Analysis On The Evolution Characteristics And Driving Factors Of Semi-arid Watershed In The Changing Environment

Most scholars have focused on the trend of runoff changes and simulated predictions for the main rivers and their tributaries in China.However,runoff characteristics under the influence of climatic fluctuations and human activities on the semi-arid regions of the northern half of the plateau and the inland river basin of the plateau have been relatively lacking in data.However,there are few literature reports on the analysis and simulation prediction.Therefore,this paper takes the WulanMulun River Basin and Balager River Basin in Inner Mongolia as the research area.Utilizing the data of hydrometeorology,land use and socio-economic analysis of the WulanMulun River Basin from 1997 to 2015 and the Balager River Basin from 1959 to 2015,the double-accumulation curve method,the cumulative anomaly method,and improved Mann-Kendall were used.Trend test method,remote sensing interpretation,principal component analysis,wavelet transform method,BP neural network simulation,SWAT model runoff simulation and cumulant slope change rate comparison methods were used to analyze runoff and urbanization in the study area from different time scales.climate and socio-economic trends have revealed the impact of climate,socio-economic rapid development and urbanization processes on the runoff of the river basin,identified major drivers of runoff changes at the annual and seasonal scales of the study area,and established Scaled runoff mapping function relations.The main research results of the paper are as follows:1.Significant inflection point changes occurred in the WulanMulun River basin in 2005,and significant inflection point changes occurred in the Balager River Basin in 1998.Precipitation occurred before and after the significant inflection point(base period vs.change period)in the basins of the two study areas.-The natural relationship between runoff changes,the impact of human activities increases significantly,and the runoff changes add to the influence of human activities;2.From the perspective of age change,the annual runoff in the two study areas,the runoff in the wet season,and the dry season runoff have generally declined over the years,while the precipitation in the basin has not changedsignificantly.3.There is no significant trend in the fluctuation of climate factors such as precipitation,evaporation and temperature during the period of change in the WulanMulun River Basin.Before and after 2005,the urbanization area and GDP increased significantly,and rapid urbanization changed the natural runoff.The occurrence mechanism and the law of change are the main driving factors for the reduction of runoff in the WulanMulun River basin.The fluctuation of climate change does not make a significant contribution to the reduction of runoff in the study area;the Balager basin compares all climatic factors in the reference and change periods.The temperature,precipitation,and wind speeds vary greatly,being 65.12%,-16.97%,and-13.3%,respectively,while other climatic factors are very close,with changes less than 5%.Temperature,precipitation,and wind speed are the main factors affecting runoff changes in climate factors.In the study area,the period of change in the primary industry and the reference period increased by 3.8 times,the number of sheep increased by 12.06%,and the population growth was 9%.The human activities in the study area during the change period were significant.4.The contribution rate of climate change to runoff reduction in the WulanMulun River Basin is 30.41%.The contribution rate of human activities to runoff reduction reaches 69.59%.The contribution rate of climate change in the Balager River Basin to runoff reduction is 44.14%.The contribution rate of human activities to the reduction of runoff reached 55.86%.It can be known from the comparison of the drainage areas of the two research areas that human activities are the main driving factors for the reduction of runoff.5.The BP neural network model has a better overall simulation effect on the non-linear function relationship between runoff and climate and human activity factors in the Balager River Basin.It shows that when the distributed hydrological simulation cannot be realized,the application of the BP neural network model in the watershed can be considered method.Based on DEM digital elevation data,land use data,soil data and hydro-meteorological data in the Balahal River Basin,a SWAT model of the catchment was established to simulate the runoff of the catchment.The results showed that the evaluation indexes of the runoff simulation effect were Re and R2.And Ens are between 19.57%-22.69%,0.58-0.61 and 0.53-0.58,respectively.According to the SWAT evaluation index table 26,the SWAT model is only satisfactory in the simulation of the runoff changes in the Balahal River Basin,and the simulation results are general.