What are the causes and regions of drought?

Elephant disaster: Drought

Clicks on June 6, 2005: 154 times Source: "China Meteorological News"

Drought refers to the long period of clear weather without rain or Lack of rain, lack of soil water, and dry air have caused disasters such as withered crops and insufficient drinking water for humans and animals. Considering weather conditions, drought also includes hot and dry winds, high temperatures and heat waves. Drought is the most serious meteorological disaster in my country's agriculture, causing serious losses. According to relevant statistics, the average drought-stricken area of ??crops in my country reaches more than 300 million acres, and the disaster-affected area reaches 120 million acres. The annual output reduction due to drought reaches an average of 10-15 billion kilograms, and the annual economic losses caused by water shortage reach 200 billion yuan. Drought disasters have many characteristics such as large impact area, obvious seasonality, persistence, regionality and latent nature, as well as interannual changes.

Defense against drought disasters

South-to-North Water Diversion Project: Constructing the South-to-North Water Diversion Project to divert water from the Yangtze River to the north can fundamentally solve the drought problem in the north;

Build water conservancy and Scientific irrigation: In agricultural production, attention should be paid to the construction of water conservancy projects and the construction of reservoirs, which is not only beneficial to flood control, but also to drought relief. For areas where droughts often occur, it is particularly important to use reservoirs to promote water-saving irrigation technology and develop irrigated agriculture;

Vegetation construction: converting farmland into forests and greening the environment are important methods to prevent drought;

Pay attention to the forecast of drought disasters: my country’s meteorological department has always regarded drought and other meteorological disasters as the main content of monitoring and forecasting. Therefore, we must pay attention to meteorological forecasts, make full use of this important information, make decisions about drought relief, and take measures to reduce drought disasters;

Artificial rainfall enhancement: Artificial rainfall enhancement is a proactive measure to combat drought disasters. The method is to sow catalysts in clouds with rainfall-forming conditions to promote early and heavy rain in the clouds. As early as 1958, our country had carried out research and experiments on artificial weather modification. At present, many provinces (autonomous regions and municipalities) have carried out artificial rainfall enhancement operations, gained a lot of valuable experience, and achieved remarkable results;

Interception and storage of rainwater and mist: Interception and storage of rainwater A variety of methods can be used, such as building small reservoirs in the mountains, building dams, small low dams and large water cellars in valleys, water storage cellars on hillside, rain collecting cellars, etc. The method of "opening a net" can be used to collect fog water. This method is more suitable for mountainous areas and rural areas with more fog;

Promote drought-resistant varieties and drought-resistant sowing methods;

Free of charge Farming methods: For farming in dry and water-scarce areas, no-till methods can be adopted to reduce water and soil erosion.

Drought

From a natural perspective, drought and drought are two different scientific concepts. Drought usually refers to a climate phenomenon in which the total amount of fresh water is insufficient to meet human survival and economic development. Drought is generally a long-term phenomenon, but drought is different. It is only an occasional natural disaster. Even in areas that are usually rich in water, droughts can be caused by temporary climate abnormalities. Drought and drought have been major natural disasters faced by humans since ancient times. Even today, when science and technology are so advanced, their disastrous consequences still abound. It is particularly worth noting that with the economic development and population expansion of mankind, water shortages have become increasingly serious, which has directly led to the expansion of dry areas and the aggravation of aridification. The aridification trend has become a global concern. The twentieth century is about to pass, and mankind is about to enter a new era. Faced with the increasingly serious global drought trend, it is very necessary to explore the causes and find countermeasures.

Development, Utilization and Protection of Climate Resources in the Northwest Arid Zone

The land area of ??the Northwest Arid Zone accounts for about 30% of the country’s total land area, and its population accounts for about 3.8% of the country’s population. Administratively Including all of the Xinjiang Uygur Autonomous Region, most of the Inner Mongolia Autonomous Region (with the exception of the Daxinganling Mountains in the northern part of the Hulunbuir League) and the Ningxia Hui Autonomous Region (with the exception of the Liupan Mountains), as well as the Hexi Corridor in Gansu Province and the Bashang area in Hebei Province.

The arid geographical environment in northwest my country has been initially formed in the late Cretaceous and early Tertiary periods. Subsequently, it experienced the Himalayan orogeny and the uplift of the Tibetan Plateau, and the degree of drought became more severe, gradually forming the current special geographical environment.

