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Anchor Chart: Researchers Take Notes that Follow the Structures of Their Texts ( from Grade 3: Unit 4: Research Clubs) 

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Anchor Chart: Researchers Take Notes that Follow the Structures of Their Texts ( from Grade 3: Unit 4: Research Clubs) 

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Disaster Zone: Droughts

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Volcanoes

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Hurricanes

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Tornadoes

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Tsunamis

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Floods

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Blizzards

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https://www.nationalgeographic.org/video/droughts/

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Droughts can cause a variety of problems to local communities, including damage to ecosystems, crops, and a shortage of drinking water.

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The Big Thirst: The Secret Life and Turbulent Future of the Water 

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The Big Thirst: The Secret Life and Turbulent Future of the Water 

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Volcano Facts and Photos

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How Volcanoes Form

In 1980 in Washington, after 123 years of hibernation, Mount St. Helens erupted. The blast destroyed and scorched 230 square miles (370 square kilometers) of forest within minutes. The eruption released an avalanche of hot ash, gas, steam, and rocks that mowed down giant trees up to 15 miles (24 kilometers) away.

When magma finds a way to escape from beneath the earth's surface, it creates a volcano.

Volcanoes erupt in different ways. Some, like Mount St. Helens, explode. Explosive eruptions are so powerful, they can shoot particles 20 miles up (32 kilometers), hurl 8-ton boulders more than a half mile (0.8 kilometers) away, and cause massive landslides. Explosive eruptions also create an avalanche of hot volcanic debris, ash, and gas that bulldozes everything in its path. Explosive volcanoes cause most of the volcano-related fatalities.

Volcanoes, like Mauna Loa in Hawaii, are effusive. Rather than a violent explosion, lava pours or flows out. Fatalities from effusive volcanoes are rare because people can usually outrun the lava. However, some people get too close or become trapped with no escape. The flowing lava burns, melts, and destroys everything it touches including farms, houses, and roads.

A volcanic eruption forever changes the landscape. Though volcanoes destroy, they also create mountains, islands, and, eventually, incredibly fertile land.

Carpet of Ash

Volcanic eruptions can cause damage hundreds of miles away. Volcanic ash causes airplane engines to fail, destroys crops, contaminates water, and damages electronics and machinery. The ash carpets the ground, burying everything, sometimes even causing buildings to collapse. Mount St. Helens produced more than 490 tons of ash that fell over a 22,000 square mile (56,980 square kilometer) area and caused problems in cities 370 miles (600 kilometers) away.

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When magma finds a way to escape from beneath the earth's surface, it creates a volcano.

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https://kids.nationalgeographic.com/explore/nature/hawaii-volcanoes/

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Searing-hot gases rise from a giant volcanic crater called a caldera on Hawaii's Big Island. Beneath the caldera's rim, a lake of lava bubbles and steams. This is Kīlauea, one of two active volcanoes at Hawai'i Volcanoes National Park. The other is called Mauna Loa. These lava-spewing formations help make the park the perfect spot for visitors who have, um, a burning desire to see cool geological activity.

The park was founded in 1916, and today more than 1.5 million tourists arrive each year to check out two of the most active volcanoes on Earth (Kīlauea has been continuously erupting since 1983!) Tourists can watch the volcanic activity from a safe lookout point on a bluff about 400 feet above the Kīlauea's caldera.

But the park has another purpose: protecting traditional Hawaiian culture. That's because the park's landscape and the plants and animals that live there are all sacred to Native Hawaiian people, who have lived on the islands for about 1,600 years. So protecting the parks also helps preserve traditional practices and beliefs.

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See pictures and read about Hawai'i Volcanoes National Park on National Geographic Kids.

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https://kids.nationalgeographic.com/explore/science/tornado/

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Find out what causes these deadly twisters—and how to stay safe.

