The Loess Plateau is located between the alpine plateau in the west and the hilly plain in the east of China. It is a rugged plateau and the ground is quite broken. The whole loess plateau is almost covered by Quaternary loess.
Loess is a typical aeolian deposit, which is formed by the accumulation of fine-grained materials below the silt layer transported by the wind from the northwest inland during several interglacial periods in Quaternary. Its earliest loess is 2.4 million years ago.
Originally, the Loess Plateau was densely forested and had an excellent ecological environment. However, due to the long-term predatory production in the Loess Plateau (especially in recent 2000), large areas of forests and grasslands have been devastated, and exposed loess has been strongly washed away by rain and runoff, resulting in serious soil erosion, forming spider-web landforms such as loess gullies, loess residual hills and loess mounds. The surface erosion of the Loess Plateau is shocking. Gully density is generally more than 2 ~ 5 kilometers per square kilometer, and in some places it can reach more than 6 ~ 8 kilometers. The cutting depth can reach more than100 ~ 200m, and the ground fissure is about 20% ~ 50%, and the highest can reach more than 65%. Gully areas cover nearly two-thirds of the land surface area. Therefore, the Loess Plateau presents a special geographical landscape with numerous gullies and fragmented ground.
2. The climate is obviously transitional.
The Loess Plateau is located between the eastern coast of China and the northwest inland, just on the channel where the warm and humid air from the southeast monsoon of the Pacific Ocean blows to the northwest of China, so the climate here has obvious transition, from the warm and humid monsoon climate in the southeast coast of China to the arid climate in the northwest inland, belonging to a semi-humid and semi-arid temperate continental climate. Generally speaking, the geographical distribution of temperature and precipitation in the Loess Plateau is decreasing from southeast to northwest.
From the point of view of temperature, the Loess Plateau has the continental climate characteristics of Leng Xia fever in winter, with drastic changes in summer, and the annual average temperature in most places is between 8 ~ 13℃, belonging to a warm temperate zone. Crops can be divided into three crops every two years or two crops a year. The warmest place on the Loess Plateau is the Luo Yi Valley in the southeast of Henan, and the annual average temperature can reach about 65438 04℃, which is close to the subtropical zone. Datong basin in the northern part of the Loess Plateau, northwestern Shanxi, Guyuan in Ningxia and eastern Qinghai belong to the middle temperate zone with an average annual temperature of only about 4 ~ 7℃ due to its high terrain and low temperature.
The Loess Plateau is deep inland, with a strong continental climate and a wide temperature range, with the general daily range exceeding 10℃ and the extreme daily range exceeding 25℃. The large temperature difference between day and night is beneficial to crop growth. Because of the high temperature during the day, the absorption capacity of crop roots is strong, which is beneficial to photosynthesis and the formation of dry matter. At night, the effective radiation on the ground is large, the temperature is low, and the respiration of plants is weakened, which can reduce the consumption of plant nutrients and contribute to the accumulation of dry matter and sugar. This is a favorable natural factor for high grain yield and high sugar content in fruits in the Loess Plateau.
The favorable factor for the climate of the Loess Plateau is abundant light energy resources. The annual total solar radiation in this area is between 5-5.5 billion Joules/m2, which is second only to the arid areas of Qinghai-Tibet Plateau, Xinjiang and Inner Mongolia. Sunlight is the main energy source for green plants to produce organic matter through photosynthesis, and sufficient sunlight is beneficial to the growth and development of crops and the ripening of fruits. The loess plateau has long sunshine time and abundant light energy, which is very beneficial to increase agricultural production. But at present, the utilization rate of light energy in this area is still very low, only about 1% ~ 2.5%, which has great development potential. Strengthening intercropping, interplanting and moderate close planting among crops can improve the utilization rate of light energy and increase crop yield.
3. There are many rivers and ditches, small runoff and water shortage.
The Loess Plateau has the largest number of channels in the world, and criss-crossing channels are a major natural landscape of the Loess Plateau. According to a rough survey, there are more than 300,000 channels with a length exceeding 1 km in the Loess Plateau, with a total length exceeding 1 10,000 km. These gullies are all formed by mountain torrents, especially flood gullies. More than 80% of them are dry gullies, and there is basically no running water. Therefore, although there are many gullies in the Loess Plateau, there are few water sources and poor runoff.
Surface runoff from the Loess Plateau flows into the Yellow River and Haihe River respectively. The main stream of the Yellow River runs through the Loess Plateau, including Taohe River, Huangshui River, Wuding River, Yanhe River, Fenhe River, Weihe River (and Luohe River north of Jinghe River), Luo Yi River and Qinhe River, which control the western, central and southeastern parts of the Loess Plateau. Haihe River system is distributed in Taihang Mountain area in the east, with tributaries of Sanggan River, Tanghe River, Hutuo River and Zhanghe River.
