Quantitative Study Of Desertification In The Ordos Plateau Since The Qing Dynasty

Desertification is an important issues facing the world today.Desertification not only erodes land resources,but also causing ecological destruction and economic losses.In recent years,desertification control has made remarkable achievements in China,but the situation of desertification is still severe.The process of desertification in the historical period and its driving factors are not only one of the important contents of historical geography research,but an indispensable foundation for understanding modern desertification.From historical period to modern times,China's arid and semi-arid regions have experienced a series of desertification processes,but the limitation of the desertification-related literature records and the lack of high-resolution data' have led to the different support of desertification research.Quantitative research is needed on the desertification process and its driving mechanism.Exploring the quantitative research on the desertification process and its driving forces in the historical period is not only helpful to break through the current bottleneck of desertification research,clarify some historical desertification research misunderstandings,but also to provide a theoretical basis for the formulation of desertification control policies.This thesis selects the Ordos Plateau as the research object since the Qing Dynasty.Based on the analysis of the desertification process of the modern Ordos Plateau,a desertification model is established,and the richer climate and human activity data from the Qing Dynasty are used to substitute the model to reconstruct the dynamic evolution of the Ordos Plateau desertification since the Qing Dynasty.Compared with NPP,which indicates the process of desertification development under climatic conditions,and analyzed the driving mechanism of the desertification of the Ordos Plateau since the Qing Dynasty.At the same time,the following conclusions were obtained:1)The desertification area of the Ordos Plateau showed a decreasing trend from 1986 to 2015.The desertification area was fluctuating from 1986 to 1994.The desertification area increased and decreased in different years,but the desertification area remained at a high level,especially in the western and southern plateaus.The desertification area in 1994-2000 ushered in rapid development stage.After 2000,the desertification trend of the Ordos Plateau began to reverse significantly,and the area of desertification land reduction was concentrated in the eastern and southern parts of the plateau.The desertification area of the Ordos Plateau gradually decreased in fluctuation from 2001 to 2015,but the desertification area increased in 2004-2005 and 2009-2010.After 2012,the desertification area in the western part of the plateau increased slightly.2)From 1650 to 2015,the desertification area of the Ordos Plateau showed an increasing-decreasing-increasing-decreasing trend.Specifically,from 1650 to 1920,the desertification area increased slowly,and from 1920 to 1945,the desertification area gradually decreased.From 1945 to 2000,the desertification area showed a sharp increase trend.After 2000,the trend of desertification in the Ordos Plateau began to significantly reverse.Since 2012,the desertification area in the western part of the plateau increased slightly.3)From 1630 to 2015,the simulated value of the NPP on the Ordos Plateau fluctuated greatly,and there was a tendency of a slow rise as a whole.1630-1690 NPP simulation values were lower than the multi-year average.From 1690-1725,the simulated value of NPP showed a rising trend and was at a relatively high level.From.1726 to 1765,the simulated values gradually decreased.From 1765 to 1880,the NPP simulated values fluctuated around the average value for a long time.From 1880-1950,the simulated value of NPP in the Ordos Plateau was at a relatively low level.After 1950,except for the very short period of low NPP,the overall NPP simulation value in the study area was at a relatively high value level.4)By observing the desertification area,the NPP simulation value curve,and the slope ratio curve,it can be seen that climate change and human activities have played different roles in different stages of the desertification of the Ordos Plateau since the Qing Dynasty.The slope ratio from 1650-1805 was 1.01,indicating that climate change played a leading role in this stage of desertification,but the role of human activities cannot be ignored.From 1805-1911,the slope ratio was 0.36.At this stage,human activities had a greater impact on desertification than climate change.The slope ratio from 1912-1948 was 1.39.Climate change played a leading role in this stage of desertification,and human activities had a weaker impact on desertification.From 1949 to 2000,the desertification area showed a gradual increase in fluctuation,and the amplitude exceeded the NPP simulation value.From 2001 to 2015,the change in the area of desertification and the change in climate change gradually became consistent,and the slope ratio was 1.59,indicating that climate change was the determining factor in the process of desertification in the first 15 years of the 21st century.