Flood precursor

Preliminary study on flood precursors (Feng Lihua)

: //hwcc Time: May 2002 16 09:0 1 Source: Disaster Science, March 2000.

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According to historical floods and existing research, various flood precursors are systematically analyzed, which provides certain theoretical basis for flood forecasting. At the same time, it is pointed out that in order to improve the forecast accuracy, it is necessary to comprehensively analyze the flood precursors, eliminate the false and retain the true, and finally achieve the purpose of flood control and disaster reduction.

Keywords: flood precursor; Flood forecast; Precursor anomaly

China Library Classification Number: P338+.6 Document Identification Number: A Document Number:1000-81x (2000) 01-00210-06.

Flood forecasting, especially long-term and ultra-long-term flood forecasting, is a long-term problem.

An important reason here is that the symptoms or signs before the flood, that is, flood precursors, are difficult to understand and master.

In fact, just like there are precursors before an earthquake, there will be some obvious precursors before a flood.

These precursors include the influencing factors and related phenomena of flood formation.

Because their appearance indicates that a region may have floods in the future, they are all precursor information of floods and play an important guiding role in flood forecasting [1].

Therefore, according to historical floods and existing analysis, this paper makes a preliminary study on flood precursors for discussion.

1 precursor of flood

1. 1 sunspot activity

The sunspot activity has a periodic change of 1 1a, and floods in some river basins have obvious corresponding relations with sunspot activity.

In order to analyze this relationship, the annual maximum flood level of Hankou Station of the Yangtze River 1 13a is arranged according to the sunspot activity phase of 1/a, and the number of times that the annual maximum flood level of this station exceeds the warning level (26.30m) is obtained (table1).

It can be seen from the table 1 that the years when the station exceeds the warning water level are mainly concentrated in the peak year (m year) and the valley year (m year) of sunspot activity and their surroundings.

In order to further analyze this relationship, the annual average maximum flood level arranged at Hankou Station according to the cycle of 1 1a is plotted as 1 (where =(H- 1+2H0+H+ 1)/4, which shows that it is closely related to sunspot activity.

Sunspot activity also has a 22-year magnetic cycle change, corresponding to the valley year of 1 1a cycle.

1998 accords with this correspondence, so there was a serious flood disaster in the Yangtze River basin this year [2].

It can be seen that the annual variation of sunspot activity is an important flood precursor in the Yangtze River basin.

1.2 Sun proton flares

Solar proton flares is a kind of flare that can radiate high-energy protons. By disturbing the geomagnetic field, the polar vortex moved southward, and the western Pacific subtropical high extended westward and northward, which eventually led to floods in some basins [3].

Statistics show that about 8 1.3% of proton flares events (peak proton flux ≥ 100 pfu) occurred in the first month, and the rainfall in the middle and lower reaches of the Yangtze River increased obviously, which is prone to floods.

199 1 At the turn of spring and summer, the proton flares of the sun appeared on the surface of the sun twice in a row.

It first appeared in May13 ~18,3 * * *; The second time appeared in 15 from May 29th to June, and there were 7 times * *. The peak flow of radio bursts in proton flares was more than 14000sfu, which was more than 30 times of non-bursts.

Twenty-seven days and thirty days after these two proton flares events, two rainstorms occurred in Taihu Lake and Huaihe River Basin, the first one occurred on June 9 ~ 17, and the second one occurred on June 28 ~ July 13, which caused serious floods in this area and the direct economic loss was as high as 45 billion yuan.

Figure 1 Relationship between annual maximum flood level and sunspot activity at Hankou Station

1.3 solar eclipse

The uneven zonal distribution of solar radiation energy on the earth makes the poles become low-temperature heat sources and the equator become high-temperature heat sources, which leads to the operation of atmospheric circulation.

There is a certain relationship between solar eclipse and flood, because when the solar eclipse occurs, the solar radiation received by the earth decreases, which makes the atmospheric circulation change abnormally and produces flood [4].

There have been two rare total solar eclipses since 1900.

The first time was on1June 20, 955. The bad weather stopped all the prepared scientific investigations. The second time was1June 30, 973, and abnormal weather occurred in many parts of the world.

The solar eclipse was used to forecast the flood of major rivers 198 1 ~ 1987 in China, and the success rate was 84.7%.

