INFLUENCES OF PDO AND ENSO ON DISCHARGE FROM COASTAL CALIFORNIA RIVERS

Streamflow is largely dependent on regional climate, which in turn is related to larger scale phenomena occurring in the oceans and the atmosphere. Much work has been done recently to improve our understanding of the El Niño-Southern Oscillation (ENSO) and its relationship to climate and streamflow throughout the United States. More recently the Pacific Decadal Oscillation (PDO) has been characterized as influencing continental climate of North America, with the highest correlation in the Pacific Northwest (Mantua et al., 1997; Latif and Barnett, 1994). PDO events persist for 20 – 30 years, with evidence of reversals in the oscillation occurring around 1925, 1947, 1977 and possibly in 1999.

Here we show that the signature of both ENSO and PDO are evident in annual discharge from coastal California Rivers. For example the Salinas River of central California has significantly higher annual discharge during warm phases of ENSO (El Niño) than during non-El Niño years. This is due to the high likelihood of strong winter storms in central California during El Niño years. During warm phases of the PDO there are also significant increases in annual discharge (cool phases have significant decreases). High flow years during the warm phase of PDO are all El Niño classified years, while El Niño years during cool-phase PDO produce significantly lower discharge. This is likely due to the interaction between the PDO and ENSO, which favors El Niño like conditions during warm PDO phases (Mantua et al, 1997).