Specification of surface characteristics for use in a high resolution regional climate model: on the role of glaciers in the swiss alps

Abstract

Certain aspects of the specification of the land cover characteristics for use in high-resolution regional climate models (RCMs) are considered in this paper. We demonstrate the importance of specifying the appropriate surface characteristics at high horizontal resolution and discuss their impacts on the simulated surface prognostic variables, on the surface energy flux as well as on the surface winds in the alpine domain of Switzerland, using the Canadian regional climate model (CRCM). Fixing lower boundary conditions consists in prescribing primary ground characteristics such as land-use (vegetation and soil types and their relative spatial coverage), and the surface height with respect to mean sea level. In the current version of the CRCM land-surface scheme, the land-use serves to fix the surface albedo and the large-scale roughness height, the vegetation type affects the soil water holding capacity, the evapotranspiration efficiency, the snow masking depth, while the soil type determines the soil thermal conductivity and specific heat, thus determining the behaviour of the momentum and sensible heat fluxes, as well as the evapotranspiration at the surface. This in turn may have significant effects on mesoscale circulations. The sensitivity of certain simulated surface fields in the CRCM is assessed through an appropriate specification of glaciers in the Swiss Alps. Until recently, the reference file containing primary ground characteristics was only available at a grid spacing of 1 degrees resolution, so its use in high resolution RCMs is inadequate. Modern techniques used in the exploitation of high-resolution geographical data bases combined with existing satellite imagery now enable the resolution of surface characteristics with much improved definition, hence leading to greater confidence on the spatial distribution of the simulated fields computed by the land-surface scheme in RCMs.