1.4 zodiac year

At perihelion, the earth is most attracted by the sun and has the fastest revolution speed. Eclipses occur at the beginning and end of a year, which is called perihelion eclipse year [5].

On the one hand, in the perihelion eclipse year, the tidal force of the sun and the moon caused the perihelion eclipse year tide and caused the El Ni? o phenomenon. On the other hand, the earth receives 7% more solar radiation at perihelion than at apohelion, and the equatorial warm current sends the absorbed heat to China's coast through Kuroshio, and the warm current evaporates more, which enhances the active energy of the Pacific subtropical high, thus affecting the abnormal changes of hydrometeorology in China and leading to catastrophic floods.

Since 1860, the catastrophic floods in the Yangtze River have all occurred in the perihelion food year, including 1860, 1870, 1935, 1945, 1954 and/kl.

1.5 supernova

Supernova is a more violent celestial explosion phenomenon than bright nova.

When the radiation with higher photon energy in supernova radiation passes through the atmosphere, the height of ionization enhancement zone will be lower, which will cause floods in China, and its time will lag for decades [6].

Since 1500, seven supernovae have been recorded and speculated. According to the research on the historical data of drought and flood in China in recent 500 years, after these seven supernova explosions, there have been serious flood periods in China, with ZZK index less than 2.55 and lag time ranging from 25 to 40 years.

1.6 astronomical period

The instantaneous phase of the solar projection of four astronomical singularities on the ecliptic plane running on a three-point straight line with the sun and the earth is regarded as an astronomical period [7].

On that day, Wen Qi pointed out that the tidal force of celestial bodies on the earth reached the maximum, and the atmospheric circulation also changed abnormally, which led to floods.

It is proved that there is a good statistical correlation between the known astronomical period and the drought and flood in the Yangtze River basin, and the correlation rate can reach 94%.

1.7 nine planets converge

The convergence of the nine planets refers to the phenomenon that the earth is alone on one side of the sun, other planets are on the other side of the sun, and the geocentric angle between the outermost two planets is the smallest [8].

When the nine planets meet in the winter half year, the earth is alone on the side of the sun, and the center of mass of the solar system is opposite to the direction of the earth, so the revolution radius of the earth will inevitably increase.

In the summer of this year, the earth also moved to the other side of the sun, while several giant planets (Jupiter, Saturn, Uranus and Neptune) moved slowly, and the center of mass of the solar system was still on the side of the sun, which shortened the revolution radius of the earth in the summer of this year.

Therefore, in the convergence of the nine planets, the earth's winter half year is prolonged and the summer half year is shortened, which reduces the total amount of solar radiation received by the northern hemisphere.

This is the instantaneous effect of the convergence of nine planets.

This effect has accumulated for several years, and finally led to the trend of cooling climate in the northern hemisphere.

On the contrary, if the nine planets converge in the summer, it will lead to a warming trend in the northern hemisphere and cause various meteorological disasters.

Since 1000a recently, the annual catastrophic floods in the Yangtze River Basin 1 153, 1368, 1870, 198 1 year are all at the intersection stage of nine planets. In the past 500a years, there have been four catastrophic floods in the Yellow River Basin, with the years of 1482, 1662, 176 1 843 respectively, of which, except17/.

1.8 interstellar gravity

Among the tidal force of the sun, the moon and the planets on the earth, the tidal force of the moon is the largest, followed by the sun and Jupiter [9].

Although their tidal force is very small, when their directions collide, the tidal force will increase, which will cause the change of gas tide and stimulate the formation and development of abnormal weather processes.

Statistics show that since 1 153, there have been eight catastrophic floods in the middle and upper reaches of the Yangtze River (1 153, 1560, 1788, 1796,/.

Especially around the summer of 1954, Mercury crouched, Mars retreated, Saturn retreated, and all three stars were close to the earth and superimposed on a straight line, so that the Yangtze River basin experienced a once-in-a-century catastrophic flood.

1.9 atmospheric circulation anomaly

Atmospheric circulation is the main factor restricting hydrological changes in a region, and large-scale floods are always accompanied by large-scale atmospheric circulation anomalies.

For example, 199 1, the intensity of the subtropical high is strong, and it jumps northward nearly one month earlier than normal. The position of the ridge line of the subtropical high reaches19 ~ 20 N in mid-May and remains between 20 ~ 26 N until mid-July. At the same time, the Urals Mountains in West Asia maintained a blocking high pressure, which led to the frequent southward movement of Siberian cold air, making cold and warm air continuously cross the Yangtze River and Huaihe River basins, resulting in a 56-day Meiyu period.

