colorado Rockies; between these two areas a northwest/southeast elevation gradient is observed. The warmest snow zones (warmest JFMLST) are at lower elevations of the Cascades/Sierra Nevada and in the southwest, whereas coolest snow zones (coldest JFMLST) are in the interior northern Rockies, mid to higher elevations of the Cascades, and the higher elevations of the Colorado Rockies and the Sierra Nevada. The warmest snow zones are likely to be most sensitive to climate warming, as these locations are vulnerable to shifting toward intermittent winter snow cover.


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climate change


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