Impact of Intensive Irrigation Activities on River Discharge Under Agricultural Scenarios in the Semi-Arid Aksu River Basin, Northwest China

The Aksu River is a principal headwater tributary of the Tarim River in northwest China providing 70-80 % of its water supply. This study aims to simulate the impact of potential future irrigation and cropping schemes on river discharge in the semi-arid and irrigation intensive part of the Aksu River basin. To achieve this goal, the eco-hydrological model SWIM (Soil and Water Integrated Model) was developed further by including an irrigation module and a river transmission losses module. The performance of the SWIM model in the region was then compared with that of another water management model, WEAP (Water Evaluation And Planning). The results show that both models are capable of reproducing the monthly discharge at the downstream gauge well using the local irrigation information and the observed upstream inflow discharges as inputs. Still, the SWIM model performs better than the WEAP model because it accounts for both hydrological processes and agricultural impacts. Therefore, SWIM was used for the scenario study. Different irrigation scenarios were developed based on the recent trends of agricultural practices. The study showed that the improvement of irrigation efficiency was the most effective measure for reducing irrigation water consumption and increasing river discharge downstream. The expansion of irrigation area in the basin leads to an increase in water consumption while the changes in crop structure (composition of crop types) on arable land do not have significant impact on the river discharge downstream.