Skill of Global Climate Models in Capturing Dependence of Great Basin Precipitation on Pacific Modes of Variability

Abstract:

It has been shown that Great Basin precipitation is greatly affected by modes associated with the Pacific Ocean, mainly El Nino—Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). We completed an assessment of 20 models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) using historical (1900-2005) monthly model precipitation and sea surface temperature (SST) output. We evaluated model performance of the effects of ENSO and PDO on Great Basin precipitation and compared the results to observations. The results of the study informed a filtering of the future (2010-2099) precipitation output of the top performing models over the western US under a high emissions scenario (RCP 8.5). In general, average precipitation in the top models tended to increase in a late future period (2070-2099) over the northern portion of the western US and decrease over the southern portion, with the zero-line centrally located over the Great Basin. This is consistent with the variance ratio computed for the same time period, which tended to increase where average precipitation increased and vice versa. One challenge for the models identified across the ensemble stems from the connectivity between ENSO and the PDO. The effect of ENSO on western US precipitation is modulated by the phase of the PDO. To better understand how the ocean interacts with the atmosphere and results in precipitation over the Great Basin, the storm track dynamics were analyzed by computing the stream function and correlating it with precipitation.