Land Desertification Monitoring In Tarim Basin Based On Data For Consecutive Years

Nowadays land desertification is one of the most serious ecological environmental problems,and it is also the main ecological environmental problem in northwest arid region of China,which directly threatens the security of human living environment and the stability of society and economy.Monitoring the change of land desertification by using remote sensing data for consecutive years has become one of the important means of land desertification research at present,however,what kind of data and methods are used in specific areas is still a scientific problem that needs in-depth study.Taking the Tarim Basin in Xinjiang as the study area,this paper selects seven kinds of data of MODIS-NDVI-1000 m,MODIS-NDVI-500 m,MODIS-NDVI-250 m,MODIS-EVI-1000 m,MODIS-EVI-500 m,MODIS-EVI-250 m and SPOT-NDVI-1000 m from 2000 to 2018,and calculates the annual monitoring data of 7 kinds of data by the maximum annual synthesis method.Based on the comparative analysis of seven kinds of annual monitoring data of land desertification area,grid accumulation method and transfer matrix method,the data suitable for monitoring land desertification in Tarim Basin are determined.Based on the study of land desertification monitoring in Tarim Basin,the main conclusions are as follows:1)the comparative analysis of land desertification area from 2000 to 2018 shows : the monitoring data of 7 kinds of land desertification area show the dynamic trend of interannual fluctuation and gradual improvement.7 kinds of monitoring data all show that the area of non-desertification in Tarim Basin wavelike rises and the area of extremely severe desertification decreases from 2000 to 2018,and the areas of mild desertification,moderate desertification and severe desertification remain basically unchanged.At the same time,there are differences in non-desertification area and extremely severe desertification area among 7 kinds of monitoring data.MODIS-EVI data is higher than MODIS-NDVI data in extremely severe desertification area,while MODIS-NDVI data is higher than MODIS-EVI data in non-desertification area.There are also differences in the interannual increase and decrease in 5 categories of desertification grades of 7kinds of data,and the changes of extremely severe desertification and non-desertification in MODIS-EVI data are larger than those in MODIS-NDVI data.SPOT-NDVI data is similar to MODIS-NDVI data,but SPOT-NDVI has abnormal years,which is not suitable for multi-period continuous monitoring.2)comparing and analyzing the results of MODIS-NDVI and EVI grid accumulation method,it is found that the spatial distribution of these two kinds of data is similar,but the improvement rate of NDVI data is lower than that of EVI data,and the deterioration rate of NDVI data is higher than that of EVI data.NDVI is sensitive to the change of low vegetation area,but has a low recognition rate to the change of high vegetation area,while the EVI data is just the opposite,it is more sensitive to the change of high vegetation area,and the recognition rate of low vegetation area is low.NDVI data are suitable for desertification monitoring in low vegetation areas of Tarim Basin,while EVI data are suitable for land desertification monitoring in high vegetation areas.3)The matrix transfer results of MODIS-NDVI and EVI monitoring data show that the transformation of land desertification in Tarim Basin is mainly between extremely severe and severe,mild and non-desertification,severe and moderate,mild and moderate,but the each transfer number of NDVI is slightly higher than that of EVI,and the spatial distribution of each transfer of NDVI is wider than that of EVI.On the annual,there is a great difference in the net transfer of land desertification between NDVI and EVI data.In 2001,2002,2004,2009,2011,2014 and 2015,there is a big difference in net transfer among MODIS-NDVI-1000 m,MODIS-NDVI-500 m and MODIS-NDVI-250 m,while the difference among MODIS-EVI-1000 m,MODIS-EVI-500 m and MODIS-EVI-250 m is small,and the consistency of EVI data is slightly better than that of NDVI data.4)MODIS-NDVI and EVI both show that the middle and lower reaches of Tarim River and Chechen River Basin are the key control areas of land desertification in Tarim Basin,but there are differences among different resolutions.Both NDVI and EVI show that with the improvement of data resolution,the transfer patches become smaller and smaller,while the key transfer areas become more and more difficult to identify.5)The results of transfer matrix show that the change of land desertification in Tarim Basin mainly occurs in grassland,cultivated land and unused land.The different resolution of the data has an impact on the number of transfer.In the process of deterioration,the deterioration area of unused land and woodland of NDVI-500 m is higher than that of NDVI-250 m,and the deterioration area of grassland and cultivated land of NDVI-250 m is higher than that of NDVI-500 m.In the process of improvement,the two are on the contrary.6)According to the analysis of transfer matrix data,the main transfer ways of land desertification in Tarim Basin from 2000 to 2018 are as follows: extremely severe desertification→severe desertification→ moderate desertification →mild desertification→ non-desertification,but the data resolution has an impact on the number of transfer.The quantity and proportion of improved transfer of MODIS-NDVI-500 m between adjacent land desertification grades are higher than that of MODIS-NDVI-250 m,and the number and proportion of deterioration transfer of MODIS-NDVI-250 m between adjacent land desertification grades are higher than that of MODIS-NDVI-500 m.