What was the Yellow River like in the past? Is that clear?

On the morning of September 10/0, a discussion on "A Journey to the Great River and Sword Pointing at Gansu" was held in Lanzhou "The First Bridge of the Yellow River". Many experts went to the Yellow River to discuss swords. Com was broadcast live via satellite. Behind the "River Tour", we specially invited Professor Yang Dawen from the Department of Water Resources and Hydropower Engineering of Tsinghua University to visit Tencent on September 10 to conduct an online interview on the water resources of the Yellow River. Welcome netizens to ask questions in advance and participate in the interaction!

Moderator: Hello, netizens, and welcome to the series of interviews with Tencent News Channel "Son of the River". I'm the host Fenfen. Today is Teacher's Day on September 10, and I wish the teachers all over the country a happy holiday, good health and peaches and plums all over the world! The guest we invited for you today is Professor Yang Dawen from Tsinghua University Water Conservancy Department.

Yang Dawen: Hello, netizens, I am very happy to come to Tencent and talk about our mother river.

Moderator: We wish Professor Yang a happy holiday! Professor Yang is very supportive of our work. After learning about the public welfare and environmental protection activities of our river trip, he readily agreed to this interview. The problem of the Yellow River is very serious. In your book, there are many studies on the water resources of the Yellow River. Excuse me, why did you choose the Yellow River water resources as the research object of China water resources?

Yang Dawen: Last time I had a meeting in Tsinghua University, I talked about global water resources and water crisis, as well as the four major civilizations in the world. Chinese civilization originated from the Yellow River, and three of the four civilizations originated from river civilization-the Yellow River in China, the Ganges River in India and the Nile River in Egypt. The world's rivers have created world civilization. The 5,000-year history of Chinese civilization began in the Yellow River, which is not only the mother river of the Chinese nation, but also one of the cradles of world civilization.

Moderator: Can you talk about the characteristics of the Yellow River water resources compared with other rivers?

Yang Dawen: The biggest feature of the Yellow River is sediment and quicksand. Why is it called the Yellow River? Because the color of the Yellow River is yellow, the skin of China people is yellow. You see, the water in the Yellow River is not as blue as the water in the south. Its largest sediment is several hundred tons, all from the Yellow River Plateau. What problems will this bring? A large number of rivers in the lower reaches were silted up and floods occurred many times. The Yellow River has not only brought us splendid culture, but also brought us many disasters. With the development of China's economy, the water resources of the Yellow River are increasingly scarce. Back to the early days of the founding of the People's Republic 50 years ago, our population was only 400 million, and now it is 65.438+400 million.

Moderator: What changes have taken place in water resources in the past 50 years?

Yang Dawen: In terms of natural harmony, water resources have not fundamentally changed. The water resources 50 years ago and 50 years later have not changed much, not that water was abundant in the past, but that we have little water now, which is not the case. Why is water shortage? The main reason is population growth, which needs food and development, urban growth needs water, and industrial growth needs water. So there is less and less water in the Yellow River, and we can see less and less water resources.

Moderator: The population is getting smaller and smaller, the water resources are getting less and less, and the downstream is cut off.

Yang Dawen: The biggest cause of environmental change is human influence. Sometimes there is a flood, sometimes there is a drought. This is a natural phenomenon, it is cyclical, and it is a natural law. What we are seeing now is the phenomenon that the Yellow River is cut off. There are climatic reasons, natural reasons and man-made reasons. If there were not so many high-speed industrial development and the rapid increase of water demand, the phenomenon of network disconnection might not be so serious, which aggravated the occurrence of network disconnection. In the 1990s, there was another phenomenon, that is, persistent drought, which may also be one of the reasons for the cut-off of water resources. In my article, I mentioned that the root cause of the interruption of the Yellow River is the over-exploitation of water resources by human beings. But there are also natural reasons. First, the climate is dry, the rainfall continues to be less, the global climate is warming, and the temperature continues to rise. Water resources are decreasing, and our demand is increasing, which will cause water cut-off.

Moderator: What is the current situation of water resources development and utilization in the Yellow River Basin in recent years?

