Causes of drought in Yunnan

I. History of Drought in Yunnan

1. 1 ancient Yunnan climate

1.2/kloc-the development of drought in Yunnan since the 4th century.

Second, the cause analysis: What caused the drought in Yunnan?

2. 1 atmospheric circulation anomaly?

2.2 Weak foundation of water conservancy facilities?

2.3 Global warming?

2.4 Special geographical location and complex geological structure influence?

2.5 forest coverage rate?

Third, the history of drought in Yunnan is the history of natural forests being cut down and disappeared.

3. 1 Yunnan ancient forest

3.2 Deforestation from Ming and Qing Dynasties to the Republic of China

3.3 After liberation, the Great Leap Forward deforestation "Big Steelmaking" campaign and the "Grain as the Key Link" deforestation campaign.

3.4 After the reform and opening up, "developing the economy and guiding the masses to get rid of poverty as soon as possible" was used as an excuse to destroy forests and become rich.

At the beginning of 3.5 2 1 century, the movement of deforestation and tree planting was "unswervingly developing the forestry-paper integrated industry"

3.6 The current campaign to destroy natural forests: "The horn of transforming 60 million mu of low-yield forests in Yunnan Province blew [40][4 1] to change the situation of" only trees are not rich "."

Fourth, similar cases in the world.

Verb (short for verb) reflection

5. 1 Weak knowledge of ecological science

5.2 the danger of numerical indicators game results

5.3 Interest groups hijack media and policies

Vi. Century Warning: More than half of Yunnan will become a sandy desert by the end of this century.

Seven, the solution: towards ecological civilization.

7. 1 Idea Innovation: Establishing the World Outlook of Ecological Civilization

7.2 Policy shift: shift to sustainable development policy.

7.3 Ecological agriculture and forestry: Establish ecological agriculture and forestry model to prevent soil erosion.

7.4 Social correction: advocate a simple and economical green lifestyle.

Eight. refer to

I. History of Drought in Yunnan

Throughout the history of Yunnan, we will find that the drought in Yunnan for three consecutive years in recent years is not an accidental event, but has been aggravated year by year since the Ming and Qing Dynasties, especially at the beginning of 2 1 century, which eventually led to an unprecedented three-year drought.

1. 1 ancient Yunnan climate

Historically, Yunnan has a mild and humid climate. The average annual rainfall in most areas of Yunnan-Guizhou Plateau is about 1, 100mm, with abundant rainfall. "There is no shortage of spring water, and there is plenty of rain" [2]. South Yunnan has a tropical rainforest climate, and the climate is more humid. The soil in Yunnan is mainly lateritic red soil and mountain red soil. Because it is located in a warm and humid environment, the weathering and leaching are strong and the iron content is high, which makes the soil appear red [3]. Although there is a clear distinction between rainy season and dry season every year, there are few serious droughts. At the end of the Eastern Han Dynasty, there was a nationwide drought, but there was no record of Yizhou (Yunguichuan) being affected [4].

1.2/kloc-the development of drought in Yunnan since the 4th century.

The obvious drought in Yunnan began in the Ming and Qing Dynasties. Since14th century, the frequency table of floods and droughts in Yunnan (frequency: year) [4](P25-29) (the disaster data in the table ends at 1990). As can be seen from the table, the number of floods and droughts has increased since14th century, the number of floods has increased from 7 to 57 in a hundred years, and the number of droughts has increased from15th to 6 1 th, among which the number of droughts in a hundred years was18th in the 4th century and/kloc-in the 5th century. 132 times in the 7th century,129 times in the 8th century,135 times in the 9th century and 6 times in the 20th century; The frequency of flood and drought disasters has developed from 4.55 years to 0.77 years. The most frequent floods and droughts occurred in the 20th century. With the passage of time, the number of disasters is increasing day by day, and its frequency tends to increase [1].

Since 196 1 year with meteorological records in Yunnan, the annual precipitation in Yunnan has shown a decreasing trend. In the past half century, the annual precipitation has decreased by 39mm, with a decreasing rate of -8mm/ 10a, and the decreasing trend in summer and autumn is more obvious than that in spring and winter. The most notable example is that the number of annual precipitation days in Xishuangbanna has dropped sharply from 270 days per year in 1950s to 150 days at present. The annual foggy days were reduced from 180 days to 30 days, which obviously changed the humid tropical rain forest climate in the past [5].