This vast territory is rich in natural resources such as land, minerals, solar energy, and wind energy, as well as some water resources and biological resources. For thousands of years, people of all ethnic groups have extensively developed and utilized it, establishing many fertile farmlands and rich pastures. The land is vast and sparsely populated, and the level of industrial and agricultural production is low. Desolate and barren sandy deserts (deserts) and stony deserts (Gobi) are widely distributed. There are also many serious natural disasters, such as drought, salt-alkali, wind and sand, etc. In this ecologically fragile area, unreasonable land use can easily lead to land degradation and reduced productivity.

The climate characteristics of the northwest arid area are mainly characterized by drought and little rain, drastic changes in cold and heat, windy and sandy weather, and strong solar radiation.

The annual precipitation is generally less than 400 mm, and decreases from east to west as the mileage from the sea increases (except in western Xinjiang), east of the Sunitzuo Banner - Bailing Temple - Otok Banner - Yanchi line , the annual precipitation is generally 300 to 400 mm, and the dryness degree is 1.5 to 2.0. It is a semi-arid area, and the natural vegetation is mainly steppe. It has been the best pasture in my country since ancient times; dry farming can also be carried out reluctantly, but "nine droughts in ten years" ”, the output is very unstable, and it is easy to cause serious desertification problems. Between this line and the Helan Mountain line, the annual precipitation is 200 to 300 mm, and the dryness degree is 2.0 to 4.0. The natural vegetation is mainly desert grassland, and farming must be irrigated. In the vast desert area west of Helan Mountain, the annual precipitation is less than 200 mm and the dryness degree is greater than 4.0. Crops must be irrigated more than 3 to 4 times a year, and planting trees and grass also requires multiple waterings.

Precipitation in this area is extremely variable, with rain often falling for several months to more than half a year. The early spring and "stuck neck" droughts in April, May and early June are particularly serious; but in In summer and autumn, 1/2 or even 2/3 of the annual total rainfall can fall within one or two days, sometimes even causing floods.

Due to drought and little rain, solar energy resources are very abundant. The annual sunshine generally reaches 2,500 to 3,000 hours, and the Xingxing Gorge near Gansu and Xinjiang reaches 3,549 hours. Solar radiation generally reaches 54×108~63×108 Joules/m2·year, which is beneficial to the growth and development of crops and pastures, and creates favorable conditions for the widespread use of solar energy.

In terms of temperature conditions, the Tarim Basin and the southwestern part of the Hexi Corridor belong to the warm temperate zone. The accumulated temperature during the period of ≥10℃ is more than 4000~4500℃, and the frost-free period is more than 200~220 days. Crops can be harvested twice a year or three crops every two years. When mature, crops with high economic value such as long-staple cotton, melons and fruits can be planted. The other vast areas are all temperate zones. The accumulated temperature during the period ≥10℃ is 1700-3500℃, and the frost-free period is 100-200 days. Spring wheat, millet, cereals, potatoes, Crops such as flax can be harvested once a year. Due to the prevailing continental climate, there are drastic changes in cold and heat. The average temperature in the coldest month (January) is generally around -20°C in northern Xinjiang and Inner Mongolia. The extreme lowest temperature in Fuyun (1,177 meters above sea level) is -51.5°C, while the extreme highest temperature is in Turpan (-15 meters above sea level) not far away. The temperature reaches 47.4℃ (the unofficial record is 49.9℃), and the temperature difference between day and night is also very large. It is generally above 10-20℃. In the areas adjacent to the Gobi in Xinjiang and Gansu, it is even above 35-40℃. In addition, on the surface of the vast desert Gobi , the midday temperature in summer and autumn can reach above 50-60℃, and optical phenomena such as mirages are common, which is obviously detrimental to plant growth and human life.

Windy sand is also one of the major natural transformation problems in the arid areas of northwest China. In spring and autumn, due to the violent alternation of warm and cold air currents, there are frequent storms when it is warm and cold at first. In summer, the vertical air flow is strong, there are also "hot easterly winds", and there are also "foehn winds" in the foothills. Coupled with factors such as arid climate, flat ground, sparse vegetation, and abundant sand sources, sandstorms often occur in most areas and most of the time, especially near mountain passes and in the center of the Great Desert. For example, Minqin City, surrounded by the Tengger Desert, has an average of 133.5 windy days over the years; Anxi City, surrounded by the Great Gobi Desert, has an average of 38.8 windy days over the years, and is known as the "World Wind Bank"; another "land The average number of windy days in Tuokxun City, the wind bank, is 72 days; and in Alashankou (Junggar Gate) in the west of the Junggar Basin, the average number of windy days is 165 days. The maximum wind speed is near Tuokxun, and strong winds of more than 50 meters/second have been measured.

