Scale effect of water productivity for winter wheat in Shijing Irrigation District

The objective of this study is to investigate the scale effect of net inflow water productivity and net irrigation water productivity in the winter wheat production in well-canal combined irrigation areas. To achieve this goal, the 2007-2009 growing season data of winter wheat from the Shijing Irrigation District are collected. The Hydrus-1D software package and the USGS MODFLOW model (Modular Three dimensional Finite-difference Ground-water Flow Model) are applied to calculate the water budgets across different spatial scales including the crop, the field, the sub-main canal, the main canal and the irrigation system. The results show that ① from the crop scale to the irrigation system scale, the net inflow water productivity and net irrigation water productivity will be reduced by 9.49% and 16.59% respectively due to the increase in water loss; ② the groundwater depth is so large that too little percolation could recharge the groundwater system for water reuse during the growing season of winter wheat. Thus, the net irrigation water productivity has a marginal advantage in water reusing over the traditional irrigation water productivity; ③ on a multi-year time scale, all the percolation could recharge the groundwater for water reuse, and the net inflow water productivity increases with spatial scales. Meanwhile, the net irrigation water productivities for different spatial scales could be improved between 37% and 65% on the basis of those at the winter wheat time scale.