Application and improvement of Hydrus-1D model for analyzing water cycle in an agricultural field

Water cycle during 2006-2009 in a typical agricultural field of the Weishan irrigation district, which is located along the downstream of Yellow River in the North China Plain, was analyzed using the Hydrus-1D model. The equation for calculating the bulk surface resistance was modified according to the observed data. The simulated ET was compared with the observed ET by the eddy covariance system, and the result showed that simulation using modified resistance equation provided much better results than that of the original model. ET analysis showed that, for areas covered with seasonal vegetation, LAI determined the seasonal variation of ET, while weather condition determined ET variation at a much smaller time scale (e.g., one week). Comparing the simulated soil water content with the observed data by TDR, showed that the model could simulate soil water appropriately. Water balance analysis showed that about 80% of the rainfall and irrigation were consumed by ET, and drainage from the field mainly occurred during rainy season.