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https://kids.nationalgeographic.com/explore/science/flood/

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Rain is pouring hard and fast-more than eight inches in just an hour, turning river water brown with mud. Earthworms wiggle up to the ground as the soil becomes too wet for them. A flood might be coming.

Just about any place on Earth can experience flooding. When so much rain falls that the ground can't absorb it or waterways can't hold it, the overflowing water becomes a destructive force. In the United States, flooding causes more death and damage than tornadoes, hurricanes, or lightning.

How floods develop

During a rainstorm, precipitation-or the water that comes from rain or snow-goes to different places. Some of it flows into streams, lakes, or city water systems. Other precipitation evaporates and returns to the atmosphere.

But much of the rainwater is absorbed by soil. It flows through the top layer of the ground, to plant roots below the surface. This helps provides plants with the water and nutrients they need to grow. The excess water moves deeper into the ground through layers of dirt and rocks where until it becomes part of natural underground wells called groundwater.

A habitat can naturally absorb a healthy amount of rainfall it needs to thrive. But too much rain can cause lake and river levels to rise and overflow their banks, or the soil to become too wet to absorb more water. And though you might think extremely dry habitats would welcome too much rain, it turns out that the parched dirt can't absorb the rain fast enough to capture it all.

Severe coastal storms, quickly melting ice and snow, and collapsed barriers (like concrete dams) can also cause floods. Even damaged beaver dams can lead to an overflow of water that the surrounding earth can't absorb.

Different types of floods

Floods can form slowly over several days or overwhelm an area with little warning. How quickly a flood forms often depends on the habitat.

Slow-forming river flooding happens in regions called floodplains. These are large, flat areas of land along waterways with very shallow banks. When big storms hit, the water overflows the banks and spreads out across the plains.

This type of flooding isn't always bad. It brings nutrients to the surrounding soil, making it fertile for growing crops. That's why many people live in or near floodplains.

But too much water can destroy crops and damage homes. Rushing water can disrupt ecosystems by moving aquatic plants and animals to other habitats. And if flooding is so severe that it flows into local water treatment facilities, experts must monitor the incoming water to make sure the water is safe.

Another type of flooding is called a flash flood, when a flood happens within six hours of a heavy rainfall-as much as eight inches an hour. With no place to go, the moving water will tear through highways, valleys, and canyons, washing away vehicles, roads, bridges, and houses.

Quickly melting ice and snow can also cause flash flooding, especially when mountain snowmelt overflows the waterways below. On coastlines, hurricane rains cause water levels to rise, and the high winds push that water onto land. Called a storm surge, this also causes flash flooding.

Flooding in the future

Scientists believe that warming temperatures caused by climate change are increasing the risk of floods all over the world, especially in coastal and low-lying areas.

Warmer water changes the patterns of ocean currents, which changes global weather patterns. This means that some places will receive more rainfall than the ground can absorb. Other places will get less rain so the land will be drier-and unable to handle rainfall when it does occur.

Scientists think that climate change could also cause stronger hurricanes, with more rain and higher winds causing bigger storm surges. A warmer climate could also mean more snowmelt overwhelming the soil; melting polar ice could cause sea levels to rise and increase flooding. ( Find out how you can help slow climate change.)

How to survive a flood

Experts might issue a flash flood watch if weather conditions are right. It doesn't mean flooding will happen but that meteorologists want people to be prepared. When experts are sure a flash flood is on the way, they issue a warning so people can evacuate immediately. Here's how to keep you and your family safe.

Before a flood
* Know your neighborhood. Research how close you are to streams, drainage channels, canyons, and any other low-lying areas that might flood.
* Keep emergency contact phone numbers in one place so you can get in touch with family members.
* Put together an evacuation plan and share it with everyone in your household. Know what paths and routes you can use to quickly get to a high, dry place.
* Conduct flood drills to practice evacuating quickly.
* Maintain an emergency kit with a three-day supply of food and water. Experts recommend canned or dried foods that don't need to be cooked, and at least one gallon of water per day for each person and pet.

