An appropriate agricultural water-land nexus can help to effectively take advantage of limited water and land resources, which is of great significance for guaranteeing food security. An R index was proposed to evaluate the regional agricultural water-land nexus from a green-blue water perspective in the current paper. The effects of irrigation on the agricultural water-land nexus were revealed for the first time based on this index in evaluations of all (Rt) and irrigated (Ri) arable land in the 31 provinces, autonomous regions and municipalities (PAMs) of China during 1999-2018. The national annual average values of Rt and Ri were 1.94 and 3.55 m3/m2, respectively; the former was steady during the observed period, while the latter showed a significant decreasing trend (P < 0.01) from 4.35 m3/m2 in 1999 to 2.66 m3/m2 in 2018. The values of both Rt and Ri values in South China were higher than those in North China. The maximum values of Rt and Ri appeared in Xizang (Rt = 99.15 m3/m2; Ri = 201.99 m3/m2), while the minimum values occurred in Ningxia (Rt = 0.30 m3/m2; Ri = 0.44 m3/m2). The Gini coefficient for Ri (Gi) in each year was higher than that for Rt (Gt), demonstrating that the agricultural water-land nexus in irrigated arable land was highly imbalanced during the last two decades. From the perspective of the equitable distribution of irrigation water, irrigation facilities should be developed in the Southeast and Southwest PAMs to improve the effective irrigation rate. In addition, the government should simultaneously implement water transfer plans to reduce the agricultural water pressure in the PAMs in the North China Plain and Northeast China.
Keywords: Gini coefficient; Green-blue water; Irrigation; Water-land nexus.
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