| With the improvement of the regional ecological environment,the runoff and sediment of the Yellow River has been drastically reduced.It is essential to study the changes of daily runoff in the Yellow River Basin and its driving factors.This study was to analyze the characteristics of runoff changes in the Huangfuchuan Basin and the Yanhe River Basin from the year-month-day scale.The Mann-Kendal trend test,Pettitt mutation test,anomaly accumulation method,concentration period,and flow duration were used.The curve method was used to analyze the characteristics of runoff changes on the year-month-day scale of the regional watershed.The method of defining the frequency distribution and calculating the number of days of extreme daily mean flow was further proposed.The change process of the daily runoff was carefully described and the hydrological analysis method was used to quantify the data.The influence of precipitation and human activities on the extreme runoff provides a reference for the assessment of the environmental effects of regional water and soil conservation and ecological construction and the development and utilization of water resources.The main results obtained are as follows:(1)Changes of Annual Runoff in the Huangfuchuan River and Yanhe River Basins.The average annual runoff of Huangfuchuan River and Yanhe River Basin showed a significant decreasing trend from 1953 to 2015(P>0.01).For the Huangfuchuan river,the average annual runoff was 130 million m~3,and the maximum runoff was 508 million m~3(1954);the minimum value is 0 million m~3(2011).For the Yanhe River,the average annual runoff was205 million m~3,the maximum runoff was 502 million m~3(1964),and the minimum was 95million m~3(2008).The two river basins were divided into three phases using the method of cumulative anomalies.The Huangfuchuan drainage basin was the abundant section(1953~1984),the weaker year(1985~1996),and the dry period(1997~2015);Yanhe River Basin was the more abundant(1953~1970),the period of less abundant period(1971~1996),and the dry period(1997~2015).(2)The distribution characteristics of the year of Huangfuchuan and Yanhe River basins.The annual distribution of runoff in the Huangfuchuan river and Yanhe river during1953-2015 was“double-peak”.The wavelet peaks in March and the major wave peaked in July-August.For the Huangfuchuan River,the maximum monthly average runoff was 668.56m~3/s,and the Multi-year average non-uniform coefficient was 1.80,and the overall degree of concentration showed an increasing trend,The maximum was as high as 3.31(2009),The azimuthal variation of the concentration period was 127.79°~254.06°(from May7 to September 10);For the Yanhe river,the maximum monthly average runoff was597.09m~3/s,and the Multi-year average non-uniform coefficient was 0.96,The concentration was mostly small and fluctuating around the mean(0.48),and its concentration period was158.29°~269.81°(June 6 to September 25),which was comparable to Huangfuchuan watershed was more concentrated.(3)Characteristics of the daily mean flow variation in the Huangfuchuan and Yanyan rivers.The daily average flow in the Huangfuchuan River Basin was mainly concentrated on the 181st to 241st days,that is,from July to August,while the average daily flow in the Yanhe River Basin taked a 30-day cycle,with peak values in July and August.Combined with annual runoff Pettitt mutation test and phase analysis results,the two basins basically showed a large amount of water in the flood season and a small amount of water in the non-flood season,and they all had the most water in the first stage(14.2m~3/s in the Huangfuchuan flood season,1.8m~3/s in non-flood season;15.33m~3/s in Yanhe flood season,3.64m~3/s in Yanhe non-flood season),followed by the second phase(9.06m~3/s in Huangfuchuan flood season,0.68m~3/s in non-flood season,13m~3/s in Yanhe flood season,3.59m~3/s in Yanhe non-flood season),and the third phase was the smallest(3.55m~3/s for the Huangfuchuan flood season,0.09m~3/s for the non-flood season,8.22m~3/s for the Yanhe flood season,and 3.21m~3/s for the non-flood season).In the Huangfuchuan River Basin,the high flow and constant flow decreased more,but the daily flow curves of the three phases in the Yanhe River Basin basically coincide,the high flow characteristic value decreased with the phase change,and the constant flow and low flow characteristic values was increased trend with the phase.(4)Changes in the days of extreme daily average flow in the Huangfuchuan and Yanyan rivers.According to the frequency analysis method,the days of extreme daily average traffic thresholds was defined and the indicators are determined(the threshold days for the maximum and minimum daily traffic in Huangfuchuan were 45.6m~3/s and 0.36m~3/s,and Yanhe were 32.3m~3/s and 1.65m~3/s).The average daily average discharge days of the Huangpuchuan River averaged 5.6 days,and the maximum was 23 days(1959).Since the1880s,there have been zero occurrences,and the average daily average flow days have been in the period from 1953 to 2015.The trend of decrease was significant(P>0.01),which was the same as that of annual runoff.However,the days of minimum daily mean discharge was opposite to that of annual runoff.In 1992,when it was the year of mutation,it first decreased and then increased.For large changes,the number of years of average annual occurrences was193.7 days,the maximum was 365 days(2011),and the minimum was 16 days(1954).The days of average daily and maximum daily discharges in Yanhe River showed a significant(P>0.01)decrease from 1953 to 2015,similar to the trend of annual runoff,and the average number of days of great daily average flow was 8.6 days.The value was 26 days(1964)and the minimum was 0 days(2008).The average daily number of days of minimum daily flow in Yanhe is 83.7 days,the maximum number of days is 159 days(1992),and the minimum is 13days(1964).In terms of distribution during the year,the indicators of the maximum daily flow in the two basins were concentrated in the period from July to August in the flood season.The minimum daily flow occurred mainly in winter(decreasing trend between years)and summer(mostly during the years).(5)The number of days in which the turbulence occurred in Huangfuchuan increased with the progress of the year.The number of years of average annual turbulence was 151 days.The trend of the minimum runoff and the number of days in which the minimum daily flow occurred was opposite;Yanhe only had a 12-day cut-off,and the extreme runoff was in the same trend as the days of extreme daily mean flow.(6)Soil and water conservation activities are the main driving factors for extreme runoff changes in the Yanhe River Basin,and the contribution rate exceeds 60%.However,precipitation is still the main factor affecting the reduction of the maximum runoff in the Huangfuchuan River Basin.The contribution rate is as high as 57.23%. |
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