Physiographic and climatic controls on snow cover persistence in the Sierra Nevada Mountains

The persistence of snow cover across mountainous landscapes influences land-atmosphere energy exchange, water availability, the partitioning of snowmelt into various hydrologic pathways, vegetation productivity, and fluxes of nutrients. Understanding the processes controlling snow cover persistence has been limited as relationships between physiography, climate, and snow persistence are nonlinear and difficult to characterize empirically. The work detailed herein uses 7 years of remotely sensed snow cover persistence observed from the Moderate Resolution Imaging Spectroradiometer over the Sierra Nevada Mountains as a dependent variable in binary regression tree models with a suite of independent variables comprised of both physiographic and climatic metrics. Annual snow cover persistence over 2001-2007 revealed significant inter-annual variability, with domain-average snow persistence values exceeding 4.01 (i. e. early April) in the wettest year of 2005 and reaching as low as 2.90 (i. e. late February) in the driest year of 2007. Regression tree models revealed that elevation was the most important explanatory variable regarding snow cover persistence, ranking first in the hierarchical models in 10 out of 13 watersheds. Precipitation (Feather and Owens River basins) and temperature (Kern River basin) were the first-ranking variables in the remaining three watersheds. Second, the order variables of importance included vegetation, which ranked between 2nd and 5th in 10 of 13 watersheds, and slope, which ranked 4th and 5th in 12 of the 13 watersheds. Interestingly, solar radiation and aspect were of tertiary importance but were more influential in watersheds with north-south orientation (e. g. in the Feather, Mokelumne and Stanislaus watersheds). These results have implications for understanding the sensitivity of snow cover persistence to changes in climate as watersheds where elevation and/or temperature strongly influence snow cover persistence may be more sensitive to future warming. Further work is needed to identify associated ecosystem sensitivities to future changes in snow cover persistence. Copyright (C) 2014 John Wiley & Sons, Ltd.