Spatiotemporal Change And Driving Force Of Aeolian Desertification Land Distribution In Northern China

Northern China is a typical aeolian desertification region.It is significant to require the aeolian desertification land distribution and its driving forces.Desertification is a type of land degradation in which a relatively dry land region becomes increasingly arid,typically losing its bodies of water as well as vegetation and wildlife.Here we exploit Gaofen-1(GF-1)and Moderate Resolution Imaging Spectroradiometer(MODIS)data to develop a quick and efficient method for large scale aeolian desertification dynamic monitoring in northern China.This method which is based on Normalized Difference Desertification Index(NDDI)calculated by band1 & band2 of MODIS reflectance data(MODIS09A1).Mean Absolute Distance(MAD)was calculated between the MODIS-NDDI time series image and the MODIS-NDDI time series image of aeolian desertification land to acquire the aeolian desertification distribution from 2001 to 2015.Then spatial-temporal change of aeolian desertification area and its possible influencing factors were analyzed,such as precipitation,temperature,wind speed and population by Convergent Cross Mapping(CCM)algorithm.The results of this thesis are shown as follows:(1)To realize dynamic monitoring of aeolian desertification land in northern China by using multi-source remote sensing data.In this study,band1 & band2 of MODIS reflectance data exhibited a large disparity in their spectral responses of different land covers.So these two bands were used to calculate a new spectral index called Normalized Difference Desertification Index(NDDI).The MODIS-NDDI time series data and GF-1 data were used to obtain the aeolian desertification land distribution in northern China.The overall accuracy of the result is 88.38%.(2)To realize dynamic monitoring of fractional vegetation cover in northern China by using multi-source remote sensing data.In this study,Normalized Difference Vegetation Index(NDVI)data,Fraction of Photosynthetically Active Radiation(FPAR)and Leaf Area Index(LAI)products acquired from MOD09A1 and MOD15A2 were selected to acquire fractional vegetation cover in northern China during 2001~ 2015.When 1<Leaf Area Index(LAI)<3,the no-dense model was used and dense model was used under other conditions.The determination coefficient(R2)of MODIS and TM estimation was 0.85 with Root Mean Square Error(RMSE)of 0.50.(3)To realize the analysis of aeolian desertification land distribution at spatiotemporal scale.In recent 15 years,aeolian desertification situation of 70 counties was expanded with low slope values and 250 counties was reversed.The aeolian desertification situation in most areas was improved in recent 15 years.Gravity center of the aeolian desertification had a trend to move towards the direction of the high latitude and low longitude.It moved towards north about 0.06 degrees and west about 2.2 degrees between 2001 and 2015.The main distribution area is between 90~100°E,30~40°N and altitude which less than 2000 m in desert and steppe climate zone.Aeolian desertification is worsening in recent 5 years around rivers and lakes.In recent years,the government has made great efforts to strengthen ecological construction with positive effect,but we still need to pay more attention to environment deterioration of rivers,lakes and the nearby areas in the future.(4)To realize the analysis of the driving forces for aeolian desertification land in northern China in recent 15 years.We analyze spatiotemporal change of aeolian desertification area and detect its possible influencing factors,such as precipitation,temperature,wind speed and population by CCM algorithm.It suggests that aeolian desertification area with population indicates feedback(bi-directional causality)between the two variables(P< 0.05).Meanwhile,we find aeolian desertification area is significantly affected by temperature,as expected.However,there is no obvious forcing for the aeolian desertification area and precipitation.Aeolian desertification area with wind speed indicates feedback(bi-directional causality)between the two variables with significant signal(P< 0.01).(5)From the large scale,aeolian desertification is greatly affected by natural factors.Anthropogenic factors can lead to aeolian desertification expansion or inversion at local scale.From the result,aeolian desertification area covers a large area in northern China threatening human life.If the desertification land area continues to grow,it will reduce the habitable zone and lead to a large number of population migration and growth.It is also a big dust origin in northern China.For the aeolian desertification in China,we are greatly convinced that aeolian desertification prevention is important.Meanwhile,we should also pay attention to climate change.If some climatic factors change,it will inevitably lead to drastic changes of aeolian desertification land.Further,aeolian desertification land also has a profound impact on the climate.