Floods and flash floods: why they are so dangerous
Short answer
Floods happen in every U.S. state and territory and anywhere it rains. Fast-moving water is far stronger than it looks: about 6 inches can knock an adult over, 12 inches can carry away most cars, and 2 feet can carry away SUVs and trucks. So never drive or walk into flood water: Turn Around, Don't Drown. [S1][S2]
Key points
- Cities are at high risk of flash floods, because roads, roofs and parking lots stop rain soaking into the ground and increase runoff. [S1]
- More deaths come from flooding than from any other thunderstorm hazard. [S2]
- A flooded road may have collapsed under the water. [S2]
Claims
- id: C1 claim: Flooding occurs in every U.S. state and territory. source: S1 evidence: "Flooding occurs in every U.S. state and territory"
- id: C2 claim: Pavement and buildings increase runoff in populated areas. source: S1 evidence: "increases runoff by reducing the amount of rain absorbed by the ground"
- id: C3 claim: Six inches of fast-moving water can knock over an adult. source: S2 evidence: "A mere 6 inches of fast-moving flood water can knock over an adult."
- id: C4 claim: Twelve inches of rushing water can carry away most cars. source: S2 evidence: "It takes just 12 inches of rushing water to carry away most cars"
Sources
- [S1] Severe Weather 101: Flood Basics. NOAA. https://www.nssl.noaa.gov/education/svrwx101/floods/ . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Turn Around Don't Drown®. NOAA. https://www.weather.gov/safety/flood-turn-around-dont-drown . License: US government work, public domain. Accessed 2026-11-04.
License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).
License: CC-BY-4.0 · Summary by iinventedlight (AI-assisted). Sources: NOAA, Severe Weather 101: Flood Basics, US government work, public domain; NOAA, Turn Around Don't Drown®, US government work, public domain.
Cite this
iinventedlight. 2026. "Floods and flash floods: why they are so dangerous." iinventedlight Library, iil:note:1my2zx86, version of 2026-11-04. https://iinventedlight.com/library/notes/flood-basics/. License: CC-BY-4.0.
@misc{iil_note_1my2zx86,
author = {{iinventedlight}},
title = {{Floods and flash floods: why they are so dangerous}},
howpublished = {iinventedlight Library},
year = {2026},
date = {2026-11-04},
url = {https://iinventedlight.com/library/notes/flood-basics/},
note = {Permanent ID iil:note:1my2zx86. License: CC-BY-4.0.},
}Spotted a mistake? Use the MCP feedback tool or email hello@iinventedlight.com.
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