Yang Dawen: Since the 1990s, this cut-off has intensified. 1997 is the most serious. About two-thirds of the time, there is about 700 kilometers of water in the lower reaches of the Yellow River, which is the most serious. Later, the central government began to attach importance to and strengthen management. Nowadays, network disconnection no longer happens too much. One reason is that our management has been strengthened, and another reason is that the climate has changed. Sometimes it is a continuous drought, and sometimes it will become a normal climate. There were floods in some places last year, and you can see the recovery of climate and the increase of rainfall. This year, we have made a lot of observations in the lower reaches of the Yellow River in Shandong Province, and a small amount of farmland has poor drainage. There has also been a small flood this year.

Compere: The phenomenon that the Shandong reach is piled up into an underground river because of sediment?

Yang Dawen: Kaifeng is the most serious. Kaifeng Tower is15m higher than the Yellow River levee, and the ground on both sides of the Yellow River levee is 5m higher. It's easy for us to get water for irrigation when we get to the downstream. It is easy for the Yellow River to open floodgates and release water. This will cause drought downstream.

Netizen: Can you tell me about the differences in the water quality of the Yellow River in different provinces?

Yang Dawen: Basically, I have been to the source and estuary of the Yellow River. Let me first talk about the impression that the Yellow River gave me this year: the Yellow River water I saw in Lanzhou is still dirty in Lanzhou and has begun to become turbid. When we arrived at Heyuan, the water was very clear. In that place, the Yellow River is still in a natural state, and human influence is not great. The water quality of the Yellow River is still Class I water and Class II water. The first and second kinds of water refer to natural water that has not been influenced by human beings, and the third kind of water is artificially influenced water, which can also be used as water source; When it comes to the four types of water, it can no longer be used as domestic water, and the five types of water can not be used as industrial water at all, but can only be used for irrigation. In the present situation of the Yellow River, the proportion of first-class water and second-class water is very small, and it is estimated to be 4% now. Only in Qinghai, it is difficult to find outside Qinghai. There used to be tributaries, such as Fenhe River. Now there is no good water in Fenhe River and no good water in Weihe River.

Yang Dawen: Nearly 50% of the Yellow River water is below the four types of water. In which cities did the Yellow River reach, and the water quality began to deteriorate? Lanzhou is a big city, Yinchuan and Baotou are both industrial cities. What impressed me very much was that we measured the water quality in the upper reaches. From the upstream to Lanzhou, the water quality of the Yellow River has changed greatly. In Yinchuan, the water quality is also very poor, muddy and smelly. We all want to develop cities, and our wishes are good, but the consequences are very serious. Our sewage treatment is basically poor. The Yellow River water has deteriorated since Lanzhou, and the Weihe River has deteriorated in Xianyang and Baoji. The water quality of the Yellow River is getting worse and worse. Even many dry tributaries are running out of water.

Netizen: The Yellow River management has also attached great importance in recent years, but why haven't we seen obvious results?

Yang Dawen: There are still some results. The effectiveness of the Yellow River regulation, from the point of view of cut-off, was still very serious in 1997, but it is much better now, and it can basically flow through the water; Secondly, the sediment in the Yellow River is very serious, so people don't pay much attention to the sediment problem, because the Yellow River has always had sediment problems. After 1998, we put forward many policies, such as returning farmland to rivers and mud. Now we can see that many original cultivated lands have been planted with trees. Last year, I saw trees planted in many places, which changed a lot. Not only Lanzhou can see a lot of returning farmland to forests. The state has policies that can be implemented in this way, and the changes and effects are still great. Our population is under great pressure, and it is impossible to let the Yellow River flow downwards in one day. We should take our time. But the most important thing is that we have a plan

Netizen: After the implementation of the South-to-North Water Transfer Project, what impact will it have on the Yellow River Basin?