In the 2 1 century, droughts in Yunnan became more frequent and serious.

200 1: Close to the "biggest drought" in history.

2005: The worst drought in recent 50 years.

2006: The worst drought in 20 years.

2009: A drought once in 50 years.

20 10: The once-in-a-century drought scorched Yunnan.

20 1 1 year: The precipitation in 25 counties of Yunnan province suffering from persistent local drought is at least record-breaking.

20 12: the drought in Yunnan continues to increase.

Second, the cause analysis: What caused the drought in Yunnan?

2. 1 atmospheric circulation anomaly?

The main reason for the abnormal atmospheric return is El Nino phenomenon, also known as El Nino flow, which is a climate anomaly caused by the imbalance between the ocean and the atmosphere in the Pacific equatorial belt. It usually happens every 2-7 years. The whole process of El Nino is divided into occurrence period, development period, maintenance period and attenuation period, which generally lasts for about one year, reversing the wind direction and ocean current. Therefore, it cannot explain the phenomenon that the drought in Yunnan is getting worse year by year. What's more, it can't explain the drought for three consecutive years, because the El Ni? o phenomenon can't appear for three consecutive years.

2.2 Weak foundation of water conservancy facilities?

From a historical point of view, the increasingly serious drought in Yunnan since the Ming and Qing Dynasties is directly proportional to the increasing construction of water conservancy facilities since the Ming and Qing Dynasties. Obviously, the weak foundation of water conservancy facilities is not the cause of drought. On the contrary, the more water conservancy facilities, the more droughts. In addition, drought resistance and vigorous development and utilization of groundwater are not long-term solutions. Over-exploitation will also lead to the continuous decline of groundwater level and drought and desertification on the surface. Once the groundwater is exhausted, the land desertification is serious and everything is late [6].

2.3 Global warming?

The data shows that the annual average temperature in Yunnan has been on the rise since the meteorological records were recorded in 196 1. By 20 10, the annual average temperature in Yunnan has increased by 0.74℃ in the past 49 years, and the annual warming rate is 0.0 15℃/ year [5]. Although there is a certain connection, historically, for example, the temperature in the Jurassic period was about 3 degrees Celsius higher than today, but the Jurassic period was one of the wettest periods in the history of the earth [7]. Therefore, global warming is not the main cause of drought in Yunnan.

2.4 Special geographical location and complex geological structure influence?

Yunnan is located in the subtropical high pressure area attached to the Tropic of Cancer. Most of the places where the Tropic of Cancer passes are vast deserts: Sahara Desert in North Africa, Rubhari Desert in Arabian Peninsula, Little Nestor Desert, thar desert in Indian Peninsula ... This special geographical location may indicate that the climate in Yunnan is doomed to be dry, but ancient Yunnan is famous for its warm and humid climate, and it has only gradually turned to drought in the last hundred years, especially in the last decade. What caused it?

2.5 forest coverage rate?

In the history of Yunnan, the forest coverage rate was extremely high, which was 70% in northwest Yunnan and 90% in south Yunnan before the Song Dynasty. The forest coverage rate declined slowly, but it was still around 70% before the middle of Qing Dynasty [1], and dropped to 50% by 1935, 47% in the early 1950s and 24% in the 1970s [8]. Obviously, the increase of drought in Yunnan in history is obviously related to the decrease of forest coverage rate year by year. The lower the forest coverage, the more droughts. Climate drought is not the cause, but the result, because there is no vegetation, the surface temperature rises sharply during the day, the air rises upwards, clouds and humid air cannot enter, and it is swept out of the area [9].

However, after the reform and opening up, the officially announced forest coverage rate rose from 40.8% in 2005 to 47.5% in 20 10 [10], and it recovered to 49.9% in 2009, and even reached 52.0/month in 20165438+/kloc-0. The official coverage rate is 52.93%, and scholars find that Google Maps shows less than 30%[ 12]). However, drought is still getting worse year by year, even accelerating to become more frequent and serious. The conclusion is that after the reform and development, with the rapid increase of forest coverage, the drought will increase rapidly?

