Study On Soil Erosion In Xihe River Basin Based On SWAT Model

Soil erosion can destroy land,divert nutrients from soil and decrease productivity of land,which is not conducive to the growth of surface vegetation,thus causing deterioration of natural ecological environment and frequent natural disasters.It is one of the main ecological environment problems in the world,and has become a key research topic for many scholars at home and abroad.There are many factors affecting soil erosion,including climate change and human activities.Exploring the change characteristics of soil erosion under different influencing factors can further understand the physical process of the surface,improve the theoretical level of scientific research in related fields,and provide scientific suggestions for the measures taken to control regional soil erosion,so as to improve the effectiveness of soil conservation,which has become one of the important tasks of macro-decision-making for controlling regional soil erosion.The Xihe River Basin is located in the northeast of China.According to the hydrological yearbook,sediment transport has decreased in recent decades.In order to explore the main factors affecting soil erosion in the Xihe River Basin,the SWAT hydrological model of the Xihe River Basin has been established.The contribution rate of climate change and human activities to runoff and sediment change has been quantitatively estimated.The effects of different climate and land use combinations on soil erosion and the changes of landscape pattern on soil erosion were analyzed.Specific research contents and results are as follows:(1)The trend of hydrometeorological elements in the Xihe River Basin from1969 to 2015 was analyzed by using the linear trend method.In order to obtain the mutation information of Hydrometeorological variables,Mann-Kendall method,ordered clustering method and Pettitt mutation test method were used to detect the year of mutation.The results show that the annual precipitation and temperature in the study area increase while the annual runoff and sediment load decrease during the study period.During the study period,precipitation and runoff did not undergo significant abrupt changes,temperature increased abruptly in 1988,and sediment load decreased abruptly in 1988.(2)The changes of land use types in Xihe River Basin in recent years were studied.The results showed that the area of urban land in the study area changed the most,and the increased area accounted for 9.23%of the total watershed area,followed by woodland and cultivated land,and the reduced area was 5.89%and5.31%of the total watershed area,respectively.In addition,woodland is mainly transferred to urban land,arable land and grassland,while urban land is mainly transferred from arable land,woodland and water.(3)The spatial database is constructed by using the digital elevation model(DEM),land use type map and soil type map of the Xihe River basin.Based on the world soil database and the meteorological data from 1969 to 2015,the attribute database is constructed.Finally,the SWAT model of the Xihe River basin is established.Sensitivity analysis of runoff and sediment parameters was carried out using measured hydrological data combined with SWAT-CUP,and calibration and verification were completed.The results show that during the calibration period,the R~2 and Ens of the runoff and sediment simulation is 0.92、0.91and 0.60、0.55,respectively.During the validation period,R~2 and Ens is 0.90、0.87and 0.70、0.69respectively.Which meet the applicability criteria of the model and can basically accurately simulate the hydrological cycle process of the fine river basin.(4)Comparing the measured runoff and sediment transport with the model simulation results,the contribution rate of climate change and human activities to the runoff and sediment load changes in the river basin was quantified by single factor rotation method.The study period was divided into two periods by using the break point as the break point:the base period(1971-1987)and the evaluation period(1988-2015).Compared with the base period,the average annual runoff in the evaluation period decreased by 29.95 m~3/s.The contribution rate of climate change is-26.54%and that of human activities is 126.54%.The annual average sediment load in the evaluation period is reduced by 4.1×10~5t,of which the contribution rate of climate change is-8.8%and that of human activities is 108.8%.(5)The spatial and temporal distribution characteristics of soil erosion under climate and land use change were compared by scenario simulation method.The average annual soil erosion in the four scenarios were 3.52×10~5t、3.76×10~5t、2.63×10~5t和2.78×10~5t,respectively.Compared with the average annual soil erosion in scenario one,under the influence of climate change,the amount of soil erosion increased by6.53%.Under the influence of land use change,the amount of erosion decreased by25.28%,and under the combined influence of the two,the amount of erosion decreased by 21.02%.The erosion amount of sub-basin 22 is the highest,while the minimum erosion amount is fixed in sub-basins 11 and 7.(6)Taking the change of soil erosion modulus as dependent variable and the change of landscape pattern index as independent variable,the influence of landscape pattern on soil erosion was analyzed by stepwise multiple linear regression method.The results showed that among the 10 landscape indicators selected in this paper,the changes of SHDI(fragrance diversity index)and COHESION(patch combination index)had the most significant impact on the change of soil erosion modulus in the Xihe River Basin.