Yang Dawen: The first thing we talked about is that there are different schemes for the South-to-North Water Transfer Project. Now the East Line Project is being implemented to supply water to Tianjin. It crosses the Yellow River, and water will not enter the Yellow River. It will replace some water resources that used to rely on the Yellow River. For example, the middle line of water transfer from Danjiang Reservoir to Beijing. It is also the intersection with the Yellow River. The first phase of planning will not enter the Yellow River, nor will it greatly improve the lower reaches of the Yellow River. Xixian county goes directly from the Yangtze River to the source of the Yellow River, and then downstream from the source of the Yellow River. This has a great influence, and this influence is very far-reaching. During drought and flood, the amount of water that does not flow out is 58 1 m3. The water we want from Xixian County is 1 10 cubic meter, which is basically one third. In this way, the water situation of the Yellow River has fundamentally changed and moved to the place where the Yellow River is most short of water, which has a great impact on the Yellow River.

Yang Dawen: At present, there are different views on the influence of the Yangtze River. When we need water, there is not much water in the Yangtze River. The Yellow River needs water in March, April and May. At this time, the water in the Yangtze River is also very small. So we have to build reservoirs and transfer water, so there are reservoir problems and ecological problems, so this is very complicated. You can't just say whether it is good or not, you can only say that the advantages outweigh the disadvantages. Why is the midline so urgent? Because Beijing's water use is very difficult, it is basically solved by the middle line.

Moderator: Just now you also talked about the key reservoirs of water conservancy projects. What impact do some projects like this have on the management of water resources and the development and utilization of the Yellow River?

Yang Dawen: I study water conservancy myself. Since I went to college, I have said that we should develop water resources and prevent floods. To build a reservoir, one is power generation, the other is irrigation, and the third is flood control. The first large-scale water conservancy project was in the Yellow River. We all know the famous Sanmenxia Reservoir. At that time, the flood threat in the lower reaches of the Yellow River was very great, and we needed to control the flood in the lower reaches. So a large reservoir was built in Sanmenxia to reduce the threat of downstream floods, and we also need to generate electricity. This is a very good idea, but the Yellow River has a special problem, that is, sediment. Basically, our Sanmenxia project failed. At the end of 1950s, the Yellow River was mainly developed by agricultural irrigation. After the difficult period, we need a lot of food. In this context, we mainly focus on agricultural irrigation, like the downstream water conservancy hub, focusing on agriculture.

Yang Dawen: Since 1958, we have developed a large number of water resources of the Yellow River for agricultural development. When there is water, we will irrigate a lot. After a large amount of soil is irrigated in the north, the groundwater will rise a lot and evaporate strongly. There is very little precipitation in the north, with an average of about 450 mm. We irrigate a lot and evaporate a lot, which leads to a lot of salinization of the land. This influence is very great. Everyone talked about this lesson. I went to college and saw the water in Bai Rushuang. Later, irrigation improved. Now the problem of salinization in the downstream has been basically solved, but there are still such problems. In 1990s, the development of water resources gradually tilted towards rivers. When necessary, we went to establish a project, and the demonstration time was longer than before. This is not a question of ideological struggle, but a question of advantages and disadvantages. Why build Xiaolangdi in Sanmenxia? Why didn't it cut off after 2 1 century? Restore the downstream water flow, and finally adjust the downstream water quantity. In addition, our Yellow River sediment disaster is disastrous. We hope to stop the sandstorm, which is beneficial to the development of water resources. The operation of the project is basically successful, but there are still some potential problems.

Netizen: A few days ago, it was said that the reservoir was blocked. Is there any other good way besides building some reservoirs now?

Yang Dawen: I saw a soil erosion protection project in People's Daily. At present, we want to prevent the sand from reaching the local area, increase the local water and filter the local sand, which can improve the ecology. If grass and trees increase and change the ecology, the sand in the Yellow River will decrease. If we succeed, it will be very beneficial to the middle and lower reaches of the Yellow River. We plan to build hundreds of thousands and millions of sand dams, but when we stop sand, we also stop water. There is less water entering the Yellow River and less water downstream, which is not good. Now this water diversion resource is not used downstream, but locally. Is the local benefit higher or lower than the downstream? I basically see that it is higher than the downstream.

