Hydro-agro-economic optimization for irrigated farming in an arid region: The Hetao Irrigation District, Inner Mongolia

Water shortage and soil salinization are the key limiting factors in agricultural production of arid and semi-arid regions. Located in western Inner Mongolia of China, the Hetao Irrigation District (HID) is one of the top three largest irrigation districts in China. Irrigation water overuse and high level of soil salinity have curbed the agricultural productivity, adversely affected farmers' revenues, and threatened long-term sustainability of irri-gated farming in the HID. Nevertheless, opportunities still exist to improve the situation. Irrigation water allo-cation, salt accumulation and leaching, crop productivity and farming decisions are intrinsically connected and thus require taking a holistic approach to investigate into the interactions among all those factors and devise appropriate technological, management and policy interventions. Towards this goal, we develop an integrated hydro-agro-economic optimization model to reconcile agricultural net revenue, irrigation practices, and envi-ronmental sustainability in the HID. Positive Mathematical Programming is used for model calibration to ensure the model can replicate the base year observations of crop acreage, making the model suitable for evaluating alternative scenarios. Scenario analyses are conducted to analyze the effects of water supply reduction, reducing winter irrigation, water-saving irrigation, and crop commodity price change on optimal agricultural water management practices. Results show that water supply reduction without complementary measures increases land fallow, exacerbates soil salinization, and reduces net benefits. Winter irrigation can conserve soil moisture and increase the net salt leaching in the root zone, and a reduction in winter irrigation will incur a benefit loss to the HID. Water-saving irrigation can stabilize planting areas under water shortage but exacerbate soil saliniza-tion. Price increase of a cash crop, if it has a large area share, tends to "crowd out" grain crops growing in the same season. These results provide a holistic perspective and useful insights for water management and policy in the HID.