Desert And Sandy Field In North China On The Basis Of Remote Sensing Analysis And Its Relationship With Climate Factors During 1992-2015

To assess climatic impact on desert area change,the Normalized Difference Vegetation Index,Net Primary Difference,vegetation greenness and other indicators are commonly used to indicate the change of desert area.To date there is no interannual area series obtained by remote sensing image for the deserts in Northern China.This thesis uses the area of Gobi,bare bedrock,saline-alkali land,alpine desert,tundra and other unused land of 1 km resolution land cover and land use data to calibrate the 19922015 CCI-LC bare land areas(including desert,Gobi,bare rock,saline-alkali land and alpine desert,tundra and other unused areas).Then,using SVM supervised classification to interpret the Tengger Desert total 8 scenes remote sensing images in the year of 2000 and 2002 for the desert area accuracy evaluation,the error is smaller then 10%.Based on the revised 1992-2015 Northern China desert area data and the climate data,the spatial and temporal changes and climate impact mechanism on the deserts in Northern China were analyzed.The results showed that deserts/sandy field reduce up to～86,704 km2,with a reduction of 7.43%from 1992 to 2015 in north China.Compared with the desert area of 1992,the desert/sandy field in the northwestern arid region,Tibetan Plateau high and cold region and East Asian monsoon dominated region contracted～46,109 km2,～23,470 km2 and～17,125 km2,respectively,showing a reversal trend of desertification in north China.The reduction of desert/sandy field in East Asian monsoon dominated region is the greatest.The total desert/sandy field reduction was～118,000 km2 by 2015 compared with that of 1992,whereas with a newly expanded desert/sandy field area of～31,300 km2 at same time.The reduced area were mainly located in northwestern Mu Us sandy field and southeastern Tengger Desert,the southern Gurbantungut Dersert,the northwestern Gonghe sandy field,the eastern Horqin sandy field and the northern Kumutage Desert.On the other hand,the newly expanded area of desert/sandy field are mainly located in Otindag sandy field and the Southwestern Horqin sandy field.Temperature and evapotranspiration of these three climatic subzones in China were increased year by year,but precipitation was decreased.The soil moisture in the Northwestern arid region and Tibetan Plateau high and cold region has been increased,which restrains the dune activity and therefore was the determined factor for the desert/sandy field reduction.The precipitation,relative humidity and soil humidity have a direct impact on variation of the desert/sandy field in the monsoon dominated region,but we find wind speed decrease and human protection may be the predominated factors force the reduction of desert and sand field in Northern China over the past 26 years.