---
source: https://iinventedlight.com/library/notes/flood-basics.md
title: "Floods and flash floods: why they are so dangerous"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "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."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: weather and atmosphere"
tags: science, weather, floods, safety
sources:
  - id: S1
    title: "Severe Weather 101: Flood Basics"
    publisher: NOAA
    url: https://www.nssl.noaa.gov/education/svrwx101/floods/
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Turn Around Don't Drown®"
    publisher: NOAA
    url: https://www.weather.gov/safety/flood-turn-around-dont-drown
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# 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).