Century-long annual precipitation time series at 168 stations in the central United States are analyzed with special attention given to interdecadal variations. The results show statistically significant precipitation variations of interdecadal timescales in the region. In particular, one variation has a quasi 20-yr period, and another one possesses a quasi 12-yr period.
The negative phases of the 20-yr variation match with the major drought periods in the region's history, that is, the 1910s, 1930s, 1950s, and the late 1970s. The positive phases of this variation correspond well to the wet periods between the dry epochs. The 12-yr variation shows an amplification after the mid-1960s, while the 20-yr variation shows a reduced amplitude following this time. Concurrent with these changes, the annual precipitation in the region has increased since the mid-1960s.
A plausible mechanism connecting the interdecadal variations of annual precipitation in the central plains region and slow timescale variations in the midlatitude and subtropical North Atlantic regions is briefly discussed.
