Quantifying the Impact of Climate Change and Human Activities on Multiobjective Water Resource Management in the Hanjiang River Basin, China

The water resources system is at risk of water deficit due to climate change and significant agricultural and industrial development. Comprehensively quantifying the impact of climate change or human activities on water resources allocation is crucial in order for reservoir managers to understand potential risks. A two-parameter hydrological model and a multiobjective reservoir operation model were used in this study to understand the impacts of climate change and human activities on runoff and water resources management in the Hanjiang River Basin. We compared the measured runoff in the prechange period (1960-1989) with the simulated runoff obtained from the hydrological model in the postchange period (1990-2019). The results showed that human activities contributed to 79% of the runoff reduction, and climate change accounted for 21%. Seasonal contribution analysis indicated that human activities were the dominant reason for the runoff reduction, whereas climate change was primarily responsible for altered seasonal runoff patterns. A multiobjective reservoir operation model was established based on the actual runoff and the model-based runoff. The results showed that the impact of human activities had a more significant impact than climate change on the downstream water supply dispatching for human needs and irrigation. Its contribution rates increased to 88% and 83%, respectively. Climate change had a more significant impact on power generation, with its contribution rate increasing to 70%. By analyzing the dispatching process, it was found that climate change reduced the stability of monthly water level processes, leading to a decrease in the guarantee rate of water supply and power generation. Water diversion projects substantially reduced the available water volume and increased the risk of water deficit. It is recommended that the operation rules of the reservoir should be adjusted to adapt to the altered runoff patterns and water consumption patterns.