Natural disasters are a phenomenon existing in highly complex systems composed of natural systems and human social systems, in which a natural event or force often leads to the appearance of another natural disaster. We call the latter natural disaster a secondary disaster.
For example, heavy rain will induce geological disasters and floods; typhoons will generate storm surges; earthquakes will induce other natural disasters such as collapse, landslides, and tsunami; droughts easily induce pests; besides, earthquakes and soil erosion can also induce collapses and landslides. These are all common phenomena. After the earthquake (grade 7.5) in Songpan and Diexi of Sichuan in 1933 occurred, a large landslide group of 150 million cubic meters collapsed, blocking the Minjiang River to form a dammed lake. With the water impounding beyond 450 million cubic meters, the dammed lake broke to form an explosive flood with more than 40m water head, sweeping across 11 villages on both sides of Minjiang River and killing 9300 people. In addition, in May 2008, the earthquake (grade 8) in Beichuan, Sichuan Province also caused large-scale collapses and landslides, and formed many large and small dammed lakes. But, fortunately, due to timely and appropriate treatment, the collapse did not cause any casualties.
Meteorological disasters are closely related to the geological actions in the evolution of the Earth itself, and also have related disaster chains with geological disasters. The collision of the Indian Ocean plate with the Eurasian plate caused a sharp rise of the Himalayas and a strong uplift of the Tibetan Plateau, forming a unique monsoon climate in China. In turn, In turn, the distribution of geological disasters in China presents a regional feature closely related to the climate zones. For example, the south and southwest regions of China, where rainfall is strong and rainy, have many widely distributed geological disasters; Precipitation, temperature, and wind force will affect the changes in the properties of rock and soil and hydrodynamic conditions, destroy the original state of geologic balance, and lead to erosion, weathering, deformation, metamorphism, transportation, accumulation, sedimentation, corrosion, and consequently induce the disasters of sand liquefaction, collapse, landslide, debris flow, soil erosion and so on.
Therefore, we must comprehensively study the chain of disasters to gain a better understanding and control of complex natural disasters.
The secondary disasters caused by meteorological reasons not only include the geological disasters mentioned above, but also refer to river floods, mountain torrents, urban floods, water logging, water waves, storm surges and other marine disasters, forest and grassland fires, and air pollution, agricultural and forestry diseases and pests, etc. Because these disasters are closely related to meteorological conditions, we cannot get the specific risk of these disasters without the analysis and research of the meteorological conditions. Therefore, we refer to secondary disasters caused by meteorological causes as generalized meteorological disasters.
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