When forced with the same precipitation data, the three land surface models exhibit remarkable seasonal cycle in evaporation. The CLM2-TOP model generates larger evaporation than NOAH and SSiB models. However, runoff from CLM2-TOP is in good agreement with gauge measurement, while NOAH and SSiB overestimate runoff. In addition, model results also suggest that summer evaporation accounts for more than 40% of overall annual mean in the Mississippi River basin. This ratio is larger than the annual ratio of precipitation and runoff. Monthly anomalies of precipitation, evaporation and runoff show strong interannual signal, in particularly during 1988 and 1993, which corresponds to two extreme (drought and flood) water cycle events in the Mississippi River basin, respectively. The June-July-August evaporation anomalies show an intimate relationship with all seven ENSO events during 1986 to 1995; anomalies of precipitation and runoff are only associated with four ENSO events.
The simulated net shortwave radiation from the three models is consistent with each other. All three models capture the seasonal variation of latent and sensible heat, with maximums occurring in the summer, and minimums in the winter. In addition, the anomalies of latent heat and sensible heat exhibit extreme interannual variability during 1988 and 1993, which are consistent with the corresponding water cycle variability.
In order to verify above conclusions, comparison of the model simulated water budget and energy with the observed precipitation, evaporation, net radiation, latent and sensible heat will be presented.