Why do flash floods occur?

In the US, flash floods—rapid floods that occur within six hours of rain—kill more people than tornadoes, hurricanes, and lightning.

Rapid intensification is the increase in a hurricane's sustained wind speed by at least 35 miles per hour within 24 hours, which can strengthen it by up to two categories.

Storm surges, not winds, are the leading cause of hurricane-related fatalities

A storm surge is an abnormal rise in water levels generated by a storm that exceeds predicted tides. It is particularly dangerous in coastal regions, where it can generate extreme flooding well before the hurricane makes landfall.

Flood recurrence intervals are based on independent probabilities

The term "100-year flood" does not mean the event will only occur once every 100 years, but it has a 1% chance of occurring in any given year. Soil saturation, watershed size, and urban development can impact flood severity.

Explore and visualize AI-driven riverine and flash-flood forecasts across more than 150 countries to anticipate these natural disasters up to seven days in advance.

Lightning storms are more common in coastal and tropical regions

Water-abundant areas that receive increased solar radiation, such as those near the equator, experience increased rates of evaporation, which produce tall clouds as moisture rises, cools, and condenses. Mountain ranges can also steer air to higher altitudes, creating collisions between atmospheric particles that generate charge imbalances—the precursors to lightning.

Thunder occurs when fast-flowing electricity heats and pressurizes air, causing it to expand and produce a shockwave at each point along the bolt at multiple frequencies.

Heat is the leading cause of death in natural disasters

Floods are a distant second, followed by hurricanes. That's according to data reported by the National Oceanic and Atmospheric Administration.

Learn all about different types of extreme weather

Find out in more detail about different types of extreme weather, from flooding to thunderstorms, from tropical cyclones to sandstorms, and more (w/ helpful videos).

A tsunami—Japanese for 'harbor wave'—can begin with a drop in sea level before rising, which has contributed to its mistaken categorization as a tidal wave, despite being unrelated to the moon's gravity.

Bomb cyclones can produce heavy rain, blizzard conditions, and intense winds

Known as "bombogenesis" in meteorology, these systems get their colloquial name from their rapid intensification over a 24-hour period—a phenomenon seen in some tropical cyclones. They occur most commonly along the coasts of the Northeast and Northwest US when there is a severe temperature difference between colliding air masses.

Fast-changing conditions during their formation make tornado forecasting difficult

The final steps of tornadogenesis—the process of forming a tornado—depend on near-surface details, such as local geography, which are difficult for radar to observe and affect how funnel clouds make contact with the ground. Inconsistencies in storm behavior have limited the amount of advance warning people receive before tornadoes touch down.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

Hurricane Helene dumped enough water to fill Lake Tahoe

Alongside a rainstorm that moved into the region ahead of it, the hurricane released an unprecedented 40 trillion gallons of rain on the southeastern US, causing catastrophic flooding and at least 100 deaths. Meteorologists suggest climate change is exacerbating the severity of such events.

Atmospheric processes amplify the strength of storms by coalescing clouds

Research has shown that turbulent mixing of air at the edges of clouds and other small-scale thermal activity beneath them help clouds group together, intensifying short bursts of rainfall, especially in tropical regions. Simulations reveal this produces more powerful storms than predicted by older models, though they may occur less frequently.

Some scientists hypothesize that stressed rocks can discharge built-up static electricity in the form of lightning—a phenomenon known as fracto-luminescence, or earthquake lights.

Rising wildfire smoke can create 'fire clouds'—towering clouds that can help combat fires through downbursts of rain or complicate firefighting efforts by triggering new fires via lightning strikes.

How do hurricanes form?

Tropical cyclones, also called hurricanes and typhoons, cause catastrophic damage when they strike land. This four-minute video explores the life cycle of cyclones—how atmospheric conditions, ocean temperatures, and the Earth's rotation combine to create them, and how they are driven by winds and eventually weaken after moving over land.

Rather than being triggered by a massive displacement of water from a geological event, meteotsunamis are caused by rapid changes in air pressure from fast-moving weather systems.

The unpredictability and brevity of lightning make lightning power impractical

While a typical lightning strike provides 30,000 amps at 300 million volts, the bolt only lasts about 30 microseconds. If the electrical surge could be captured—assuming one knew beforehand where it would strike—it would only provide enough electricity to power one home for about 6.4 hours.

Tsunamis can last for days as their successive waves hit a coastal area, with early warning systems indicating the likelihood of a tsunami's arrival on a scale from watch to advisory to warning.

The way hurricanes are categorized may mislead the public to their dangers

The Saffir-Simpson scale categorizes hurricanes based on wind speed, but tropical cyclones' main dangers are storm surges and heavy rainfall. To better communicate risks to the public, a new system that incorporates hurricane size, water content, and other complexities should be developed.

Whirlpool Rapids formed in a matter of days during the last ice age

Niagara Falls' dramatic whirlpool rapids were created in a matter of weeks when the retreating Falls intersected a buried ice age riverbed—generating North America's largest standing waves.

The deadliest aspect of volcanic eruptions is often not lava, but pyroclastic flows—avalanches of ash, gas, and rock that can move more than half the speed of sound.

Most tornadoes occur during the afternoon and evening hours

While there is no official national tornado season as with Atlantic hurricanes, many tornadoes form in the presence of thunderstorms, which are fueled by solar heating and the energy released by the condensation of water vapor. The airflow instabilities created from this energy build throughout the day until the sun sets.

Harmful algal blooms can occur in warm, nutrient-rich, stagnant waters and are often associated with the rapid reproduction of blue-green algae—a misnomer for cyanobacteria, not algae.

