Modelling water, carbon and nitrogen dynamics of the boreal forests in Canadian Land Surface Scheme (CLASS)

Abstract

The Canadian Land Surface Scheme (CLASS) was a "second-generation" land surface model developed in the late 1980's for the Canadian GCM. This research is to develop the "third-generation" land surface scheme based on the current version of CLASS V2.6. This new generation model can be characterized by physiologically coupling the plant water and carbon dynamics, implementing the plant litter and soil carbon biogeochemical cycles, and emphasizing the role of nitrogen in the land surface energy, water and carbon processes. The CLASS model is now improved not only by including carbon exchanges between the atmosphere and ecosystems, but also by feeding back GCMs with dynamically based vegetation parameters.

Simulations were implemented on two vegetation types: deciduous trees and conifers. Data from the old aspen site (OA) in the southern study area (SSA) and the old black spruce site (OBS) in the northern study area (NSA) of the Boreal Ecosystem-Atmosphere Study (BOREAS) experiment were used for the model initializations and tests. Comparisons of energy, water and CO2 fluxes between the model output and eddy correlation measurements were made. For the SSA-OA site, annual root mean square errors (RMSE) and correlation coefficient for daily evapotranspiration and carbon exchange were 0.76 mm H2O d-1 and 0.85, and 1.28 g C m-2 d-1 and 0.91, respectively. The model predicted this aspen ecosystem as a net carbon sink of 163.6 g C m-2 y-1 and 203.2 g C m-2 y-1 for 1994 and 1996, respectively. It took about 16.7% of the total gross primary production (GPP) on the average for the two years. For the NSA-OBS site, annual RMSE for hourly evapotranspiration and carbon exchange were 0.03 mm H2O h-1 and 0.07 g C m-2 h-1, respectively. Annual RMSE for daily evapotranspiration and carbon exchange were 0.45 mm H2O d-1 and 0.7 g C m-2 d-1, respectively. The model predicted this spruce ecosystem as a net carbon sink of 79, 7, and 45 g C m-2 y-1 for 1994, 1995, and 1996, respectively. It took about 5.7% of GPP on the average for the three years.