Implementation and Evaluation of the Impact of a Lake Model in the French CNRM-CM Global Climate Model.

Abstract:

In numerical weather prediction (NWP) and climate models, substantial efforts have been dedicated to the modeling of natural and ocean surfaces at the expense of lake surfaces. The increase of horizontal resolution of these models allow now to resolve smaller lakes. For that reason, accounting for lakes in modeling systems, has become challenging, especially in regions where lake fraction is high. The lake model FLake (Mironov, 2010) implemented in the surface modeling platform SURFEX (Masson et al., 2014) was first set up off-line at global scale driven by ERA-Interim reanalysis to estimate the best configuration of parameters such as lake depth and extinction coefficient of light, albedo of water, ice and snow. The 30-yr off-line simulations were evaluated for the biggest lakes against satellite surface temperature, freeze-up and break-up periods derived from ARC-Lake products. To assess the impact of lakes in the French CNRM-CM GCM, two global coupled simulations were performed, one with FLake model activated and the second where lakes were replaced by land. Results highlight a regional impact caused by the presence of lakes. Particularly a strong cooling and moistening effect in summertime in the lake vicinity is exhibited, with a direct impact on surface fluxes: stronger latent heat flux due to moister air, lower sensible heat flux due to thermal effects and stronger momentum flux caused by roughness effects.