资源环境科技发展态势分析平台

Climate inter-annual variability over the North American monsoon (NAM) region is associated with El Nino-Southern Oscillation (ENSO) and Pacific decadal variability (PDV), which drive a warm season atmospheric teleconnection response. Using the North American Regional Climate Change Assessment Program (NARCCAP) simulations, previous studies have found that regional models forced with an atmospheric reanalysis (NARCCAP Phase I) represent the NAM reasonably well as a climatological feature. However, when these same regional models are forced with global climate model projections (NARCCAP Phase II), their ability to represent the NAM as a salient feature substantially degrades. The present study evaluates NAM inter-annual climate variability through the continental-scale patterns of summer precipitation within the NARCCAP simulations (Phases I and II), in relation to ENSO-PDV, and the presence of the driving atmospheric teleconnection response. Multivariate statistical analyses are applied to sea surface temperature and precipitation data sets to determine dominant variability at continental scale, with focus on the southwest. The analysis reveals that NARCCAP Phase I simulations are able to portray the spatial pattern of precipitation associated with ENSO-PDV in a similar way to observations. However, all NARCCAP Phase II simulations, with the exception of the HRM(Hadcm3) regional-global model pair, fail to reproduce this climate variability. Although including all possible NARCCAP model simulations to generate a multi-model ensemble mean would increase the statistical degree of confidence in climate projections, this type of result would not increase confidence in the physical climatology of model representations of warm season climate variability. More physically based, process-oriented metrics are needed to evaluate model quality in assessing the uncertainty of future climate change in multi-model ensemble products used for climate change impacts assessments.