by Weather forecasts sometimes warn of storms that unleash so unusual rainy that they are described as a 100-year-old or even 500-year floods.
Here you can find out how scientists determine how extreme a flood is and how often these extreme events become.
What does a 100-year-old flood mean?
Scientists use mathematics to understand people how unusual a heavy flood is and how the intensity of a flood can compare with another.
According to the US Geological Survey, a statistical scientist is the percentage that a flood of a certain size will occur. A 500-year-old flood means that such an event occurs a 1-to-500 chance or 0.2%in one year.
Another concept that scientists use is how often an event of a certain intensity is expected. For example, a meteorologist can consider the average recurrence of expected flood and see that a similar event is only expected every 25 years.
Agencies have preferred to express the percentage of flooding instead of the repeat interval, since these statistics are better the fact that rare floods can occur within a few years. It is like rolling a few cubes and twice in a row twice six. It is rare, but statistically possible.
Another term that people hear during an upcoming flood is that it is a one -time or unique event in a generation or a unique event. A casual way of saying a flood could be different from everything that many people have experienced.
How the flood is changed with the climate
Researchers at the University of Chicago calculated that Houston, Texas, was met by three 500-year flood events within 24 months from 2015 to 2017. Hurricane Harvey, the heaviest registered precipitation in the US houses and companies, were among the events, and the cars were swept away by the floods.
Although math can calculate how often the flooding of certain sizes expect, nature has its own plans, including irregularities. Many interconnected systems in the area, such as local weather patterns and larger events such as El Nino, can contribute to the changing probability of floods.
Legal events in most USA have become more and more common since the early 20th century, and the floods have become a major problem, according to the National Oceanic and Atmospheric Administration. Gases emitted by people such as carbon dioxide and methane warm the atmosphere and enable him to keep more water vapor. The atmosphere can keep almost 4% more water for every degree that the temperature heats up, which increases by 7% for every 1 -degree -Celsius, said Victor Gensini, professor of atmospheric science at the University of Northern Illinois. This steam finally falls back on the floor as rain or snow. “We have seen absolutely a shift in the probability distribution of strong rainfall in the past three decades,” said Gensini.
Other regions have experienced dryness due to the changing precipitation patterns. According to NASA, larger droughts and periods of excessive precipitation have occurred more often. The intensity of extreme wet and dry events worldwide is closely associated with global warming. ___
Seth Borenstein contributed to this report from Washington, DC,
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