| In recent years,the global hydrological cycle system has accelerated,which has changed the spatial and temporal distribution of precipitation,and the runoff of many rivers has shown a significant decrease.The Daxia River nourishes the natural ecological environment of central Gansu and is a first-level tributary of the Yellow River.However,water resources in the Daxia River have changed with the continuous disturbance of the construction of cascade power stations in the basin.Therefore,find out the characteristics of runoff changes in the Daxia River Basin,and explore its influencing factors and the degree of influence of each factor.It can provide data reference and theoretical support for the future development and utilization of cascade power stations in the Daxia River Basin.In this paper,methods such as non-uniformity coefficient,extreme value ratio,anomaly accumulation curve,trend coefficient and R/S analysis method are used to analyze the change characteristics of runoff at Xiahe Station,Shuangcheng Station and Zheqiao Station in the Daxia River Basin from 1956 to 2018.The double accumulation curve is used to study the degree of influence of the factors affecting the runoff changes of the Daxia River.The conclusion as below:(1)The runoff of the Daxia River Basin is unevenly distributed throughout the year,mainly in summer and autumn.The runoff during the flood season accounts for about 2/3 of the annual runoff.After 1985,the runoff in the basin changed significantly,the concentration degree decreased,and the concentration period was 2-4 days earlier.The annual runoff in the Daxia River Basin showed a general downward trend with little annual variation range.The downward trend will remain unchanged for a period of time in the future,and the decreasing rate will gradually increase from the upper reaches to the lower reaches.The 1960 s runoff in the Daxia River Basin was relatively high,while in the 1990 s and 2000 s it was low,and the annual runoff showed an alternating change process of "abundant-low-abundant-flat-low-flat".(2)The annual distribution characteristics of precipitation and runoff in the Daxia River Basin are similar,and both show a single peak pattern.The annual precipitation in the Daxia River Basin showed a downward trend,and the annual change was small.In the 1960 s,1970s and 2010 s,the precipitation in the Daxia River Basin was relatively abundant,and the rest of the years were relatively dry.The sudden change in precipitation occurred around 1974.(3)The evaporation of water surface in Daxiahe River Basin is the highest in summer and the lowest in winter.The evaporation from April to August accounts for about 49%-55% of the annual evaporation.Since 1976,the water surface evaporation at Xiahe Station and Zhaqiao Station has shown a decreasing trend,while that at Shuangcheng Station has an increasing trend,and each station will maintain its original changing trend in the future.(4)The woodland and grassland in the Daxia River Basin account for about82.24%,and the forest vegetation coverage in the basin is high.The area of construction land and arable land increased from the end of 1970 to 2015 in the Daxia River Basin,while the area of other types of land decreased.Affected by "returning farmland to forest" and "natural protection project",after 2000,cultivated land decreased and woodland increased.(5)After 1985,the runoff in the Daxia River Basin decreased due to the influence of precipitation.The decreasing trend of downstream runoff slowed down from 1999 to 2018.Human activities reduced the runoff in the upper reaches of the Daxia River,increased the runoff in the second period in the middle reaches,and reduced the runoff in other periods.The impacts of human activities on runoff in the downstream regions fluctuated greatly.During 1985-1993 and 1999-2018,the impacts of human activities reduced the runoff,and the impact rate of human activities was above-70%,while the impact rate of human activities in 1994-1998 was 51.16%. |
PDF Full Text Request