What are extreme weather events?

Extreme weather events are rare events that occur in a specific area and time (within one year). There are many definitions of "rarity", but the rarity of extreme weather phenomena is generally equivalent to the observed probability density function being less than the10th percentile. By definition, in absolute terms, extreme weather characteristics vary from region to region. A single extreme event cannot be directly attributed to man-made climate change, because there is always a limited probability: extreme events may occur naturally. When a kind of extreme weather lasts for a certain period of time, such as a season, it can be classified as an extreme weather event, especially when the event produces an average extreme value or a total extreme value (such as drought or rainstorm in a season).

For example, at about 23: 30 on August 6, 2009, a mountain collapse occurred at Houyan, Shunhe Township, Hanyuan County, Sichuan Province, blocking the Dadu River. Nearly 400,000 square meters of rocks hit the Dadu River to form huge water waves and hit the mountains on the other side, causing landslides on the left and right banks of the Dadu River, which is a rare geological disaster.