Study On Climate Change And The Human-earth Relationship In Dingxi Region During The Holocene

Dingxi area is located in the west of Loess Plateau, ecological environment is extremely bad. The soil erosion, poor soil, the water resources short and a series of ecological environment problems are restricting the human society and the economical sustainable development. Based on the records of environmental changes in Lujiagou loess section, ¹⁴C, magnetic susceptibility, carbonate, particle size, organic matter content and other means to obtain a higher resolution of the Holocene environmental changes sequence and reconstracted climatic changes process of the Holocene in Dingxi area. Meanwhile, in combination with other historical documents, we discussed the human activities process, points out humanity's activities and changes of the climatic and environmental close related. The main findings are as follows:Climatic changes of the Holocene in Dingxi area can be divided into three stages: (l)Early the Holocene (11200-7560 cal aB.P.), climate is becoming warm and wet, but it is cold, on the whole. But there are several times during the wet or dry and cold or warm changes.9740-8300 cal aB.P., this stratum frequency magnetic susceptibility increases, the organic content maintains a high value, indicated that the summer monsoon strengthens, the precipitation increases, there is a weak palaeosoil developmented.During the early Holocene also a short-term cold and dry event, the time is in 8000 - 7560 cal aB.P.. (2)Middle the Holocene (7560-3600 cal aB.P.), the climate is warm and humid, but less precipitation early, in later 4350-3600 cal aB.P., maximum precipitation in this region during this period. There occurred a cold and dry weather event in 4100-3900 cal aB.P..(3)Late the Holocene (3600-1167 cal aB.P.), the climate is becoming drying, in the period 2800 to 2560 cal aB.P., developed a palaeosoil layer, but a weak soil strength, and it indicated that the summer monsoon has a short-term summer monsoon enhancement. Contrast with the other areas of climatic changes, we found that climatic changes in this district during the Holocene not only has the distinct regional characteristics, but also has the global consistency.But the climate stages and the climate events's beginning and ending time, the change scope and the duration have the region differences, possibly is as a result of the differences of regional terrain and the atmospheric circulation situation, causes differences of the global climate changes response time and the sensitive degree.Humans have already lived in the western of Loess Plateau in the Early Holocene, mainly hunts and non-agricultural production ways to life, although have carried on the simple agricultural production, but the productive forces is very low, the slash-and-burn cultivation production method have few influence on the environment.Middle Holocene, climate is warm and humid, and may be a superior natural environment for ancient human's survival and development , the prehistoric culture started to expand massively to the west to the Zuli River basin.About 6000 the scope and depth of human activities in Dingxi area dramatically expanded, and simultaneously the influences also strengthened on the environment.Has developed the Yangshao culture, the Majiayao culture, the Qijia culture successively, although the primitive farming is developed, but this time humanity's productive forces level is backward, the production of the original agriculture,to a certain extent,have influences on the vegetation, but it was only partial, the human activities does not significantly impact on the environment.Moreover, as a result of the climate optimum, the environment self-adjustment and antijamming ability is also quite strong.Since the late Holocene, climate is becoming dry, the impact of human activities also increasing. Before the Qin and Han Dynasties, Dingxi area vegetation cover is good, climate dry desiccation development by natural factor primarily.After the Qin and Han Dynasties, on the one hand as a result of climatic conditions worsening, on the other hand population of Dingxi area sharp growth, productive forces level enhanceed, humanity created the better physical conditions for their survival, they started to reclaim land, reclamation deforestation, over-grazing to maintain the survival, coupled with the prevalence of the Loess Plateau since ancient times were thin at the round-Arakawa system, which severely damaged the ecological environment. This kind of large-scale human activities,causes the natural vegetation'destruction, the surface lack the vegetation protection, causes the soil erosion to intensify, thus causes the soil erosion, the land to be barren, water resources short and a series of ecological environment problems. The deterioration of the ecological environment in Dingxi area, begins in the Northern Song Dynasty on the whole.But the massive destruction, in the Ming and Qing Dynasties.Thus it can be seen, The deterioration of the modern ecological environment in Dingxi area, has been past 3600 for many years, has superimposed the double impact of the natural process and human activities, but this kind of change by human factor majority.Serious soil erosion and the extreme lack of water resources are the main reasons for the deterioration of the ecological environment and economic backwardness in Dingxi area.