Evaluating the Impact of a New Land Surface Package on the Medium Range Weather Forecast in Canadian Numerical Weather Prediction System

A new land surface package for implementation in Environment and Climate Change Canada (ECCC)’s medium-range global deterministic numerical weather prediction (NWP) system is evaluated in this study. The global medium range model forecasts are compared with the screen-level analyses of air temperature and humidity. The new land surface package includes i) new databases to specify soils and vegetation characteristics, ii) improved initialization of land surface variables by the assimilation of space-based remote sensing observations, and iii) a more sophisticated land surface scheme. The evaluation is performed by generating lead-time-averaged difference maps as well as plots of lead time evolution of the standard deviation of errors (STDE) and of the temporal correlation between forecasts and analyses. The new land surface package resulted in smaller STDEs and larger temporal correlation for air temperature and humidity comparing to the current operational configuration . The improvement is greater for humidity than for air temperature. The objective evaluation confirms the positive impact of the new land surface package on the medium-range forecast of near-surface air temperature and humidity for a summertime period with the maximum impact around 7-day lead-time. The effect of land-surface modifications on planetary boundary layer and upper atmosphere is also investigated in this study.