| The ecological environment of study area is fragile and soil erosion is serious,which potentially threatens the ecological security and sustainable development of this region and surrounding areas.Therefore,it is of great significance for the prevention and control of soil erosion to explore the spatio-temporal characteristics of regional soil erosion distribution,evolution,driving forces and their influencing relations.Compared with the previous studies,this paper firstly divided in space and distinguished different types of soil erosion.Based on the soil erosion models(USLE,RWEQ),the spatial heterogeneity and evolution rule of soil erosion dynamics were detected,and the temporal and spatial differences and variation characteristics of various driving factors in different regions were observed.Furthermore,the spatial analysis method is used to study the relationship between dynamic changes of soil erosion and driving factors,and reveal the multiple regional response characteristics of soil erosion,which is the premise of controlling,predicting and preventing soil erosion.Among them,climate factor can be used as a comprehensive factor to represent the state of interaction and mutual restriction among various natural factors to reflect regional difference,which is different from human action and is the main driving force of soil erosion.Vegetation is a major soil and water conservation measure that integrates natural and human activities,and can be targeted under the background of natural environment and within the scope of human activities;the effects of vegetation ecological restoration on soil erosion dynamics were also illustrated.The main results are as follows:(1)The study area is generally high in the northwest with little rain and high evaporation,while the southeast is relatively low,warm and humid with abundant rainfall.Therefore,the study area is divided into the Bashang plateau region(Ⅰ),the northern North China′s mountainous region(Ⅱ),and the North China plain region(Ⅲ).The plateau region is is divided into five sub-regions of the plateau hilly region(IN1,IN2,IW3),Yin Shan region(IW4),hilly and gully region(IW5).The mountainous and hilly areas in the northern North China are divided into two sub-regions,namely,Yan Shan region(IIE)and Tai Hang region(IIS).(2)Water erosion is dominant in the southeastern part of the study area.Wind erosion was dominant in the northwest part of the study area,and the wind-water erosion is easy to occur in the transition zone of wind and water erosion in the study area.According to the soil erosion amount accumulated over many years in the study area,the water erosion,wind erosion and wind-water erosion areas in the study area accounted for more than 11%,28%and 5%of the total area,respectively,among which the most serious areas accounted for 5.41%,4.05%and 0.98%,respectively,mainly located in the southern part of the Tai Hang region,the northwestern part of the Yan Shan region,and the plateau hilly area of Hebei province.During the period of 1998-2018,the water erosion in the study area decreased significantly(S=-12.21t/(km~2·a)),and 84.6%of the region showed a downward trend.The number of areas in the study area with little or no wind erosion increased nearly six fold in 2018(77.35%)compared to 2000.(3)The spatial pattern of the average multi-year drought index from 1998 to 2018 showed obvious heterogeneity.The high-value region was located in the hilly plateau region of the southern margin of Inner Mongolia and Yin Shan region.From 1998 to 2018,97.97%of the areas in the whole region showed a trend of decline.Comparatively speaking,the degree of drought in the southwest of the study area decreased significantly,and the possibility of water erosion risk existed or increased.During 1998-2018,the correlation between drought index and water erosion modulus in the study area was significantly different in the spatial region,among which the positively correlated area(14.20%)was mostly distributed in the eastern part of the study area,while the soil and water loss in the western part increased with the decrease of drought index(19.04%).For wind erosion,the positively correlated regions(53.81%)were mostly distributed in the southwest of the study area,in the hilly and gully region and the Tai Hang region,in the north of the plateau and hilly region,and in the south of the plain region.(4)From 2000 to 2018,the conversion of land use types was dominated by the conversion from cropland,grassland to urban and forest land.The relative contribution rate of forest land to soil erosion was the highest in the areas with unchanged land use type.The introduction and implementation of the Beijing-Tianjin Sand Source Restoration Project has improved the vegetation coverage,which is the main reason for the reduction of soil erosion area.Land use type change in the region into grass,woodland area of soil erosion changes the relative contribution of higher;corresponding to the implementation of the Grain to Green Project,the conversion of forest,grass and farmland improved the surface covering form.In general,the ecological remediation project affects the type and degree of land use,and soil erosion changes are significantly affected by it.The spatial contribution of human activities and natural factors to the decreasing variation of water erosion is dominated by human activities,while wind erosion is reduced by both of them.The contribution rates of water and wind erosion for increase were both dominated by natural factors.From the perspective of the spatial distribution of the main driving forces,the impact of human activities on soil erosion is greater than that of climate factors.(5)Our results revealed a significant increasing trend in Normalized Difference Vegetation Index(NDVI)and the improved area accounted for more than 80%of the study area.The response of vegetation variation to climatic factors displayed a high correlation with precipitation for a1-month lag in the semi-humid area,especially in forestland,and with temperature for a 0-month lag in the semi-arid area,particularly in farmland.The human activity was the dominant factor controlling vegetation changes in terms of the spatial distribution of major drivers;notably,the implementation of the vegetation restoration projects affected the spatiotemporal patterns of vegetation cover.The increased vegetation coverage played a dominant role in reducing water erosion of the forestland,and it had a vital impact on lessening wind erosion in open land and sparsely vegetated areas,while the increased fractional vegetation coverage(FVC)may have been a contributing factor to aggravated soil erosion in the wind-water erosion zone of grassland and forestland. |
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