The first known instance of a fire tornado occurred in 2003

During pyro-tornadogenesis, many processes that create thunderstorms from wildfires, such as rising hot air and steam from evaporated water in forests, fuel the formation of a fire tornado. The increasing rates of wildfires due to climate change are expected to make this phenomenon and other extreme weather more common.

Extreme weather conditions heighten cholera risks in settings like refugee camps

Runoff from sewage—exacerbated by situations like flooding or extreme rains—heightens this threat. Increasing temperatures also create the ideal conditions for the bacteria to reproduce, increasing transmission risks.

Quicksand—a mixture of sand with clay or silt soaked in water that gives way when enough pressure is applied—is denser than the human body, meaning you naturally float inside it.

Atmospheric rivers are the largest freshwater transport mechanism on Earth

Serving as highways that carry the water vapor equivalent of up to 15 times the average flow of water at the mouth of the Mississippi River, atmospheric rivers are approximately 400 to 600 kilometers (250 to 375 miles) wide and provide 30-50% of the annual precipitation of the US West Coast.

Lightning forms when streams of rising and falling charged particles connect

In cloud-to-ground lightning, a buildup of negative charge at the bottom of clouds repels electrons on Earth's surface, leaving behind positively charged particles. When descending negatively charged air—the stepped leader—meets rising positively charged particles—the upward streamer—brightening runs up the connection, producing intense flashes known as return strokes.

Available data suggest that while hurricane frequency has not increased over the past century, average hurricane intensity has, a trend scientists attribute to rising air and ocean temperatures.

The air around lightning can reach a temperature of about 30,000 degrees Celsius (54,000 degrees Fahrenheit)—five times hotter than the surface of the sun.

View the various types of lightning

The most common form of lightning involves channels of electricity between oppositely charged regions within a cloud or between two clouds to reestablish electrostatic equilibrium. While cloud-to-ground lightning is understood best, research is ongoing to fully model the mechanisms behind rarer forms of lightning, such as transient luminous events.

Avalanches, which kill an average of 27 people in the US each year, typically require mountain slopes between 30 and 45 degrees and a layer of sturdy snow atop a weak, unstable layer, which can be put into motion by a trigger.

The ingredients that make up severe weather

A seven-minute video illustrating how a storm is made. These factors—moisture, instability, lift, and shear—are explained through a series of data sets and creative, descriptive diagrams.

Lightning is the sudden flow of electricity in the atmosphere as two oppositely charged regions seek to become balanced via the movement of electrons.

The risk of tornadoes and storm surges is greatest on the 'dirty side' of a hurricane

Winds in the right-front quadrant of the storm are amplified by the hurricane's motion and its rotation, which both move air in the same direction. Upon making landfall, these winds pull water from the Gulf and Atlantic onto land, creating storm surges. Tornadoes can also be generated from large differences in wind speed and direction at various heights.

As of 2025, the longest lightning bolt in the world spanned several states

Although the average bolt measures less than 16 kilometers (10 miles), the 2017 "megaflash" spanned 829 kilometers (515 miles) from eastern Texas to Missouri. Severe thunderstorms are common in the region, where warm, humid air from the Gulf collides with cool, dry air from the north, generating atmospheric instability.

There are no outdoor locations that are safe from lightning

If your hair stands up amid an approaching storm, seek shelter immediately, as a local buildup of charge imbalance precedes cloud-to-ground lightning. If you are stuck outside, move to a lower altitude, such as a valley or ravine, and avoid open fields, water, and isolated tall objects. Do not lie down or crouch.

Homes in areas increasingly prone to natural disasters often aren't covered by private insurance

Instead, they're often covered under insurance plans of last resort, known as FAIR (Fair Access to Insurance Requirements) plans. However, as more and more homes become covered by FAIR, the program is facing strain. This interactive visual helps explain the new problems FAIR is facing.

After a landslide, repeat activity may follow the appearance of cracks, springs of water, or dirt, sand, and rocks tumbling down from scars—exposed portions of Earth where the initial landslide began.

The National Weather Service communicates tornado risks on a three-tier system

During a tornado watch, atmospheric conditions favor the development of a tornado, and residents in an area should be prepared to seek refuge. A tornado warning is issued if a tornado has been detected, while a tornado emergency indicates a violent tornado has touched down in the area, with severe threats to human life and property expected.

While landslides are associated with the downward flow of unstable terrain, the term encompasses a variety of geological processes, which are distinguished by how the material moves and what materials are involved.

City structures cause localized heat zones hotter than nearby rural areas

Urban materials like asphalt and concrete trap heat, while cities lack cooling features like trees and water. Due to hot runoff, urban streams can heat up by as much as 18°F more than forested streams.

The Federal Emergency Management Agency leads the US response to disasters

Established in 1979, FEMA coordinates the government's response to hurricanes, wildfires, floods, and other disasters, providing funding, logistical support, and recovery assistance. In FY 2024, the agency spent $35.1B, nearly 40% of the Department of Homeland Security's total budget.

Tsunamis are a series of waves rather than a single one, and boats are safer from them in deeper waters, where tsunami waves are smaller.

A third of Americans now live in wildfire risk zones

Climate change and human development into fire-prone regions have extended the wildfire season, with some areas experiencing fire conditions year-round. Extreme conditions, poor compensation, and exposure to carcinogens have complicated firefighter recruitment, further exacerbating wildfire risks.

More extreme heat days are putting human health at risk in both the short and long term

America is generally experiencing more frequent extreme heat days, over a longer period, in certain parts of the country. The heat-related death toll is rising, and beyond those direct deaths, extreme heat can also have troubling ripple effects including elevated violence and decreased productivity.

Space weather phenomena, including solar flares, coronal mass ejections, and solar wind, are driven by the sun's magnetic field and can affect Earth's ground- and space-based technological systems.