The geomorphology of this area is dominated by two inland basins (Junggar Basin, Tarim Basin) and two plateaus (Inner Mongolia Plateau, Ordos Plateau), and the Hexi Corridor is a transitional type between the two. The general altitude is 1,000 to 1,500 meters, and some depressions can be below 500 meters. Aydin Lake in the Turpan Basin is only -155 meters, which is the lowest land point in the country. The plateau and basin are surrounded by high mountains with an altitude of over 3,000 to 4,000 meters, forming a special mountain environment.

This area has almost no perennial rivers. The main rivers all originate from the surrounding mountains. After leaving the mountains, their water volume gradually decreases, and finally disappears in inland lakes or moraine salt marshes. The only exceptions are the Yellow River and the Irtysh River, which flow into the Pacific Ocean and the Arctic Ocean respectively. The distribution of groundwater sources is very unbalanced. Generally, the foothills of mountains and river banks are rich in water and the water quality is good, while the rest of the vast ground is extremely poor. The biggest problem of water resources is improper utilization and serious waste. It is estimated that the existing water resource utilization rate in the vast area west of the Helan Mountains is only about 30%. For example, the Tarim River, the largest inland river in my country, has an annual runoff of up to 5 billion cubic meters, there are still 3.25 billion cubic meters near the dam, and the irrigated farmland is only 1 million acres.

The soil is relatively poor, with undeveloped profiles, low organic matter content and high salt content. Coupled with the rough texture, it is generally unfavorable for farming. However, there is still a lot of land suitable for agriculture along the middle and lower reaches of the river.

In addition, the distribution of plant resources in this area is very unbalanced and can be divided into three main zones: ① The steppe zone is east of the Wenduer Temple-Bailing Temple-Otok Banner-Yanchi line , dominated by grasses and forbs, with a coverage of more than 50%, is the richest grassland in my country; ② The area between this line and Helan Mountain is a desert steppe zone, dominated by forbs, semi-shrubs, and small semi-shrubs, covering The coverage is about 30-50%, which is still a good pasture; ③The vast area to the west of Helan Mountain is a desert, dominated by shrubs and semi-shrubs, with a coverage of mostly less than 10%, and there are also large areas of barren and barren areas. In addition, significant vertical distribution phenomena occur in the surrounding mountains. For example, the Tianshan Mountains, Altai Mountains, and foothills are all desert grasslands, and the slopes are dominated by mountain grasslands and coniferous forests.

The development, utilization and protection of climate resources in the arid areas of northwest China should: ① Make full and rational use of limited water sources and improve water utilization efficiency. Based on the characteristics of severe spring drought, concentrated summer rain and high temperature, select crops that are drought-tolerant and have basically the same water demand and precipitation distribution rules, and adopt effective dryland farming and moisture conservation measures to collect rainwater and cover snow to prevent drought. Build reservoirs, block floods and intercept water, renovate water conservancy projects, and prevent channel leakage. For example, the effective utilization coefficient of most channels in Xinjiang is only 0.3 to 0.35; if it is increased to 0.5, the spring drought and water shortage in the existing cultivated land will be better adjusted. Level the farmland and change the irrigation method of flood irrigation; ② Return farmland to grazing in a planned way, plant grass and afforestation, and prevent wind and sand. At the front edge of wind and sand, protect sand-fixing plants and build sand-proof forest belts to prevent sand dunes from moving forward. Build a farmland protective forest network inside Wozhou to prevent soil erosion and green the sand dunes; ③ Make rational use of seasonal grasslands and strengthen grassland construction. Due to the high terrain and abundant rainfall, summer and autumn pastures have high forage yields, large livestock carrying capacity, and insufficient utilization; while winter and spring pastures have poor grass growth, low livestock carrying capacity, and are overgrazed and overloaded. Therefore, strengthening grassland construction, adjusting some autumn pastures to winter and spring pastures, and improving the livestock carrying capacity of winter and spring pastures are important measures for the development of agriculture in this region.