After the completion of the Three Gorges Dam, the climate in southwest China has been abnormal. Is it its influence?

Nature retaliates against human beings, overexploits water resources and destroys forest vegetation. Especially in recent years, the construction of a large number of hydropower stations has greatly destroyed the ecological balance in this area. You can check it. How many such projects have been under construction in southwest China since the Three Gorges Project began? These projects have not been built for a long time. The drought began in the southwest, which has a lot to do with human activities. For example, the reclamation of Dianchi Lake, 78 Dianchi Lake has not been completed for several years. Calling for more protection of nature and less development is a serious damage to the local climate and environmental balance, and it will take a long time to reach a new balance. I. Drought disasters and their classification

Drought disaster refers to a disastrous weather phenomenon in which the normal crop growth and human activities are destroyed because of the serious shortage of precipitation, soil evaporation and water loss, and the decrease of river flow for a long time. As a result, crops and fruit trees are reduced, people have difficulty drinking water and industrial water is in short supply. In China, the normal growth of crops is usually affected by water shortage, which is called drought, and the drought-stricken areas are called drought-prone areas.

From a disciplinary point of view, drought can be divided into four categories: meteorological drought, agricultural drought, hydrological drought and socio-economic drought.

Second, the causes of drought

Drought is related to specific geographical environment and atmospheric circulation system. In addition to the special natural geographical environment (such as Gobi and desert areas), the formation of drought mainly depends on the climate. The direct cause of drought is less rainfall and more evaporation, while the abnormal atmospheric circulation and air-sea interaction will lead to less rainfall and more evaporation, which is the fundamental cause of drought.

Drought is a common natural disaster in the world. Generally, the area with annual precipitation less than 250 mm is called arid area; Areas with annual precipitation of 250 mm to 500 mm are called semi-arid areas. 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. Semi-arid areas account for about 30% of the land area, including parts of North Africa, Southern Europe and Southwest Asia. Central North America and northern China.

Third, the main characteristics of drought disasters in China

Drought disaster is one of the most serious meteorological disasters in China. Most of China belongs to the Asian monsoon climate zone, and the precipitation is affected by land and sea distribution, topography and other factors. The regional, seasonal and inter-annual distribution is very uneven, and the period and degree of drought have obvious regional distribution characteristics.

1, drought is seasonal.

According to the seasonal distribution, the drought types in China mainly include spring drought, summer drought, autumn drought and winter drought, among which spring drought is the most serious, mainly occurring in North China, Northwest China and Northeast China north of Qinling Mountains and Huaihe River, and the upper reaches of the Yangtze River and Yunnan-Guizhou Plateau also occur from time to time.

2. Drought is very regional.

The arid area in China is wide, unevenly distributed and with great regional differences. Severe drought areas are mainly distributed in Huanghuai area, Zhejiang, southwestern Jiangxi and northern Guangdong, as well as the Loess Plateau and central Yunnan.

Statistics in recent 50 years show that there are five obvious drought centers in China: the northeast drought area, mainly concentrated in the spring and summer seasons from April to August; The arid areas of the Yellow River and Huaihai River have frequent droughts in spring and summer, even in spring, summer and autumn, which is the largest drought-stricken area in China. In the Yangtze river basin, the probability of drought is the highest from July to September; In South China, drought mainly occurs in late autumn, winter and early spring. The drought in southwest China is small, mainly in winter and spring. The occurrence of drought is not only relatively concentrated in time series. For example, among the 170 droughts that occurred in Beijing during 1470- 1949,10/5 droughts occurred year after year. In addition, it appears in large numbers in space. For example, in the spring of 1950, droughts occurred in most parts of Inner Mongolia, Hexi Corridor in Gansu, northern Hebei and northwestern Shaanxi, and droughts occurred in large areas in the Yangtze River, Huaihe River, Yellow River and Hanshui River basins from July to September. 1950- 1980.

Drought is often accompanied by high temperature.

Many drought disasters often occur at the same time as high temperature, which aggravates the drought, which is most obvious in the summer drought period of the Yangtze River Basin. For example, in the summer of 2006, Sichuan and Chongqing in the middle and upper reaches of the Yangtze River suffered from the drought that had never happened in a hundred years since meteorological records were recorded.

Four. The situation and causes of this drought

Since the autumn of 2009, the precipitation in Yunnan, Guizhou, southern Sichuan and other places in China is 30% to 50% less than normal, and the average temperature is 65438 0℃ higher than normal. In 20 10, Yunnan, Guizhou, Guangxi and Chongqing suffered from continuous high temperature and little rain, which aggravated the drought.

According to the statistics of the civil affairs department, the drought lasted for five months. Up to March 23rd, 200010, 613.06 million people were affected in Guangxi, Chongqing, Sichuan, Guizhou and Yunnan provinces, and the affected area of crops was 5.034 million hectares, resulting in a direct economic loss of 23.66 billion yuan.

