Improving efficiency and sustainability of water-agriculture-energy nexus in a transboundary river basin under climate change: A double-sided stochastic factional optimization method

In this study, a double-sided stochastic fractional programming (DSFP) method is developed for identifying optimal water-allocation schemes of water-agriculture-energy nexus (WAEN) system under considering climate change impact. The advantages of DSFP are (i) handling complex uncertainty of double-sided randomness, (ii) addressing conflicting objectives with optimal system efficiency, and (iii) achieving trade-off between marginal benefit and system risk. Then, a DSFP-based water-agriculture-energy nexus (DSFP-WAEN) model is formulated for water resources allocation in a transboundary river basin of Central Asia, where 48 scenarios are designed to examine the impacts of climate change, irrigation efficiency, and system risk over a long-term planning horizon (2026–2050). Results reveal that: (i) among all agricultural activities, cash crop cultivation shows the greatest change in adaption to climate change, with the share of cash crop cultivation increasing to 70.7% by 2050 under RCP4.5; (ii) Kazakhstan, which has the largest irrigation needs and is the county most sensitive to water supply risk, should be the first to be constrained in the case of severe water shortages and poor delivery levels; (iii) the improvement of irrigation efficiency can increase the inflow to the Aral Sea by 2.7%, and reduce water loss of infield irrigation by 11.3% even under severe water shortage (i.e. p = 0.01). Compared with the models based on the traditional stochastic programming and single-objective methods, DSFP-WAEN has advantages in optimizing water-use efficiency and reflecting system complexity with flexible solutions. To coordinate transboundary water conflicts, strategies from both demand and supply sides related to quota management and water-saving techniques are suggested for the Syr Darya River basin, such as clean energy transition, drip irrigation promotion and canal system improvement. From a long-term planning perspective, WAEN schemes should be adapted to risk attitude and climate change, which can help address water scarcity and achieve future sustainability.