Variability of Annual Precipitation and Its Relationship to the El Niño–Southern Oscillation

The importance of El Niño–Southern Oscillation (ENSO) to annual precipitation variability is assessed by dividing stations into regions of ENSO and non-ENSO influence as defined by Ropelewski and Halpert and then comparing these regions by Köppen climate type for significant differences in the zone average of the variability of annual precipitation. Of the 13 Köppen climate types that had 10 or more precipitation stations in both ENSO and non-ENSO influenced regions, 8 had significant differences in the zone average of the variability [defined as the coefficient of variation (Cυ)] of annual precipitation with the variability of annual precipitation being higher in the ENSO than the non-ENSO zone in every case. The range of increase in the Cυ of annual precipitation was generally 5%–25%. These results confirm earlier findings in relation to the variability of annual runoff and also are consistent with earlier findings in relation to the variability of annual precipitation. However, the impact of ENSO on variability of annual precipitation of 5%–25% reported in this note is considerably less than the 33%–50% reported previously.