A Grid-based Integrated Surface–Groundwater Model (GISMOD) was developed to estimate the required irrigation water using a control-site method. The entire catchment is divided into multiple grid cells of equal size, and several grid cells can be chosen as the control sites by users in this model. The grid cells from the upper stream of each control site, which have a land-use type of farmland, are automatically identified as a controlled grid cell. The crop information around each controlled grid cell is set to be the same as its corresponding control site. Next, the irrigation water requirement for each controlled grid cell is calculated using a crop coefficient method that is integrated into the human water-use module of the GISMOD. After runoff is generated, the actual discharge of each control site is computed by comparing the available water sources with the irrigation water requirement based on the water-supply operation rules of the model. This paper subsequently presents a case study in the upper-middle reaches of the Heihe River to evaluate the performance of the GISMOD. The results demonstrate that the actual water consumption for irrigation in the Heihe River basin could be generally estimated by the GISMOD on a monthly basis.

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