Ecological water requirements and the water–carbon–economy coupling in rubber plantations: estimation and optimization in Southwestern China

The mountainous region of Southwest China, as a globally significant rubber-producing region, faces the critical sustainability challenge of balancing ecological water requirements (EWR) with the water–carbon–economy (WCE) nexus. Large-scale rubber cultivation has driven economic growth, water consumption, trade-offs between socio-economic and ecological objectives. We developed a triple-objective the Non-dominated Sorting Genetic Algorithm III (NSGA-III) framework that maximizes economic benefits and carbon sequestration while minimizing EWR. The framework embeds age-dependent actual crop coefficients (K c,actual ) derived from Bowen ratio-energy balance measurements at rubber plantation. It generates hydrology-specific Pareto frontiers (wet, normal, dry) years and ranks the 500 non-dominated solutions using Technique for Order Preference by Similarity to Ideal Solution(TOPSIS) under S0 (balanced), S1 (economic-priority), S2 (carbon-priority), and S3 (ecological-priority) management schemes. The results indicate that: (1) the annual EWR of rubber plantations in Southwest China ranges between 871.3 and 1098.4 mm, with seasonal variations and water deficits during the dry season; (2) the Pareto optimality-based optimization scheme balanced economic and ecological benefits, reducing EWR by 4.8–5.0% across all hydrological years. The most significant improvement in carbon sequestration occurred under wet and normal years conditions, increasing 17%; (3) wet year demonstrated the greatest optimization potential, 2.3-fold improvement. Due to water restrictions, economic benefits decreased 11.9% (normal year) and 8.1% (dry year) but increased 127.3% in wet year. Carbon sequestration improved 21% in wet and normal years but declined –1% in dry year. The innovative contribution of this study lies in proposing a coupled WCE multi-system analysis framework, which provides a quantitative decision-making tool for the sustainable management of rubber plantations and offers insights for resource optimization in tropical crop planting regions.