Due to less precipitation, the loess plateau has strong loess permeability, sparse vegetation, poor water conservation conditions, small surface runoff and water resources shortage. For example, there are nine tributaries in the Yellow River Basin that are over 300 kilometers long, of which only four are Weihe River, Taohe River, Huangshui River and Luo Yi River, with annual runoff exceeding 3 billion cubic meters. The total annual runoff of the Yellow River system (including the main stream) is less than that of Xiangjiang River, a tributary of the Yangtze River, which shows the poverty of runoff in the Loess Plateau.
The formation and distribution of groundwater in the Loess Plateau are controlled by geological structure, lithology, landform, precipitation and river hydrology, showing great regional differences.
As far as precipitation is concerned, the annual precipitation in the Loess Plateau is basically between 400-600 mm. The 400 mm isohyet is roughly accompanied by the Great Wall, and only a few counties such as Tongxin, Yanchi, Jingyuan and Xunhua are below the 400 mm isohyet. In the southeast, the northwest of Henan and the southeast of Shanxi are at the forefront of the southeast monsoon entering the loess plateau, with more rain, and the annual precipitation can reach 600 ~ 850 mm, which is a rainy area on the loess plateau. The wettest places on the Loess Plateau are the windward slopes of Wutai Mountain and Taihang Mountain, and the annual precipitation can reach more than 800 mm.
The precipitation in the Loess Plateau has the problems of uneven seasonal distribution, large variability and low guarantee rate. More than 70% of the precipitation in the Loess Plateau is concentrated in the second half of the year (especially from June to September), which is the peak season for crop growth, and rainy weather is very beneficial to agriculture. In spring, there is less precipitation, the temperature rises rapidly, and spring drought is more common, which often affects spring sowing and leads to reduced production. The annual precipitation in rainy years can be more than 2 ~ 4 times different from that in rainy years, and the precipitation variability is too large and the precipitation guarantee rate is low, which is very unfavorable for high and stable agricultural production.
4. The land is vast, with more arable land and less forests and grasslands.
The Loess Plateau has a vast land, which is one of the areas with the richest land resources in China. The total land area of the whole territory is 775.5 million mu, much higher than that of the southeast provinces of China. However, there are great differences in this area. The hilly area of western Henan in the southeast of the Loess Plateau is narrow and densely populated, with only 3.2 mu of land per capita. Since then, from north to west, per capita land has increased, with 7.8 mu in Shanxi Province, 7.7 mu in Shaanxi Province, 1 1.3 mu in Gansu Province, 16 mu in Dong Qing hilly area and 26.7 mu in Ningxia. The loess hilly area in Inner Mongolia has the most land per capita, reaching 32.3 mu.
In the Loess Plateau, we must follow the objective laws, take the road of agriculture, forestry and Mu Zhi, and make rational use of land according to local conditions, so that the Loess Plateau will have a way out. If the hillside is reclaimed indiscriminately and planted extensively, the harvest will be poor, which will cause serious soil erosion and low yield per unit area, leading to long-term food and clothing problems. Only by completely changing the farming system, adjusting the land structure and turning the earth mountain into a green hill can we fundamentally improve the environment, enrich the forest and grain, and change the backward face of the Loess Plateau.
5. Rich in mineral resources
The Loess Plateau is one of the regions with the richest mineral resources (especially coal) in China. Mineral resources have many advantages, such as many kinds, large reserves, good combination and moderate location, and occupy a particularly important position in China. More than 20 species of 120 have been discovered in the Loess Plateau, of which 77 species have been proved, accounting for 56% of China (37 species have been proved). It includes seven categories, the main minerals are: energy minerals (coal, oil, natural gas, oil shale); Ferrous metals (iron, manganese, chromium, vanadium, titanium); Nonferrous precious metal ores (copper, lead, zinc, bauxite, nickel, cobalt, tungsten, tin, molybdenum, gold and silver); Rare metal minerals (niobium, lithium, rubidium, germanium, gallium, indium, thallium); Metallurgical auxiliary ores (flux limestone, flux dolomite, silica, refractory clay, fluorite, bauxite); Chemical raw materials (sulfur, phosphorus, potassium-bearing rocks, chemical limestone, mirabilite, trona, magnesium salt, barite and peat); Building materials minerals and other non-metallic minerals (mica, asbestos, graphite, gypsum, feldspar, quartzite, crystal, perlite, zeolite, vermiculite, bentonite, marble, granite, building stones and various clays), etc. Among these minerals, 30 mineral reserves rank among the top three in China, among which coal, bauxite, gallium, rhenium, zeolite, refractory clay, bauxite, marl, alkali limestone, building limestone, glass sandstone, gneiss and diabase rank first in China. The proven coal reserves in the Loess Plateau exceed 500 billion tons, accounting for more than 50% of China. Bauxite is another mineral in the Loess Plateau that ranks first in China, with a reserve of over 654.38 billion tons, accounting for more than half of China. In addition to the above, gallium, rhenium, refractory clay, bauxite, perlite, zeolite, limestone, glass sandstone, titanium, magnesium salt, rock salt and vermiculite in the Loess Plateau all occupy one of the best positions in China. The potential value of the main mineral resources in the Loess Plateau accounts for a considerable share in China. Rich mineral resources are another extremely favorable condition for the economic development of the Loess Plateau.