中文摘要：

利用Crank—Nicolson有限体积元方法和特征投影分解方法建立二维非饱和土壤水流问题的一种很少自由度、精度足够高的降阶外推仿真模型，并给出这种降阶外推仿真模型的降阶近似解误差估计和算法实现．最后用数值例子说明数值结果与理论结果相吻合，并阐明这种降阶外推仿真模型的优越性．

英文摘要：

A reduced-order extrapolating simulation model with sufficiently high accuracy and fews degress of freedom for the two-dimensional unsaturated soil water flow problem was es- tablished by means of the Crank-Nicolson finite volume element （CNFVE） method and POD technique. The error estimates of the reduced-order approximate solutions and the algorithm implementation for the reduced-order extrapolating simulation model were provided. Finally, a numerical example was taken to illustrate that the results of numerical computation are consist- ent with those of theoretical solutions. Moreover, the advantage of the reduced-order extrapola- ting simulation model lies in its simpler computation and higher accuracy.