Modeling the Effect of Land Surface Evaporation Variability on Precipitation Variability. Part I: General Response

This is the first of a two-part article that investigates the impact of land surface evaporation variability on the interannual variability of precipitation and compares it with the impact caused by sea surface temperature variability. Previous works by Koster and Suarez and Koster et al. provide the general strategy to control oceanic and land surface evaporation. For this part of the study, their numerical experiments are repeated using the Center for Ocean–Land–Atmosphere Studies (COLA) general circulation model. However, emphasis is put on the dynamics of the response, including a discussion of the changes in the mean climate; in particular, it is observed that the suppressed land evaporation variability changes the mean Northern Hemisphere storm track and the mean position of the intertropical convergence zone, which in turn affect the mean precipitation. The analysis of the precipitation variance reveals a general agreement with previous works for the midlatitudes, whereas in the Tropics a stronger land-induced signal is detected. Furthermore, important regional differences in the response are found. Specifically, there is a predominant land signal over the Amazon region, in contrast to an equivalence between the land and ocean forcings over the Congo basin region. Finally, the model appears to be slightly more sensitive to seasonal–interannual variations of the land forcing than is the one adopted by Koster et al.