The atmospheric circulation anomaly in this area 1954 is similar to this, resulting in a rainstorm group precipitation consisting of nearly 20 rainstorm processes lasting for 4 months.

1. 10 tropical cyclone

Tropical cyclone, especially tropical cyclone above tropical storm level, is the strongest rainstorm weather system in southeast coastal areas of China.

Rainstorms with daily rainfall ≥200mm are mostly caused by tropical cyclones, which mainly appear in July-September.

Tropical cyclone, with abundant water vapor, strong updraft and strong precipitation intensity, is the most obvious flood precursor in southeast coastal areas, which often leads to catastrophic floods.

1994No. 17 severe tropical storm hit Zhejiang province, with the affected population reaching13.33 million and the direct economic loss as high as14.4 billion yuan. 1975 No.3 strong tropical storm went deep into central Henan province, and the maximum rainstorm in Zhuanglin Station reached 1605mm in three days, making it the largest rainstorm record in Chinese mainland.

1. 1 1 western Pacific warm pool

The western Pacific warm pool refers to the area from the southeastern Philippines to Indonesia where the SST is ≥28℃.

Statistics show that the sea surface temperature in the western Pacific warm pool, especially at the depth of125m, is closely related to the drought and flood in the Jianghuai basin.

When the SST in the western Pacific warm pool is low, the convection from the Philippines to Indo-China Peninsula via the South China Sea is weak, while the convection near the international international date line is strong, and the subtropical high is strong to the south, showing a zonal structure. There is more precipitation in the Jianghuai basin, which is prone to floods.

In the past few decades, this relationship has been basically maintained in the Jianghuai Basin.

The SST anomaly of 1. 12 in the previous winter.

By analyzing the relationship between the SST anomaly in the North Pacific before winter (65438+ February of the first year ~ March of that year) and the drought and flood years in the Yangtze River basin, it is shown that in the previous winter SST anomaly, the drought and flood years are different, and the anomaly precursor is more prominent in the drought and flood years [10].

If n represents the positive anomaly of SST and l represents the negative anomaly of SST, then according to the variation of SST in the North Pacific from west to east, four types of SST anomalies can be obtained, namely NNLNLNNL (partial waterlogging) LNLNLN (partial drought), NL (heavy waterlogging) and LNL (severe drought).

For example, in the winter of 1953 ~ 1954, the Kuroshio sea area grew strongly, from the subtropical ocean surface in the northwest Pacific Ocean to the Sea of Japan in the direction of warm current, while the vast sea area in the northeast Pacific Ocean was almost cold water area (NL type). In the corresponding flood season of 1954, the Yangtze River basin experienced a catastrophic flood that never happened in a century.

1. 13 ENSO phenomenon

ENSO phenomenon is the general name of El Nino phenomenon and Southern Oscillation, which has a great impact on global atmospheric circulation and ocean anomalies, and eventually leads to land floods.

Statistics show that from 1949 to 1998, there were 12 El Nino years, and floods occurred in the Jianghuai Basin (including 1998) that year or the following year. In recent 50 years, the annual runoff in jinhua station, Zhejiang Province is w >；; The year of 5 billion m3 * * * is 13a, among which 9 years also occur in the same year or the following year of El Nino, and the annual runoff is the largest and the second largest in the series of 1954 and 1973.

1. 14 Earth rotation rate

The change of the earth's rotation rate includes many periodic and irregular changes, and it mainly affects the flood through the formation of El Ni? o phenomenon [1 1].

During the period when the earth's rotation speed is greatly slowed down, due to the "braking effect", the sea water and the atmosphere gain an inertial force to the east, thus weakening the equatorial ocean current and the equatorial trade wind flowing from east to west, resulting in the El Ni? o phenomenon of sea water warming.

According to textual research, most of the flood waters in the history of western Sichuan basin occurred near the turning point of the irregular movement of the earth's rotation rate from slow to fast and from fast to slow [12]; 199 1 year, when the Yangtze-Huaihe river basin was flooded, also coincided with the end of the deceleration period of the earth's rotation rate.

1. 15 geocentric motion

The direction of the earth's rotation axis is constantly changing, including long-term change, periodic change and other changes, among which the periodic change in 6-7 years is very obvious [13].

