Where are the critical points of water transfer impact on grain production from the middle route of the south-to-north water diversion project?

While mitigating the water resource shortage in the recipient area, water diversion will concurrently reduce discharge volume and available water in the downstream regions. As agricultural water holds the lowest priority it will be primarily affected. If water diversion disrupts the balance between irrigation supply and demand in these areas, it could jeopardize food production security and sustainable development. This study proposes the critical points of influence of the middle route of China's South-to-North Water Diversion project (SNWD) on grain water use in 19 counties and cities in the middle and lower reaches of the Han River, and the economic loss caused by it was evaluated. Initially, the measurement of grain irrigation water demand and supply was conducted for both the base year and the planning year under varying precipitation frequencies. Subsequently, diverse scenarios were formulated considering three key factors - the rainfall frequency, water diversion scale and changes in the water demand in other sectors - to assess potential gaps between irrigation water supply and demand in each scenario. The objective was to identify scenarios that pose a threat to grain irrigation and find the critical points. Ultimately, the economic impact of water diversion on grain growth was modelled and estimated. The findings demonstrate that the combination of large-scale water transfer and extreme climatic conditions may result in unsustainable grain production. Furthermore, the increased water demand in other sectors could exacerbate the pressure on irrigation water resources. In normal flow years, regardless of whether the scale of water transfer is 9.5 billion m3 or 14.5 billion m3, its impact on regional grain production water remains minimal. However, when the scale of water transfer reaches 9.5 billion m3 in 2030, the critical point of irrigation water supply and demand imbalance first appears in the extremely dry year P = 95%. As the water transfer increases to 14.5 billion m3 by 2040, the critical points occur at P = 75% and P = 95%, resulting in an increase in both the gap between irrigation water supply and demand and grain production losses.