Analysis Of Land Use/Cover And Vegetation Changes In The Yellow River Basin Based On Google Earth Engine And Complex Network

The Yellow River Basin plays an important role in China's social and economic development and ecological security.Natural evolution and human activities in the past decades have had a profound impact on it.The fragile ecological environment and underdeveloped social economy have made the Yellow River Basin a hot area of competition between human and nature.In the past decades,land use/cover change(LUCC)in the Yellow River Basin has been dramatic.In recent 20 years,due to the largescale ecological protection and ecological restoration plan implemented by the Chinese government,the Yellow River Basin and its central region(Loess Plateau)have shown the largest trend of vegetation greening in China and even the world.In addition to the impact of natural factors such as climate,severe human activities and land use change are also important factors affecting vegetation coverage.Under the great pressure of population growth,resource consumption,and environmental change,the dynamic changes of the social system and ecosystem in the Yellow River Basin are intensive and complex.Taking the Yellow River Basin(including the whole Loess Plateau)as the research area,this study first created a long-time series of continuous high-resolution land use/cover data set by using the geoscience remote sensing big data and its processing platform.LUCC and vegetation change patterns and possible driving forces in the region were studied and analyzed.The main conclusions are as follows:(1)The results of LUCC analysis show that the LUCC of the Yellow River Basin,driven by policy,social and economic factors,presents complex spatial and temporal characteristics during the whole study period.Through the method of Landsat data filtering and abnormal data repair,the accuracy of this land use/cover data set was improved by integrating a multi-source feature set,feature variable selection,and result optimization strategy.According to 640 verification points of field survey and 3456 independent stratified random sampling verification points collected in Google Earth,the overall accuracy of this data set in 15 secondary classifications is 78.3%and 80.0%,respectively.A reliable production method and strategy of long-time series and highprecision land use/cover data are constructed,which can accurately depict the change of land surface environmental pattern in the study area.(2)The results of LUCC analysis show that the LUCC of the Yellow River Basin,driven by policy,social and economic factors,presents complex spatial and temporal characteristics during the whole study period.The most important change was from forests,grasslands,and croplands to orchard and terrace(19.8%of the total change area).The second is the transfer from croplands to urban and built-up(5.7%of the total change area).The main LUCC patterns in the study area include:no change or little change,cropland loss and urban expansion,grassland restoration,increase in orchard and terrace,and increase in forest.In the past 33 years,the area of orchard and terrace has increased greatly.The economic trees planted on orchards and terraces can not only increase the green of the region,but also increase the income of farmers.This shows that the Yellow River Basin is moving towards the sustainable development goals of livelihood security,economic growth,and ecological protection.However,the phenomenon that some ecological trees are transformed into economic trees also reminds us to continue to protect natural and ecological land and realize the scientific and sustainable utilization of land resources.(3)Using the complex network method to analyze the land use/cover transfer network of the Yellow River Basin,the key land types and stability of the land system are analyzed:In the land system of the Yellow River Basin,the transfers between other land types and high coverage grasslands,low-vegetated lands,and mixed forests are frequently,which are the key land type nodes in the land system of the Yellow River Basin.In addition,the transfers of orchard and terrace,croplands,and urban and built-up,which are closely related to human activities,are important types of transfer in the land system.There are three unstable periods in the land system of the Yellow River Basin in 19931998,2001-2007,and 2011-2014,which may be caused by a large number of agricultural land development,the Grain for Green program,and the increase of the area of orchard and terrace.The change and mutual transfer information of different types in the land system is the key to understand the dynamic evolution of social,economic,and natural interaction in the basin.(4)By constructing the causal network of vegetation evolution,the characteristics of vegetation evolution in each regional unit of the Yellow River Basin were studied:Precipitation,air temperature,vapor pressure deficit,orchard and terrace,and desert and low-vegetated lands play the major driving role in the vegetation evolution system of the whole Yellow River Basin.In view of the vegetation change(LAI)in the Yellow River Basin,the main driving factors are air temperature,runoff,vapor pressure deficit,and soil temperature.In the whole study area,LUCC is not the decisive factor in vegetation change,but in some areas dominated by land use/cover,the intensity of the causal effect of LUCC on LAI will be greater than some climatic and environmental factors.Among them,orchard and terrace are the most important land types which have the greatest causal impact on LAI.The urban and built-up has a strong positive causal effect on vegetation change in some areas.The increase of area of urban and built-up in these areas indicates the increase of population and human activities in corresponding areas.It can be seen that human activities in some areas have a positive impact on vegetation status in these areas.In addition,the increase of vegetation in some areas is dominated by the area of forests,which is a remarkable achievement of the Grain for Green program.The results show that the new causal network research method is feasible and has advantages.It also highlights that LUCC plays a strong role in vegetation change in some areas under the background of vegetation change,and affirms the positive role of human activities in vegetation greening in some areas.