Evaluation of the ENSO and PDV natural climate variability on the North American monsoon region using a set of CMIP3 dynamically downscaled products from NARCCAP

In the southwestern U.S during the warm season, terrain-forced monsoon thunderstorms are the dominant source of precipitation and a key water source. The North American monsoon (NAM) climate variability is mainly associated with the large-scale variability of both the El Niņo Southern Oscillation (ENSO) and Pacific Decadal Variability (PDV). Wet and dry conditions over the southwestern U.S. are determined by an atmospheric teleconnection related to ENSO-PDV. Therefore, considering the important role of ENSO-PDV on warm season precipitation variability, a robust assessment of future climate projections should also include an in-depth evaluation of this mode. This study extends on the work by Bukovsky et al. (2013) that evaluated North American Regional Climate Change Assessment Program (NARCCAP) simulations over the NAM region. However, they did not evaluate NAM natural variability forced by ENSO-PDV, only mean climate. We thus evaluate the NARCCAP models with respect to their ability to reasonably represent this climate response. We found that only one of the NARCCAP models (HRM3[hadcm3]) reasonably represents the ENSO-PDV warm season teleconnection response over North America and its effect on the continental-scale distribution of precipitation. This same model was also determined to best represent the mean climate in the earlier study. The majority of the NARCCAP simulations do not represent a known source of climate variability, which adversely effects confidence in the NARCCAP-generated future climate projections and their use for impacts assessment.