The phasing of winter-to-summer precipitation anomalies in the North American monsoon (NAM) region 2 (113.25°W-107.75°W, 30°N-35.25°N-NAM2) of southwestern North America is analyzed in fully coupled simulations of the Last Millennium and compared to tree ring reconstructed winter and summer precipitation variability. The models simulate periods with in-phase seasonal precipitation anomalies, but the strength of this relationship is variable on multidecadal time scales, behavior that is also exhibited by the reconstructions. The models, however, are unable to simulate periods with consistently out-of-phase winter-to-summer precipitation anomalies as observed in the latter part of the instrumental interval. The periods with predominantly in-phase winter-to-summer precipitation anomalies in the models are significant against randomness, and while this result is suggestive of a potential for dual-season drought on interannual and longer time scales, models do not consistently exhibit the persistent dual-season drought seen in the dendroclimatic reconstructions. These collective findings indicate that model-derived drought risk assessments may underestimate the potential for dual-season drought in 21st century projections of hydroclimate in the American Southwest and parts of Mexico.
Bibliographical noteFunding Information:
This work was supported by NOAA award NA11OAR4310166 and NSF award AGS-1243204. Additional support for B.I. Cook was provided by National Aeronautics and Space Administration Modeling Analysis and Prediction Program WBS 281945.02.04.02.74 (“Cool and Warm Season Moisture Reconstruction and Modeling over North America”). Additional support for D. Griffin was provided by the NOAA Climate and Global Change Postdoctoral Fellowship. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1) for producing and making available their model output. For CMIP the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portal. The data for this paper are available from the Program for Climate Model Diagnosis and Intercomparison (http://cmip-pcmdi.llnl. gov/cmip5/). LDEO contribution 7917. We thank three anonymous reviewers for their comments that improved the quality of this manuscript. We, further, thank Haibo Liu and Naomi Henderson for their considerable computational support.