To predict soil water variation in the crop root zone,a general exponential recession (GER) model was developed to depict the recession process of soil water storage.Incorporating the GER model into the mass balance model for soil water,a GER-based physicoempirical (PE-GER) model was proposed for simulating soil water variation in the crop root zone.The PE-GER model was calibrated and validated with experimental data of winter wheat in North China.Simulation results agreed well with the field experiment results,as well as were consistent with the simulation results from a more thoroughly developed soil water balance model which required more detailed parameters and inputs.Compared with a previously developed simple exponential recession (SER) based physicoempirical (PE-SER) model,PE-GER was more suitable for application in a broad range of soil texture,from light soil to heavy soil.Practical application of PE-GER showed that PE-GER could provide a convenient way to simulate and predict the variation of soil water storage in the crop root zone,especially in case of insufficient data for conceptual or hydrodynamic models.
A key issue of applying remotely sensed data to estimate evapotranspiration （ET） for water management is extrapolating instantaneous latent heat flux （LE） at satellite over-passing time to daily ET total. At present, the most commonly used extrapolation methods have the same assumption that evaporative fraction （EF） can be treated as constant during daytime （so-called EF self-preservation）. However, large errors are reported by many documents over various ecosystems with the same approach, which indicates that further analysis of the diurnal pattern of EF is still necessary. The aim of this study is to examine the diurnal pattern of EF under fair weather conditions, then to analyze the dependencies of EF to meteorological and plant factors. Long-term flux observations at four sites over semi-arid and semi-humid climate regions in the northern China are used to analyze the EF diumal pattern. Results show that the EF self-preservation assumption no longer holds over growing seasons of crops. However, the ratio of reference ET to available energy is almost constant during the daytime, which implies the climate factors do not have much effect on the variability of EF. The analysis of diurnal pattern of air temperature, vapor pressure deficiency （VPD）, and relative humidity （RH） confirms the assumption that ET diurnal pattern is mainly influenced by stomatal regulation.
为了估计具有垂向空间异质性的田间尺度土壤水分运动参数,提出利用原位多点土壤含水率观测数据反演多层土壤持水和导水特征参数的Bayes方法。该方法基于Hydrus-1D模拟模型建立Bayes推断模型,采用Markov Chain Monte Carlo(MCMC)方法求解Bayes联合概率分布,得到参数的后验边缘分布。将该方法应用于华北平原一典型农田土壤剖面,参数反演结果反映了空间变异性,与室内试验值具有较好的一致性,相应的土壤水分运动模拟具有较高精度,从而验证了该方法的有效性。
