A coupled model of land surface CO2 and energy fluxes using remote sensing data

Considering the coupling of plant transpiration with plant photosynthesis through stomatal opening, this paper develops a dual-source model that simulates the energy and CO2 fluxes between a vegetated land surface and the lower atmosphere. Two versions of the CO2-energy coupled model (CECM) are presented. The version CECMSM uses daily surface soil moisture measurements or estimates along with meteorological variables and vegetation parameters as inputs. The other version CECMTr utilizes remotely sensed radiometric surface temperature instead of surface soil moisture estimates. The two versions of the model are evaluated by comparing their predictions of CO2 (Fc), latent heat (LE) and sensible heat (H) fluxes and surface temperature (Tsf) with three datasets 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 datasets, the correlation coefficients between the predictions of H, LE and Tsf from both versions of CECM and their observations ranged from 0.77 to 0.97. The Fc 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 LE was generally better than H where MAPD values ranged from 15–35 to 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 Monsoon’90 experiment which have adapted to the semiarid environment. After these parameters were adjusted to give similar stomatal resistance from other work, the LE and H predictions from CECM were improved.