To simulate the soil moisture variation in cropland, a two-parameter exponential recession model was derived to depict the recession process of soil moisture in the root zone. The model is based on the assumption that the recession rate of soil water is proportional to the potential evapotranspiration rate and the difference of soil water content and steady soil water content. Two parameters in this model are soil texture-dependent recession constant and steady soil water content. The model was calibrated and validated with measured soil water data at two experiment sites in North China with different soil textures and cropping systems. Coefficients of determination between measured and model simulated soil water content were all greater than 0.7, indicating that both models gave satisfactory simulation results. Results showed that values of two parameters mentioned above are both larger for finer soil than those for coarser soil. At the same potential evapotranspiration rate and soil water content, the recession rate of finer soil is usually lower than that of coarser soil. The proposed model can be used in irrigation management to predict approximate date for irrigation, as well as be embedded into watershed hydrological models to estimate the antecedent precipitation index.
Crop-water production functions quantitatively describe the relationship between crop yield and field evapotranspiration. The crop water sensitivity indexes of crop-water production functions, a key factor for optimizing irrigation scheduling in case of water scarcity, are usually obtained from field experiments or other sources for crop growth stages, while their values in shorter intervals are preferred for practical irrigation scheduling. We proposed a method to downscale the sensitivity index from growth stages to shorter intervals by monotone piecewise cubic interpolation of the cumulative sensitivity index curve. This method was used to estimate sensitivity indexes in irrigation intervals of about 10 d for corn and wheat in central Shanxi Province of China. Results showed that the downscaled sensitivity index could reflect the impact of water stress on crop growth both at different growth stages and within each stage. Scenario analysis of water stress at a single growth stage of wheat showed the rationality of downscaling water sensitivity index from growth stages to shorter intervals through interpolation of cumulative sensitivity index, and this proposed downscaling method was superior to the traditional linear downscalin~ method.
为评价干旱区灌区的灌溉效率,该文以作物生长期灌溉地的蒸散发扣除降水量作为灌溉水的有效利用量,将灌溉水有效利用量与灌溉净引水量(总引水量减去退、排水量)的比值定义为灌溉水有效利用系数。利用遥感蒸散发模型可以较为准确地估算灌溉地蒸散发,从而可以避免传统灌溉水利用系数评估中难以准确估算通过灌溉到达作物根系层水量的问题。以河套灌区为研究对象,利用遥感蒸散发模型(surface energy balance algorithm for land,SEBAL)计算了区域内灌溉地作物生育期的蒸散发量,并结合降水量与净引水量的观测资料,对节水改造以来(2000-2010年)河套灌区灌溉水有效利用系数进行了分析和评价。结果表明,灌溉水有效利用系数近年来有增加趋势,同时灌溉水有效利用系数随降水量和净引水量的减小而增大,减少供水对灌溉水有效利用系数的影响要大于灌区节水改造工程的影响。另一方面,在灌区净引水量减少的情况下,灌溉地蒸发量能够维持在较稳定的水平,反映了近年来灌区节水改造的效果较好。
