Allocation of water and land resources and ecological security in the black soil area of Northeast China

<p indent="0mm">In the context of rigid water resource constraints, realizing the rational allocation of water and land resources in the black soil area of Northeast China is of great significance in guaranteeing sustainable food production and ecological security. A continuing international frontier problem is how to integrate water resources, planting structure, food production, economic efficiency, carbon sequestration and ecosystem pattern in the optimal allocation of soil and water resources. Therefore, this study firstly analyzed the evolution of water and land resources in the black soil area of Northeast China, and then developed a water and land resource optimization model based on water-carbon-economy-ecology coupling. The model was solved with the NSGA Ⅲ intelligent algorithm. Finally, the developed model was used to analyze the optimal allocation of water and land resources and ecological security of 40 cities under four scenarios: conventional irrigation in a normal water year, water-saving irrigation in a normal water year, conventional irrigation in a dry water year, and water-saving irrigation in a dry water year. The results show the following: (1) Land-use types have changed considerably under the influence of climate change and human activities over the past <sc>40 years,</sc> with the areas of paddy fields and dry fields increasing by 91% and 14%, and the areas of woodlands, grasslands and wetlands decreasing by 2%, 27% and 10%, respectively. During the 10-year period from 2000 to 2010, land-use transformation was the most intense. (2) From 2001 to 2020, the total water resources in the black soil area of Northeast China fluctuated between 1267×10⁸ and <sc>2929×10⁸ m³,</sc> with average total water resources of <sc>1972×10⁸ m³.</sc> With a few exceptions, most of the cities showed an increasing trend in terms of surface water resources, groundwater resources and total water resources. (3) Under the four scenarios, the gross irrigation water requirements for four crops are 588×10⁸, 491×10⁸, 722×10⁸, and <sc>600×10⁸ m³,</sc> respectively. Climatic conditions in different hydrological years directly affect the balance between supply and demand of agricultural water resources, resulting in some areas not being able to satisfy the current irrigation requirements. After optimizing the allocation, the area under rice cultivation can still be increased by 13.7% in normal hydrological years by enhancing agricultural water-saving. Moreover, adjusting the crop planting structure and enhancing water conservation can also significantly increase the grain yield, farmers′ income, carbon sequestration and ecological benefits in other hydrological years, save water resources by reducing the exploitation and utilization of water resources, and guarantee food security and ecological safety. The ecological benefits are only slightly reduced under conventional irrigation conditions in a dry hydrological year, which are related to the indirect constraints of limited water resources. In response to the current problems of water and land resources, we suggest that the government should actively carry out agricultural water-saving in the field and process, and adjust the agricultural planting structure based on limited water resources. At the same time, based on the existing spatial distribution pattern of forest, grass and wetland and arable land, adjust the planting structure and the area of forest, grass and wetland. In water-scarce areas (e.g., Chifeng City, Tongliao City, etc.), the area of corn and woodland can be appropriately increased to improve the carbon sequestration capacity of ecosystems and agricultural systems. This study will provide strategic support for the project of increasing grain yield and ecological security in the black soil area of Northeast China.