Using Semi-distributed Hydrological Model to Improve Water and Salt Management in Hetao Irrigation District.

[Objective] Available water for irrigation in Hetao irrigation district has been reduced consistently over the past decades. Improving its water management to alleviate soil salinity is critical to sustaining crop production in this region. The purpose of this paper is to seek optimal water-saving irrigation schemes for this region by using process-based models. [Method] The semi-distributed hydrological model (SahysMod) is used in our study. We consider spatial variability of numerous factors in the modelling, which include meteorology, hydrogeology, soil, irrigation and crops. The model is then combined with GIS to simulate the spatiotemporal dynamics of soil water and salt under different scenarios. Data measured from 2007 to 2012 and 2013-2016 were used to calibrate and verify the model, respectively. [Result] ①In a business as usual scenario, the annual drainage decreases first before gradually stabilizing, with the average annual drainage being 531 million m³; salinized lands in the middle and upper reaches of the irrigation district decrease slightly, but increase significantly in the lower reach. ②Considering water-saving in the whole irrigation district and ecological demand for water in the downstream and the Wuliangsuhai lake, the total water diversion from the canal head should be reduced by 15% from the current level. This will save up to 646 million m³ of water. ③If the current irrigation amount remains unchanged, the water utilization coefficient of the canal can be improved 17.6% at the best. ④If the reduction in total water diversion from Yellow River is the same, reducing irrigation amount in the field is the best way to boost salt leaching. In this scenario, reducing irrigation amount should be the priority, followed by improving water utilization coefficient of the canal. [Conclusion] In addition to saving water, considering ecological demand of the downstream for water is also important in optimizing water management in Hetao Irrigation District. [ABSTRACT FROM AUTHOR]