Dynamic evaluation of the matching degree and utilization condition of generalized agricultural water and arable land resources in China

Water and land resources are the core elements of agricultural development, and their matching situation and degree of utilization determine agricultural sustainability and food security in China. In order to promote the optimal allocation of agricultural water and land resources in China, based on the statistical data for the 31 provinces in the mainland of China from 2000 to 2020, this study dynamically evaluated the matching degree of agricultural water and arable land resources according to the generalized agricultural water and land resources matching index and Gini index, determined the agricultural water and land resources zoning by integrating their matching degree and the utilization condition. The results showed that: 1) During the study period, there was a large gap between the distribution of irrigation water and arable land in China, with the mean Gini index calculated as 0.424, and the matching situation had deteriorated. The distribution of generalized agricultural water resources and arable land resources was relatively reasonable, with the mean Gini index calculated as 0.360, and the change was relatively stable. Great differences on the matching degree existed between provinces and geographic areas. The matching conditions in North China, Northeast and Northwest were "more land and less water", and the matching conditions in East China, Central China and Southwest were "more water and less land". The average values of the generalized agricultural water and land resources matching index were 2.06 for Guangdong and 1.02 for Yunnan, presenting the lowest and highest matching degrees among the provinces, respectively. The variation in the generalized agricultural water and land resources matching index increased with the value of the matching index, and the values of the matching index were related to the share of precipitation, showing a first increasing and then decreasing trend with the increase of the share of precipitation. 2) The utilization degree of agricultural water resources fluctuated with the abundance and decline of water resources from 2000 to 2020.The spatial heterogeneity of agricultural water and land resources utilization was obvious, with the reclamation rate generally "high in the southeast and low in the northwest" and the utilization degree of agricultural water resources "high in the north and low in the South". Especially, the reclamation rates in Henan and Shandong were more than 40%, while those in the northwest were less than 10%. And the utilization degrees of agricultural water resources in Tianjin (78%) and Hebei (74%) were higher than the development and utilization limit in 2020. 3) The agricultural water and land resources zoning in 11 provinces had changed from 2000 to 2020. The allocation of water and land resources in Jilin, Xinjiang and Jiangsu provinces deteriorated to the type of low matching high utilization zoning, while the allocation of water and land resources in Beijing improved to the type of high matching low utilization zoning. The main reason for the zoning changes was the change of matching degree for Xinjiang and Jiangsu and the changes in the utilization degree of water and land resources for Beijing and Jilin. As of 2020, 5 provinces, including Hebei, Shanxi, Jiangsu, Jilin and Xinjiang, belonged to the type of low matching and high utilization zoning, presenting the worst allocation of water and land resources, while 8 provinces, such as Beijing, Shaanxi, Sichuan and Qinghai, belonged to the type of high matching and low utilization, presenting good allocation of water and land resources. The results can provide support for the relevant decision making of the optimal allocation of agricultural water and land resources in China and are of great significance to achieve national food security and agricultural sustainable development.