Apr 15, 2005

Changes toward Earlier Streamflow Timing across Western North America

Iris T. Stewart, Daniel R. Cayan, and Michael D. Dettinger
American Meteorological Society
  • States that the highly variable timing of streamflow in snowmelt-dominated basins across western North America is an important consequence, and indicator, of climate fluctuations
  • Investigates changes in the timing of snowmelt-derived streamflow from 1948 to 2002 in a network of 302 western North America gauges by examining the center of mass for flow, spring pulse onset dates, and seasonal fractional flows through trend and principal component analyses
  • States that widespread and regionally coherent trends toward earlier onsets of springtime snowmelt and streamflow have taken place across most of western North America, affecting an area that is much larger than previously recognized
  • States that these timing changes have resulted in increasing fractions of annual flow occurring earlier in the water year by 1–4 weeks
  • States that the immediate (or proximal) forcings for the spatially coherent parts of the year-to-year fluctuations and longer-term trends of streamflow timing have been higher winter and spring temperatures
  • Notes that although these temperature changes are partly controlled by the decadal-scale Pacific climate mode [Pacific decadal oscillation (PDO)], a separate and significant part of the variance is associated with a springtime warming trend that spans the PDO phases