The influence of land surface roughness on the large scale atmospheric circulation and rainfall was examined by comparing three sets of simulations made with a general circulation model in which the land surface roughness length, z0, was reduced from 45 cm to 0.02 cm. The reduced surface roughness produced about a two-fold increase in the boundary layer wind speed and, at the same time, a two-fold decrease in the magnitude of the surface stress. There was almost no change in the surface evaporation and surface sensible heat flux. There was, however, a larger change in the horizontal convergence of the water vapor transport in the boundary layer and a corresponding large change in the rainfall distribution mainly as a consequence of the change in the cut of the surface stress. The result suggests that the height of the earth' vegetation cover, which is the main determinant of the land surface roughness, has a large influence on the boundary layer water vapor transport convergence and the rainfall ... Abstract The influence of land surface roughness on the large scale atmospheric circulation and rainfall was examined by comparing three sets of simulations made with a general circulation model in which the land surface roughness length, z0, was reduced from 45 cm to 0.02 cm. The reduced surface roughness produced about a two-fold increase in the boundary layer wind speed and, at the same time, a two-fold decrease in the magnitude of the surface stress. There was almost no change in the surface evaporation and surface sensible heat flux. There was, however, a larger change in the horizontal convergence of the water vapor transport in the boundary layer and a corresponding large change in the rainfall distribution mainly as a consequence of the change in the cut of the surface stress. The result suggests that the height of the earth' vegetation cover, which is the main determinant of the land surface roughness, has a large influence on the boundary layer water vapor transport convergence and the rainfall ...