Multi-objective water resources allocation for synergistic coupling of the water-ecology-economy nexus in arid river basins

• Reveals distinctive 'S'-shaped and 'J'-shaped nonlinear relationships between crop water shortage rates and growth decay rates. • A novel method for characterizing pairwise coupling relationships in WEE nexus subsystems is developed. • A multi-objective water resources allocation model balancing ecological benefits, economic benefits and carbon sequestration is constructed. Rational water resources allocation is crucial for achieving the synergistic development of the water-ecology-economy (WEE) nexus in arid basins. Quantitative assessment of individual water users’ benefits under different water shortage rates provides a robust basis for allocation strategies. This study clarifies the pairwise coupling relationships between the water system and other subsystems using a growth curve function. These relationships are integrated as efficiency functions into a multi-objective water resources allocation model that simultaneously optimizes economic benefits, ecological benefits, carbon sequestration, and spatial equilibrium. The water supply volumes allocated to four vegetation types are designated as decision variables. Four scenarios are evaluated: ecological priority, economic priority, balanced optimization, and comprehensive benefit maximization. Allocation performance is assessed using the coupling coordination degree (CCD) method. This research takes the Tarim River Basin, a typical arid basin, as a case study. Key findings reveal that "S"-shaped and "J"-shaped nonlinear relationships exist between crop growth decay rates and water shortage rates. To avert significant losses, it is advisable to maintain water shortage rates below the first inflection point. Notably, most sub-basins perform optimally under the comprehensive benefit maximization scenario, exhibiting the highest CCD in the WEE nexus. These findings provide scientific guidance for both efficient water resource utilization and sustainable development of the WEE nexus in arid basins.