What is drought and flood protection?

Drought makes the soil moisture insufficient, which can not meet the needs of crop and pasture growth, resulting in a disaster of reducing production or crop failure. Drought is a universal natural disaster, which not only affects agriculture, but also seriously affects industrial production, urban water supply and ecological environment. In China, the normal growth of crops is usually affected by lack of water during the growing period. This phenomenon is called drought, and the reduction of production by more than 30% due to drought is called disaster. Drought-prone areas are called drought-prone areas.

The formation of drought in drought-prone areas mainly depends on climate. Usually, the area with annual precipitation less than 250mm is called arid area, and the area with annual precipitation of 250-500 mm is called semi-arid area. The global arid areas account for about 25% of the global land area, and most of them are concentrated in the edge of the Sahara desert in Africa, the Middle East and West Asia, western North America, most parts of Australia and northwest China. In these areas, the annual rainfall is scarce and the evaporation is large. Agriculture mainly depends on snow melting in mountainous areas or water from upstream. If the amount of snow melting or incoming water decreases, it will cause drought. The semi-arid areas in the world account for about 30% of the global land area, including parts of North Africa, Southern Europe and Southwest Asia. Central North America and northern China. The rainfall in these areas is small and uneven, which is easy to cause seasonal drought, or perennial drought, or even persistent drought.

Most parts of China belong to the Asian monsoon climate zone, and the precipitation is influenced by land and sea distribution, topography and other factors, and the distribution between regions, seasons and years is very uneven, so the period and degree of drought have obvious regional distribution characteristics. The spring drought is prominent in the area north of Huaihe River in Qinling Mountains, which is called "Nine Spring Drought in Ten Years". Huang-Huai-Hai region is often dry in spring and summer, even in spring, summer and autumn, which is the largest drought-stricken area in China. The middle and lower reaches of the Yangtze River are mainly dry in summer and persistent in autumn. Although some years are rainy, shortening the rainy season or less rain will lead to drought. Most areas in northwest China and western northeast China are dry all the year round. Drought in southwest China has a great influence on agricultural production, while drought in summer and autumn often occurs in east Sichuan. Drought also occurs from time to time in southern China.

Drought is a common phenomenon all over the world. The largest and most severe drought occurred in some countries around sub-Saharan Africa in the late 1960s. In the early 1980s, it spread to 34 countries, and nearly 1 100 million people were threatened by hunger.

There are frequent droughts in China, and there are drought records in historical books, local chronicles, court archives, inscriptions, inscriptions and other cultural relics. From 206 BC to 1949 BC, there were 1056 droughts in China. From16th century to19th century, severe droughts affecting more than 200 counties occurred in 1640, 167 1, 1679,172/kloc-. 1640 (13th year of Chongzhen in Ming Dynasty), droughts in different areas lasted for 4-6 years, and in arid areas, "bark was eaten up and people ate people"; 1785 (50 years of Qingganlong), 13 provinces suffered from drought. According to records, "the grass roots and bark are exhausted, the refugees carry the road, the hungry are wild, and the dead sleep"; 1835 (the 15th year of Qing Daoguang), 15, a severe drought occurred in the province, and it was recorded that "people ate Guanyin powder and many people died". Since the 20th century, severe droughts have occurred in Shaanxi, Henan, Hebei, Shandong and Shanxi provinces from 65438 to 0920, affecting 20 million people and killing 500,000 people. 1928, 535 counties in North China, Northwest China and Southwest China 13 provinces suffered from drought; During the drought from 1942 to 1943, millions of people died of hunger and disease in Henan province alone.

