Spatial-temporal Pattern Change Monitoring And Attribution Analysis Of Forest And Grass Vegetation In Hetao Irrigation Area

Hetao Irrigation District is an important production area in western China,and its natural ecological system is extremely fragile.A large number of forest and grass vegetation are facing a series of ecosystem problems such as intensified desertification and increased landscape fragmentation,which seriously restricts the sustainable development of ecological environment in the irrigation district,and it is urgent to carry out relevant basic research.Therefore,this thesis takes Hetao Irrigation District in Inner Mongolia as the research area,based on land use products and forest-grass vegetation coverage extracted by remote sensing cloud platform,and uses land use dynamic attitude,trend analysis,gravity migration model and other methods to monitor the spatial and quantitative changes of forest and grassland in Hetao Irrigation District from 2000 to 2019,as well as the temporal and spatial evolution characteristics of forest-grass vegetation coverage.Logistic regression analysis and geographical detector were used to analyze the driving force of the annual changes of forest-grassland position and vegetation coverage in Hetao irrigation area,and the zoning range of driving factors suitable for forest-grass vegetation growth was explored.The conclusions of this thesis are as follows:(1)Based on the remote sensing cloud platform,the vegetation coverage of 20 stages of forest and grass in Hetao Irrigation District was extracted by using the pixel dichotomy model.Through the field measurement of vegetation coverage and using the root mean square model to verify the accuracy of the inversion value,the inversion accuracy of forest and grass vegetation coverage in each irrigation area is above 0.85,indicating that the results of forest and grass vegetation coverage extracted by pixel dichotomy model meet the accuracy requirements.(2)The forest and grassland in Hetao irrigation area accounted for 16.64%-22.03%of the total area from 2000 to 2019,and the total area of each irrigation area decreased to665.93 km~2.In the past 20 years,the total transfer of forest and grassland was 1618.08 km~2,of which the maximum transfer was 631.66 km~2from 2004 to 2009.The total transfer of forest and grassland was 1403.17 km~2,of which the maximum transfer was 464.99 km~2from 2009 to 2014.The transfer part was mainly distributed in the east of Yichang irrigation area and the northwest of Jiefangzha irrigation area,and the transfer part was mainly distributed in Ulanbu and irrigation area.(3)The grassland vegetation cover in Hetao irrigation area is mainly low vegetation cover,accounting for 37.02%～43.53%of the total area of grassland vegetation;the second is the middle vegetation cover,while the forest and grassland covered with high vegetation cover are the least distributed.It accounts for 3.8%～6.24%of the total area of forest and grass vegetation.The coverage of forest and grass vegetation in Hetao irrigation area was high in east and low in west.The multi-year average FVC was about 0.26.The migration of gravity center of each cover showed a general trend of migration to the southwest,and the change of standard deviation ellipse of each cover was relatively stable.(4)The results of regression analysis showed that natural factors were the dominant factors leading to the change of forest and grassland.The top four driving factors from2000 to 2009 were temperature(1.144),distance from cultivated land(-0.934),precipitation(0.539)and groundwater(0.208),and the top four driving factors from2009 to 2019 were temperature(0.889),distance from cultivated land(0.785),precipitation(0.428)and distance from water area(0.295),indicating that hydrothermal conditions were the key factors affecting the change of forest and grassland in Hetao irrigation area.(5)Using the geographical detector to detect and analyze the driving factors,it is found that the distance from water area,groundwater depth,temperature and precipitation have relatively strong explanatory power for the spatial differentiation of vegetation coverage.Through the risk detector analysis,the driving factors suitable for the growth of forest and grassland are:147～157 mm precipitation area;8.9～9.2°C temperature range;1.8～2.8 m groundwater depth range;the distance interval of 7537～11250 m from residential area;10014～13121 m from the road distance range;1566～2254 m distance from cultivated land;the distance range from 0～670 m to water area.