Meteorological forecasts sometimes warn of storms that unusual so unusual rain that is described as floods of 100 years or even 500 years.
This is what you should know about how scientists determine how extreme is a flood and how common these extreme events are becoming.
Scientists use mathematics to help people understand how unusual it is a severe flood and how to compare the intensity of one flood with another.
According to him US Geological Service.A statistic used by scientists is the percentage of possibilities that an avalanche of a specific magnitude occurs. A 500 -year flood means that such an event has a probability of 1 in 500, or 0.2%, to occur in a year.
Another concept that scientists use is the frequency with which an event of a certain intensity is expected. For example, a meteorologist can observe the average recurrence interval of an early flood and see that only a similar event is expected once every 25 years.
Agencies have preferred to express the percentage of possibilities that a flood occurs instead of the recurrence interval because that statistic represents better the fact that rare floods can occur a few years apart. It is like shooting a couple of dice and obtaining double six times in a row. It is rare, but statistically possible.
Another term that people listen to an imminent flood is that it could be a unique event in generation or once in life, an informal way to say that a flood could be different from anything that many people have experienced.
Researchers From the University of Chicago, he calculated that Houston, Texas, was reached by three 500 -year flood events within 24 months from 2015 to 2017. The events included Hurricane Harvey, the strongest rain recorded in the houses and companies of the United States. UU. They were destroyed by floods.
Although mathematics can calculate how often expecting floods of specific magnitudes, nature has its own plans, including irregularity. Many systems interconnected in the environment, such as local climatic patterns and larger events such as the child, can contribute to the changing probability of floods.
Since the beginning of 1900, precipitation events have become heavier and more frequent in most United States and floods are becoming a major problem, according to the Oceanic and atmospheric national administration. Gases emitted by humans, such as carbon dioxide and methane, are heating the atmosphere, allowing it Keep more water vapor. For every 1 degree of Fahrenheit that the temperature is heated, the atmosphere can contain almost 4% more water, which is an increase of 7% per 1 degree Celsius, said Victor Gensini, a professor of atmospheric sciences at the University of Northern Illinois. That steam finally returns to the ground like rain or snow. “We have absolutely seen a change in the probability distribution of heavy rains in the last three decades,” Gensini said.
Other regions have experienced drought due to changing precipitation patterns. According POTThe main droughts and periods of excessive precipitation have occurred more frequently. Worldwide, the intensity of extreme wet and dry events is closely linked to global warming.
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Seth Borenstein contributed to this Washington report, DC
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