| Soil erosion is a global eco-environmental problem,which seriously threatens the sustainable development of human living environment.In recent years,with the increase of population and the development of economy and society,unreasonable human activities,such as unreasonable agricultural cultivation methods,deforestation and overgrazing,have intensified the impact on regional soil erosion,seriously affecting the safety of land resources.Soil erosion in China has a wide range of distribution and complex erosion types,with obvious undulation of the whole terrain,loose surface composition and extremely low vegetation coverage in some areas,which makes the problem of soil erosion in China more serious.Therefore,it is necessary to deeply study the mechanism of regional soil erosion,analyze the distribution pattern and spatial-temporal characteristics of regional soil erosion,accurately assess the amount of regional soil erosion,and understand the impact path of regional soil erosion driving factors has important theoretical significance to protect surface soil resources,reduce land degradation,protect ecological environment and alleviate soil erosion in China and even the world.The existing research on soil erosion mainly evaluates the amount of regional soil erosion,analyzes the formation mechanism of soil erosion and understands its development characteristics from the perspective of region.Most of these studies ignore the spatial characteristics of soil erosion and its factors from a macro perspective.In view of this,this paper introduces the concept of“spatial marginal effect”into the study of regional soil erosion,trying to analyze the spatial and temporal characteristics of regional soil erosion and its driving factors from a macro spatial perspective.Taking China as an example,the characteristics of global spatial autocorrelation,local spatial autocorrelation,spatial distribution and aggregation pattern,spatial lag effect and spatial effect of soil erosion driving factors were studied.The specific research contents and results include the following aspects:(1)According to Chinese soil loss equation(CSEL)and revised universal soil loss equation(RUSLE)of the United States,the amount of soil erosion in this study area was evaluated and its spatial distribution characteristics were analyzed.This is the data basis for the follow-up analysis of the spatial and temporal characteristics of soil erosion and its factors.In this paper,the rainfall erosivity factor,terrain factor,soil erodibility factor and vegetation cover and management factor of soil erosion in the study area are calculated respectively.According to the calculation results of these four soil erosion factors,the soil erosion amount in the study area is obtained.The results show that rainfall erosivity factor,vegetation cover and management factor and regional soil erosion have significant East-West differentiation spatial distribution characteristics.(2)The global spatial autocorrelation and local spatial aggregation model of regional soil erosion and its factors were analyzed by exploratory spatial data analysis method(ESDA)in spatial econometric theory.The global spatial autocorrelation of regional soil erosion and its factors is tested by global Moran's I statistic.Local Moran's I_i,local Getis-Ord G_i and local Geary C_i statistics are used to test and analyze the local spatial distribution and aggregation characteristics.The results showed that there were significant positive spatial correlation between regional soil erosion and four soil erosion factors.The spatial clustering characteristics of rainfall erosivity factor and regional soil erosion show that the northwest region is a low-low value aggregation area,while the southeast region is a high-high value aggregation area.The results of spatial distribution and aggregation model analysis of soil erosion and its factors show that the soil erosion of each subregion in this study area is not an independent state,and there is a spatial correlation.This conclusion is the premise of spatial theory to analyze the spatial effect of regional soil erosion and its factors by spatial model.(3)Based on spatial Markov theory,the spatial lag effect of regional soil erosion and its factors was analyzed.In this paper,the“spatial lag term”is introduced into the traditional Markov theory model,and a spatial Markov theory model is established to analyze the spatial lag effect of regional soil erosion and its erosion factors.The traditional Markov probability matrix and spatial Markov probability matrix of regional soil erosion and its factors are calculated respectively.By comparing the results of the two Markov state transition probability matrices,the spatial lag effect of regional soil erosion and its erosion factors was analyzed.The results show that the regional soil erosion and its erosion factors have significant spatial lag effect.The specific performance is that different spatial neighborhood state types have influence on the state transition direction and probability value of regional soil erosion and its erosion factors.This result can be explained by an abstract“Matthew effect”,that is,when the erosion state of soil erosion and its erosion factors in adjacent areas is high grade,the probability of soil erosion or the change of erosion factors to high grade erosion state in observation area is higher;at the same time,when the erosion state of soil erosion and its erosion factors in adjacent areas is low grade,the probability of soil erosion in observation area is higher,the probability of erosion or erosion factors changing to low grade erosion state is higher.(4)The spatial effects of driving factors of soil erosion were quantitatively analyzed by establishing a spatial econometric model of regional soil erosion.Specifically,it includes the spatial lag effect of natural driving factors of soil erosion and the spatial spillover effect of human driving factors of soil erosion.The results of lagrange multiplier test(LM),Wald test and likelihood ratio test(LR)show that the spatial Durbin panel data model(SDPDM)of soil erosion can best fit the soil erosion data of this study area,so we established a spatial Dubin panel data model of soil erosion to analyze the spatial lag effect and spatial spillover effect of regional soil erosion driving factors.The results show that the driving factors of regional soil erosion have significant spatial lag effect and spatial spillover effect.The specific performance is that the influence of the driving factors of soil erosion in the observation area and adjacent areas will cross the boundary of their zoning and affect the state of soil erosion in the adjacent areas.This study shows that the geographical process of regional soil erosion is not an independent state in the macro perspective,and the soil erosion state of each subregion is related to the soil erosion state of its surrounding regions.At the same time,the influence of regional soil erosion driving factors is not limited to the inner part of the region,and its influence will overflow from the regional boundary to the neighborhood with“spatial proximity”relationship,thus affecting the soil erosion state of the adjacent region.The innovation of this paper is to introduce the spatial econometric theory into the study of regional soil erosion,establish the spatial theoretical model of regional soil erosion,and try to analyze the spatial and temporal characteristics of regional soil erosion and its erosion factors from the macro spatial perspective.In addition,this study breaks through the traditional thinking of establishing cross-section data model in soil erosion research,introduces spatial panel data model into regional soil erosion research,and analyzes the spatial effect of regional soil erosion driving factors.The research conclusion can more truly analyze the influence mechanism of driving factors on regional soil erosion process.Finally,two important spatial theories of soil erosion are put forward:one is to construct a framework model of spatial theory of soil erosion,which can be used to analyze a series of spatial and temporal characteristics of regional soil erosion and its erosion factors,such as global spatial correlation characteristics,local spatial aggregation model,spatial spillover and lag effect;the other is based on the spatial theory of soil erosion based on the research results of spatial effects of soil erosion driving factors,a spatial conceptual model of regional soil erosion assessment was proposed.Specifically,the amount of soil erosion caused by spatial spillover effect and spatial lag effect of soil erosion driving factors was added into the process of regional soil erosion assessment.This study not only enriches and develops the existing soil erosion theory,but also provides a new theoretical basis for the accurate assessment of regional soil erosion. |
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