Climate Effects of Pacific Decadal Oscillation on Streamflow of the Feather River, California

The timing of maximum monthly-mean streamflow for the Feather River in northern California has come earlier in the year in recent decades (since the 1950s), as have timings in most rivers throughout California and the western United States. Much of the timing shift in the Feather River basin appears to coincide with interdecadal changes in the North Pacific climate regime. The coincident timing changes are seen as a shift in the month of maximum streamflow from April-May during the cooler Pacific Decadal Oscillation (PDO) phase to March-April during the warmer phase. The change in streamflow timing in the Feather River basin became an issue during the testing of a new set of watershed models of inflow to Lake Oroville, because model performance degraded in simulations of recent years (1998-2001). The model calibration period (1971-97) was dominated by the warmer (1977-98) PDO phase. However, the 1998-2001 period mostly corresponds to a newly reestablished cool PDO (beginning late 1998). Simulations during 1998-2001 failed to reproduce streamflow as well as simulations of the calibration period, probably because some model parameters, like those associated with rain-snow mixes or temperature and precipitation distributions, are not calibrated for climatic conditions that occur during a cool PDO.