During a flood
* Never wait for orders to leave; if you think a flood might be coming, evacuate immediately.
* If flooding hasn't started, move important items to upper floors of your house.
* If flooding has already started where you are, move to the highest place you can find, like a roof of a house or car. Bring as much food, water, and sheltering blankets as possible.
* Never walk through flood water, especially if it's moving. Hazardous chemicals, sewage, and even wild animals are often in floodwater, and just six inches of moving water can knock you off your feet.
* If you must walk through water to escape, walk where the water is still. Never touch electrical equipment if you are standing in water, or even if you're wet.
* If water is quickly rising while you're in your car, leave your vehicle and move to higher ground, like a hill or bridge.

After a flood
* If you've evacuated your house, return only after you're given the all-clear from officials.
* If you stayed put, check your house for damage to electrical systems and appliances. Get rid of any food that might be contaminated from floodwater (or because it's been unrefrigerated for awhile).
* Check your home for wild animals, especially snakes. They can get washed into your home with the floodwater.
* Ask an adult before you use water to brush your teeth, make food, or even wash your hands. Flooding can contaminate water and make you sick.
Learn more about floods at National Geographic.
Flood safety tips from the Nat Geo Kids book Extreme Weather by Thomas Kostigen

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Learn about what causes flooding, different types of floods-and how to stay safe.

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Hurricanes

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The wind at the beach is whipping at 95 miles an hour. Waves 16 feet tall are crashing down. Even sharks are heading out to calmer waters. A hurricane is on its way.

These powerful storms have different names depending on where in the world they form. They're called hurricanes if they occur in the Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and eastern Pacific Ocean. In the western Pacific Ocean, they're known as typhoons; in the southern Pacific and Indian Oceans, they're called cyclones.

Scientists know them all as tropical cyclones. As many as 150 occur around the world each year.

How a hurricane forms

Hurricanes are strong storms that start in the ocean and have winds of at least 74 miles an hour. In the Northern Hemisphere (the part of Earth north of the equator), hurricanes generally occur between mid-August to late October. In the Southern Hemisphere (the area south of the equator), storm season is between April and December, with peak storm activity around May and November. During these times, oceans have warmer water, which is what a hurricane needs to form.

Hurricanes begin when a tropical depression forms in the ocean. A tropical depression is a line of rain showers and weak thunderstorms that circle around an area of low air pressure. If the water is at least 79°F, a hurricane might form.

The low air pressure causes the hot, humid air from the ocean to rise in a spiral shape. As that warm air rises, it releases heat, cools down, and condenses into gusty bands of clouds and storms. The low-pressure area continues to suck up hot, moist air, and the spiral gets stronger and faster.

When winds reach 39 miles an hour, the tropical depression becomes a tropical storm. When winds reach 74 miles an hour, it's officially a hurricane.

As a hurricane moves over cooler water or hits land, it loses the warm water that fuels it and begins to weaken. But dangerous winds can still cause damage, and storm surges-when a strong storm pushes ocean water ashore-can flood coastal areas with more than 20 feet of water. Heavy rains and floods can continue far inland.

Understanding a hurricane's strength

Hurricanes are classified by wind speed and the amount of damage that scientists predict the storm will cause when it reaches land. (In the United States, this is done by the National Hurricane Center, part of the National Oceanic and Atmospheric Administration.)

For example, a Category 1 storm has wind speeds of 74 to 95 miles an hour and will probably damage some homes and cause a few power outages. But a Category 5 hurricane is considered a powerful, destructive storm. These storms have winds of 156 miles an hour or more and will likely cause so much damage that people must abandon their communities, which will need months to clean up.

These rankings can help predict the severity of an approaching storm, but any hurricane can be devastating. For instance, Hurricane Katrina was only a Category 3 storm when it hit the U.S. Gulf Coast around Louisiana and Mississippi in 2005. The storm caused over $100 billion in damages, and nearly 2,000 people died.

