Monitoring And Assessment Of Desertification From Remote Sensing In The Northern China

Desertification is among the most serious problem facing the global terrestrial ecosystem which gravely hinder the sustainable development of economy and society in arid and semi-arid areas.China is one of the most seriously affected countries by desertification in the world with almost a third of its land area is under threat.In order to monitor the spatial-temporal development of desertification in Northern China,and further reveal the driving mechanisms behind the phenomenon,this research established a monitoring and evaluation model by the aid of satellite image time series.We established a scheme for monitoring the spatial-temporal variations of desertification and quantitatively assessing the draving factors in the desertification process,which may be beneficial for the alleviation of desertification.Main conclusions of this research are as follows:(1)The desertification climatic regionalization based on Thornthwaite method is totally dependent on data from ground-based meteorological stations,without considering the vegetation,topographic and geomorphic characteristics.By contrast,this study retrieved the moist index based on its relationship with NDVI and elevation,further zoning the climatic areas,which may counteract the disadvantages of the existing desertification climatic regionalization.The result of the new regionalization shows that the potential range of desertification occupies 3.643 million km~2,and comprises 37.8%of land area in China.(2)Based on analysis and comparison of current monitoring methods,we selected three indicators(MSAVI,Albedo,BSI)considering the superficial phenomenon and nature of desertification process.We analysed the spatial characteristics of the indicators by using the Landsat and MODIS satellite images.(3)We established three remote sensing monitoring model based on logistic regression model,decision tree model and random forest model in the Ordos Plateau.Through comparison and analysis,the decision tree was showed to be the most accurate among the three models.Using Landsat data and decision tree model,we acquired the desertification status of Ordos Plateau of 2000,2006,2010 and 2015.The result shows that the desertification in Ordos has been through a recovery trend during 2000 to 2015.(4)We retrieved the NPP of Ordos using the CASA model,and established a model for evaluating the desertification driving forces using PNPP and HANPP representing the quantitative roles of climate change and human activities respectively during desertification process.Our result shows that human activities was the main cause of recovery during 2000 to 2015.Climate change was the dominant factor in degradation the period of 2006 to 2010.During 2000 to 2006 and 2010 to 2015,however,both climate change and human activities played important roles in the expansion of desertification.(5)Using MODIS data and decision tree model,we monitored the status and dynamics of desertification of Northern China during 2001 to 2015 on a national scale,and further assessed the percentile roles of different factors.During 2001 to 2015,the desertification status of Northern China has been through a recovery trend,with the desertification area decreased from 1.8032 million km~2 to 1.6681 million km~2,and the DI(desertification intensity)decreased from 0.2107 to 0.1888.During 2001 to 2005,climate change and human activities both played important roles in the reversion and degradation.However,during the period of 2005 to 2015,climate change was the main reason for desertification reversion.(6)On national scale,climate change including the variations of temperature and precipitation is the dominant factor in the desertification process.On regional scale,however,human activities such as reforestation and afforestation can improve the local ecological environment effectively.Therefore,the ecological programs must be continuously implemented in order to promote harmonious development between nature and human society in Northern China.