Global Desertification Index Building And Desertification Trend Analysis Based On Remote Sensing Image

According to the United Nations statistics, about 35 percent of the global land is in the edge of desertification, and about 20 million hm2 arable lands is deserted followed by crop yield reduction about 12%~21%, which directly result in annual economic loss reaching up to 26 billion. S ince increasingly severe desertification has significant impact on the environment, human life, and socio-economic, monitoring and analyzing the trends of desertification have become a hot issue around the world.The desertification phenomenon displayed on remote sensing images shows enhancement of surface signal and reduce of vegetation signal, which can be quantitatively evaluate by albedo, temperature, humidity, vegetation coverage, and so on. Therefore, the trend of desertification is evaluated based on MODIS data.Firstly, the desertification difference index(DDI) is constructed to assess the global desertification. Based on the NDVI and Albedo, it establishes the Albedo-NDVI feature space and utilizes the negative correlation between the Albedo and NDVI, which contributes to the construction of DDI. In addition, the global desertification thematic products are completed, which is used to mapping and evaluating the global desertification.Secondly, based on DDI for 15 years, the desertification degree and trends within different areas is evaluated and analyzed, such as the global, the continents, as well as all provinces of China. Based on the global DDI thematic products, it shows the state of desertification in different areas in the form of hierarchical diagrams. Through times series trend fitting analysis, the distribution of global DDI within 15 years is completed. Subsequently, the comparison of DDI within 15 years is conducted in different areas.Finally, the comparison of Global Environment Monitoring Index(GEMI) and other vegetation indices on the monitoring of vegetation fully validates the effectiveness of GEMI for global vegetation monitoring. On one hand, the global GEMI products are completed and used to assess the global vegetation cover. O n the other hand, the currently(2000~2014) global environment is evaluated based on the GEMI and DDI for the past fifteen years.The major conclusions for this paper are given as following:1. In recent 15 years, the global vegetation coverage gradually decreases and the desertification increases.2. The distribution of global desertification is almost consis tent with the distribution of global vegetation coverage. Details of the conclusions include:(1) Around the equator dominated by evergreen broad- leaved forest, the vegetation coverage is relatively high with a mean DDI of 1.45;(2) In the North America and Asia with high latitude dominated by coniferous forest and deciduous broad- leaved forest, the mean value of DDI is around 1.1 ~ 1.3, while in the east coast of North America and Europe, the mean value of DDI reach up to 1.4;(3) The mean value of DDI of North America, Oceania, Africa, the Eurasian, and South America for 15 years is 0.70, 0.79, 0.96, 1.12, and 1.17, respectively.