Variability of extreme precipitation events in Tijuana, Mexico

Abstract

We investigated the variability of 1 d precipitation extremes (top 10%) in Tijuana (Mexico) during 1950-2000. Interannual rainfall variability is associated with El Nino/Southern Oscillation (ENSO), which explains 30% of rainfall and 36% of 1 d extreme precipitation variance. Interannual precipitation exhibits a large change, with a relatively dry period and less variability dur- ing 1950-1976, followed by a relatively wet period and more variability during 1976-2000. All extremely wet years (>1 SD) and the largest frequency of 1 d extremes occurred after 1976-1977, with 6 out of 8 extremely wet years characterized by El Nino episodes and 2 by neutral conditions. However, more than half of the 1 d extremes during 1950-2000 occurred in non-ENSO years, providing evidence for the fact that neutral conditions contribute significantly to extreme climatic variability in the region. Extreme events that occur in neutral (strong El Nino) conditions are associ- ated with a 'pineapple express' and a 'neutral Pacific/North America (PNA)' (negative tropical/north- ern hemisphere (TNH)) teleconnection pattern that links an anomalous tropical convective forcing west (east) of the date line with a strong subtropical jet over the study area. The neutral PNA is a vari- ant of the typical ±PNA teleconnection pattern; it is shifted northwestward of the +PNA (typical of El Nino) and southeastward of the -PNA (typical of La Nina) and is characterized by a strong ridge over the Gulf of Alaska and a deep low over California. We believe that the trough in the jet, typical of extreme events during neutral and strong El Nino years, is further intensified by thermal interaction with regional anomalies of a warm California Current off Baja California, low-level moisture advec- tion from the subtropical warm sea-surface region, and intense convective activity over the study area.