Spatial-temporal optimal allocation of distributed multi-water sources in irrigation areas

Abstract: This research aims to fully consider the spatial and temporal distribution in the process of water supply and demand. A case study was selected as the Zhangfuhe irrigation area, Handan City, Hebei Province, China. The soil moisture and its correction coefficients were also calculated at different growth stages using remote sensing inversion. The demand for each unit was then evaluated in the study area. An optimal allocation model of multi-water sources was established in the irrigation area, particularly with the allocation objectives of the minimum water shortage for the reservoir and the maximum benefit in the irrigation area. The temporal and spatial distribution of water allocation was obtained for the different water sources under nine scenarios, including the high water storage and high precipitation (VH-PH), high water storage and low precipitation (VH-PM), high water storage value and low precipitation value (VH-PL), water storage median and precipitation abundance (VM-PH), water storage median and downgrade value (VM-PM), median impoundment and withered precipitation (VM-PL), low water storage and high precipitation (VL-PH), low water storage and low precipitation (VL-PM), low water storage and low precipitation (VL-PL). The results showed that there was high soil moisture in April and June of the growth period in the irrigation area, and relatively low in August and November. The soil moisture correction coefficient in the Fuyang River district was outstandingly higher than that in the Minyou district. The annual water demand of the irrigation area was 1.133×109 m3. Specifically, the water demands in May and December were the maximum and minimum of the whole year, accounting for 25.3% and 1.2%, respectively. The water demand peak of crops was from April to August. Among them, the ratio of cumulative water demand in the five months to the total water demand in the whole year was as high as 76.8 %. The soil moisture correction coefficient using remote sensing inversion was a better agreement with the actual situation. Among the external water sources, the water volume allocated from the south to the north was slightly higher than that of the Yellow River. But, the water volume allocated per unit area of the south to the north water transfer was significantly lower than that of the Yellow River. It infers that the Yellow River was preferentially selected as the external water source in the model. The allocation of water of the Minyou district was higher than that of the Fuyang River district in different scenarios, where the spatial distribution changed outstandingly. The allocation of water in the model better coincided with the practical situation. The economic benefits of the irrigation area were positively related to the precipitation and the total water shortage, while negatively related to the total allocation of water, the allocation of water of the reservoir, the water allocation of the south to the north water, and the allocation water of the Yellow River. Therefore, there was a significant correlation between the water sources, indicating the close internal linkage of the water system. The improved model can provide a new idea for the zoning management of irrigation water, considering the spatial and temporal distribution of multiple water sources and the variation of soil moisture at different growth stages of crops in the irrigation area.