Assessing the effects of water resources allocation on the uncertainty propagation in the water-energy-food-society (WEFS) nexus

The water-energy-food-society (WEFS) nexus is profiled for sustainable development. The WEFS nexus exhibits strong uncertainty owing to the stochasticity of model structure, and water availability uncertainty under climate change and human activities. The WEFS nexus remains highly risky, as the uncertainty propagation in the WEFS nexus under the regulation of water resources allocation has rarely been investigated. In this study, white Gaussian noises were integrated into a system dynamic model for the WEFS nexus simulation, transforming the nexus from deterministic to stochastic. Based on a Monte Carlo simulation of the stochastic WEFS nexus with water availability uncertainty, the copula function was applied to evaluate the joint distributions between water availability and water shortage rates in the upstream and downstream zones to investigate the uncertainty propagation in the WEFS nexus. The effects of water resources allocation on the uncertainty propagation were analyzed by setting different water resources allocation schemes. The proposed approach was applied to the mid-lower reaches of Hanjiang River basin in China as a case study. The results indicate that an effective water resources allocation scheme can ensure water supply, and diminish the impacts of water availability uncertainty on water supply through reservoir operation. The annual average water supply rate increased from 84.74% to 93.45%, and the standard deviation decreased from 3.37% to 1.78%. The high-level environmental awareness evoked by water or food shortages decreased significantly with smaller uncertainty. The co-evolution of the WEFS was ensured through its nexus. Water storage capacity was the vital factor to regulate the uncertainty propagation in the WEFS nexus. The impacts of upstream water availability uncertainty were efficiently regu-lated via reservoir operation for the zones with sufficient water storage capacity. Water supply was ensured and there was no significant response of the WEFS through its nexus to different water resources allocation schemes. If there was few water storage capacity in a zone, the water supply was remarkably influenced by the water availability uncertainty in the upstream zone. The water supply was difficult to ensure, and was sensitive to different water resources allocation schemes. The environmental awareness evoked by water or food shortages increased. The environmental awareness feedback under the impacts of the noises increased water demand uncertainty by altering the socioeconomic expansion, further increased WEFS uncertainty through its nexus, particularly when water availability was much smaller than water demand. The proposed approach can help quantify the effects of water resources allocation on the uncertainty propagation in the WEFS nexus and contribute to the sustainable development of the WEFS nexus.