Assessment of Ecological Water Requirements for Maintaining Ecological Balance under the Current Development Pattern of the Hetao Irrigation District

The Hetao Irrigation District, located in northwestern China, is characterized by severe water scarcity, with water supply for production and daily use highly dependent on diversions from the Yellow River. The annual average water withdrawal of the irrigation district accounts for approximately one seventh of the total Yellow River water use in Inner Mongolia. Under the unified management of water resources across the Yellow River Basin, future water diversions to the Hetao Irrigation District are expected to further decrease, exacerbating water scarcity and associated conflicts. Therefore, clarifying the ecological water demand required to maintain ecological balance, as well as the proportion of different ecological water consumption components under current conditions, is of great significance for ensuring ecological stability and sustainable socioeconomic development in the irrigation district.

Based on the concept of ecological water consumption, this study systematically analyzes the composition of ecological water use and its major influencing factors in the Hetao Irrigation District. Using the WACM model, 11,819 calculation units were delineated to construct an ecological water consumption assessment framework. Model parameters were calibrated using data from 1990–2018 and validated with observations from 2019–2023. On this basis, total water consumption, Yellow River water consumption, ecological water consumption, and ecological Yellow River water consumption were quantified, and the recommended water demand for maintaining ecological balance under the current development pattern was determined.

The results indicate that water consumption in the irrigation district is mainly influenced by meteorological conditions, underlying surface characteristics, and human activities, among which meteorological factors play a dominant role. Model performance was evaluated in terms of water surface evaporation, drainage processes, and the spatial distribution of groundwater depth. The relative error of simulated water surface evaporation was less than 10% with a Nash–Sutcliffe efficiency (NSE) exceeding 0.8, while the relative error of drainage simulation was less than 20% with an NSE greater than 0.7. The simulated spatial pattern of groundwater depth was consistent with observations, demonstrating good model applicability.

From 2009 to 2023, the annual average total water consumption of the Hetao Irrigation District was 6.18 billion m³, including 4.53 billion m³ of agricultural water consumption and 1.65 billion m³ of ecological water consumption. The annual average Yellow River water consumption was 4.39 billion m³, of which ecological water use accounted for 0.91 billion m³. Agricultural water use constituted the largest proportion of both total water consumption (73.3%) and Yellow River water consumption (72.5%), but exhibited a declining trend over time, whereas ecological water consumption showed a continuous increase. Within ecological water use, Wuliangsuhai Lake accounted for the largest share (approximately 32%) and remained relatively stable at about 0.29 billion m³, providing an important reference for determining its ecological water supply. The study concludes that, under the current water use pattern, maintaining ecological balance in the Hetao Irrigation District requires an annual water demand of approximately 6.70 billion m³, including 4.53 billion m³ diverted from the Yellow River.