Decadal Variability of Precipitation over
Western North America
Daniel R. Cayan, Michael D. Dettinger, Henry F. Diaz, and Nicholas Graham
Journal of Climate, 11, 3148-3166.
Decadal (> 7 yr period) variations of precipitation over western North
America account for 20% - 50% of the variance of annual precipitation.
Spatially, the decadal variability is broken into several regional [O(1000 km)]
components. These decadal variations are contributed by fluctuations in
precipitation from seasons of the year that vary from region to region and
that are not necessarily concentrated in the wettest season(s) alone.
The precipitation variations are linked to various decadal atmospheric
circulation and SST anomaly patterns where scales range from regional
to global scales and that emphasize tropical or extratropical connections,
depending upon which precipitation region is considered. Further, wet or
dry decades are associated with changes in frequency of at least a few
short-period circulation "modes" such as the Pacific-North America
pattern. Precipitation fluctuations over the southwestern United States
and the Saskatchewan region of western Canada are associated with extensive
shifts of sea level pressure and SST anomalies, suggesting that they are
components of low-frequency precipitation variability from global-scale
processes. Consistent with the global scale of its pressure and SST connection,
the Southwest decadal precipitation is aligned with opposing precipitation
fluctuations in northern Africa.