Impact of the Canadian land surface scheme on monthly ensemble predictions of water and energy budgets over the Mackenzie river basin

Abstract

As part of the Mackenzie GEWEX Study (MAGS), Canadian global spectral forecast model (SEF) monthly simulations of surface water and energy fluxes averaged over the Mackenzie river basin are examined. We study the impact of the more sophisticated Canadian Land-Surface Scheme (CLASS) on the predictability of the fluxes, using the operational configuration of the global model with the force-restore land-surface scheme as a baseline for comparison. The model, connected successively to the current operational force-restore land surface scheme and to CLASS, generates nine-member ensemble simulations of one month duration from analyses perturbed with the Monte-Carlo method, for spring, summer, fall and winter cases. The perturbations are comparable in magnitude to observational errors. The flux predictability is measured by the degree to which the individual forecasts in the ensembles vary from one another. The mean of the ensemble forecasts is compared with monthly accumulations of surface energy and water fields constructed from 12-hour forecasts of the operational Regional Finite Element (RFE) model as well as with satellite-derived observations of precipitation. We found that, overall, the replacement of the force-restore scheme with CLASS in the Canadian Meteorological Centre (CMC) global forecasting system has a beneficial effect on the predicted MAGS energy and water budgets. While their sensitivity to initial conditions increases only slightly, the budgets, forecast with CLASS, compare better with their counterparts constructed from the short-term predictions of the CMC regional forecasting system than the output of the model coupled with the operational force-restore scheme. © 2001 Taylor & Francis Group, LLC.