The severe drought disaster has brought great influence to the residents' life, agricultural production, social economy and other aspects in Southwest China. The drought in southwest China this year shows no signs of easing. What caused such a long and extensive drought? Judging from the current situation, most climate experts believe that high temperature and little rain are the direct causes of drought, but what causes high temperature and little rain? There are different opinions about the reasons.

1. Drought and lack of rain are the most direct causes of drought.

"High temperature and lack of rain are the most direct causes of drought in southwest China," said Wang Yongguang, chief forecaster of the National Climate Center. He explained that from the atmospheric circulation situation, since the winter, the south branch trough is weak, and the warm and humid airflow from the southwest of the Indian Ocean is weak, resulting in insufficient water vapor supply. In addition, the climate in the south lags behind the El Ni? o phenomenon, and the southwest is prone to meteorological drought.

Qian, a professor and doctoral supervisor in the Department of Atmospheric Sciences of Peking University Institute of Physics, told the reporter, "The direct cause of drought in southwest China is the weak southwest airflow from the Bay of Bengal in the lower atmosphere. The reason behind this is that the SST in the Indian Ocean and its southern Asian marginal sea is relatively high, while the temperature in the northern and eastern land areas of China is relatively low, that is, the temperature gradient direction of the underlying surface is abnormal all the year round. "

2. Whether the drought in southwest China is caused by "man-made disaster" has different opinions.

The explanation of climatologists has not been widely recognized. Some people put forward the "man-made disaster theory". For economic benefits, some provinces in southwest China have been cutting down original ecological forests and vigorously planting rubber forests and eucalyptus forests. These two kinds of fast-growing and high-yield forests are both vividly called "pumps". Large-scale planting will lead to the decline of groundwater level and the weakening of water holding capacity. In addition, eucalyptus is also a kind of "overlord tree", and its growth will force other species to decline, eventually causing subversive damage to the ecology. At present, the area of rubber forest in Yunnan reaches 3 million mu, and the planned area of eucalyptus forest reaches 30 million mu. Is such a huge ecosystem change the cause of drought?

In addition, in recent years, hydropower stations have been built intensively in southwest China, and a hydropower station will bring great changes to the basin ecology. The existing "one reservoir and eight levels" power stations in the upper reaches of Jinsha River are under construction or will be built soon. The accumulation of river water in the upper reaches will not only dry up the downstream rivers, but also reduce the groundwater level. The total installed capacity of hydropower development in southwest China is expected to reach the level of dozens of Three Gorges dams. What kind of ecological impact will such a large-scale hydropower development have, and is it also the cause of drought?

Then there is the pollution of rivers. During the drought, the reporter drove along the way in Guizhou and found that many local rivers were looking in all directions due to pollution from coal mining, and the water surface stretching for dozens of kilometers was "dark". In the drought, a drop of water is precious, but at the same time, a large area of water is inedible because of pollution. Isn't this worthy of vigilance?

Five, in the face of extreme drought disaster countermeasures and suggestions

In recent years, drought has become the meteorological disaster with the highest "exposure rate" in China. Among the "Top Ten Weather and Climate Events in 2009" issued by China Meteorological Bureau, three events are related to drought.

Comprehensive analysis shows that in the next ten days, there will still be no obvious rainfall in the heavily arid areas in southwest China, and meteorological droughts will continue or develop in Yunnan, Guizhou, southern Sichuan Plateau and northern Guangxi. Not only that, the spring drought in North China has gradually developed, and the difficulty of drinking water for people and livestock in parts of Northeast China, North China and Northwest China has become more prominent. China will face the unfavorable situation of drought resistance in both north and south. Southwest China continues to maintain a high meteorological level of forest fire risk, and the situation of drought relief and forest fire prevention is still grim.

Faced with such a situation, how should we take timely and effective measures?

(1) In view of the severe drought in southwest China, all government ministries and commissions should conduct unified command and comprehensive coordination, judge the development trend of the disaster situation and jointly do a good job in drought relief. It is also necessary to mobilize all sectors of society to actively seek water sources, ensure people's domestic water use, and strive to carry out drought relief and production.

(2) Make active use of atmospheric, hydrological and natural resources, and study and apply modern technologies and water-saving measures such as artificial precipitation enhancement, spray drip irrigation, plastic film mulching, moisture conservation, and temporary utilization of inferior water sources to minimize losses caused by high temperature, summer heat and drought.

(3) While developing the regional economy, deepen the awareness of environmental protection and take the initiative to take drought prevention measures: building water conservancy and developing farmland irrigation; Improve farming system, change crop composition, select drought-tolerant varieties and make full use of rainfall; Afforestation, improve the regional climate, reduce evaporation, reduce the harm of drought and its secondary and derivative disasters.

(4) Meteorological and hydrological departments should make full use of data, deeply study the occurrence, development and causes of drought disasters, and strengthen the comprehensive study of climate interaction. Under the background of global warming, accelerated water and energy cycle and frequent extreme climate, we should strengthen cooperation and exchange, establish a scientific evaluation mechanism, attach importance to the monitoring, diagnosis and prediction of extreme weather and climate, and improve the ability of forecasting and early warning of drought disasters.