Quantitative Assessment Of The Relative Role Of Climate Change And Human Activities In Sandy Desertification

As the main type of desertification, sandy desertification is becoming one of the most serious global social-economic-environmental issues of our time, which threatens human survival and development. China is one of the countries which are severely affected by sandy desertification in the world. Sandy desertification caused a lot of problems such as reduction of land quality, decrease of land resources, sand storm, etc., which seriously impede the sustained development of economy and construction of harmonious society. The whole country is still in a serious condition though we have achieved some good results in preventing sandy desertification in recent years.Assessing the driving forces of sandy desertification is fundamental and important for sandy desertification research. Climate change and human activities are main driving forces of sandy decertification. The research of the relative role of climate change and human activities in sandy desertification at different temporal and spatial scales has important significance in the prevention of sandy desertification and the research of sandy desertification theory. The quantitative assessment of the relative role of climate change and human activities in sandy desertification is the foundation for accurately evaluating the dynamic progress of sandy desertification, researching the sandy desertification in response to climate change and formulating the strategies of preventing the sandy desertification. Exploring effective methods to carry out the quantitative assessment of the relative role of climate change and human activities in sandy desertification and breaking the present research bottleneck, which not only can enrich the theoretical basis of sandy desertification research and clarify some mistakes in sandy desertification research, but also can provide theoretical basis for formulating strategy of sandy desertification prevention on the district and country scale. In this study, Ordos plateau was selected as the typical research region. Based on analyzing the character of climate change and human activities, this study formulated quantitative monitoring of sandy decertification and quantitative assessment of the relative role of climate change and human activities in the process of sandy decertification, and carried out the research of the relative role of climate change and human activities in sandy desertification in Ordos plateau at multi-scales. This paper takes the quantitative research as masterstroke and breaks the research of driving forces in the progress of sandy desertification from methodology's point of view. The followings are the productions and conclusions of this dissertation:1 Developed a quantitative method for monitoring sandy desertification in Ordos Plateau based on Landsat data. Based on the characteristics of the change of land surface induced by sandy desertification, the author selected NDVI, MSDI and Albedo as the indicators to represent the abundant of vegetation, landscape and micrometeorological condition of land surface with sandy desertification respectively for monitoring sandy desertification. Based on the characteristics of Landsat data, the author developed the methods for retrieving the there indicators, and built the quantitative method for monitoring sandy desertification based on Decision tree model with considering the effects of vegetation types and the image date on the value of indicators. According to the results of accuracies checking, there was relative higher accuracy of this method, which made it can be applied to monitor sandy desertification in Ordos Plateau accurately in this study.2 From 1980 to 2005, some regions of Ordos Plateau experienced sandy desertification reversion and some places experienced sandy desertification expansion; however, there had a situation that the area of sandy desertification reversion was higher than that of sandy desertification expansion in this period. From 1980 to 1990, the distribution of the area of sandy desertification reversion was relatively scattered while the distribution of the area of sandy desertification expansion was relatively concentrative. The areas of reversed sandy desertification were mainly distributed in the transition zone between temperate deciduous scrubs and desert steppe in the south east of Hanjin Banner, temperate steppe in the east of Zhunger Banner and the temperate deciduous scrubs in the south of Etuokeqian Banner. From 1990 to 2000, the area of sandy desertification reversion was higher than that of sandy desertification expansion. The regions experienced obviously sandy desertification reversion mainly distributed in the transition zone between temperate deciduous scrubs and temperate steppe in the north west of Yijinhuoluo Banner, and the temperate deciduous scrubs in the west of Etuokeqian Banner. However, the area of sandy desertification expansion mainly distributed in Dalate, Hangjin, Zhungeer, Wushen Banner and Dongsheng city. From 2000 to 2005, mean annul revised sandy desertification area in this period was biggest in the three periods, which mainly distributed in the most areas of Zhunger Banner, Dalate Banner and Dongsheng city, while the areas of reversed sandy desertification centralizely distributed in Yijinhuoluo Banner and the transition zone between temperate steppe and temperate deciduous scrubs in the north west of Wushen Banner.3 Formulate a quantitative method for assessing the relative role of climate change and human activities in sandy decertification. NPP was selected as the indicator to measure and assess the impact of climate change and human activities on sandy desertification in this study. Potential NPP and the difference between potential NPP and actual NPP were used to measure and assess the impact of climate change and human activities on sandy desertification. Through the process of splitting the driving forces of sandy desertification and basing on the scenarios between the sandy desertification reversion and expansion and the changes of NPP induced by climate change and human activities, formulate the quantitative assessment of the relative role of climate change and human activities in sandy decertification. On the basis of setting up the conceptual model, the author quantified the required date in the assessment process. CASA model was used to simulate the actual NPP, and establish the calculate method of potential NPP based on CASA model. According to the validation of the actual NPP and the results of quantitative assessment, it proved that the quantitative assessing method developed in this study can be used to assess the relative role of climate change and human activities in sandy decertification.4 The relative role of climate change and human activities in sandy desertification of Ordos Plateau showed significant differences when it assessed at different temporal scales. When it was assessed at the temporal scale from 1980 to 1990, climate change was the dominant factor that induced the reversion of sandy desertification, and the area of reversed sandy desertification which was induced by climate change was 89.45 percent of the total area of reversed sandy desertification. While human activities was the dominant factor that induced the expansion of sandy desertification, and the area of expanded sandy desertification which was induced by human activities was 83.93 percent of the total area of expanded sandy desertification in this period. When it was assessed at the temporal scale from 1990 to 2000, human activities was the dominant factor that induced the reversion of sandy desertification, and the area of reversed sandy desertification which was induced by human activities was 90.04 percent of the total area of reversed sandy desertification. While climate change was the dominant factor that induced the expansion of sandy desertification in this period, and the area of expanded sandy desertification which was induced by climate change was 91.20 percent of the total area of expanded sandy desertification. When it was assessed at the temporal scale from 1980 to 2000, human activities was the dominant factor that induced the reversion of sandy desertification, and the area of reversed sandy desertification which was induced by human activities was 93.02 percent of the total area of reversed sandy desertification. While climate change was the dominant factor that induced the expansion of sandy desertification, and the area of expanded sandy desertification which was induced by climate change was 85.77 percent of the total area of expanded sandy desertification. However, when it was assessed at the temporal scale from 1980 to 2005, both climate change and human activities induced the reversion of sandy desertification, but the areas of reversed sandy desertification which was induced by climate change were slightly bigger and reached 59.71 percent of the total revised area; while human activities was the dominant factor that induced the expansion of sandy desertification in this period. The area of expanded sandy desertification which was induced by human activities was 62.35 percent of the total area of expanded sandy desertification.5 When it assessed at different spatial scales, there were also differences in the relative role of climate change and human activities in sandy desertification of Ordos Plateau. Along with the increase of spatial scale, there is a growing tendency for the areas of reversed sandy desertification which was induced by both climate changes and human activities, and both of them reached the biggest when it assessed at banner scale. But the expansion of sandy desertification induced by climate change and human activities and error area in the process of assessment are represented by the trend of lowing after increasing, and both of them reached 0 when it assessed at banner scale.