IPCC’s Twentieth-Century Climate Simulations: Varied Representations of North American Hydroclimate Variability

The annual cycle of precipitation and the interannual variability of the North American hydroclimate during summer months are analyzed in coupled simulations of the twentieth-century climate. The state-of-the-art general circulation models, participating in the Fourth Assessment Report for the Intergovernmental Panel on Climate Change (IPCC), included in the present study are the U.S. Community Climate System Model version 3 (CCSM3), the Parallel Climate Model (PCM), the Goddard Institute for Space Studies model version EH (GISS-EH), and the Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL-CM2.1); the Met Office’s Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO-HadCM3); and the Japanese Model for Interdisciplinary Research on Climate version 3.2 [MIROC3.2(hires)]. Datasets with proven high quality such as NCEP’s North American Regional Reanalysis (NARR), and the Climate Prediction Center (CPC) U.S.–Mexico precipitation analysis are used as targets for simulations. Climatological precipitation is not easily simulated. While models capture winter precipitation very well over the U.S. northwest, they encounter failure over the U.S. southeast in the same season. Summer precipitation over the central United States and Mexico is also a great challenge for models, particularly the timing. In general the UKMO-HadCM3 is closest to the observations. The models’ potential in simulating interannual hydroclimate variability over North America during the warm season is varied and limited to the central United States. Models like PCM, and in particular UKMO-HadCM3, exhibit reasonably well the observed distribution and relative importance of remote and local contributions to precipitation variability over the region (i.e., convergence of remote moisture fluxes dominate over local evapotranspiration). However, in models like CCSM3 and GFDL-CM2.1 local contributions dominate over remote ones, in contrast with warm-season observations. In the other extreme are models like GISS-EH and MIROC3.2(hires) that prioritize the remote influence of moisture fluxes and neglect the local influence of land surface processes to the regional precipitation variability.