The characteristic and cause of runoff variation in Jinsha River basin

Jinsha River is the mainstream of the upper reaches of the Yangtze River, which originates from the Tanggula Mountains Galadan Snow Mountain. The river has superior hydropower development conditions, but it is also accompanied by serious soil erosion problems. In recent years, large-scale water and soil control and water conservancy project construction activities have been carried out in the Jinsha River basin (JRB), which has affected the intra-annual and inter-annual variation process of runoff to some extent. In the future, with the continuous demonstration and implementation of a series of major national strategic projects, the trend of water resources demand in JRB will rise significantly and continue to increase. Therefore, it is of great significance for the sustainable utilization of water resources to carry out the analysis and research on the characteristics and causes of runoff under the changing environment in the Jinsha River basin.Based on 60 years of measured precipitation and runoff data of JRB, the impact quantity change process of long-term human activities such as reservoir projects and production and living water intake on runoff was estimated and the water balance method wsa used to calculate and restore the natural runoff. The Mann-Kendall test, wavelet analysis, and other mathematical statistics methods were used to study the variation trend, change cycle, and possible abrupt years of precipitation and natural runoff in JRB. At the same time, the concept of normalized vegetation index was introduced to analyze the variation causes of natural runoff, and the correlative relationship between natural runoff and the combined effect of precipitation and normalized difference vegetation index was constructed. The results show that: (1) The average annual precipitation is 604.6 mm, and the average annual natural runoff is 149 billion m3in JRB. Both of them show an increasing trend, but the increasing trend of precipitation is obvious, and the increasing trend of natural runoff is not significant. The corresponding ten-year average increment of precipitation and natural runoff is 7.7 mm and 860 million m3, and the ten-year relative increase percentage is 1.28% and 0.57%, respectively. The precipitation and natural runoff in JRB generally change periodically, and the main change cycle is consistent, which is 28 years. The precipitation has an abrupt point in 1990, and the natural runoff shows that there is no abrupt point. (2) The precipitation is the main impact factor causing runoff changes in JRB, but the relative increase percentage of natural runoff is smaller than that of precipitation. The reason for the difference in increased amplitude between the two research objects is mainly due to the increase of vegetation cover in the basin. There is a negative correlation between vegetation cover and runoff change. Overall, the better the vegetation cover, the more pronounced the runoff attenuation. The average normalized difference vegetation index of JRB was 0.592, and the increasing trend was obvious, with a ten-year average annual increase of 0.045. (3) Compared with the single impact factor analysis of precipitation or normalized difference vegetation index, the established response relationship correlation between natural runoff and the combined effect of the two impact factors increases, and the correlation coefficient reaches 0.940. Considering the combined effect of precipitation and vegetation can more accurately reflect the actual situation of runoff change. The relationship between natural runoff and the combined effect of precipitation and normalized difference vegetation index is R = 0.017 7 P1.691N?0.923. The research results can provide decision-making reference and scientific guidance for hydropower development and comprehensive management in JRB.

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