Compared with the Qin and Han dynasties, why is the climate in northwest China getting drier and drier?

Although the agricultural development in Qin and Han dynasties played a positive role, it had a great negative impact on the ecological environment. During the Qin and Han Dynasties, the scale and depth of agricultural development in China were unprecedented, which aggravated the deterioration of ecological environment caused by dry climate, especially in the ecologically fragile areas in northwest China. Ecological environment is the material basis for the survival and development of human civilization. In the pre-Qin period, there were abundant forest resources, various kinds of creatures, abundant wetlands and water resources, vast grasslands and oases, and beautiful and pleasant ecological environments in various places. During the Qin and Han dynasties, due to frequent human activities, ecological and environmental problems appeared. During the Qin and Han dynasties, the northwest region was vast and sparsely populated, and the environment was difficult. The forces of Xiongnu and other ethnic minorities continued to grow and develop, posing a serious threat to the Central Plains dynasty. In order to resist the Huns, the imperial court stationed a large number of troops in the northwest, constantly migrating population, opening up wasteland and developing the northwest. Hexi, Hehuang, Hetao and the Western Regions were developed on a large scale at this time. But this development is the strategic development of the imperial court, which is very military and mandatory. The development of northwest China by the imperial court mainly focused on land reclamation and farmland water conservancy, which played an inestimable role in promoting local economic development, resisting the attacks of Xiongnu and other ethnic minorities, consolidating border defense, ensuring economic development and social stability in the mainland, and strengthening economic and cultural exchanges and communication between the East and the West. At the same time, due to excessive land reclamation, large areas of grassland and woodland are gradually replaced by farmland, and the number of animal and plant species is decreasing. In addition, the northwest region itself has a dry climate and windy sand, and intense human activities have increasingly interfered with the ecological environment, eventually breaking through its carrying capacity, causing ecological problems such as soil erosion and land desertification. The Qin and Han Dynasties was the first climax of agricultural development in the history of China, and the scale of reclamation by immigrants was unprecedented. At the same time, the Qin and Han Dynasties was also the first disaster-prone period in ancient China. This shows that the agricultural development in northwest China is closely related to the emergence of ecological and environmental problems.

First of all, trace back to the ecological environment of northwest China in the pre-Qin period;

Secondly, it introduces the grand occasion of northwest agricultural development in Qin and Han dynasties by region;

Thirdly, the ecological environment problems brought by agricultural development are analyzed in detail.

Fourthly, evaluate the ecological and environmental consequences of agricultural development in Qin and Han dynasties from both positive and negative aspects, and how to learn the lessons of agricultural development in Qin and Han dynasties in contemporary western development.

The increase of cultivated land is mainly concentrated in the loess hilly area with serious soil erosion, with a net increase of 272x 10000 square meters, accounting for 69% of the net increase of cultivated land in the loess plateau, which makes these areas fall into the economic and ecological poverty of "getting poorer and poorer".

Due to the unreasonable blind behavior of human beings to nature, soil erosion has been aggravated. Soil erosion is serious and harmful, and it is also one of the reasons for climate drying.