Jul 1, 2016

Historical and Future Relations Between Large Storms and Droughts in California

Dettinger, Michael
San Francisco Estuary and Watershed Science
  • Analyzes the extent to which contributions of the wettest days to overall precipitation dictate the state’s precipitation seasonality and frequent multiyear periods of drought (as precipitation deficit) and plenty is analyzed, historically and in projections of future climates
  • States that the wettest 5% of wet days in California contribute about a third of precipitation but about two-thirds of the variance of water-year precipitation
  • States that year-to-year fluctuations in precipitation strongly reflect year-to-year fluctuations of contributions from the largest storms, with the large-storm contributions explaining about twice as much precipitation fluctuation as do contributions from all remaining storms combined
  • States that this extreme dominance of large storms is largely unique to California within the United States
  • Finds that in climate-change projections, eight of ten climate models considered here yield increases in precipitation from the largest storms, and when the increases are large, total precipitation follows suit
  • Finds that all of the models project declines in contributions from the smaller storms and models projecting total-precipitation declines reflect this decline
  • Projected changes in variance of water-year precipitation reflect changes in variance of large-storm contributions
  • Results indicate that the disproportionately large overall contributions from California’s largest storms, and their outsized year-to-year variability, ensure that the state’s largest storms dictate the state’s regimes of wet and dry spells, historically and in climate-change projections