Estimation Of Regional Soil Reosion Under A Changeable Environment In Northwestern Sichuan And Southern Gansu

Regional soil erosion triggered lots of land degradation in the world,which have been paid much attention in various ecologic and environmental fields.The Northwestern Sichuan and Southern Gansu(NSSG),located in the upstream of China’s famous large reivers including the Yellow River and the Yangtze River,is one of the important areas for water conservancy and land surface ecology protection.Study of regional soil erosion is the precondition for land productivity assessment and vegetation restoration,as well as the knowledge base for water resources protection and ecologic civilization construction in the area.In this study,different-sourced data and a set of methods were collected and treated and used for a USLE based estimation of regional soil erosion in NSSG during the time period from 2000-2015(as the present)and 2020-2099(for the future).Main conclusions are as the following.1.The Wischmeier method was verified as the suitable one in the selected 9 models for calculation of regional rainfall erosivity.Simulations of USLE resulted into a value range of 0～360 t/(hm~2·a)for erosion modulus.Total soil erosion was then quantified into 2.3×10~8 t/a in NSSG,leveled at a mild erosion degree as the whole.During the time period from 2000 to 2015,vegetation activities was strengthened under the background of warming in the area,which have led to a mitigation of regional soil erosion,meant that soil ecology and land quality have been presenting a better situation.2.Three of GCMs outputs were selected and weight-based integrated for future precipitation prediction under three RCP scenarios(RCP2.6,RCP4.5 and RCP8.5).Predictions were used for calculation of rainfall erosivity and USLE-based estimation of regional soil erosion.Results revealed that all the three variables including precipitation,rainfall erosivity and erosion modulus would increase along with intensification of emissions under the three RCP scenarios.Statistics resulted in additional ratios of 14.80 MJ·mm/(hm~2·h·a)and 1.46 t/(hm~2·a)for rainfall erosivity and erosion modulus,respectively,given a 10%increase of precipitation in the area.3.Field experiments and monitoring of artificial rainfall-runoff process were conducted for mechanism exploration.Two regressive equations delineating land surface runoff generation influenced by various environmental factors were validated based on the experimental observations.Ranges of runoff coefficients were calculated into 0.1～0.6 and 0.05～0.2 when artificial rainfall was given with high intensity and middle-low intensities,respectively.It was found that degradation of alpine meadow would facilitate land surface runoff while reduce the water infiltration in soil layers,which might lead to higher soil erosion in the region.4.During the time period from 2000 to 2015,it was climatic issues which dominated the reduction of regional soil erosion in NSSG.The reason might lie in the enhanced vegetation dynamics and better land cover in the cold alpine area under the background of warming.Increase of precipitation in future might facilitate soil erosion cause to higher rainfall erosivity that will induce.Protection and restoration of vegetation could help to slow down the process.Findings of this study might be a support in both methodology and data for soil ecology health,regional water conservancy and better soil-water management in such a water source area of large rivers.