| Summary: | One of the goals of the Mackenzie GEWEX Study (MAGS) is to model the critical components of the water and energy cycles that affect the climate of the Mackenzie Basin. The land surface - hydrological model WATCLASS is used to simulate the energy and water transports at and below the surface. Atmospheric input to WATCLASS is provided by the output from the atmospheric model GEM. There may be significant uncertainties in the GEM incoming solar radiation due largely to difficulties in simulating clouds and their radiative properties. The question that we address is how these uncertainties affect the simulation of the energy and water budgets of this northern river watershed. To assess this sensitivity, two series of two WATCLASS model runs are compared. Both runs are driven by atmospheric data from GEM for the 1998--99 water-year, but in the second run shortwave radiation fluxes retrieved from satellite measurements replace the GEM fluxes. Land cover differs in the two series of runs and so provides an assessment of the sensitivity to vegetation variability. Results show that the atmospheric model overestimates the incoming solar radiation field by 36%. This results in an increase in the basin annual average surface temperature of about 1°C and an overestimation in net longwave radiation, and sensible and latent heat fluxes. Snowmelt starts earlier with a decreased first snowmelt peak in runoff and discharge hydrographs. The overall consequence is an annual discharge underestimation.
|
|---|