Why do flash floods occur?

Flash flooding can be more dangerous than traditional floods, occurring within the span of hours and exhibiting rapid currents. Here's how atmospheric conditions and geography combine to make some locations ripe for the disaster.

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.

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.

Between 2006 and 2021, 444 people died from lightning strikes in the US

The National Oceanic and Atmospheric Administration reports that the odds of being struck by lightning in one's lifetime are one in 18,864. Participation in outdoor activities during the summer months in Florida, Texas, and Colorado increases one's risk of exposure.

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.

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.

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.

Hurricanes may kill 300 times more people than officially reported

A recent study suggests that, since 1930, more than 3.5 million people have died due to hurricanes. This incorporates the long-term effects of storms on people's health and economic well-being, contributing to thousands of premature deaths each year.

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.

Being struck by lightning has a mortality rate of about 10%

Near-immediate deaths are the result of electrical disruptions in the heart and nervous system, causing cardiac arrest, but severe skin burns, temporary paralysis, and blown eardrums are more common. About 74% of survivors are left with a long-term disability, which includes brain damage and changes in memory and mood.

Within an 18-hour period in 1974, 13 states were hit by 148 tornadoes

From April 3-4, a tornado outbreak killed over 300 people and caused $600M in damage ($3.8B in 2024 dollars). The event revealed deficiencies in various technologies, including crude radar imaging and slow typewriter-based communication systems, which quickly bottlenecked and became outdated as tornado watches became tornado warnings.

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.

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.

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).

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.

Visualizing the year in US tornadoes, 2024

Between January and November 2024, over 1,700 tornadoes were documented to have touched down in the US, a relatively high number (and similar to the numbers in 2004, 2008, and 2011). This map shows their location across the country to help capture the number.

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.

Visualizing the multibillion dollar cost of US weather disasters

The US has sustained 332 weather and climate disasters since 1980 where overall damages/costs reached or exceeded $1B (including CPI adjustment to 2022). The total cost of these 332 events exceeds $2.275T.

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.

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.

View the ten deadliest tornadoes in US history.

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.

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.

The air around lightning can be five times hotter than the sun's surface

The rapid discharge of electricity—flowing electrons—between oppositely charged regions across a narrow filament can raise temperatures to 30,000 degrees Celsius (54,000 degrees Fahrenheit). If lightning strikes a tree, the speed of the temperature spike can almost immediately turn all its water into pressurized steam, causing it to explode.

As of 2025, the world's largest tropical cyclone spanned half the continental US

Typhoon Tip traveled across the western Pacific Ocean in 1979, achieving winds of 300 kilometers per hour. Though it weakened significantly before making landfall in Japan, its rainfall produced over 600 mudslides and killed 42 people.

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.

Being near a lightning strike—even without getting struck—can be fatal

Because animal tissue is generally more conductive than soil, electricity moving along Earth's surface after a strike tends to travel up and back down an animal's legs, discharging dangerous amounts of energy along the way, with risks increasing the farther apart the legs are. This ground current accounts for about half of all lightning-related deaths and injuries in humans.

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

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.

Track active wildfires, floods, and other natural disasters across the US in real time with this interactive map.

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.

Every day, lightning releases several Hiroshima bombs' worth of energy into the atmosphere

If all this lightning struck one location at once, the bolt would be the diameter of the center circle of a basketball court, turning the entire court into a crater. Its heat would ignite surfaces for miles around, and its shockwave would demolish buildings.

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.

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.

Flood insurance policies from the National Flood Insurance Program cost just over $1,100 per year on average

Private residential policies range from $600 to $2,800 per year. Taking steps to lower flood risk in your home, such as installing flood vents or elevating home utilities, can make premiums cheaper.

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.

See the lists of the worst hurricanes in the US through 2024

Several metrics, including wind speed, pressure, damage costs, and casualties, may be used to define the most devastating hurricanes. This page provides the top 10 hurricanes across each of these sorting methods.