Effects Of Precipitation Variation And Human Activities In Runoff And Sediment Variation

Precipitation variation and human activities are the key influencing factors of runoff and sediment in the watershed.Quantitative study of their effects on runoff and sediment variation has important scientific significance for ecological construction in the watershed.Based on the hydrological and sediment data of the Zhangshui watershed in the upper of the Ganjiang River from 1961 to 2020,this study used linear trend rate method,moving average method,wavelet analysis,Mann-Kendall test,sliding T test and other methods to analyze the annual distribution,interannual variation,periodic variation and mutation characteristics of precipitation,runoff and sediment.The land use change in Zhangshui watershed was analyzed by land use dynamic degree method and land use transfer matrix.The contribution rates of precipitation variation and human activities to runoff and sediment were quantitatively calculated by using the cumulative slope change rate comparison method.The critical value of the response of runoff and sediment effect of human activities to annual precipitation was explored by empirical statistical analysis.The results show that:(1)From 1961 to 2020,the annual distribution of precipitation in Zhangshui watershed was uneven,showed a single-peak curve distribution,and the precipitation was mainly concentrated in March to June;precipitation showed a non-significant downward trend at a tendency rate of-0.59 mm/10 a,with an average annual precipitation of 1425 mm.The precipitation mainly had three periodic changes of 3～7 a,8 ～20 a and 25～32 a,and the first main cycle of precipitation change was 16 a.The precipitation abruptly changed in 2003.The main human activities in Zhangshui watershed from 1961 to 2020 were land use change and water conservancy and water conservation project construction.Among them,human activities mainly based on reservoir construction and soil and water conservation project implementation were the dominant factors for water and sediment reduction in Zhangshui watershed.(2)The annual distribution of runoff and sediment discharge in Zhangshui watershed from 1961 to 2020 was uneven,and both were unimodal curve distribution.The runoff and sediment discharge were mainly concentrated from April to June.The runoff showed a nonsignificant downward trend.The sediment discharge showed a significant downward trend.The runoff mainly had three periodic changes of 3～7 a,8～20 a and 25～32 a,and the first main cycle of runoff change was 30 a.The sediment discharge mainly had three periodic changes of 3～7 a,8～21 a and 24～32 a,and the first main period of sediment discharge change was 16 a.The runoff changed abruptly in 2003,and the sediment load changed abruptly in1998.There were significant positive correlations between precipitation-runoff,precipitation-sediment and runoff-sediment.The correlation between precipitation-runoff was stronger than that between precipitation-sediment,and the correlation between runoffsediment was stronger than that between precipitation-sediment.(3)The contribution rates of precipitation variation and human activities to runoff reduction in Zhangshui watershed were 10.7% and 89.3%,respectively,and the contribution rates to sediment reduction in Zhangshui watershed were 3.5% and 96.5%,respectively.Whether for runoff or sediment,the contribution rate of human activities was much greater than that of precipitation variation.(4)The runoff and sediment effect of human activities was restricted by precipitation conditions.The critical value of the response of the runoff reduction effect of human activities to annual precipitation was 1170 mm.When the annual precipitation was greater than 1170 mm,human activities lead to runoff reduction,and the water reduction effect of human activities was positive.When the annual precipitation was less than 1170 mm,human activities lead to an increase in runoff,and the water reduction effect of human activities was negative.The critical value of the response of the sediment reduction effect of human activities to annual precipitation was 858 mm.