Climate Change Analysis on Extreme Precipitation over Three Watersheds in Northern California Based on 137-Year Long-Term Dynamical Downscaling

Long-term historical precipitation over Northern California was reconstructed for 137 water years from October, 1871 through September, 2008 by dynamical downscaling based on NOAA Twentieth Century Reanalysis version 2 (20CRv2). The annual maximum values of 6-, 12-, 24-, 48-, 72-, and 96-hour basin-average precipitation were obtained from the reconstructed results for three watersheds in Northern California; American River watershed, Yuba River watershed, and Upper Feather River watershed. The reconstructed results for 137 water years are long enough to conduct a moving window analysis. Then, the moving average of annual maximum basin-average precipitation for each duration is calculated based on a 50-year moving window to analyze the trend of annual maximum values of basin-average precipitation. The analysis shows a clear upward trend for the 50-year moving average over all the three watersheds.