So, what forests have been added? Since 2000, Xishuangbanna has built 3 million mu of rubber, and the rubber forest area has increased from 1 1 1600 mu to 1500 mu. Along the Lancang River bordering Myanmar and Laos, the virgin forest on the China side almost disappeared, and rubber trees or other economic trees were planted regardless of conditions. China Science News reported in February, 2065438+02: At present, in Xishuangbanna, which occupies half of china rubber, tap water in many villages has been cut off and well water has dried up. Scholars from Xishuangbanna Tropical Botanical Garden of Chinese Academy of Sciences said that the study of runoff data in Xishuangbanna found that even in a year with very little rainfall, the tropical rain forest had obvious continuous surface runoff, while the rubber forest was frequently cut off [13]. APP (China) Company of Guangjin Group entered Yunnan Province in September, 2002, and plans to introduce 27.5 million mu of fast-growing and high-yield forest, mainly eucalyptus, and build the largest forest industry project in Yunnan history-the forest-pulp-paper integration project [14]. Scholars in the forest industry have long reached a consensus that artificial pure forests are likely to lead to a series of problems such as soil erosion, aggravation of pests and diseases, disappearance of biodiversity, and increase of forest fires. Scientists are worried about planting artificial eucalyptus forests on a large scale in Yunnan [15].

In fact, rubber trees and eucalyptus trees are not harmful to the ecology in the natural forests of origin. What really causes soil erosion is to cut down the mountain native forest in order to plant artificial economic forests such as rubber trees and eucalyptus forests. "All shrubs, weeds and ferns in the woodland are cut down, soil preparation and fertilization are carried out, and chemical herbicides are used" to completely remove the vegetation on the surface [16]. Even "mountain-burning" (which is artificially controlled) is a silvicultural measure for people to clear forest land by burning on the cutting land or suitable forest land [17], which completely destroys the natural mountain forest ecosystem in this area, and the eradication of surface vegetation and land preparation and ploughing have caused serious soil erosion [18]. Because "it is not suitable to plant eucalyptus on barren land [20]", the barren hills whose forests have been destroyed for a long time are barren and the soil layer is thin, and the economic benefits of planting eucalyptus and other economic forests on these forestless barren hills are low, so investors put their claws into the woodland and put forward the so-called "transformation of middle and low yield forests [2 1]". In fact, the so-called primitive secondary forests and other species-rich natural mountain vegetation with low economic benefits have been shoveled away [16] and replaced by fast-growing high-yield forests and single-species economic forests. The so-called "afforestation" and "transformation of low-and medium-yield forests" under this pretext have even more serious damage to the primary ecosystem in mountainous areas than simply cutting down natural forests. After cutting down natural forests, shrubs, herbs and saplings remain. As long as the natural secondary forest is well protected, it can be gradually restored, but planting fast-growing and high-yield forests will eliminate all natural forest species in the region [16] [17] [18]! After several years, it will be cut down in turn, consuming soil fertility and becoming a real barren mountain. It has aggravated the more serious soil erosion and ecological deterioration in Yunnan in this century. It is one of the reasons why the drought in Yunnan has become more and more serious in recent years. In fact, the rapidly increasing plantation area and the area of "transformation of middle and low yield forests" are mostly areas where the natural forest ecosystem in Yunnan mountainous areas has been completely destroyed, so this is precisely the reason why the "forest coverage rate" in Yunnan has increased rapidly in recent years and the drought has also increased rapidly.

According to Dr. Xie Yan of Chinese Academy of Sciences, the reason why artificial pure forests are called "green deserts" is that the species of plants in such forests are extremely single and cannot provide food or suitable habitats for most animals, so the animals in the forests are very rare; Second, the forest surface vegetation is very poor, the water retention capacity is very poor, and it is prone to fire when it is dry; Third, the level of biodiversity of this forest is extremely low, so the ecology is very fragile. Without natural enemies to control pests, it is easy for the disease-causing people to suffer disasters and cause extensive damage. Afforestation used to be the spiritual sustenance and excuse for deforestation in China. The so-called "cutting one tree to make ten trees" has actually caused great damage and degradation of forest resources in China to a certain extent. Afforestation reflects the serious problems existing in the management of natural resources in China, such as the management department is both the manager and the biggest beneficiary [22].

