Meteorological disaster-the destruction of climate and environment by drought in southwest China

Drought, flood, typhoon, tornado, sandstorm, cold wave and frost are all meteorological disasters. Meteorological disaster refers to the harm caused by the change of meteorological conditions to human life, means of production and ecological environment. The formation of meteorological disasters must meet two conditions, one is the change of meteorological conditions, and the other is the bearing capacity of the affected body. When meteorological conditions change and exceed the bearing capacity of the affected body, meteorological disasters will occur.

Drought and flood

From August to October 20 10/early October, 2009, a large-scale and persistent autumn drought, winter drought and spring drought occurred in Yunnan, Guizhou and Sichuan in southwest China. More than 6,000 rivers have dried up, most wells and springs have dried up, and tens of millions of people and livestock are short of water. The water volume of the famous Lijiang River in Guilin has dropped sharply, and the water flow has almost stopped. Disasters happen once in a hundred years (Figure 6- 1).

Figure 6- 1 Dry Lijiang River

From May to June, 20 10, southern China suffered from continuous heavy rainfall and floods. From May 13 to May 14, there was heavy rainfall in northern Guangxi, and some areas experienced torrential rain of more than 200mm (Figure 6-2).

Figure 6-2 Lijiang River Flood

The warm and humid air flow is weak, and the continuous high temperature and lack of rain are the direct causes of this drought. From May to June, 2065438+000, the cold and warm air currents in the south of China met many times, causing many heavy rains, which was the direct cause of the flood disaster. Human-induced climate change needs long-term accumulation. A specific drought or storm cannot be absolutely blamed on human beings, but extreme meteorological disasters are not unrelated to human activities.

Drought can be divided into atmospheric drought and soil drought. The so-called atmospheric drought means less rain and low relative humidity, often accompanied by high temperature and strong winds. The simplest drought standard is rainfall, and the general rainfall (year or season) is less than or equal to 80% of perennial drought; When the precipitation is less than or equal to 40% of a year, a serious drought will occur. Generally speaking, the soil drought index is determined according to the soil moisture parameters of crops. For example, Kulik proposed that the soil moisture in the 20cm soil layer is 20mm within 10 day, which is called semi-arid and 10mm is called drought. The standard deviation of precipitation can also be used to determine the drought and flood index, and the calculation formula is:

Geology and environmental protection

Where: I is the index of drought and flood; IX is the total precipitation in a certain year; Is the average precipitation in this area over the years; σ is the standard deviation of annual precipitation.

Drought judgment:-1

The harm of drought is that the recharge of surface water and groundwater is greatly reduced, or even there is no recharge, and the evaporation intensity is greatly improved, resulting in a large reduction or even drying up of surface water and a greatly reduced groundwater level. People's life and production are short of water, and a large number of plants die.

Flood is the opposite of drought. Long-term rainy or rainstorm, river flooding, flash floods, or waterlogging in low-lying areas, submerged or destroyed plants, induced geological disasters such as collapse, landslide and debris flow. The flood standard is: 1

At 2: 65438 on May 23rd, 2065438, due to continuous rainfall, the yujiang county-Dongxiang (K699+700m) landslide of Shanghai-Kunming Railway was buried, which derailed the K859 passenger train from Shanghai to Guilin, injuring 7 1 person and killing 91person.

Figure 6-3 Train Derailment

(2) Typhoon

In 2006, the No.4 strong tropical storm Billis landed on the coast of Fujian at noon on July 14, causing floods in the south. From July14 to16, a rainstorm occurred in Chenzhou, Hunan Province (the intensity in some areas is once in 500 years) (Figure 6-4 and Figure 6-5).

Figure 6-4 Strong Tropical Storm "Blissful Causes Chenzhou Flood"

Figure 6-5 Strong Tropical Storm "Billy Destroys Houses"

Typhoon is a powerful and deep tropical cyclone formed on the tropical ocean, with a wind speed of 20 ~ 50m/s and a maximum of 1 10m/s ... Tropical cyclones are generally divided into four levels according to their intensity, and tropical depression (the maximum wind speed in the center is less than 7, and the maximum wind speed is1m/s). Tropical storm (the maximum wind speed in the center is 8 ~ 9); Strong tropical storm (maximum wind speed in the center10 ~12); Typhoon (the maximum wind speed in the center is equal to or greater than 12, and the maximum wind speed is above 32.6m/s).

A typhoon must have two conditions, that is, sufficient water vapor and seawater temperature exceeding 26℃. The great energy of typhoon mainly comes from the latent heat released when water vapor condenses.

Typhoons in the northern hemisphere mostly occur in summer and autumn, and typhoons in the southern hemisphere occur in1~ March. Typhoon is extremely destructive and brings heavy rain, causing houses to collapse, crops to be washed away, trees to be pulled up, fallen and folded, especially affecting aviation, navigation and transportation. The eastern coastal areas of China, especially the coastal areas of the East China Sea and the South China Sea, were most seriously affected by typhoons.

