Characterization of Air and Ground Temperature Relationships within the CMIP5 Historical and Future Climate Simulations

The relationships between air and ground surface temperatures across North America are examined in the historical and future projection simulations from 32 general circulation models (GCMs) included in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The difference between surface air (2 m) and ground surface (10 cm) temperatures is affected by simulated snow cover, vegetation cover, and precipitation by means of changes in soil moisture and soil properties. In winter, the differences between air and ground surface temperatures, for all CMIP5 simulations, are related to the insulating effect of snow cover and soil freezing phenomena. In summer, large leaf area index and large precipitation rates correspond to smaller differences between air and ground temperatures for the majority of simulations, likely due to induced changes in latent and sensible heat fluxes at the ground surface. Our results show that the representation of air-ground coupling, analyzed using the difference between ground and air surface temperatures as metric, differs from observations, the North American Regional Reanalysis product and among the CMIP5 GCM simulations, by amounts that depend on the employed land surface model. The large variability among GCMs and the marked dependence of the results on the choice of the land surface model illustrate the need for improving the representation of processes controlling the coupling of the lower atmosphere and the land surface in GCMs as a mean of reducing the variability in their representation of weather and climate phenomena.