A coupled photosynthesis-evapotranspiration model over winter wheat was developed according to the theory based on SPAC. The model consists of three submodels, i.e., a canopy evapotranspiration model, a canopy photosynthesis model and a model of water and heat transfer in soil. The canopy evapotranspiration model comprises a solar radiation transfer sub-model, a heat radiation sub-model, an energy balance sub-model and a canopy resistance sub-model. The canopy photosynthesis model comprises a leaf photosynt...