Determining the spatial distribution of percolation for winter wheat based on system dynamics and semi‐distributed modelling^*

Abstract

Percolation is one of the important factors in the field water cycle, which affects designing irrigation schedules and increasing water productivity. However, the measurement of percolation is both costly and time-consuming. This study established a point-scaled system dynamic model (SDM) for water movement in the root zone of winter wheat in Shijin Irrigation District (SID) and proposed a semi-distributed method to extend the SDM from the point to regional scales (SM). Observations of soil moisture of the root zone (0-2 m) of winter wheat from 2007 to 2009 were used to evaluate the SDM and SM. Both could accurately simulate soil water movement during the winter wheat growth period (R 2 > 0.6, RMSE < 0.032). Meanwhile, three extreme scenarios and sensitivity analysis were also applied to ensure the stability and plausibility of the SDM. The distribution of percolation indicated that irrigation was the main reason for percolation. Furthermore, well irrigation reduced the percolation when compared with canal irrigation. Meanwhile, wells were the main water source (56.3%) for the SID and percolation consumed about 22.1% income water. Future study should focus on improving simulation accuracy for spatial variability and consider the lateral exchange of soil water for regions with hills and mountains.