Yang Dawen: How many trees can survive in this climate? To what extent can sediment be controlled, 50%, 80%, 20%? We don't know the effect yet. If we manage it successfully now, 80% of the sediment can be stopped. Now we should also save water and don't irrigate as much as in the past. There is still great potential for agricultural water saving. At present, many cities in our country depend on water, and they all develop along the river, which poses a great threat to the river. It is disastrous for the Yellow River to be discharged directly into the Yellow River without strict treatment. Last year, we saw hundreds of kilometers of sewage flowing out of the Huaihe River basin, which shocked the world. The Huaihe River has been harnessed for so many years. If the Yellow River has not received equal attention, similar problems will occur. So we should protect the water quality of the Yellow River.

Yang Dawen: Now let's look at the water resources of the Yellow River. In the source area of the Yellow River above Lanzhou, water resources account for 60%. Basically, the development level of the upper reaches of Longyangxia is still relatively low, and the water quality is still relatively good. This kind of water diversion resource is too precious. If it is not well protected, there will be no clean water in the Yellow River. The Yellow River has been polluted by water discharged from downstream cities. We have protected the natural water and treated the water resources in the downstream areas such as Lanzhou, Baoji and Xianyang, so there is still hope for the water control of the Yellow River.

Netizen: If the source of the Yellow River wants to develop its economy, it is likely to sacrifice some environment. How can we ensure that the environment is not polluted while developing the economy?

Yang Dawen: This is a very difficult question. People living in cities and developed countries always say that developing countries should protect the environment, while people living in cities always tell rural people to protect the environment. We are now in the middle and lower reaches of the Yellow River. You must protect the water. For the upstream, we have the right to develop. Why can't it develop? This is a contradiction. On the other hand, it is protective development or destructive development. For example, there are many places with very good ecological environment, and we just destroy them for development. This kind of loss is very huge. If we protect water resources, such as tourism, and do not undermine development, it will be very good for the environment.

Yang Dawen: There are also many problems in China tourism. If we in China improve our quality and stop littering, there is still great potential for tourism development. A few years ago, I went to Xinjiang, and when I arrived in southern Xinjiang, you could see the magnificence of our mountains and rivers. At that time, my biggest feeling was to protect resources, not to develop them, and so was the Yellow River. If we can protect water resources, it doesn't mean that people along the Yellow River have no hope of development. For example, when our downstream people are economically developed, the upstream people will also get some benefits. We will protect the upstream first, develop the downstream first, and give some financial support.

Yang Dawen: The Ministry of Water Resources has many good ideas now. Through market regulation, good phenomena may appear. The mother river flows through my house, but you have no right to destroy this water. The mother river flows through Lanzhou, and Lanzhou people have no right to destroy the mother river. The downstream people use the water of the mother river to develop first, and the upstream people make sacrifices to protect water resources. In this case, you should help the upstream develop together. These are two problems, how to realize the coordinated development of resources and development, so as to realize a harmonious society.

Moderator: Did you and your colleague * * * co-write a book on the water resources of the Yellow River?

Yang Dawen: Some colleagues and I are working on a cooperative project. Many people ask me why you care about the Yellow River in Japan. As I said at the earliest time, one of the four major civilizations in the world is the Yellow River. The interruption of the Yellow River prompted the implementation of the project, and we are still doing it, not only this project, but also in the Netherlands and Europe. We also simulated how to control the sediment in the Yellow River. What is the effect of repairing the mud dam? I can't see the effect for a year or two. What will happen in a few decades? We will do this simulation, and if it works well, we will do it. For China people, we should be more concerned about the Yellow River.

Moderator: You have also done research in Japan for several years. Is there water resources management in Japan? Is there a good way for us to learn from?

Yang Dawen: What we are doing now is the cooperation between the China government and the Japanese government in water resources management and construction. I was also invited to participate in the research of this project, and we held a seminar in Tsinghua University. This paper discusses how to establish a water resources management system in China suitable for China's national conditions. We mentioned the issues of water right and water market. The United States, Europe and Australia all rely on water rights and water market management. Now it's all managed by the government, but the cost is very high. To a certain extent, relying on market regulation to reduce the burden on the market and achieve good results, this idea can be put into practice and achieved good results, and we are now implementing it.

