Western U.S. Precipitation During Pacific Decadal Oscillation Phase Changes

Water scarcity in the western United States presents a growing challenge to residents of the region, who depend on runoff for drinking water and irrigation. The effects of climate change have only exacerbated the problem, increasing the frequency and intensity of droughts. Consequently, a well-rounded knowledge of precipitation variability could contribute to water management efforts in the West. One source of precipitation variability is the Pacific Decadal Oscillation (PDO), a multidecadal climate pattern based on spatial and temporal characteristics of sea surface temperatures (SSTs) in the northern Pacific Ocean. The PDO has two distinct phases, warm and cold, which are associated with regional precipitation teleconnections in the western US. Unlike the El Niño Southern Oscillation (ENSO), which has a well-defined neutral phase, the period between PDO phases and its associated precipitation impacts are somewhat ambiguous. Teleconnections from other climate variability patterns such as ENSO may complicate relationships between PDO phase, or lack of phase, and precipitation. However, investigating PDO phase changes within the framework of ENSO variations may promote a greater understanding of western US precipitation. In this work, we analyze how the amount and distribution of precipitation varies in the western US during a PDO phase change and if there is a relationship with ENSO variability. Because a PDO phase can last 15-25 years, few instances of a PDO phase change exist in the observational record. As a result, we utilize the Community Earth System Model 2 (CESM2) Large Ensemble to generate a larger sample. An empirical orthogonal function (EOF) analysis of modeled SSTs is used to calculate the PDO index, the basis for defining PDO phases. Using these simulated phase changes, this work evaluates the amount and distribution of precipitation in the western US and its relationship with ENSO.