A 1000-year control simulation of the NCAR CCSM2 climate model was analyzed with regard to continental runoff effects. The results were compared to observational data and previous simulations using CCM3. The interannual variability of the river discharge in the control simulation was comparable to stream-gage data in some cases. At times the variability of the simulation exceeded that of observations. In a statistical analysis using the coefficient of variation, the Mississippi River showed the greatest similarity in interannual variability between the control simulation and the observed data. The variability of the Nile and St. Lawrence Rivers however was much higher than the observations indicated.

River discharge into the Arctic Ocean improved significantly over the earlier CCM3 simulations, based on monthly hydrograph averages from the CCSM2 control simulation. The Niger, St. Lawrence, and Congo Rivers were among those that still did not show the appropriate discharge into the oceans. The sea surface salinity responded as expected to the influx of fresh water from rivers, decreasing in the regions near the river outlet points. Other oceanic properties from the simulation results were also examined. The stability of the CCSM2 control simulation allowed examination of the variability of the water cycle on a multi-century scale.