1950 ~ 1986, the average annual drought-affected area in China is 300 million mu, resulting in disasters 1. 1 100 million mu. 1959, 1960, 19 1, 1972, 1978, 1986 all have drought-affected areas of more than 450 million mu, and the affected area exceeds one hunhun. During the period of 1972, there was little rain in the north, and drought occurred in spring and summer, which caused serious disasters. The drought-affected area in some parts of southern China is 460 million mu, causing 200 million mu of disasters. During the period of 1978, the drought in China was extensive, lasting for a long time and serious. In June1-June 10, the precipitation in some provinces was 30% to 70% less than normal, and the drought in the middle and lower reaches of the Yangtze River was the most serious, with an area of 600 million mu and an area of 270 million mu, the highest since statistics were available.

Whether drought in nature causes disasters is affected by many factors, and the degree of harm to agricultural production depends on human measures. The main measures to prevent drought in the world are: ① building water conservancy and developing farmland irrigation; ② Improve farming system, change crop composition, select drought-tolerant varieties and make full use of limited rainfall; (3) Planting trees can improve the regional climate, reduce evaporation and reduce the harm of dry wind; ④ Study and apply modern technology and water-saving measures, such as artificial rainfall, spray drip irrigation, plastic film mulching, soil and water conservation, and temporary utilization of inferior water sources, including inferior groundwater and even seawater.

Since 1949, China has built a large number of water conservancy projects, developed irrigation and drainage, and improved its drought resistance. By the end of 1987, there were 5.935 million irrigation and drainage machines with 62.422 million kilowatts and 2.43 million electromechanical wells, and the effective irrigation area in China reached 720 million mu. Despite the severe drought in 1978, due to various water conservancy projects, various measures such as water diversion, water lifting and water storage were taken to tap water sources and expand irrigation area, which still ensured agricultural production in that year. Farming measures accumulated by the people of China for water storage, moisture conservation and drought resistance have played a certain role in overcoming drought. However, the drought resistance in many parts of the country is still low, the threat of drought still exists, and the task of drought resistance is still very arduous.

Cause of flood

Flood disaster has dual attributes, both natural and socio-economic attributes. Its formation must meet two conditions: first, natural conditions: flood is the direct cause of flood disaster. Only when the natural variation intensity of flood reaches a certain standard will disasters occur. The main influencing factors are geographical location, climatic conditions and topography. Second, socio-economic conditions: only when there are human activities will there be floods and disasters. The areas most threatened by floods are often the middle and lower reaches of rivers, which are often economically developed areas because of their rich water resources and flat land.

Types of floods

Floods can be divided into river floods, lake floods and storm floods. Among them, river floods can be divided into the following types according to their causes: rainstorm floods, mountain torrents, snowmelt floods, ice floods and dam-break floods. The most influential and common flood is river flood, especially the long-term rainstorm in the basin caused the high water level of the river to lead to dam failure, which caused the greatest damage to regional development and even caused a large number of deaths.

Flood and waterlogging characteristics

From the mechanism of flood disaster, flood has obvious seasonality, regionality and repeatability. For example, almost all floods in the middle and lower reaches of the Yangtze River in China occur in summer, and the causes are basically the same, but they have different characteristics in the Yellow River basin.

At the same time, flood disasters are very destructive and universal. Flood disaster not only harms society, but also seriously harms adjacent river basins, causing changes in water system. In addition, floods may occur in different areas, including mountainous areas, coastal areas, river estuaries, middle and lower reaches of rivers and areas around glaciers.

However, floods are still defensive. It is impossible for mankind to completely eradicate the flood disaster, but through various efforts, the impact of the disaster can be minimized as much as possible.

Flood prevention and control

The prevention and control of flood disaster includes two aspects: on the one hand, it is to reduce the possibility of flood disaster, on the other hand, it is to minimize the loss of flood disaster as much as possible.

Strengthening dike construction, river regulation and reservoir engineering construction are direct measures to avoid floods, and long-term and lasting implementation of soil and water conservation can fundamentally reduce the probability of floods.

Scientific flood and weather forecast and reasonable flood storage and detention area planning can reduce the loss of flood disasters. Establishing an emergency system for flood control and emergency rescue is the last measure to reduce disaster losses.