Simulation Of The Impact On Climate Variability And Land Use Change On The Runoff Change In The Yuaniiang River Basin

Gobal climate change result the changes of climate factors such as temperature and precipitation,which had affected directly or indirectly the hydrological process.Meanwhile,land-use changes have changed the hydrological process such as interception,infiltration,and evaporation,thereby affecting the water cycle of the basin.With the intensification of climate change and human activities,the study of changes in runoff under the context of climate change and land use change is one of the hot issues in water science research in the 21st century.This work takes the Yuanjiang River Basin as a case study,to analyze the impacts of climate change and land use change on the runoff,which would provides scientific basis for the soil and water conservation and utilization and management of water resources.The runoff data at Manghao hydrographic station from 1960 to 2012 and the meteorological data from 22 meteorological stations were used to analyze the spatial-temporal variations of meteorological and hydrological factors in the basin.Based on the land use data in the four years of 1985,1995,2000 and 2010,the characteristics of spatial-temporal change of land use were studied using the transition matrix and dynamic degree.Combined with the basin meteorological hydrological data and spatial information,SWAT distributed hydrological model in Yuanjiang River Basin was established.The four-phase land-use changes were input into the SWAT model to explore the trends and patterns of runoff changes in the context of land-use change.Through the"single factor analysis method",the impact of climate change and land use change on watershed runoff is quantitatively distinguished.The main conclusions obtained are as follows:?1?The temperature in the Yuanjiang River Basin increased significantly from1960 to 2012?p<0.01?at a rate of 0.19°C/10a.Precipitation has an insignificant decreasing trend with a rate of 13.25mm/10a?p>0.1?.Runoff had an insignificant decreasing trend with a rate of-12.63m³/s/10a.Decrease in precipitation and increase in temperature result in decrease in runoff.?2?The land use types in the four phases of the basin are mainly woodland,grassland and cultivated land accounting for about 98%of the basin area.The main characteristics of land use change are as follows:cultivated land was transformed into forestland and grassland from 1985 to 1995;forestland and grassland were converted into cultivated land from 1995 to 2000;both forestland and cultivated land turned into grassland during 2000-2010 and 1985-2010.?3?The SWAT model simulates the daily runoff relative error|PBAIS|less than6%,and the R² and E_NS coefficients are all greater than 0.7,indicating that the SWAT model can better simulate the daily flow process in the Yuanjiang River basin.Under the same climatic conditions,the runoff changes during the four-phase land use scenarios ranged from-0.87%to 1.71%.The annual average runoff decreased by0.87%from 1985 to 1995;the average annual runoff increased by 1.71%from 1995to 2000;and the average annual runoff decreased by 0.14%from 2000 to 2010.The impact of land use change on runoff in the Yuanjiang River Basin is mainly reflected in the increase of forest land and grassland,which results in a reduction in runoff,while the increase in arable land increases the runoff.On the monthly scale,the area of woodland decreased and the monthly runoff increased,especially from January to April and from October to December.?4?Based on the validated SWAT model,the contribution of climate change and land use change from the 1980s to the 1990s,the 1990s to the early 21st century,and the 1980s to the 21st century to runoff was quantitatively distinguished by"single factor analysis method".The results showed that the runoff increased by 53.33mm in the 1990s compared to the 1980s,and land-use changes led to a decrease of 1.92mm in runoff.Climate change resulted in an increase in runoff of 56.03mm.The contribution rates of land-use change and climate change to runoff were 3.27%and95.40%respectively;Early 2000s relative to the 1990s runoff reduction 19.64mm,land use change lead to increased runoff 4.91mm,climate change leading to runoff reduction 27.68mm.The contribution rates of land use change and climate change to runoff were 13.75%and 77.49%respectively.The climate change is the main factor affecting the change of runoff.Howerver,the impact of land use change on the runoff intensified since 1990s.