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May 2, 2024 · May 2, 2024, 4:47 PM PDT / Updated May 3, 2024, 7:05 AM PDT. By Phil Helsel. Mandatory evacuations were ordered in parts of Texas, and residents in Harris County, home to Houston, were told to be...
- 58 sec
- Phil Helsel
6 days ago · At least four people have died in Houston as severe weather blasted through the city, an official said, as strong storms lashed parts of Texas with destructive winds and dangerous flooding.
- Overview
- How floods form
- Dramatic pictures reveal Venice flooding
- Impacts of flooding
- Flood prevention
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Floods are among Earth's most common–and most destructive–natural hazards.
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A flood occurs when water inundates land that's normally dry, which can happen in a multitude of ways.
Excessive rain, a ruptured dam or levee, rapid melting of snow or ice, or even an unfortunately placed beaver dam can overwhelm a river, spreading over the adjacent land, called a floodplain. Coastal flooding occurs when a large storm or tsunami causes the sea to surge inland.
Most floods take hours or even days to develop, giving residents time to prepare or evacuate. Others generate quickly and with little warning. So-called flash floods can be extremely dangerous, instantly turning a babbling brook or even a dry wash into rushing rapids that sweep everything in their path downstream.
Climate change is increasing the risk of floods worldwide, particularly in coastal and low-lying areas, because of its role in extreme weather events and rising seas. The increase in temperatures that accompanies global warming can contribute to hurricanes that move more slowly and drop more rain, funneling moisture into atmospheric rivers like the ones that led to heavy rains and flooding in California in early 2019.
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People walk on a catwalk in a flooded St. Mark's Square during a period of seasonal high water in Venice, Italy, on October 29, 2018.
People walk on a catwalk in a flooded St. Mark's Square during a period of seasonal high water in Venice, Italy, on October 29, 2018.
Floods cause more than $40 billion in damage worldwide annually, according to the Organization for Economic Cooperation and Development. In the U.S., losses average close to $8 billion a year. Death tolls have increased in recent decades to more than 100 people a year. 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.
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.S. are even going beyond federal estimates and setting higher local standards for protection.
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Learn about different kinds of floods and what causes them, from excessive rain to climate change. Find out how floods affect people, property, and the environment, and how to prepare and prevent them.
- 3 min
- Christina Nunez
Apr 3, 2024 · Deadly storms with flooding rain and tornadoes leave path of destruction in multiple states. At least two people died and 27 million people were under the risk of severe storms with heavy rain,...
- 2 min
- Marlene Lenthang,Kathryn Prociv,Selina Guevara
Learn about the causes, effects, and types of floods, a type of extreme weather that affects many regions of the world. Explore how floods can be natural or human-made, and how they can benefit or harm the environment and human society.
A flood is an overflow of water (or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civil engineering and public health.
Mar 21, 2024 · Learn about the types, causes and risks of flooding in the United States and how to protect yourself and your property. Find out how to evacuate, get flood insurance, and access emergency alerts and resources.