Predicting the path

Meteorologists can predict the path that a hurricane will travel-and where it will make landfall-by analyzing changes in temperature, cloud formations, and air circulation patterns. That data is gathered by specialized aircraft, satellites, and weather surveillance radar from above the Earth. Other scientific devices that float in the ocean can measure winds, waves, and air and sea temperatures.

The information from these tools is used to create computer forecasting models used by scientists to learn when a storm is forming, where it might travel, and how severe it will be. That can help local officials release warnings or even evacuation orders in order to keep people safe from the coming hurricane.

Naming hurricanes

Once a storm's wind speed reachers 39 miles an hour, it becomes a tropical storm and is given a name. The name is chosen from a list of about 20 names issued by the World Meteorological Organization at the beginning of the hurricane season. They alternate between female and male names.

But you won't see David, Katrina, Andrew, or Laura on that list-those hurricanes were so destructive that the names have been removed. And you won't hear of any hurricanes starting with Q, U, X, Y, or Z, since few names begin with those letters.

More powerful storms in the future?

In the future, scientists don't expect to see more hurricanes, but they do expect more powerful ones. That's because hurricanes get bigger more quickly in warmer water. As climate change causes ocean temperatures to rise, scientists predict that future hurricanes will be rainier and longer lasting.

How to survive a hurricane

The safest thing to do is to follow local instructions and leave the area, or evacuate, if officials say you should. Here are other tips for staying safe if a hurricane is headed your way.

Before a hurricane
* Know the evacuation routes in your neighborhood, and make sure your parents have put gas in the car.
* Check your yard to see if any branches are broken on trees and alert an adult if they are. (Those branches could break off and soar through a window!)
* Bring in anything that could blow away, like garbage cans and outdoor furniture.
* Close all your windows, storm shutters, blinds, and curtains.

During a hurricane
* If you haven't evacuated, stay indoors where it's safe.
* Fill all bathtubs and sinks with clean, cold water in case water lines are damaged or the supply becomes contaminated.
* Ride out the storm in an interior room, such as a hallway or closet on the lowest level of your house.
* Never go near a window, even if it's boarded up.
* If it looks like the storm is going to hit your home, lie on the floor under a table or another sturdy object.
* Limit the use of cell phones to free up space for emergency calls.

After a hurricane
* Listen to weather reports to make sure the storm has passed. A calm sky might be just the hurricane's eye, or center, and more storm fun will be on the way.
* If you evacuated, return only when officials say it's safe.
* Check all food for spoilage. Remember: If in doubt, throw it out.

Adapted from the Nat Geo Kids book Extreme Weather by Thomas Kostigen, revised for digital by Laura Goertzel

Learn more about hurricanes, typhoons, and cyclones at National Geographic.

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Learn what causes these deadly storms-and how to stay safe.

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https://www.nationalgeographic.com/environment/natural-disasters/tsunamis/

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A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore.

What Causes a Tsunami?

These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly, it displaces the water above it and launches the rolling waves that will become a tsunami.

Most tsunamis-about 80 percent-happen within the Pacific Ocean's "Ring of Fire," a geologically active area where tectonic shifts make volcanoes and earthquakes common.

Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth's ancient past, by the impact of a large meteorite plunging into an ocean.

Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour-about as fast as a jet airplane. At that pace, they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they lose very little energy along the way.

In deep ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.

What Happens When It Hits Land

A tsunami's trough, the low point beneath the wave's crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. This retreating of sea water is an important warning sign of a tsunami, because the wave's crest and its enormous volume of water typically hit shore five minutes or so later. Recognizing this phenomenon can save lives.

A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore. People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations.

Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.

The best defense against any tsunami is early warning that allows people to seek higher ground. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.

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Learn more about these destructive surges of water from National Geographic.

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https://www.natgeokids.com/au/discover/geography/physical-geography/tsunamis/

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They can speed across the ocean as fast as a jet plane, swallow up islands and wipe out villages.

