Assessing water resources service value through simulation of a water supply–hydropower generation–ecosystem photosynthesis nexus system

Abstract

Water resources generate service values through water supply (S), hydropower generation (H), and ecosystem photosynthesis (E), forming a SHE nexus system that supports sustainable water resource management under the impacts of both climate change and human activities. However, these service values are often assessed in isolation, overlooking the complex interactions within the SHE nexus system and hindering the water resource management. To address this issue, we have coupled an ecohydrological model, reservoir operation rules, and a value assessment model to simulate the intricate dynamic and quantify the service values within the SHE nexus. The couple model is applied to the Han River Basin (HRB), which serves as the critical source region for the Middle Route of the South-to-North Water Diversion Project (MRSNWDP) in China. The results reveal significant trade-offs among these service values: water supply is the most prominent in low-elevation croplands, hydropower dominates high-elevation grasslands, and ecosystem photosynthesis peaks in mid-elevation forests. The synchronous variations in these service values are primarily driven by climate factors (∼ 60%) in the upper HRB, whereas hydrological processes dominate in the middle and lower reaches. Increased precipitation promotes hydropower generation and photosynthesis capacity. Reservoir operations improve water resource service values via increased streamflow; however, the MRSNWDP suppresses these gains wet seasons by reducing available flow for power and ecosystems. Therefore, our proposed model quantifies water resource service values to support integrated land–water management and water diversion operations.