Planning water-food-ecology nexus system under uncertainty: Tradeoffs and synergies in Central Asia

Vicious competition for limited water resources hinders the synergetic and sustainable development of Central Asian countries, which further threatens food security and exacerbates ecological degradation. In this study, a copula-based bi-level decentralized programming (CBDP) method is developed and applied to planning water food-ecology (WFE) nexus system. CBDP has advantages in balancing tradeoffs between different decision levels, analyzing synergies among multiple managers and reflecting joint risks of interrelated uncertain parameters. Then, a CBDP-WFE model is formulated for Central Asia, where the upper-level model aims to maximize system benefit for the region (i.e. regional-scale), and the lower-level model involves five objectives to maximize five countries' benefits (i.e. national-scale) respectively. Totally 108 scenarios are designed to analyze the impacts of joint constraint-violation risk, agricultural irrigation efficiency, and ecological water demand. Results reveal that (i) improving agricultural irrigation efficiency can optimize the water allocation pattern as well as increase the system benefit; (ii) in order to restore the regional eco-environment, the proportion of ecological water allocation should increase from 7% (of the current level) to 14.9-23.8% (by 2050); (iii) water allocations to Uzbekistan and Tajikistan should be properly controlled especially when available water is scarce. The results are helpful for managers in not only making decisions of water allocation among multiple users and countries but also gaining insight into synergetic management of WFE nexus under various system conditions.