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A hundred-year flood is a probability, not an appointment

A “100-year flood” actually describes a flood threshold with an estimated 1% chance of being equaled or exceeded in a given year. It does not promise a flood-free interval, and the estimate can change as evidence and conditions change.

3–5 min

Questions you could explore

  • What does a recurrence interval tell us that a calendar cannot?
  • How does the chance over several years differ from the chance in one year?

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The same Sun can light a blue afternoon and a red evening

Earth and weather3–5 minSunlight takes a different route through the atmosphere near the horizon than overhead. Which colors scatter along that route helps explain a blue afternoon and a red sunset.

Earth and weather

How can lines on a map show a steep hill?

A flat map can warn you that a route climbs sharply before you ever see the hill. Contour lines join places of equal height, and their spacing adds information about how quickly the ground rises.

2–3 min

How can lines on a map show a steep hill?

Earth and weather2–3 minA flat map can warn you that a route climbs sharply before you ever see the hill. Contour lines join places of equal height, and their spacing adds information about how quickly the ground rises.

Earth and weather

How can an earthquake alert arrive before strong shaking?

An earthquake alert can beat the strongest shaking to a distant location even though the earthquake has already started. Detection and communication can travel ahead of the damaging waves, but nearby places may receive little or no warning.

4–5 min

How can an earthquake alert arrive before strong shaking?

Earth and weather4–5 minAn earthquake alert can beat the strongest shaking to a distant location even though the earthquake has already started. Detection and communication can travel ahead of the damaging waves, but nearby places may receive little or no warning.

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