(3) Tornadoes

Tornadoes are funnel-shaped vortex cloud columns extending from the bottom of cumulonimbus clouds. When it extends to the ground, it causes a strong whirlwind, which is called a tornado (Figure 6-6). Tornadoes sometimes hang in the air and sometimes extend to the ground.

Figure 6-6 Tornado

Tornadoes are characterized by short duration (several minutes to more than ten minutes), small moving range (tens of meters to hundreds of meters in diameter), extremely low central air pressure (2 ~ 3 kPa), high wind speed (100 ~ 200m/s) and great destructive power, which can drag people, livestock and things into the air and take them to other places. It is generally believed that the formation of tornado is related to the strong fluctuation of airflow in cumulonimbus clouds.

Globally, tornadoes mainly occur in mid-latitude (20 ~ 50) areas. The United States is the country with the most tornadoes, followed by Australia and Japan, and China mainly appears in South China and East China.

(4) Sandstorm

Sandstorm is a weather phenomenon in which wind and sand interact, that is, strong wind blows up dust on the ground, which drastically reduces atmospheric visibility (Figure 6-7). There are various reasons, both natural and human, such as global greenhouse effect, El Ni? o phenomenon, sharp decline of forests, destruction of vegetation, species extinction, abnormal climate and other factors. Among them, the over-exploitation of natural resources, over-logging and over-reclamation caused by population expansion are the important reasons for the formation of sandstorms.

Figure 6-7 Giant Sandstorm

Sandstorms occur in areas with dry climate and sparse vegetation, and the time is from April to May every year. Under natural conditions, sandstorms are generally small in scale. People's overgrazing and overgrazing of grasslands have turned a large area of grasslands into deserts, increasing the frequency and intensity of sandstorms.

The hazards of sandstorm include: ① human and animal deaths, building collapse and agricultural production reduction. ② Air pollution and topsoil loss. Sandstorm has greatly increased the concentration of atmospheric solid pollutants, causing long-term and potential harm to the atmospheric environment, soil and agricultural production in the producing area, surrounding areas and downwind areas.

The most important way to prevent and control sandstorms is to increase the coverage of surface vegetation, specifically, planting trees and grass and fixing sand. According to the statistics of Yulin City in northern Shaanxi Province, years of planting trees and grass have reduced sandstorms from 66 days a year in the 1950s to 5 days a year now.

(5) Cold wave

From June 5, 2008 to the beginning of February, Chenzhou area in southern Hunan suffered a rare snowstorm. 65438+1On October 25th, the Chenzhou transmission tower collapsed, blocking the transportation of Beijing-Guangzhou railway, which opened the prelude to the catastrophic ice and snow disaster. After half a month, the disaster spread to half of China. From 65438 to the early morning of June 26, more than 80 kilometers of the road surface in Chenzhou section of Beijing-Zhuhai Expressway was covered with thick snow and ice, more than 8,000 vehicles were blocked and tens of thousands of drivers and passengers were trapped. At the same time, due to the destruction of the electric tower in southern Hunan, the locomotive could not supply power, and the transportation of Beijing-Guangzhou line was in a comprehensive emergency. Snow and ice disasters have also caused a large number of trees and bamboo forests to break, and the ecology has suffered serious damage (Figures 6-8 and 6-9).

Figure 6-8 Freezing Disaster in Hunan in 2008

The direct cause of the ice disaster in Chenzhou is that the Siberian cold air meets the strong cold and humid air in the southeast Pacific, and the two sides are snobbish and deadlocked over Chenzhou.

The cold wave is caused by the sudden departure of cold air from the source area and large-scale southward movement in high latitudes. There will be strong winds, cooling, frost, snowfall, freezing and other bad weather in the area where cold air passes. According to the needs of national defense construction and industrial and agricultural production, China stipulates that the cold wave standard is: the minimum temperature in the Yangtze River basin and its northern area drops above 10℃ within 48 hours, and the minimum temperature in the middle and lower reaches of the Yangtze River reaches below 4℃. There are 3 large areas on land accompanied by 5-7 gale, and 3 sea areas accompanied by 6-8 gale.

Figure 6-9 The freezing disaster in Hunan in 2008 caused serious damage to vegetation.

(6) frost

Frost refers to the phenomenon that plants suffer from freezing injury or death due to the decrease of temperature on the soil surface, plant surface and near-surface air layer during the growing season of plants. Frost usually occurs at or below 0℃. The first frost in autumn every year is called the first frost, which affects the heading, flowering and maturity of crops. The last frost in spring is called the final frost, and its harm mainly affects the greening of spring sowing, seedling emergence and overwintering crops.