ENSO and PDO Trends and Phases and Their Influence on California Climate Variability and Extreme Weather, Including Floods and Droughts

California rainfall and temperatures are influenced by Pacific Ocean climatic indices, such as ENSO and PDO. Precipitation in the state shows strong relationship with ENSO variables, such as SOI, MEI and Niņo 3.4. We find that the ENSO precipitation relationship is strongest to the south of the state and that in some years northern California behaves like the Northwest in a dipole relationship. When the south is wetter than normal, the northwest is drier than normal. However, extreme events, such as floods and droughts do not always match these relationships. Heavy rain events, often associated with atmospheric rivers (ARs), are not as predictably associated with El Niņo's. This study looks at recent PDO influences on climatic patterns in California and examines the predictability of wet and dry periods, including extremes. Heaviest flooding events, often associated with ARs, occur in non-El Niņo years as well as El Niņo years, although total annual rainfall is higher during El Niņo events. Prolonged droughts occur during negative phases of PDO, but are most frequent during La Niņa events. In comparison increasing and decreasing PDO trends show higher correlations with rainfall than PDO phases in S CA. However these PDO relationships were weaker for rainfall than those with SOI, MEI and Niņo 3.4. The PDO was also closely related to statewide temperature variations. The recent global warming hiatus may also be a result of the cool phase in the PDO. Studies such as these can be used by water managers in preparing for future extreme weather events.