But what causes tsuamis...? Join National Geographic Kids and dive into our tsunami facts to find out!

What causes a tsunami?

Meaning " great harbour wave" in Japanese, tsunamis are sometimes called "tidal waves" but their strength has nothing to do with the tides. About four out of five tsunamis happen within the Ring Of Fire, a zone in the Pacific Ocean where earthquakes and volcanic eruptions frequently take place.

Giant slabs of the Earth's crust, called tectonic plates, grind together. Sometimes, though, the plates get stuck, the pressure builds up and they suddenly slam into a new position. This causes an earthquake. If an earthquake lifts or drops part of the ocean floor, the water above rises and starts spreading across the ocean, causing a tsunami. Underwater landslides or volcanic eruptions can also displace water (cause water to spread across the ocean) and may lead to a tsunami.

How big is a tsunami?

Out in the open ocean, tsunami waves are only about one-metre high because the water is deep. However, as the water becomes shallow, the waves slow down and begin to grow. They can rise 35m or higher - that's the same as a 10-floor block of flats! However, the scariest thing about a tsunami is its wavelength, as this determines how far inland it can travel. Whereas a large wave caused by a storm might have a wavelength of up to 150m, a tsunami could reach up to a fearsome 1,000km!

How fast is a tsunami?

A normal wind wave travels at about 90kmh, but a tsunami can race across the ocean at an incredible 970kmh! Sometimes, before a tsunami hits, there is a huge vacuum effect, sucking water from harbours and beaches. People can see the ocean floor littered with flopping fish and other sea animals. Then a wave blasts onto the shore minutes later, then another and another for two hours or more. There may also be up to one hour between each wave.

Can you predict when a tsunami is coming?

To save lives, scientists established the Pacific Tsunami Warning System, based in Hawaii, in the USA. Its network of detectors can track quakes that may cause a tsunami. These waves can race from one side of the Pacific Ocean to the other in less than a day, so people need to be warned in time to head for higher ground!

What do you think of these tsunami facts? Let us know by leaving a comment, below!

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Tsunami facts: check out the mighty wave! - National Geographic Kids

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They can speed across the ocean as fast as a jet plane, swallow up islands and wipe out villages. But what causes tsuamis...? Join National Geographic Kids and dive into our tsunami facts to find out! Meaning " great harbour wave" in Japanese, tsunamis are sometimes called "tidal waves" but their strength has nothing to do with the tides.

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https://kids.kiddle.co/Blizzard

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A blizzard is a severe snowstorm. It brings low temperatures, strong winds, and a lot of blowing snow. Blizzards start when a high pressure system touches a low pressure system.

The word blizzard is sometimes used incorrectly by news media to talk about big winter storms, even if the storm is not a blizzard.

The difference between a blizzard and a snowstorm is the strength of the wind, not the amount of snow. To be a blizzard, a snow storm must have sustained winds or frequent gusts that are greater than or equal to 56 km/h (35 mph) with blowing or drifting snow which reduces visibility to 400 m or 0.25 mi or less and must last for a prolonged period of time-typically three hours or more.

Some areas are more likely to be hit by blizzards than others, but a blizzard can occur in any place where snow falls. In North America, blizzards happen often in the northern-east states, and in the provinces of Canada. In this region, blizzards can happen more than twice each winter.

They also occur often in the mountain ranges of western North America. Because these regions have low populations, blizzards sometimes are not reported.

A very dangerous type of blizzard is a whiteout. In a whiteout, downdrafts and snowfall are so thick that people cannot tell the ground and sky apart. People caught in a whiteout lose their sense of direction very fast. This is a large danger to pilots when they are flying airplanes, because they cannot tell how close they are to the ground, and may crash.

Who cleans up after blizzards?

The community cleans up after a snowstorm/blizzard occurs. Blizzards only usually go for 3 hours so everything won't be too damaged, meaning it won't be as hard as an earthquake or tsunami to clean.

