Land Use And Soil Erosion Research In The Loess Plateau Of Northern Shaanxi Based On Aerial Photography Of Unmanned Aerial Vehicles

The soil erosion problem is one of environmental problem in the Loess Plateau which causing much attention of our country as well as the global.Establish a small watershed in the Loess Plateau as a sample to study the regular pattern of erosion and sediment yield,the soil and water loss control strategy,and it is the most effective way to extend a small watershed to the whole river basin and the Loess Plateau.In addition,the unmanned aerial vehicle(UAV)technology is a kind of high efficiency,high precision research technique.It can be used to study the micro topography and soil erosion in small watershed.Huangtuwa natural warping dam is a typical dam in Loess Plateau.In this paper,we use the UAV aerial data to study the Huangtuwa natural warping dam,to analysisthe land utilization status and topography change,to calculatethe soil erosion situation of different land use,to discuss the distribution law of the land use,and the influence of different land use types on soil and water loss,to sum up the contribution of each soil erosion factor,to reveal the relationships between soil erosion and land use,meteorological factors,human activities in the study area.And then it can provide a practical study case for the arrangement of the agricultural production activities,and soil erosion prevention and control work in the loess plateau.The conclusion as follows:(1)It is the first time to use UAV technology to carry out aerial photography in theHuangtuwa,and obtain high precision digital surface and digital elevation information.This work needs to do good jobs of these tasks:the landing platform selection,UAV flight route setting,phase control point layout,the digital surface model and digital elevation model established.The aerial sets up 29 control points,26 routes,13 sorties,2 takeoff landing point,and the total flight range is 6.28km~2,the ground resolution is 0.06m.(2)Based on the digital surface model of UAV aerial data and field survey data to obtain high accuracy land use information in Huangtuwa watershed.The result shows that farmhouse has a total area of 2040 m~2,accounting for 0.06%of the total area of the basin;road for a total of 18,with a total length of 2815 m,corn for a total area of 465532.8 m~2,accounting for 14.78%,the potatoes for a total area of 351.4 m~2,accounting for 0.01%,the soybean for a total area of 19327 m~2,accounted for 0.61%;grain for total area of 3311 m~2,accounting for 0.11%,reed for a total area of 51.8 m~2;the terraces has a total area of 5929 m~2,accounting for 0.19%of the total;there are rarely shrub land distribution in Huangtuwa watershed,with a total area of 441080 m~2,accounting for 14%;the weeds has a total area of 2210888 m~2,accounting for 70.18%.Through the validation of 300 verified points,the classification accuracy is 82.33%.(3)With the help of UAV aerial data,we obtain the information of elevation and micro topography in Huangtuwa.The range of dam in lowland is enlarged,and the average elevation increased from 1063m increased to 1075m,increased by 12 m.In addition,the elevation of the posterior wall of the nine mountain landslide increased by 2.3m.On the contrary,in the southeast of the Huangtuwa,the height of each ditch wall is reduced by 1.7m.The variation of the height of the Huangtuwa in the past 16 years is still mainly in the decline,the main change is less than 1m.(4)Analyzed the influence factors of soil erosion about typical land,and the results show as follows.The heights of corn and potato increase,because corn and potatoes are located in the dam body,and the soil erosion caused by rain and wind will be in the dam body each time,and then the height increases;the height of soybean increases non-significantly,because it distributes in valley slope which can increase the vegetation coverage,and the slope is gentle,thus this land use plays an important role within a certain slope soil erosion;terrace makes the soil erosion mitigated,and the elevation change is weak;grassland and shrub land are mainly distributed in the gully slope top,shrub forest scattered,and not into the film,although they can increase the surface roughness and change soil composition soil composition,has certain erosion resistance,but the coverage is low,so that the soil erosion is still severe in these land use types.(5)The temporal variation of the main meteorological factors related to soil erosion in Huangtuwa is discussed.It is found that the average temperature increases obviously,and the average temperature increases from 9.6 centigrade to 10.3 centigrade,increases by about 0.7 degrees centigrade.The average rainfall showes a steady downward trend,but in 2010s,there is a certain increase in rainfall.The mean wind speed showes a trend of increasing in different years,and the average wind speed in 2010s increases by 0.5 m/s compared with 1950s.The average relative humidity showes irregular turbulence,but the average relative humidity in 2010s increases by 0.4%compared with 1950s.The change of the average sunshine hours increases first,then decreases,and then increases,and compared with 1950s,the average sunshine hours in 2010s increases by 1.1 h.The average air pressure decreases first,then remains stable,then decreases and remains stable.(6)The vegetation coverage change in Huangtuwa is analyzed.It is found that the NDVI has an increasing trend in 1982-2015,with an average annual growth of 0.0023,and the trend of NDVI increased significantly in 2000-2015,with an average annual growth of 0.0075,especially in the northern and southeast part of the region.(7)The attribution analysis of soil erosion in Huangtuwa is carried out.It is foundthat the soil erosion is reduced by 2600 T after the vegetation cover increased,and the decreasing of rainfall causes 700 T,the human activities causes 1900 T of the decreasing of soil erosion.Therefore,the contribution of rainfall and human activities to soil erosion are 27%and 73%,respectively.The results show that the reduction of soil erosion in this area is mainly due to human activities.(8)The role of meteorological factors and human activities in Huangtuwa watershed is analyzed.The main factor of the decline of the soil erosion in recent years is the measure of slope.In the aspect of meteorological elements,the decrease of rainfall leads to the decrease of sediment.However,the climate of this region is developing to warm and dry,which leads to the complex effects of meteorological factors on soil erosion.The presence of other human activities is still important.The local farmers develope land and construct cottage which resulting in land fragmentation and serious soil erosion;in the lowland,farmers artificial excavate slope,leveled pad planting area,expande farming area which resulting in soil erosion increasing;in addition,according to the national policy,the regional implement the grazing policy which reducing the destruction of vegetation,thus to reduce soil erosion.