Simulation Of CO₂, Sensible And Latent Heat Fluxes In Typical Ecosystems Using A Coupled Biophysical/Dynamical Vegetation Model

The Integrated Biosphere Simulator (IBIS) is one of the most sophisticated models in simulating terrestrial biosphere processes based on dynamic vegetation schemes. IBIS is designed to integrate a variety of terrestrial ecosystem phenomena within a single, physically consistent model that can be directly incorporated within AGCMs. To facilitate this integration, the model is designed around a hierarchical, modular structure and uses a common state description throughout.For the purpose of validating IBIS in semi-arid region and eventually improving the model's capability for specific land cover types in China, a simulation for the whole 2003 year was conducted over cropland and degraded grassland underlying surfaces in Tongyu field observation station (44°25'N, 122°52'E) in Jilin Province of China, which is one of the reference sites of international Coordinated Enhanced Observing Period (CEOP). Measurements of turbulent flux of latent and sensible heat, and NEE were performed using the eddy correlation technique (referred to from here on as EC). Model inputs include the site ecosystem characteristics and main meteorological variables. Comparisons between simulated land surface fluxes and observed EC measurements show that the model is capable of reproducing CO₂, sensible and latent heat fluxes indicated by correlation coefficients exceeding the significant level of 0.05. In general, CO₂ flux and sensible heat flux have obvious diurnal and seasonal variation both at the grassland and the cropland, while the latent heat flux, which is related to evapotranspiration, only has diurnal variation during the growing season. Meanwhile, all fluxes at the cropland are larger than those at the degraded grassland, especially in the growing season. The model generally estimates lower annual CO₂ (underestimating by 9.29% in the grassland and 3.73% in the cropland) and latent heat flux (with corresponding values 4.63% and 3.48%), and greater annual sensible heat flux (overestimating by 9.90% and 11.98%, respectively) than measured by EC. And the simulations for the cropland are better than those for the grassland, with more reasonable model-measurement agreements.