The Role of Land Surface Schemes in Short-Range, High Spatial Resolution Forecasts

Abstract

Many studies have demonstrated the importance of land surface schemes in climate change studies using general circulation models (GCMs). However, there have not been many studies that explore the role of land surface schemes in the context of short-range and high spatial resolution precipitation forecasts. The motivation of this study is to examine the sensitivity of simulated precipitation, and sensible and latent heat fluxes, to the use of different land surface schemes at two different spatial resolutions. The meteorological model used is the Mesoscale Compressible Community (MC2) model, and the land surface schemes are the force?restore method and the Canadian Land Surface Scheme (CLASS). Parallel runs have been performed using MC2/CLASS and MC2/force?restore at spatial resolutions of 10 and 5 km to simulate the severe precipitation case of 19?21 July 1996 in the Saguenay region of Québec, Canada. Comparisons of the simulated precipitation time series and the simulated 48-h accumulated precipitation at different spatial resolutions with rain gauges indicate that MC2/CLASS at 5-km resolution gives the best simulated precipitation. The comparison results show the model accuracy of MC2/CLASS at 10 km is comparable to the accuracy of MC2/force?restore at 5 km. The mechanism responsible for this is that CLASS represents the land surface vegetation characteristics in a more sophisticated manner than the force?restore method. Furthermore, in CLASS, each grid square is divided into a maximum of four separate subareas, and subvariations of the grid surface vegetation characteristics are taken into account. Therefore, for a grid square containing different types of vegetation, the subgrid-scale information can be used by CLASS, and the computed effective variables that are fed back to MC2 on a 10 ? 10 km2 grid are equivalent to computing them at a higher effective resolution than 10 km. This higher effective resolution for surface characteristics is not found in the force?restore method. The total simulated domain-averaged precipitation, and the sum of sensible and latent heat fluxes from MC2/CLASS and MC2/force?restore at different spatial resolutions, are similar. The major difference is in the partitioning of the simulated sensible and latent heat fluxes. The positioning of the simulated precipitation has been improved by using CLASS. The overall results suggest that the impact of land surface schemes is indeed significant in a short-range precipitation forecast, especially in regions with complicated vegetation variations.