Influence of Reservoir on Local Climate

2. Technical problems involved in artificial terrain climatology.

The biggest problem of artificial terrain climatology is unpredictability, because the influence of artificial terrain on climate is complex and interlocking in many aspects. 1February 23, 992, the author wrote the article "The Three Gorges Project is not suitable for construction" (submitted to the newspaper but not published). The article points out that this huge project is tantamount to a sudden and strong impact on the natural environment; Because of its complex chain reaction and consequences, human beings still lack enough experience to give a reliable prediction in advance. For the Three Gorges Project, it is equivalent to suddenly cutting off the third largest river in the world that has been flowing for tens of millions of years. Obviously, no one is qualified to say that he can foresee all the consequences of this mutation; Even if someone dares to say so, it is irresponsible boasting and cannot be used as a reliable basis for decision-making.

For example, the Three Gorges Project may change the local and nearby geological environment, and the bearing capacity of the earth's crust will change, which may lead to earthquakes or other harmful and beneficial effects. Another example is that the Three Gorges Project may change local and large-scale climate change, and the flow route and rainfall range of monsoon may also change accordingly. Arid areas may become rich in rain, but areas with favorable weather may also become water-deficient areas.

It should be pointed out that the unpredictable influence of artificial terrain on climate is largely due to the fact that the academic research on artificial terrain climatology is still in its infancy. With the in-depth study of artificial terrain climatology, unpredictable effects will gradually decrease and predictable phenomena will gradually increase.

Specifically, in order to quantitatively study the influence of artificial terrain on climate, we must first solve the problem of parameter measurement. For example, to study the influence of reservoir dam on water vapor transport, it is necessary to measure the water vapor flow in the valley for a long time before the reservoir dam is completed; After the completion of the reservoir dam, the water vapor flow monitoring of the river channel should continue for a long time. Obviously, this is not an easy task, nor can it be completed in a short time. Among them, a technical problem involved is how to quickly and accurately measure the water vapor content in low-altitude air (below 500 meters above sea level or below 500 meters in relative height), including the water content of gaseous water vapor and the water content of liquid water vapor, as well as the flow direction and speed of these water vapor.

Secondly, it is necessary to establish a corresponding database, as well as a high-quality mathematical model of water vapor flow in artificial terrain and its corresponding computer simulation system. There is no doubt that this is not an easy thing. For example, the wind resistance effect of Xin 'anjiang reservoir dam and the wind resistance effect of Three Gorges reservoir dam are not only related to the physical size of the reservoir dam, but also related to the surrounding environment, so different mathematical models may need to be established.

There is a simple reason. The influence scope and degree of wind-resistant effect of reservoir dams on local climate will vary greatly in different regions and geographical environments. Xin 'anjiang Reservoir Dam is located in Zhejiang Province, close to the coastline. Sea breeze and typhoon play a leading role in the flow and distribution of local water vapor. In contrast, the Three Gorges of the Yangtze River is located in the inland of China, and the impact of typhoon is relatively small. The main channel for transporting water vapor from the east (coastal areas) to the west (Chongqing and Sichuan basins) is the Three Gorges. Therefore, the construction of the Three Gorges Dam will inevitably have a relatively great impact on the water vapor transport upstream of the Three Gorges Dam.

Moreover, in the summer of 2006, Chongqing, eastern Sichuan and other places continued to suffer from high temperature and drought, and the water level in the middle and lower reaches of the Yangtze River and its tributaries continued to fall (this may be a very dangerous signal). Not all of them are affected by the artificial topography of the Three Gorges Dam, but they should also be related to the reservoir dams built or under construction in Nujiang Gorge, Lancang Gorge and Jinshajiang Gorge in Hengduan Mountain area, and the latter even played a more important role. The author has written for many times that Sanjiang Gorge, which runs through the Hengduan Mountains from north to south, is the throat lifeline of Chinese mainland's water resources. Water vapor from the northern Indian Ocean passes through the Himalayan Canyon through the Bay of Bengal and enters the Qinghai-Tibet Plateau. One of the most important water vapor passages is the Yarlung Zangbo Grand Canyon and the other is the Hengduan Grand Canyon. In addition, the changes of natural environment (such as the earthquake and tsunami in Indonesia) and man-made topography (coastal cities with hot wall effect) in the Indian Ocean also affect the trend and intensity of atmospheric circulation in the Indian Ocean to a greater or lesser extent. The problem is that we still lack effective means to quantitatively study the relationship between climate change and giant system artificial terrain in the above-mentioned vast areas.

3. Related disciplines involved in artificial terrain climatology.

As we all know, the appearance of reservoir dams will not only affect the climate, but also have a series of effects on the distribution of animals and plants, as well as surface landslides and crustal stress. These effects cancel each other out and overlap each other, which undoubtedly further increases the research difficulty of artificial terrain climatology. In view of this, to carry out the research of artificial terrain climatology, scholars from various disciplines should be invited to "consult" when necessary, and the crux of the problem should be found together in order to "prescribe the right medicine".

For example, after the reservoir dam is completed and impounded, due to the change of in-situ stress, the seismic activity in local areas and its surrounding areas often increases. Fortunately, after the impoundment of the Three Gorges Dam, the local seismic activity did not increase. However, this does not mean that you can rest easy from now on, because the change of geostress often has a process. It is worth noting that at the end of 2003, a serious blowout occurred in Kaixian natural gas well in Chongqing. The accident is related to the improper operation of workers, but the cause is the increase of ground stress. At the end of 2005, an earthquake suddenly occurred in Jiujiang, Jiangxi Province, where there were few earthquakes in history. The earthquake of magnitude 7 caused casualties and property losses. In the summer of 2006, several earthquakes of magnitude 5 or so occurred in Yanjin and Ludian, Zhaotong, northeastern Yunnan. August 2006 1 day 4? A second-degree earthquake. People should pay close attention to the earthquakes around the Three Gorges Reservoir.

In the summer of 2006, Chongqing experienced continuous high temperature (the highest temperature was 44? 5 degrees, lasting for more than a month) and a large area of drought; Historical experience shows that if there is abnormal continuous high temperature in a certain area, it may be related to the intensification of surface crustal activity, such as geothermal leakage caused by stress changes in the surface crust, or frictional heat generation effect caused by surface crustal movement. It is worth noting that Chongqing has developed geothermal resources, and there are hot springs in Qijiang, Banan, Beibei and other places, indicating that there are many ground fissures underground in this geographical area.

At the same time, if the wind resistance effect of the Three Gorges Dam on the Yangtze River reduces the water vapor transport from downstream to upstream by one fifth (from the Pacific water vapor); The wind resistance effect of the reservoir dam built on the Jinsha River reduces the water vapor transport from downstream to upstream by one fifth (from Indian Ocean water vapor). Then consider the wind resistance of reservoir dam to the tributary water system of the Yangtze River, and the wind resistance of urban heat island and urban heat wall in the Yangtze River basin; Then, the total water resources of the Yangtze River may be reduced by about one third (the specific figure needs to be calculated). This will not only have a serious impact on the natural ecological environment and shipping in the Yangtze River basin, but also endanger the survival and development of Shanghai. This is because the reduction of water volume in the Yangtze River will inevitably reduce the amount of sediment transported into the sea by the Yangtze River; However, the decrease of sediment into the sea will make the coastal areas of Shanghai (including Pudong New Area) and Chongming Island suffer from seawater erosion, which is likely to further evolve into land subsidence and coastal area subsidence. These are the phenomena and problems of related disciplines that need to be paid attention to at the same time in artificial terrain climatology.