Modeling the impact of drought on canopy carbon and water fluxes for a subtropical evergreen coniferous plantation in southern China through parameter optimization using an ensemble Kalman filter

[摘要] Soil and atmospheric water deficits have significant influences on CO₂and energy exchanges between the atmosphere and terrestrial ecosystems.Model parameterization significantly affects the ability of a model tosimulate carbon, water, and energy fluxes. In this study, an ensemble Kalmanfilter (EnKF) and observations of gross primary productivity (GPP) andlatent heat (LE) fluxes were used to optimize model parameters significantlyaffecting the calculation of these fluxes for a subtropical coniferousplantation in southeastern China. The optimized parameters include themaximum carboxylation rate (Vc_max), the slope in the modified Ball-Berrymodel (M) and the coefficient determining the sensitivity of stomatalconductance to atmospheric water vapor deficit (D₀). OptimizedVc_max and M showed larger variations than D₀. Seasonal variations ofVc_max and M were more pronounced than the variations between the two years.Vc_max and M were associated with soil water content (SWC). During dryperiods, SWC at the 20 cm depth explained 61% and 64% of variations ofVc_max and M, respectively. EnKF parameter optimization improved thesimulations of GPP, LE and SH, mainly during dry periods. After parameteroptimization using EnKF, the variations of GPP, LE and SH explained by themodel increased by 1% to 4% at half-hourly steps and by 3% to 5%at daily time steps. Further efforts are needed to differentiate the realcauses of parameter variations and improve the ability of models to describethe change of stomatal conductance with net photosynthesis rate and thesensitivity of photosynthesis capacity to soil water stress under differentenvironmental conditions.

[学科分类] 地球化学与岩石