How deep the snow gets

These horrible blizzards can achieve up to 25-30 feet deep. A basketball hoop is 10 ft high, so a blizzard can get snow as deep as the height of two or three hoops.

How do blizzards occur?

Firstly you need cold enough air to cause snow to fall in the clouds and ground level water and moisture is needed to form clouds and precipitation. The moisture is called water vapour to make the clouds a source of water vapour is cold air blowing across large lakes or the sea but the cold air doesn't actually make too much snow, its a combination of cold and warm air that does it. The warm air normally meets the cold air if the wind is being pulled towards the equator when they are brought together a front is formed and precipitation is formed and the warm air can go up to the clouds and the blizzard forms from there.

How strong are a blizzard's winds?

There is sustained wind or frequent gusts of 35 miles per hour or greater.

How cold can blizzards get?

Blizzards can get down to -12 degrees or lower. This makes it fairly easy to get hypothermia in a blizzard. Mostly freezing electrics and machinery making life very hard in the Hypothermic temperatures.

A blizzard brings strong winds that can cause power outages, damage property and disrupt emergency communication. As a result, people can end up without food and water supply.

Blizzards are dangerous as they may lead to injuries and even deaths on the road due to low visibility.

You should avoid being caught outdoors in a blizzard as skin left exposed to such severe conditions could lose all sensitivity within minutes. As a result, you can suffer from hypothermia and frostbite. In extreme cases it may lead to death.

Blizzards may negatively affect the environment, killing plants and animals that other species rely on in their food chain. This forces some animals to find alternative means of getting food or die if food is scarce.

Blizzards impact accumulation of water vapor in the atmosphere, which then leads to greater precipitation throughout the year.

Famous U.S. blizzards

The Great Blizzard of 1888 was very damaging for the Northeastern United States. In that blizzard, 400 people died, 200 ships sunk, and snowdrifts were 10 or 15 feet high. In the Great Plains, states were hit by the Schoolhouse Blizzard that trapped children in schools and killed 235 people.

In 1880-1881 there was a winter that people in the Dakotas called the "Hard Winter". The author Laura Ingalls Wilder wrote her book The Long Winter about that winter's story. It talks about one blizzard after another, and how it changed Laura's family and everybody around her. The book is almost all true. Her story of two men from the town of DeSmet, South Dakota, going after some wheat stored some miles south of DeSmet in February 1881 is true, and Ingalls later married one of the men, Almanzo Wilder. If the two men had not found and brought back the wheat, the people would have starved. The snow and ice thawed in April, and the railroads could start again. The train picture above was photographed on March 29, 1881, not far from DeSmet.

34 people died during a 3-day spring blizzard on March 1920 in North Dakota. One of the people who died was Hazel Miner, a teenage girl who died of freezing to death when she got lost on her way home from her one-room-school.

The Armistice Day Blizzard in 1940 surprised many people with how fast the temperature dropped. It was 60 °F (15.6 °C) in the morning, but by noon, it was snowing. Some of the people froze to death in the snow. 154 people died in the Armistice Day Blizzard.

105 years after the Great Blizzard of 1888, a giant blizzard, named the Storm of the Century, hit the U.S in 1993. It dropped snow on 26 states and reached as far north as Canada and as far south as Mexico. In many southern U.S. areas, such as parts of Alabama, more snow fell in this storm than ever fell in an entire winter. Highways and airports closed across the U.S. The blizzard also made 15 tornadoes in Florida. When the storm was over, 270 people died and 48 were reported missing.

Other famous blizzards

Related pages

Images for kids

Blizzard into Tochal Skiing resort, Tehran and involved skiers.

Conditions approaching a blizzard whiteout in Minnesota, on March 1, 2007. Note the unclear horizon near the center.

Stereoscopic view card showing "Blasting ice with dynamite from in front of steamer on the ways, by Stanley J. Morrow" ~ A view of Yankton's riverfront after the flood of March 1881.