In fact, the area of natural primary forest and primary secondary forest is shrinking. Except for some inaccessible steep mountains and protected areas, Yunnan's virgin forests have been cut down almost, and now they have reached the lowest value in history. At present, all the existing virgin forests in Yunnan may not exceed 30 thousand square kilometers! That's less than 8% of the total area of Yunnan Province [23]! It is inversely proportional to the growth trend of drought, indicating that the fundamental reason for the increase of drought is the deforestation of virgin forests.

Long Yongcheng, a former professor of China Academy of Sciences, reported: "One day in late March of 20 10, I walked through the virgin forest between Ailao Mountains in Yunnan. Ailao Mountain is one of the most important primitive forest areas in southwest China. It was a hundred-year drought in southwest China. However, when I walked into the forest, I saw a completely different scene: the mountain stream gurgled, the apes echoed in the forest, the birds sang and danced, the flowers blossomed and everywhere was full of vitality. Where is the drought? Is there really a once-in-a-century drought? Under the same blue sky, it has not rained for several months. Why is the contrast between Ailao Mountain and the disaster area so great? " Since then, they have analyzed the area of more than 6.5438+0.3 million square kilometers in five southwestern provinces. After more than half a year's efforts, the research results show that the higher the percentage of nature reserves in each unit, the less the number of drought sites. When the area percentage of nature reserves reaches 20%, the drought location is almost zero [24].

Primitive forest (so-called over-mature forest) is one of the most important ecosystems on the earth. Primitive forests maintain the natural environment, regulate the weather by controlling rainfall and evaporation, and maintain the ecological balance of the earth [25]. Forests will release a large number of condensation nuclei (ions, especially negative ions) into the air to generate clouds (there are a lot of water vapor in the air, and only the water vapor attached to the condensation nuclei can become visible water vapor clouds), so that it can rain under the action of gravity (more and more water vapor attached to the condensation nuclei) and when it is cold. The humidity above the forest vegetation is close to the humidity above the ocean, especially when the coastal forest vegetation is good (more than 50%) and there are enough forests along the water vapor transportation route (more than 30%), it is easy for him to transport a large amount of ocean water vapor to desert areas such as deep inland! Primitive forest is not just a tall tree, but a comprehensive ecosystem, including the food chain relationship between animals and plants. In virgin forests, the decline of one species can affect the survival of other species, which is more prominent in tropical rainforests. After people destroy the virgin forest, even if a large number of forests are replanted artificially, the ecological impact of the destroyed forest cannot be compensated [26]. On the other hand, there are thick humus layers and soil layers under the virgin forest. When it rains heavily, the humus layer absorbs a lot of rain like a sponge, and then slowly penetrates into the soil and underground to become groundwater. Release water slowly in dry season, which has strong flood control and drought resistance.

The fragile link of tropical and subtropical virgin forests in Yunnan lies in maintaining a high level of species diversity. Even if the jungle is not cut down, if its biodiversity level decreases, it will lead to ecological degradation in some areas.

After the virgin forest is cut down, firstly, the humus layer is easily blown by the wind and washed away by the rain, and its water retention capacity becomes weak. If it is further used to grow crops and economic forests, the remaining shrubs and herbs will be cleaned up. "Through deep digging and reclamation, all miscellaneous shrubs will be removed, and the growth of weeds will be inhibited [18]", which will expose the soil, further accelerate soil erosion, make the soil layer thinner, and gradually cause rocky desertification. Rain means flood and no rain means drought, which is a tragedy.

Yunnan is one of the provinces with the most serious rocky desertification hazards in karst areas of China. The formation of rocky desertification often goes through three stages: deforestation-land reclamation-soil erosion-bare rock, in which unreasonable human activities are the main inducement. If the rocky desertification land in southwest China is not treated in time, its scale will double in 25 years according to the current rate of advancement. The area of soil erosion in Yunnan Province has reached more than 6.5438+0.4 million square kilometers, accounting for 37% of the total land area of the province, and more than 500 million tons of soil are lost every year. According to the analysis of China Academy of Engineering, in Guizhou, Yunnan and Guangxi provinces, where the phenomenon of rocky desertification is the most serious in China, the scale will double in 25 years according to the current advancing speed. If it is not treated in time within a hundred years, half of the land area will become rocky desertification [27].