ENSO modulates rainfall in the Mediterranean Californias

A remarkable correlation is found between the total annual rainfall at Ensenada and the annual signal of the Southern Oscillation Index by suitably averaging their corresponding monthly series and dephasing the indices by four months. The result confirms the suspected-dominant influence of El Nino-Southern Oscillation (ENSO) in the interannual weather fluctuations of mid-latitude mediterranean climates and shows that their strongest relationship lies close to the annual signal. Since a particularly strong EI Nino developed in the Pacific, rainfall in the Ensenada to San Diego area has exceeded twice its long term average during the 1997-98 season. Similarly, as this event fades out, the 1998-99 rain season should be sligthly below normal, i.e. rainfall should be somewhat below half that of the previous year.