The Community Land Model and Its Climate Statistics as a Component of the Community Climate System Model

Several multi-decadal simulations have been carried out with the new version of the CCSM climate model. This paper reports an analysis of the land component of these simulations. Global annual averages over land appear to be within the uncertainty of observational data sets but the seasonal cycle over land of temperature and precipitation appear too weak. These departures from observations appear to be primarily a consequence of deficiencies in the simulation of the atmospheric model rather than of the land processes. High latitudes of northern winter are biased sufficiently warm to have a significant impact on the simulated value of global land temperature. The precipitation is approximately doubled from what it should be at some locations, and the snow-pack and spring runoff are also excessive. The winter precipitation over Tibet is larger than observed. About two-thirds of this precipitation is sublimated during the winter but what remains still produces a snow pack that is very large compared to that observed with correspondingly excessive spring runoff. A large cold anomaly over the Sahara desert and Sahel also appears to be a consequence of a large anomaly in downward longwave radiation, although in this case it is not anomalous clouds but low column water vapor that appears to be most responsible. The modeled precipitation over the Amazon basin is low compared to that observed; the soil becomes too dry and the temperature is too warm during the dry season.