In Spanish: Ventisca para niños

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Flood Facts

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A flood is an overflow of water on normally dry ground. This is most commonly due to an overflowing river, a dam break, snowmelt, or heavy rainfall. Less commonly happening are tsunamis, storm surge.

The most deadly flooding was in 1931 in China and killed between 2,000,000 and 4,000,000 people. The Kerala flood in India was another flood that has destroyed people's houses.

During a flood, people try to move themselves and their most precious belongings to higher ground quickly. The process of leaving homes in search of a safe place is called flood evacuation.

Bangladesh is the most flood prone area in the world.

Pollution of drinking water

During a flood there is plenty of water logging and overflow of water, but it is mostly polluted and not safe to drink. If people drink this dirty water, they may suffer from diseases such as typhoid and cholera, hepatitis and other such diseases. People can get ready to survive a flood by filling many containers with fresh and clean drinking water and storing other emergency supplies; like: medicine and food. During flood people try to go to higher sides because the flood water wouldn't reach high areas. Also drains overflow and mix with clean water and people who drink it might fall ill.

Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more rapidly than it can either infiltrate or run off. The excess accumulates in place, sometimes to hazardous depths. Surface soil can become saturated, which effectively stops infiltration, where the water table is shallow, such as a floodplain, or from intense rain from one or a series of storms. Infiltration also is slow to negligible through frozen ground, rock, concrete, paving, or roofs. Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation.

Riverine (Channel)

Floods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers. When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver dams.

Slow-rising floods most commonly occur in large rivers with large catchment areas. The increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. However, large rivers may have rapid flooding events in areas with dry climate, since they may have large basins but small river channels and rainfall can be very intense in smaller areas of those basins.

Rapid flooding events, including flash floods, more often occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier.

Flash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere. In that setting, the first flood water to arrive is depleted as it wets the sandy stream bed. The leading edge of the flood thus advances more slowly than later and higher flows. As a result, the rising limb of the hydrograph becomes ever quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant.

Estuarine and coastal

Flooding in estuaries is commonly caused by a combination of storm surges caused by winds and low barometric pressure and large waves meeting high upstream river flows.

Coastal areas may be flooded by storm surges combining with high tides and large wave events at sea, resulting in waves over-topping flood defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. Research from the NHC (National Hurricane Center) explains: "Storm surge is an additional rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with spring tide, resulting in storm tides reaching up to 20 feet or more in some cases."

Urban flooding

Catastrophic

Catastrophic riverine flooding is usually associated with major infrastructure failures such as the collapse of a dam, but they may also be caused by drainage channel modification from a landslide, earthquake or volcanic eruption. Examples include outburst floods and lahars. Tsunamis can cause catastrophic coastal flooding, most commonly resulting from undersea earthquakes.

Causes of floods

Flooding is usually caused when a volume of water within a water body, such as a lake, overflows outside it. Sometimes if a dam breaks, it suddenly releases a large amount of water. The result is that some of the water travels to land, and 'floods' the area. Many rivers are in a channel, between river banks. They flood when the strength of the river causes it to flow beyond the banks. This is more common at bends or meanders.

Flood damage can be prevented by moving away from places that flood. However, people have long liked to have their homes and businesses alongside water because water is good for agriculture and transport and in other ways. Floods are also caused due to improper management of drains.

Rainfall is the most common cause. Snow melt is also a cause of flooding. Tsunamis and Storm Surge are less common ways that floods happen. Coastal Flooding is another common cause of flooding, and this is caused by low pressure systems or storms.

Flood safety planning

In the United States, the National Weather Service gives out the advice "Turn Around, Don't Drown" for floods; that is, it recommends that people get out of the area of a flood, rather than trying to cross it. At the most basic level, the best defense against floods is to seek higher ground for high-value uses while balancing the foreseeable risks with the benefits of occupying flood hazard zones. Critical community-safety facilities, such as hospitals, emergency-operations centers, and police, fire, and rescue services, should be built in areas least at risk of flooding. Structures, such as bridges, that must unavoidably be in flood hazard areas should be designed to withstand flooding. Areas most at risk for flooding could be put to valuable uses that could be abandoned temporarily as people retreat to safer areas when a flood is imminent.

