A Recent Increase in Western U.S. Streamflow Variability and Persistence

Abstract

April?September streamflow volume data from 141 unregulated basins in the western United States were analyzed for trends in year-to-year variability and persistence. Decadal time-scale changes in streamflow variability and lag-1-yr autocorrelation (persistence) were observed. The significance of the variability trends was tested using a jackknife procedure involving the random resampling of seasonal flows from the historical record. The 1930s?50s was a period of low variability and high persistence, the 1950s?70s was a period of low variability and antipersistence, and the period after 1980 was highly variable and highly persistent. In particular, regions from California and Nevada to southern Idaho, Utah, and Colorado have recently experienced an unprecedented sequence of consecutive wet years along with multiyear extreme droughts.