Multi-Scale Correlation between the Western U.S. Snow Water Equivalent and ENSO/PDO Using Wavelet Analyses

Abstract

This study evaluated the correlation between the western U.S. snow water equivalent (SWE) and two major oceanic-atmospheric indices of the Pacific Ocean, namely, the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), using continuous wavelet transformation and its derivatives. Snow Telemetry (SNOTEL) data for 1 April SWE from 323 sites (out of which 258 are in six hydrologic regions) were obtained for a study period of 56 years (1961–2016). The results showed that ENSO had a much higher influence than PDO throughout the western U.S. SWE across the study period. Both ENSO and PDO showed a higher correlation with SWE at multiple timescale bands across different time intervals, although significant intervals in the higher timescales were of longer duration. ENSO showed a higher correlation in the 10-to-16-years band across the entire study period as well as in the lower timescales. PDO showed a higher correlation below the 4-years band. The relative phase relationship suggested that ENSO led SWE, with certain lags, while both were moving in the same direction in many instances. The lag-response behavior of SWE and PDO was not found to be uniform. The regional analyses, based on the western U.S. hydrologic regions, suggested significant variation across the adjacent regions in terms of their correlation with ENSO/PDO. Association with ENSO was also observed to be higher compared to PDO among the regions. Regions close to the ocean and at lower elevation showed higher correlation compared to the inland regions with higher elevation.