The greening of the McGill paleoclimate model. Part I: Improved land surface scheme with vegetation dynamics

The formulation of a new land surface scheme ( LSS) with vegetation dynamics for coupling to the McGill Paleoclimate Model (MPM) is presented. This LSS has the following notable improvements over the old version: ( 1) parameterization of deciduous and evergreen trees by using the model's climatology and the output of the dynamic global vegetation model, VECODE (Brovkin et al. in Ecological Modelling 101: 251 261 ( 1997), Global Biogeochemical Cycles 16( 4): 1139, ( 2002)); ( 2) parameterization of tree leaf budburst and leaf drop by using the model's climatology; ( 3) parameterization of the seasonal cycle of the grass leaf area index; ( 4) parameterization of the seasonal cycle of tree leaf area index by using the time-dependent growth of the leaves; ( 5) calculation of land surface albedo by using vegetation-related parameters, snow depth and the model's climatology. The results show considerable improvement of the model's simulation of the present-day climate as compared with that simulated in the original physically-based MPM. In particular, the strong seasonality of terrestrial vegetation and the associated land surface albedo variations are in good agreement with several satellite observations of these quantities. The application of this new version of the MPM ( the "green'' MPM) to Holocene millennial-scale climate changes is described in a companion paper, Part II.