SENSITIVITY OF THE CCM1 HYDROLOGIC-CYCLE TO CO2

To better understand the global hydrologic cycle, climatological simul ations with the National Center for Atmospheric Research global atmosp heric general circulation model (GCM) or community climate model (CCM1 ), coupled to a mixed layer model, are compared to available global hy drologic observations. We find that CCM I simulates, reasonably well, the large-scale precipitable water, moisture flux convergence, precipi tation, and evaporation potentials, Regional discrepancies are noticea ble, though, especially in the eastern tropical Pacific. Smaller-scale moisture flux convergence, precipitation, and evaporation also compar e less well since effects of resolution can be discerned between low-r esolution simulations and higher-resolution global observations. Sensi tivity experiments to changed CO2 show that the CCM1 hydrologic respon se is similar to other GCMs. Precipitable water, evaporation, and prec ipitation increase while snow decreases with increasing CO2. Soil mois ture changes are seasonally and regionally dependent. In middle latitu des, soil moisture increases during the winter and decreases during th e summer with increasing CO2. Changes in moisture transport between la nd and ocean are also seasonally dependent. Increased CO2 induces incr eased moisture divergence over the central equatorial Pacific during D ecember, January, February (DJF). This water is transported to the res t of the northern hemisphere land and ocean where precipitation is muc h greater than evaporation over the climatologically cold land surface . During June, July, August (JJA), water is preferentially converged o ver the western Pacific Ocean.