| Gully erosion is one of the important types of soil erosion,which destroys land landscape,causes water and soil erosion,forms sediment,and has a great impact on the erosion site and the downstream position.However,current studies on regional scale gully erosion have limitations,and it is difficult to extract large-scale data in an efficient way,so there is a lack of understanding of large-scale spatial gully erosion distribution.In this paper,the Red River Basin across China,Vietnam and Laos is taken as the research area.Arc GIS 10.4 software is used to divide the study area into small basins as survey units for random sampling.Based on field survey and high-resolution satellite remote sensing images,artificial visual interpretation method is used to extract ancient and modern gullies.Gully Density（GD）was used to measure the erosion intensity,Gully Probability（GR）,Gully Proportion（GP）and Area Proportion（AP）were used to measure the spatial distribution of gully erosion.In order to find out the spatial distribution of gullies in the Red River Basin,reveal the main environmental factors of the gullies,and further clarify the particularity of gully development in the ecologically fragile Yuanjiang dry-hot valley of the Red River Basin,the spatial distribution and influencing factors of gully erosion in the Red River Basin were studied.The main conclusions are as follows:（1）The two types of erosion gullies are mainly distributed in China under the influence of topography.The average GD of ancient gully is 3.77 km·km-2,and that of modern gully is 1.27 km·km-2.The proportion of medium and intensity erosion units in ancien gully is 83.17%,and the GR value is higher than 95%,with relatively small spatial difference.Modern gully units accounted for 56.2%,the average GD is0.77km·km-2,GR value is 46.34%～67.44%,with significant concentration.（2）The ancient gully has a wide spatial distribution andrelatively distribution and relatively small variability of GD,which is less developed in carbonate lithology.The distribution of modern gully is significantly affected by climate,topography,normalized vegetation index（NDVI）,landuse type and soil type.The gullies are mainly distributed in areas with high evaporation,low NDVIand high topographic humidity index（TWI）,and in shrubbery,torrid red soils and clastic rocks.In terms of erosion intensity,the ancient erosion gully was located at altitude.At 1340 m,GD increases with elevation classification and erodes strongly in intrusive rocks.Modern gully increases with elevation and NDVI grading,GD decreases.Modern gully was slightly eroded in middle-coverage grassland.In the soil types of torrid red soils and purplish soils and metamorphic rock,the erosion intensity is high,and the areas with erosion intensity grading of strong intensity or above are concentrated in the dry-hot valley.（3）The spatial pattern of modern erosion gullies on the dry-hot valley slopes of The Yuanjiang River is dominated by parallel gullies.The area erodes strongly,strong erosion accounted for 15.15%,extremely strong erosion accounted for 9.09%,severe erosion accounted for 57.57%.GD is not significantly affected by climate conditions,but a negative correlation with NDVI,and the units are concentrated in slope>15°,the mean value of GD increases with the increase of slope classification.GD is higher on the S,SW and NE slopes.In this area,the GD is mainly distributed in grassland,and the GD is 15.94 km·km-2in forest and 15.19 km·km-2in low coverage grassland.The fitting results of soil organic carbon content（SOC）and GD index were good;torrid red soils was an important factor for the development of modern gully under high temperature and dry climate.（4）The results of three groups of visual interpretation show that the method of regional scale gully extraction based on remote sensing image has repeatability.The average length of gully extracted by UAV and remote sensing images is 0.207km and0.211km,and the error of gully length is small,the misjudgment rate of remote sensing images is 2.6%,and the relative error is higher than 15%,accounting for25.37%.The results show that the gully data extracted from remote sensing images can be used to extract gully data in the Red River Basin to obtain reliable gully density and reflect the overall erosion status of the basin.In this paper,regional scale gully erosion research was carried out in the Red River Basin.Through sampling method,the key areas and influencing factors of gully erosion in the Red River Basin were gradually determined,which provided a standard scheme for further regional scale gully erosion research and a direction for threshold research on the main controlling factors.The study of gully erosion in dry-hot valley is of great significance to the implementation of efficient soil and water conservation measures,prevention and improvement of ecological environment. |