Planning for flood safety involves many aspects of analysis and engineering, including:

observation of previous and present flood heights and inundated areas,

statistical, hydrologic, and hydraulic model analyses,

mapping inundated areas and flood heights for future flood scenarios,

long-term land use planning and regulation,

engineering design and construction of structures to control or withstand flooding,

intermediate-term monitoring, forecasting, and emergency-response planning, and

short-term monitoring, warning, and response operations.

Each topic presents distinct yet related questions with varying scope and scale in time, space, and the people involved. Attempts to understand and manage the mechanisms at work in floodplains have been made for at least six millennia.

In the United States, the Association of State Floodplain Managers works to promote education, policies, and activities that mitigate current and future losses, costs, and human suffering caused by flooding and to protect the natural and beneficial functions of floodplains - all without causing adverse impacts. A portfolio of best practice examples for disaster mitigation in the United States is available from the Federal Emergency Management Agency.

In many countries around the world, waterways prone to floods are often carefully managed. Defenses such as detention basins, levees, bunds, reservoirs, and weirs are used to prevent waterways from overflowing their banks. When these defenses fail, emergency measures such as sandbags or portable inflatable tubes are often used to try to stem flooding. Coastal flooding has been addressed in portions of Europe and the Americas with coastal defenses, such as sea walls, beach nourishment, and barrier islands.

In the riparian zone near rivers and streams, erosion control measures can be taken to try to slow down or reverse the natural forces that cause many waterways to meander over long periods of time. Flood controls, such as dams, can be built and maintained over time to try to reduce the occurrence and severity of floods as well. In the United States, the U.S. Army Corps of Engineers maintains a network of such flood control dams.

In areas prone to urban flooding, one solution is the repair and expansion of man-made sewer systems and stormwater infrastructure. Another strategy is to reduce impervious surfaces in streets, parking lots and buildings through natural drainage channels, porous paving, and wetlands (collectively known as green infrastructure or sustainable urban drainage systems (SUDS)). Areas identified as flood-prone can be converted into parks and playgrounds that can tolerate occasional flooding. Ordinances can be adopted to require developers to retain stormwater on site and require buildings to be elevated, protected by floodwalls and levees, or designed to withstand temporary inundation. Property owners can also invest in solutions themselves, such as re-landscaping their property to take the flow of water away from their building and installing rain barrels, sump pumps, and check valves.

In some areas, the presence of certain species (such as beavers) can be beneficial for flood control reasons. Beavers build and maintain beaver dams which will reduce the height of flood waves moving down the river (during periods of heavy rains), and will reduce or eliminate damage to human structures, at the cost of minor flooding near the dams (often on farmland). Besides this, they also boost wildlife populations and filter pollutants (manure, fertilisers, slurry). UK environment minister Rebecca Pow stated that in the future the beavers could be considered a "public good" and landowners would be paid to have them on their land.

Related pages

Images for kids

A dog sitting on top of 2 feet of mud deposited by flooding in the 2018 Kerala floods in India. Flooding not only creates water damage, but can also deposit large amounts of sediment.

Minor flooding in a parking lot off Juniper street Atlanta on Christmas Eve from thunderstorms caused by an El Nino event. The same El Nino caused recorded highs for January in Atlanta

Flash flooding caused by heavy rain falling in a short amount of time.

Dozens of villages were inundated when rain pushed the rivers of northwestern Bangladesh over their banks in early October 2005. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured the top image of the flooded Ghaghat and Atrai Rivers on October 12, 2005. The deep blue of the rivers is spread across the countryside in the flood image.

In Spanish: Inundación para niños

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