Netizen: What role does the model design have on the Yellow River hydropower? Is this practical?

Yang Dawen: What we are talking about now is the water in a river basin. Water falls from the sky, part of it enters the soil and part enters the river. Water is constantly circulating, producing water resources. Now we simulate the water cycle process through computer simulation and mathematical model. What is the impact on us after the rain, what is the impact of the surface on our industry, and what is the impact on our rivers? Through simulation, we can find that different development and different management may have different effects. We may find a reasonable and better scheme guidance. If there is no such way, you can only try. The cost of failure is very high, and we can predict it by scientific means. There are many similar models for river development abroad. For example, the weather forecast is based on the global atmosphere, which is cyclic. Simulate this cycle to make a prediction. The weather forecast in China is to make a detailed simulation around China, and what weather changes we will have. We found that the weather forecast has become more and more accurate in recent ten years, which shows that our model has become more and more accurate. Our understanding of the earth is getting deeper and deeper. We now have many satellites and many models, and these models have made very good predictions for us.

Netizen: Professor Yang does research on this model. What kind of future can you show the Yellow River through your research?

Yang Dawen: First of all, the future of the Yellow River depends on the wishes of the people of China. If we want the Yellow River to flow, we hope that the water quality of the Yellow River will always be good. Now our situation is very serious, and the population is still growing. The Yellow River Basin is one of the most populous areas, especially the Huang-Huai-Hai area. Because the temperature here is very suitable for people to live in and there is a lot of cultivated land, the population in these areas is increasing and the pressure is increasing. At the same time, our city is expanding, industrialization is increasing, and this pressure is also increasing. After all, the Yellow River is still short of water, which does not mean that our water will become more and more abundant. Where is the future? It is up to us to protect and cherish every drop of water, including our agriculture to minimize the pollution of the Yellow River water, cherish every drop of water and let the Yellow River flow forever. The final management of the Yellow River needs to be explored. I hope that the Yellow River can be managed better and more effectively, which needs us and the next generation to explore.

Moderator: What will you do for the study of the Yellow River Basin next?

Yang Dawen: Natural science research accounts for the majority. How to save water resources of the Yellow River? The biggest water consumption is agriculture. How to save water in agriculture? In fact, farmers in China still have great water-saving potential. Nowadays, water conservation depends on agricultural technology, so the agricultural burden is great. We can find a feasible method to study the probability of water consumption. From this perspective, we can study a simple management method and find a more scientific basis for water saving. The second is management, what kind of effect will be achieved in the future, how much flood and sediment can be controlled by building a dam, and how much impact it has on water resources. This is what we need to explore. If we can find a way, the impact will be very great. This can't be done in a day or two, and it needs long-term research. What we want to make clear is that the energy cycle from downstream water to the atmosphere and from water, including water quality observation, was difficult to do before, but now it can be done. It doesn't mean that the problem can be solved in one year, but it may require long-term research. Hard work needs someone to do, and many people are doing it now. Second, we study management. From the government's point of view, we emphasize unified management and concentrate our efforts. From a scientific point of view, it is comprehensive management, from technology to policy, and the combination of natural science and social science. Just now we talked about water right, water market and macroeconomics. Now we have done a lot of things in natural science. Natural science and social science should be discussed together in the future.

Moderator: What are your expectations for this activity during this trip to the riverside?

Yang Dawen: I hope everyone involved will really start from themselves, protect every drop of our mother river and cherish every drop of our water. I believe that our efforts today will represent the future of the Yellow River.

Moderator: Thank you, Professor Yang, for your interview today. In the words of Professor Yang, a bright future is the result of our efforts today! It suddenly occurred to me that on the first day of the talk show, an expert made a metaphor. He compared the whole environment to a house, and each of us became a family member. If every family member litters, even the most capable housewife can't afford so much housework, which needs to be maintained by each of us. Thank you all. See you tomorrow.