The role of ENSO and PDO in variability of winter precipitation over North America from twenty first century CMIP5 projections

We investigate the combined impact of ENSO and PDO on North American winter climate in current and future climate projections from 11 global models in the Climate Model Intercomparison Project Phase 5 (CMIP5) dataset. We first analyze winter sea surface temperature, sea level pressure (SLP) and precipitation anomalies for the historical period 1951–2005, and find that the CMIP5 models reproduce well the constructive interference between ENSO and the PDO compared to observations (i.e. positive ENSO and PDO or negative ENSO and PDO). On the other hand, the destructive interference (positive ENSO and negative PDO or negative ENSO and positive PDO) is less accurately reproduced. Consistently with observations, ENSO events show generally more impact on North American winter climate than PDO events, although there is a robust increase of rainfall in the Southeastern US during the negative PDO phase. For the twenty first century projections, we focus on the 2050–2099 period under the RCP8.5 greenhouse gas concentration scenario and we find an overall strengthening of both the ENSO and PDO signals, and particularly the PDO one, on the SLP and related teleconnections. This results in an enhanced influence of the negative PDO phase on flood conditions in the Southeastern United States, and in drier conditions over the Southwest coasts of North America.