Thursday, 13 February 2003
Modeling Mackenzie basin surface water balance during CAGES with the Canadian Regional Climate Model
The Canadian GEWEX Enhanced Study (CAGES) is a research programme centred on a 14 month long field campaign running from the summer of 1998 to the fall of 1999 over the Mackenzie River Basin of northwestern Canada. As a component of the Mackenzie GEWEX Study (MAGS), it’s purpose is to improve our understanding of water and energy fluxes and reservoirs in the region during this water year through enhanced observing periods of targeted variables, as well as comprehensive modeling studies. In support of this, a developmental version of the Canadian Regional Climate Model, coupled with a third generation physics parameterization package of the Canadian Centre for Climate Modelling and Analysis GCM has simulated the entire period. The purpose of these simulations is twofold. Firstly we take advantage of a variety of specialized MAGS observed data sets to evaluate the performance of the model in a traditionally data sparse area. Secondly, given a reasonably well validated simulation we use the model to estimate the surface water budget during the CAGES water year (October 1 1998 – September 30 1999). This approach allows us to estimate budget components, soil moisture for example, that are currently not observable at the Mackenzie Basin scale.
Annual Mackenzie basin precipitation was simulated to within 9% of our best observed estimate, with a reasonable temporal and spatial distribution throughout the water year. A mean annual cold bias of about 2 K was also found, likely the result of a deficit in surface net solar radiation, as well as imperfect boundary layer processes and land surface spinup - highlighting the particular importance of these processes in high latitude regional climate modeling. Nevertheless, a realistic surface water balance was simulated. The simulation was used to drive off-line two different hydrologic models in order to simulate streamflow hydrographs at key stations within the Mackenzie basin. Results show that when sub-grid scale routing and interflow are included, streamflow timing is improved. This study represents a step in the development of a fully coupled atmosphere/land-surface/hydrologic model for high latitude regional scale cold climate process studies within MAGS.