Under favorable conditions, polar motion can make the sea level rise by 8 ~ 10 mm, so it can also change the atmospheric circulation.

The precipitation anomalies in Shanghai, Nanjing, Jiujiang, Wuhu and Wuhan in the middle and lower reaches of the Yangtze River have a periodic change of about 7 years from May to August. The annual maximum flood level in jinhua station, Zhejiang Province also varies periodically for 6-7 years.

It is considered that in the year of high amplitude polar motion, the atmospheric circulation is abnormal, and the meridional circulation index in most parts of Asia and Europe and the mid-latitude region of the Pacific Ocean increases, so the westerly index decreases and the corresponding subtropical high weakens southward, so the precipitation in the middle and lower reaches of the Yangtze River increases.

1. 16 geomagnetic anomaly

The earth's magnetic field is linearly distributed in normal months, and its linear correlation coefficient Rz = 75 ~ 100.

When the earth's magnetic field is abnormal, the Rz value will decrease [14].

1990 ~165438+10, a large area of geomagnetic anomaly areas including Anhui, Jiangsu and Zhejiang appeared in China.

By June 199 1 1, the Rz value of the anomaly center had dropped to-10.

Five months later, catastrophic floods occurred in these areas.

Therefore, geomagnetic anomaly is also an obvious flood precursor.

1. 17 earthquake

Natural disaster systems trigger each other and cause and effect each other, leading to group disasters [15].

The research shows that if a major earthquake of magnitude 7 or above occurs in the border areas of Mongolia, Xinjiang and Gansu, a major flood will often occur in the Yellow River in the following year, and the corresponding rate of this earthquake and flood can reach over 88%.

It is considered that when a great earthquake occurred in the border area of Mongolia, Xinjiang and Gansu, large-scale tectonic movement caused the water vapor carrying heat underground to overflow into the lower atmosphere, which on the one hand increased the atmospheric water vapor, and at the same time reduced the air pressure here, inducing the water vapor on the westerlies to be transported here. On the other hand, the low-pressure environment caused by the earthquake can attract the cold air from the north to the south and the subtropical high from the west Pacific to the north, thus forming a catastrophic flood in the Yellow River basin.

Therefore, the great earthquake activity in the border areas of Mongolia, Xinjiang and Gansu has become a precursor to the flood in the Yellow River basin.

1. 18 volcanic eruption

A strong volcanic eruption will form a global dust curtain.

These dust curtains can stay in the upper atmosphere for years.

They can strongly reflect and scatter solar radiation, and the direct radiation can be reduced by 10% ~ 20% within a few months after the big bang, so volcanic eruption has the function of cooling the earth.

In history, four strong volcanic eruptions in the equatorial region led to low temperature in Sichuan, and a large number of condensation nuclei led to excessive precipitation, which led to floods in quite a few areas.

According to the analysis of historical flood data, the probability of a major flood in Sichuan Basin is 85% in the second year and 79% in the third year after volcanic eruption [12].

2 conclusion

Flood is the most serious natural disaster on the earth, and its loss accounts for the first of all kinds of disasters, but flood forecasting is still a puzzling problem.

Based on a large number of data, this paper systematically analyzes various flood precursors, which provides a certain theoretical basis for flood forecasting.

On the basis of long-term research work, the author puts forward his own views on flood precursors in the Yangtze River basin. 1In September, 1995, Zhejiang Provincial Education Commission approved the subject applied by the author: "1998 Study on Early Warning of Extraordinary Floods around".

After a lot of comprehensive analysis, many papers [2 16] were published and confirmed.

Therefore, the study of flood precursors has important theoretical and practical significance for flood control and disaster reduction.

Flood precursors exist objectively, but the current level of understanding is still very limited.

Therefore, when using flood precursors to forecast floods, we should pay special attention to two points: 1 We must make a comprehensive analysis of flood precursors, because floods are the result of the comprehensive action of various influencing factors. Of course, the more flood precursors, the stronger the signal and the greater the flood magnitude; The flood precursor must be removed from the false and retained from the true, because a large number of anomalies observed include not only the flood precursor information, but also other information unrelated to the flood.

With the accumulation of data and in-depth understanding, flood precursors will undoubtedly become one of the breakthroughs to improve the accuracy of flood forecasting.

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