Spatio-temporal Dynamics And Projection Of Soil Erosion In The Yangtze River Basin

Due to extensive land use,abundant rainfall,and complex geomorphological features,the Yangtze River Basin had become one of areas suffering from the worst soil erosion.Soil erosion had seriously affected the sustainable development of economy and environment in the basin and had become one of the obstacles in implementing the policies of"Beautiful China"and"Yangtze River Protection".This study conducts spatial quantitative assessment on soil erosion and soil conservation function in the Yangtze River Basin from 2000 to 2015using the InVEST model,and analyzes its driving factors using Pearson correlation analysis.Based on the four integrated scenarios applied in the Coupled Model Intercomparision Project phase 6（CMIP6）（i.e.,SSP1-2.6:low forcing scenario,SSP2-4.5:moderate radiative forcing scenario,SSP3-7.0:medium to high radiative forcing scenario,and SSP5-8.5:high forcing scenario）,the effects of future climate and land use change on soil erosion and soil conservation in the Yangtze River Basin was explored.Finally,shadow price,shadow project and opportunity cost approach were used to evaluate the value of soil conservation service function in the Yangtze River Basin.The results of the study are as following:（1）Soil erosion in the Yangtze River Basin had significant spatial heterogeneity,which was higher in the west and lower in the east.The amount of soil erosion in the Yangtze River Basin was estimated as 6.73×10⁹t and 6.31×10⁹t in 2000 and 2015 respectively.The soil erosion intensity grades were mainly at light and mild levels,which accounted for 75～80%of the study area.The soil erosion modulus of different land use types from large to small was:bare land>cultivated land>grass land>forest land>construction land.About 52.20%of the total amount of soil erosion was found in cultivated land.Results from Pearson correlation analysis showed that soil erosion is positively correlated with slope,rainfall,edge density（ED）of grass land,number of patch（NP）of cultivated land,landscape shape index（LSI）of cultivated land,forest land and grassland,and aggregatin index of（AI）grassland.Soil erosion is negatively correlated with per capita GDP,rural per capita net income,per unit area GDP,population density,patch density（PD）and edge density of water body,patch density and edge density of construction land.（2）The total amount of soil conservation was 5.35×10¹⁰t and 5.60×10¹⁰t respectively in the Yangtze River Basin in 2000 and 2015.The soil conservation capacity of different land use types from large to small was:forest land>grass land>cultivated land>construction land>bare land.Grass land and forest land were the main contributors of soil conservation in the study area,which accounted for 88.9%of the total soil conservation,suggesting planting trees and grasses could reduce the potential risk of soil erosion.The soil conservation modulus of each city in the Yangtze River Basin mainly concentrated in the range of 0～400 t·hm^-2·a^-1.Soil conservation function is positively correlated with slope.With the increase of slope,the ability of vegetation to resist potential soil erosion and soil conservation is continuously enhanced.（3）Among the four scenarios in the future,the soil erosion under SSP3-7.0 will be the fewest.This is because the projected extent of forest land is the greatest and the extent of cultivated land is the lowest,while the soil erosion modulus of forest land is small and that of cultivated land is large.The soil erosion under SSP5-8.5 was projected to be the most serious,owing to the projected lowest extent of forest land,the greatest extent of cultivated land and a relative high level of rainfall.The areas around the Sichuan Basin and parts of the upper reaches of the Yangtze River Basin were projected to experience severe soil erosion under all scenarios.This highlights the needs for the prevention of soil erosion in these areas in long term.Accordingly,the soil conservation under the four scenarios were projected to decrease significantly.Because the extent of grass land and forest land was projected to decrease in 2050 and 2100 and the extent of cultivated land and construction land was projected to increase.The soil conservation capacity of grass land and forest land is found to be high and the soil conservation capacity of cultivated land and construction land is low.（4）The value of soil conservation function provided by the Yangtze River Basin was5940 billion CNY in 2000 and 6220 billion CNY in 2015.The value of soil fertility conservation was found to be greater than that of alleviating the siltation and land abandonment.The value of soil fertility conservation accounted for 97.83%of the total value of soil conservation.The soil conservation value per unit area of forest land and grass land was the highest,which was 5.65 CNY/m² and 3.85 CNY/m² respectively.Among the four scenarios,the soil conservation value in 2050 was found to be greatest under SSP5-8.5with 4680 billion CNY and the lowest under SSP3-7.0 with 4470 billion CNY.Whils in2100,the soil conservation value under SSP2-4.5 and SSP3-7.0 is the highest（5010 billion CNY）and lowest（4890 million CNY）,respectively.In this thesis,we demonstrate how an InVEST model could be built and can reveal the spatial and temporal characteristics of soil erosion in the Yangtze River Basin.The soil and water conservation work in the Yangtze River Basin needs to take appropriate prevention measures according to the soil erosion intensity in different regions.Attention should be paid to soil erosion prevention and control in 15～25°slope areas.Returning farmland to forest and grass will be carried out to the the middle and upper reaches of the Yangtze River basin.