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ARS Home » Research » Publications at this Location » Publication #113732


item Zhan, Xiwu
item Kustas, William - Bill

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Carbon uptake of land surface vegetation is one of the most significant sinks in the global carbon cycle. A significant change of the carbon sink would affect or imply changes in atmospheric concentrations and the global climate. Carbon uptake of an agricultural crop or an ecosystem is a key factor of the crop production and of the ecosystem net primary productivity. Thus, coupled simulation of the carbon and water/energy fluxes is essential for studying climate, predicting crop production, and estimating ecosystem net primary productivity at regional and global scales. To monitor and quantify changes in regional and global scale carbon and water/energy fluxes, it is necessary that a model use remotely sensed data from satellites which can provide information at global scales. The potential application of a modeling framework which uses remotely sensed information to define key model boundary conditions in estimating not only the energy fluxes but also the carbon fluxes of a land surface by using th coupled-simulation approach is evaluated using field data from subhumid and semiarid rangelands.

Technical Abstract: Considering the coupling of plant transpiration with plant photosynthesis through stomatal opening, this paper develops a dual-source model that simulates the energy and carbon fluxes between a vegetated land surface and the lower atmosphere. Two versions of the Carbon-Energy Coupled Model (CECM) are presented. The CECMsm uses daily surface soil moisture measurements or estimates along with meteorological variables and vegetation parameters as inputs. The second, CECMtr, utilizes remotely sensed radiometric surface temperature estimates. The two versions are evaluated by comparing their predictions of carbon, latent heat, and sensible heat fluxes and surface temperature with three data sets collected from two large-scale field experiments (FIFE '87 and Monsoon '90) which were conducted over two different types of land surface. For the three data sets, the correlation coefficients between the predictions of heat fluxes and surface temperature from both versions of CECM and their observations ranged from 0.77 to 0.97. The carbon flux predictions from CECMsm had a correlation of 0.96 and a 16% mean absolute percent difference (MAPD) with the observations. For both CECMsm and CECMtr, the agreement with measured latent heat flux was generally better than sensible heat where MAPD values ranged from 15-35% and 20-55%, respectively. The values of some parameters in the stomatal conductance and leaf photosynthesis models, obtained in the literature for general C3 plants in the temperate areas, were found inappropriate for the C3 shrubs at the site of the Monsson '90 experiment which have adapted to the semiarid environment. After these parameters were adjusted to give similar stomatal resistance from other work, the latent and sensible heat flux predictions from CECM were improved.