Irrigation water sources can greatly contribute to the reserve resources of arable land in northern China. National water network projects have also promoted the arable land reserve resources in recent years. In this study, a systematic evaluation was performed on the potential of cultivated land reserve resources under a water supply project in the northern region. The constraints of natural suitability, efficient use, and stable development were comprehensively analyzed to consider the ecological and spatial fragmentation of arable land reserve resources. The three-dimensional magic square was adopted to select evaluation units. Finally, the arable land reserve resources were optimized to fully meet the three requirements of sustainable ecology, natural quantity, and efficient quality. The results show that: (1) In rain-fed agriculture scenario, the area of unsuitable (Level I) development for cultivated land reserve resources in the unused land in the north was accounted for as high as 96 %, about 1.036 million km², and the areas of barely suitable (Level II), moderate (Level III) and high (Level IV) were 2.9×10⁴, 1.0×10⁴ and 6.0×10³ km², respectively. Thus, the unused land shared less potential space to meet the reserve development of cultivated land under the limitation of natural precipitation. (2) In the irrigated agriculture scenario, the potential of arable land reserve resources increased significantly in the north region. The area suitable for arable land reserve resources increased to about 2.0×10⁵ km², accounting for 18% of the total area, mainly located at the edge of the Junggar Basin in Xinjiang, the edge of the Tarim River, the Shule River Basin in Gansu, and part of Inner Mongolia. (3) A comparison was made between the rain-fed and irrigated agriculture scenarios. Irrigation conditions with relatively scarce water resources were required to greatly improve the arable suitability of land resources at the naturally appropriate level. The suitable cultivated area increased from less than 3 000 km² under the rain-fed scenario to about 48 000 km², in order to optimize the allocation of land resources. (4) There was a small error in the geographical location and the number of cultivated land reserve resources, compared with the previous. Therefore, the evaluation model of cultivated land reserve resources presented high accuracy and credibility. The findings can provide a strong reference for the development and utilization of arable land reserve resources under the national water network projects in China.

In order to realize the water-energy-food cooperation in the Beijing-Tianjin-Hebei region, 31 indicators were selected to construct a safety index system for water-energy-food coupling system from reliability, synergy and resilience. The security level of water-energy-food coupling system in the Beijing-Tianjin-Hebei region from 2000 to 2020 was analyzed, and the joint risk probability was calculated based on Copula function. The results show that the security index of water-energy-food coupling system in the Beijing-Tianjin-Hebei region shows an overall upward trend from 2000 to 2020. The annual average index of Beijing is the highest, reaching 0.63, and that of Hebei is the lowest, only 0.48. There is no significant difference in reliability levels among different regions, and they all exhibit poor levels. The main obstacles influencing the security of the water-energy-food coupling system include per capita water resources, per capita energy consumption, the proportion of groundwater supply, and carbon dioxide emissions. The probability of achieving a relatively safe level of reliability, synergy, and resilience in the Beijing Tianjin Hebei region is 0.723, and uneven development will affect the overall security of the water-energy-food coupling system.