Impact of cross effects between soil temperature and moisture states and soil water vapor fluxes on global climate

The multi-layer soil model of the Hydro-Thermodynamic Soil Vegetation Scheme (HTSVS) has been coupled to the Common Land Model (CLM) of the Community Climate System Model (CCSM3.0). The soil model considers, among other things, the treatment of the (vertical) heat- and water-transfer processes (including the Richards equation), freezing/thawing of the ground, water extraction by roots, water vapor fluxes in the soil pores, and so-called cross effects, i.e. that a temperature gradient can lead to a water flux and a moisture gradient can cause a change in temperature. The latter effects have been found to be important in spring during snowmelt and fall during freeze-up as well as when chemicals are involved. Results of simulations without consideration of the impact of water vapor fluxes, water vapor and cross effects are compared with those obtained with their inclusion. The impact of these processes on the global atmospheric conditions is discussed.