The destructive power of typhoon is mainly caused by three factors: strong wind, heavy rain and storm surge.
1. Strong typhoon is a huge energy pool, and its wind speed is above 17m/s, even above 6m/s.. According to the measurement, when the wind reaches 12, the wind pressure per square meter on the plane perpendicular to the wind direction can reach 23 kilograms.
2. Rainstorm typhoon is a very strong rainfall system. When a typhoon lands, the rainstorm center can drop 1-3mm in a day, even reaching 5-8mm. The flood disaster caused by typhoon and rainstorm is the most dangerous disaster. The intensity of typhoon rainstorm is high, the frequency of flood is high, the spread range is wide, and it is fierce and destructive.
3. Storm Surge The so-called storm surge means that when the typhoon moves to land, due to the strong wind and low pressure of the typhoon, the sea water is strongly piled up in the direction of the coast, the tide level rises sharply, and the water waves are overwhelming to the coast. The storm surge of a strong typhoon can raise the coastal water level by 5-6 meters. Storm surge meets astronomical high tide level, resulting in high-frequency tide level, resulting in tidal overflow, seawall burst, washed away houses and various building facilities, flooded towns and farmland, and caused a large number of casualties and property losses. Storm surge will also cause coastal erosion and land salinization caused by seawater intrusion.
after the typhoon landed, the wind was greatly weakened and the central air pressure rose rapidly due to the rough ground friction. However, at high altitude, the strong wind is still blowing around the center of low pressure, and the high temperature and high humidity air from the ocean is still rising and condensing, constantly creating raindrops. If humid air meets a mountain, the windward slope will force it to accelerate its rise and condensation, and the rainstorm there will be more fierce. Sometimes, after the typhoon landed, it was too tired to move. Not only did the wind decrease, but even the low pressure center moved slowly, even staying in one place. In this way, heavy rains poured in the same area for days and nights, and the disaster situation became more serious. According to the report of the World Meteorological Organization, the number of people who die from tropical storms around the world every year is about 2,-3,. According to relevant data, the average annual economic loss caused by typhoons in countries along the western Pacific Ocean is $4 billion. China is also a country with severe typhoon disasters.
South China is most frequently affected by typhoons, among which Guangdong and Hainan are the most serious. In some years, as many as 14 typhoons landed in the above two provinces. In addition, Taiwan Province, Fujian, Zhejiang, Shanghai, Jiangsu and other provinces and cities are also frequently affected by typhoons. Some typhoons will go further inland after landing from China's coastal areas. Among the countries along the western Pacific, there are about 7 typhoons landing in China every year on average, accounting for 35% of the total number of typhoons landing in this area. The impact of the typhoon on the landing area is enormous. For example, Typhoon No.9711 was generated at 8: a.m. on August 1, 1997 in the east of Guam, and landed in Wenling, Zhejiang at 21: 3 on August 18. Shanghai immediately experienced a severe situation of "three encounters" with strong winds, heavy rains and high tides. There are 8-1 winds in Shanghai, with 59-87 mm of heavy rain and 152.1 mm in some areas. The tidal level along the Yangtze River estuary and Huangpu River exceeded the historical record. The tidal level at Huangpu Park Station reached 5.72 meters, exceeding the warning line by 1.17 meters, which is equivalent to the water level once in 5 years. There were three breaches in the urban flood control wall, nearly 2 overflows and flows backward, 39 wires were scraped, 952 power grid failures occurred, 7 streets were flooded, more than 5 houses collapsed, and more than 2, houses were damaged. The affected farmland in the suburbs is nearly 5 square kilometers. As a result, 135 aircraft flights could not take off and land on time, and all 22 ferry lines stopped. The direct economic loss is about 63 million yuan; In 1994, Typhoon No.9417 landed in Rui 'an, Zhejiang Province, and the "wind, rain and tide" met. The affected crops in the province were 7.5 million mu, and 1126 people died. In 1996, Typhoon No.968 landed in Keelung, Taiwan Province, and Fuqing, Fujian. More than 54 million mu of crops were affected in more than 1 provinces and cities, and more than 7 people died. In 1997, Typhoon 9711 landed in Wenling, Zhejiang Province and Jinzhou, Liaoning Province, and more than 1 provinces and cities affected more than 1 million mu of crops, killing 24 people. In 21, Guangxi was hit by two typhoons "Durian" and "Yute" in succession, and there was a large-scale rainstorm or heavy rain. Tens of millions of people in 48 counties and cities in the whole region were affected, and more than 4, people were once trapped by floods.