Variability Common to First Leaf Dates and Snowpack in the Western Conterminous United States

Singular value decomposition is used to identify the common variability in first leaf dates (FLDs) and 1 April snow water equivalent (SWE) for the western United States during the period 1900-2012. Results indicate two modes of joint variability that explain 57% of the variability in FLD and 69% of the variability in SWE. The first mode of joint variability is related to widespread late winter-spring warming or cooling across the entire west. The second mode can be described as a north-south dipole in temperature for FLD, as well as in cool season temperature and precipitation for SWE, that is closely correlated to the El Nino-Southern Oscillation. Additionally, both modes of variability indicate a relation with the Pacific-North American atmospheric pattern. These results indicate that there is a substantial amount of common variance in FLD and SWE that is related to large-scale modes of climate variability.