Runoff Evolution Regularity And Attribution Analysis In Yuanshui Watershed

Affected by both abnormal climate change and human production activities,flood and drought disasters occur frequently and irregularly in Yuanshui watershed,which has an important impact on the socio-economic development of Yuanshui watershed.In this paper,the influence of climate change and human activities on runoff change in Yuanshui basin are studied by using statistical methods and SWAT hydrological model of Yuanshui basin.The main conclusions are as follows:(1)The trend and abrupt change of runoff,precipitation and temperature in Yuanshui Basin are analyzed by statistical method.The annual runoff of Anjiang Station and Pushi Station shows the increasing trends in the fluctuation with the rates of 0.84*106 m3/a,36.8*106 m3/a,while the annual runoff of Taoyuan Station shows a decreasing trend in the fluctuation with the rates of-21.5*106 m3/a.The annual runoff of Pushi Station has the greatest degree of change.Morlet wavelet analysis of runoff series shows that the main period of runoff is 5 years and 10 years.Using Mann-kendall test and sliding t test,the trend sudden change analysis of the annual average runoff series of three hydrological stations was carried out.It was found that the change occurred in 1989 and 2004.The boundary point of the hydrological series was 1989 and 2004,taking 1959-1988 as the base period,1989-2003 as the variation period I,and 2004-2014 as the variation period II.The spatial distribution of precipitation in Yuanshui River Basin is uneven,and it gradually increases from southwest to Dongting Lake area.From the distribution of precipitation in the year,there are more in spring and autumn seasons,fewer in autumn and winter seasons,and the precipitation in June is the largest.The annual precipitation in Yuanshui River Basin fluctuates greatly from 1959 to 2014,but the overall trend of decline is not significant.The precipitation series has a four-year main cycle,The succession of high and low in 1977-1992 is significant,and the precipitation series has a significant mutation in 1989 and 2004.The annual average temperature in Yuanshui River Basin shows an upward trend with an increase of 0.14?/10a.From 1989 to 2003,the temperature in Yuanshui River Basin increased the most,and then stabilized after 2004.The annual temperature series changed abruptly in 1997.(2)Statistical methods were used to quantitatively assess the impact of precipitation and human activities on runoff change in each variation period.Taking 1959-1988 as the base period,without considering evapotranspiration,In the period of variation ?,human activities are the main influencing factors of runoff change in the upper reache s of Anjiang Station in Yuanshui,with an impact rate of 60%.In the lower reaches of Yuanshui River,runoff change is mainly affected by precipitation,with an impact rate of 74.3%.In the period of variation ?,human activities have increased to varying degrees,and The contribution rate of human activities in the lower reaches of Yuanshui River Basin increased the most.(3)Based on the SWAT hydrological model of Yuanshui River Basin,the impacts of climate change and human activities on Runoff in Yuanshui River Basin were quantitatively analyzed.Yuanshui SWAT model driven by meteorological data from 1980 to 2013 and land use data from 1990,2000 and 2010.Good simulation results are obtained:The determinant coefficients of the three hydrological stations are above 0.89,and the Nash-Sutcliffe are above 0.84.After calibrating and validating the hydrological model,keeping the parameters of each basin unchanged,the SWAT hydrological model simulation method was used to quantitatively analyze the impact of climate change and human activities on the runoff of the basin.Compared with 1980-1988,the runoff caused by climate change increased by 10.87 billion m3 from 1989 to 2003,and the contribution rate of climate change to runoff change accounted for 93.5%,while the runoff caused by land use decreased by 120 million m3.From 2004 to 2013,the runoff caused by climate change increased by 791 million m3.Compared with the first stage of variation,the proportion of impacts decreased from 93.5%to 31.6%,and the runoff caused by land use decreased by 181 million m3.Generally speaking,the change of runoff in the first stage of variation was mainly caused by climate change,and the change of runoff in the second stage of variation was mainly caused by human activities.Among them,water conservancy project is the main component of human activities in Yuanshui basin.