The simulation of water vapor and carbon dioxide fluxes over irrigated farmland by modified soil-plant-atmosphere model (mSPA)

The exchange of CO₂ and water vapor in the farmland was examined with a two-layer canopy model (mSPA model). The study site is located in a southwestern end of Korean peninsular (34.55°N, 126.57°E) which is part of the Koflux sites (Haenam). The turbulent fluxes of energy and CO2 were measured from October of 2002 to September of 2003 by eddy covariance method. The landcover was the mixture of rice paddies and various agricultural crops such as beans and sweet potatoes etc. The measured turbulent fluxes represented different footprint depending on wind direction. Two cases were selected for detailed examination among southeasterly wind cases during growing seasons (June to September in 2003). In the first case, plant had low LAI and vapor pressure deficiency was relatively high. In the second case, plant had maximum LAI and vapor pressure deficiency was moderately low. Sensitivity test was performed to investigate the influence of prescribed model parameters on simulated NEE and latent heat flux during growing season. During this period, vapor pressure deficiency was moderately low and soil moisture was ample due to irrigation and rainfall. The simulated NEE showed a large sensitivity to LAI while the simulated evapotranspiration showed little sensitivity due to compensating effect of soil evaporation. For hydraulic parameters such as stem hydraulic conductivity and root resistivity, model showed little sensitivity. It is due to low water stress in this period. Key words: Farmland, Net ecosystem exchange, mSPA model, Eddy covariance fluxes