The North American Regional Climate Change Assessment Program: Overview of Phase I Results

Abstract

The North American Regional Climate Change Assessment Program (NARCCAP) is an international effort designed to investigate the uncertainties in regional-scale projections of future climate and produce highresolution climate change scenarios using multiple regional climate models (RCMs) nested within atmosphere–ocean general circulation models (AOGCMs) forced with the Special Report on Emission Scenarios (SRES) A2 scenario, with a common domain covering the conterminous United States, northern Mexico, and most of Canada. The program also includes an evaluation component (phase I) wherein the participating RCMs, with a grid spacing of 50 km, are nested within 25 years of National Centers for Environmental Prediction–Department of Energy (NCEP–DOE) Reanalysis II. This paper provides an overview of evaluations of the phase I domain-wide simulations focusing on monthly and seasonal temperature and precipitation, as well as more detailed investigation of four subregions. The overall quality of the simulations is determined, comparing the model performances with each other as well as with other regional model evaluations over North America. The metrics used herein do differentiate among the models but, as found in previous studies, it is not possible to determine a “best” model among them. The ensemble average of the six models does not perform best for all measures, as has been reported in a number of global climate model studies. The subset ensemble of the two models using spectral nudging is more often successful for domain-wide root-mean-square error (RMSE), especially for temperature. This evaluation phase of NARCCAP will inform later program elements concerning differentially weighting the models for use in producing robust regional probabilities of future climate change.

Present and future Laurentian Great Lakes hydroclimatic conditions as simulated by regional climate models with an emphasis on Lake Michigan-Huron

“…We used simulations from Phase 2 of the project, representing the historical and future (2041-2070) periods, where each RCM was driven by two GCMs amongst the following four: (i) CGCM3, (ii) CCSM3, (iii) GFDL, and (iv) HadCM3. For model references, the reader is referred to Mearns et al (2012). These NARCCAP CC simulations were generated with horizontal grid spacing of approximately 50 km over a domain covering most of North America (see Fig.…”

“…These NARCCAP CC simulations were generated with horizontal grid spacing of approximately 50 km over a domain covering most of North America (see Fig. 1 in Mearns et al 2012). The SRES-A2 emissions scenario was applied for future climate runs.…”

“…Our analysis includes a total of sixteen pairs of simulations generated with three different RCMs. These involve several numerical climate change experiments belonging to the North American Climate Change Regional Assessment Program (NARCCAP; Mearns et al 2012), as well as an ensemble of simulations generated by the Canadian RCM Version 4 (CRCM4), over one of the operational domains known as AMNO (AMérique du Nord; see Music and Caya 2007), referred to as AMNO CRCM4 simulations. We first evaluate the RCM skill in simulating Great Lakes hydrological variables.…”

Regional Climate Projections

“…After a few pioneering projects such as PRUDENCE (Christensen and Christensen 2007), ENSEMBLES (Hewitt and Griggs 2004) or the North American Regional Climate Change Assessment Program (NARCCAP) (Mearns et al 2012), regional climate projections were only recently coordinated at an international scale within the framework of the COordinated Regional Downscaling Experiment (CORDEX) (Giorgi et al 2009). This framework aims at providing downscaled global climate projections through a coordinated approach over several regions of the world, using refined, but scale-limited models which take global model output as boundary conditions.…”

“…In order to cover a wider range of possibilities, a full GCM-RCM matrix should in principle be explored, each RCM downscaling all GCMs. In practice, while some strategies to explore all combinations have been developed (Mearns et al 2012), these have not been implemented in practice. As of 2016, the EURO-CORDEX matrix largely remains to be filled for the high-resolution simulations with a 12 × 12 km 2 grid.…”