An Analysis Of Simulated Runoff And Surface Moisture Fluxes In The CCCma Coupled Atmosphere Land

Climate Modelling and Analysis (CCCma) atmospheric general circulation model (AGCM) is evaluated in an Atmospheric Model Intercomparison Project (AMIP II) simulation. In addition to the coupling between the atmospheric model and the land surface scheme, a variable velocity river flow routing model transports runoff from the land grid cells to the continental edges. Results from this atmosphere land surface hydrological model are analyzed to investigate how moisture is processed in the model and to compare model and observation-based moisture budget components. Runoff simulations and surface moisture fluxes are assessed for major river basins. Not surprisingly runoff is well simulated in river basins where GCM precipitation compares well with observations. In the model vegetation plays a major role in processing moisture at the land surface. It intercepts a large fraction of the precipitation and provides the medium for returning much of the moisture back to the atmosphere as evapotranspiration. Though important locally, the snow moisture reservoir plays a relatively minor role in the global moisture budget. The ground moisture reservoir also plays a major role and processes a similar fraction of precipitation as vegetation. The way moisture is processed at the land surface serves as a basis for model intercomparison and for understanding the modelled moisture budget and its variation as well changes with potential climate change