Several different weather conditions can cause extreme rainfall in a region. Tropical cyclones form in some tropical and subtropical areas, usually in the summer and fall. When they appear in the Atlantic Ocean or the northwest part of the Pacific Ocean and reach a certain intensity, they are called hurricanes. Tropical cyclones can produce huge amounts of rain, causing flooding and flash flooding once the storm reaches land.
They can also send a rush of water from the ocean onto coastlines in an event called a storm surge, which floods low-lying areas. Learn more about how hurricanes form. Florence dropped nearly 36 inches of rain in Elizabethtown, North Carolina, and led to widespread flooding throughout the Carolinas. Credit: NOAA. Another phenomenon that can cause extreme rainfall is called an atmospheric river. Atmospheric rivers are long, narrow conveyor belts of moisture that move through the atmosphere.
Strong atmospheric rivers can deliver enormous amounts of rain and snow in California, the Pacific Northwest and Alaska, especially during the winter months. This can lead to serious flooding and mudslides.
In China's Yellow River Valley some of the world's worst floods have killed millions of people. When floodwaters recede, affected areas are often blanketed in silt and mud. The water and landscape can be contaminated with hazardous materials such as sharp debris, pesticides, fuel, and untreated sewage.
Potentially dangerous mold blooms can quickly overwhelm water-soaked structures. Residents of flooded areas can be left without power and clean drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A, and cholera.
Learn here about flood preparation and safety tips. Flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years. Famously fertile floodplains such as the Mississippi Valley, the Nile River Valley in Egypt, and the Tigris-Euphrates in the Middle East have supported agriculture for millennia because annual flooding has left tons of nutrient-rich silt deposits behind. Humans have increased the risk of death and damage by increasingly building homes, businesses, and infrastructure in vulnerable floodplains.
To try to mitigate the risk, many governments mandate that residents of flood-prone areas purchase flood insurance and set construction requirements aimed at making buildings more flood resistant—with varying degrees of success.
Massive efforts to mitigate and redirect inevitable floods have resulted in some of the most ambitious engineering efforts ever seen, including New Orleans's extensive levee system and massive dikes and dams in the Netherlands. Such efforts continue today as climate change continues to put pressure on vulnerable areas. Some flood-prone cities in the U.
All rights reserved. Floods No other kind of natural disaster in America has caused more death and destruction than floods. Learn about different kinds of floods and what causes them. How floods form A flood occurs when water inundates land that's normally dry, which can happen in a multitude of ways. Share Tweet Email. Why it's so hard to treat pain in infants. This wild African cat has adapted to life in a big city. Animals Wild Cities This wild African cat has adapted to life in a big city Caracals have learned to hunt around the urban edges of Cape Town, though the predator faces many threats, such as getting hit by cars.
For example, if you live along a river and areas upstream from you experience heavy rains, it could lead to a serious overflow where you live. Most larger rivers include a series of dams to help manage large amounts of rainfall, and most river systems are managed by government authorities. Sometimes, however, those authorities have to make tough decisions about how to operate dams.
They often can manage the water and prevent flooding altogether — but not always. When heavy rains come, and water levels rise, aging dams can fail and unleash torrents of water on unsuspecting households. This is part of what happened after Hurricane Katrina hit New Orleans in Levees failed and made the flooding far worse than it would have been otherwise. While we have come to depend on 20th-century architecture, and much of it does its job well, there is always a possibility that a structure will fail.
Many of our cities are made of mostly concrete and other impermeable material. When you have an urban drainage basin that is made of concrete, there is no ground for water to sink into. So, when those drainage basins fill up, it is going to mean flooding for low-lying areas. This is mostly the case in large urban areas — think Houston and Los Angeles. When heavy rains strike, the basins used to drain them cannot always handle the load.
Rain is not always the culprit when it comes to flooding. Storm surges related to hurricanes and other storms can lead to significant flooding, as can tsunamis that are sometimes caused by underwater earthquakes. Given modern technology, we often know about storm surges and tsunamis before they arrive, but this is not always the case.
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