Decadal variability of precipitation over western North America

Decadal (>7- yr period) variations of precipitation over western North Amer ica account for 20%-50% of the variance of annual precipitation. Spatially, the decadal variability is broken into several regional [O(1000 km)] compo nents. These decadal variations are contributed by fluctuations in precipit ation from seasons of the year that vary from region to region and that are not necessarily concentrated in the wettest season(s) alone. The precipita tion variations are linked to various decadal atmospheric circulation and S ST anomaly patterns where scales range from regional to global scales and t hat emphasize tropical or extratropical connections, depending upon which p recipitation region is considered. Further, wet or dry decades are associat ed with changes in frequency of at least a few shea-period circulation "mod es" such as the pacific-North American 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 a nomalies, suggesting that they are components of low-frequency precipitatio n variability from global-scale climate processes. Consistent with the glob al scale of its pressure and SST connection, the Southwest decadal precipit ation is aligned with opposing precipitation fluctuations in northern Afric a.