Study on runoff abundance and depletion encounters in the upper reaches of the Yangtze and Yellow Rivers under climate change

Abstract

[Objective] The upper reaches of the Yangtze and Yellow Rivers, located in the eastern Qinghai-Xizang Plateau, serve as major water production and conservation areas. The study aims to analyze the impact of climate change on the probability of runoff abundance and depletion encounters in the water source and receiving regions of inter-basin water diversion projects in this area, thereby providing theoretical support for improving project planning, design, and operational efficiency. [Methods] A bivariate Copula function was employed to construct a runoff abundance and depletion encounter probability model, analyzing the characteristics of these probabilities in the upper reaches of the Yangtze and Yellow Rivers over the past 40 years. Distributed hydrological models and climate scenarios were used to predict changes in runoff abundance and depletion encounter probabilities by the mid-21st century and the end of the 21st century, as well as the response characteristics of diversion-favorable probabilities to climate change. [Results] During the historical period(1978—2020) in the study area, an overall increasing trend in annual runoff was observed. Significant fluctuations in runoff were recorded during the summer and autumn seasons(-3.29~11.78 m³·s^-1/a), reflecting distinct seasonal characteristics. The highest rate of increase in summer-autumn runoff was found in the Jinsha River Basin, which was generally higher than the runoff change trend in the Yellow River source region(-2.3~0.73 m³·s^-1/a), aligning with the requirements for water diversion. On an annual and flood season scale, the synchronous frequency of runoff abundance and depletion was generally higher than the asynchronous frequency, while on a non-flood season scale, it was lower. The probability of diversion-favorable conditions ranged from 68% to 75%, ensuring water supply feasibility. Future projections indicate that annual and flood season diversion-favorable probabilities will generally exceed historical values(3.53%~5.44%), whereas probabilities during the non-flood season under SSP245 and early SSP585 scenarios will fall below historical levels(-1.57%~0.91%). [Conclusion] Transitioning from SSP245 to SSP585 scenarios, the probability of asynchronous runoff abundance and depletion encounters is projected to increase, indicating that extreme climate conditions may lead to greater spatial differences in water resource distribution and more pronounced temporal-spatial variations. The average probability of diversion-favorable conditions is estimated to range from 71.2% to 73.2%, suggesting a high likelihood of compensatory water regulation. This finding is highly favorable for the implementation of the Western Route of the South-to-North Water Diversion Project, enabling compensatory water diversion during both flood and non-flood periods at different time stages.

Keywords

runoff evolution / abundance and depletion encounters / Copula function / climate change / Qinghai-Xizang Plateau / Yellow River / Yangtze River Basin / Western Route of South-to-North Water Diversion Project