Hydrological Regime Alteration And Ecological Flow Guarantee Rate In The Xijiang River Main Stream Under Changing Environment

Under the influence of climate change and human activities,the natural hydrological process of river runoff has been destroyed in the Xijiang River basin,seriously affecting the ecosystem of the basin.As two important indicators of ecosystem health,the hydrological regime and the ecological flow assurance rate are used to explore the specific changes under changing circumstances,and thus to identify the adverse impacts on the ecosystem,with a view to providing reference and guidance for the ecological protection of the Xijiang River.This paper takes four hydrological stations in the main stream of the Xijiang River,Tian’e,Qianjiang,Wuxuan,and Wuzhou,as the research objects.Based on the simulation of natural runoff at each hydrological station,the adverse effects of climate change and human activities on the ecosystem are analysed from the perspectives of hydrological regime and ecological flow assurance rate,and the attribution method based on hydrological simulation is used to investigate the degree of influence of climate change and human activities on the change of hydrological situation,the main research contents are as follows::(1)Simulation of natural runoff in the changing period of the Xijiang River main stream.The first abrupt changes at each hydrological station were found to be concentrated in the late 1980s and early 1990s by using the sliding T and M-K multi-surge tests,and this was used to classify the natural runoff period and the change period.Based on the meteorological runoff data in the natural period,a random forest model was constructed to simulate the natural runoff under the influence of climate in the changing period.and two indicators,NSE and R2,were used to evaluate the simulation effect.(2)Analysis of the changes in the hydrological regime of the Xijiang River main stream and its attribution.Based on the hydrological index method,PCA was used to select the most ecologically relevant hydrological indexes,and the overall hydrological changes were investigated from the perspectives of Do and DHRAM.The results showed that the overall changes in hydrological conditions at all hydrological stations were moderate,with Tian’e and Qianjiang stations showing more drastic changes than Wuxuan and Wuzhou stations,and the protection of the upper reaches should be a priority.Climate change and human activities are both important factors in causing changes in hydrological conditions,with the degree of influence of climate change on hydrological conditions gradually increasing from upstream to downstream.(3)Calculation of ecological flow and analysis of the variation characteristics of the ecological flow guarantee rate in the main stream of the Xijiang River.Five types of distribution curves were used to fit the natural monthly runoff series of each hydrological station,and it was found that the best-fitted curves were mostly GEV and P-Ⅲ type distributions.Based on this,the flow rate at 90%guarantee rate was used as the ecological flow rate for each month to form the ecological flow process within the year,and the calculation results were found to be reasonable and reliable after testing with the Tennant method.After a sudden change in runoff,the guaranteed rate of ecological flow decreases to a certain extent during the change period compared to the natural period,with a more drastic decrease at Tian’e and Qianjiang stations and a more pronounced decrease during the flood season(July to October).