Earth Science & Energy
Flood Recurrence Interval & Annual Exceedance Probability ($1/T$)
Calculate flood recurrence interval & annual exceedance probability ($1/t$) using the stated engineering or scientific relationship and adjustable field inputs.
Preparing your result…
What this calculator does
Calculates Flood Recurrence Interval & Annual Exceedance Probability ($1/T$) using the formula verified against the cited source.
What your result means
An estimate from the inputs you enter, within the scope stated below — not advice.
Formula
Annual exceedance probability = 1 ÷ recurrence interval
The step-by-step working for your own numbers appears with the result above and in the PDF report.
Frequently asked questions
Symbols and assumptions
- Inputs
- The values entered in the fields above
- • Annual exceedance probability fraction=1/T; percent=100/T, T years for the annual-exceedance recurrence definition.
Sources and review
Reviewed 2026-10-18 · Next review 2027-04-18
- • Require T≥1year for this probability interpretation. A100-year event has1% annual exceedance probability, not one guaranteed event per century. Nonstationarity and alternative partial-duration definitions need separate treatment; do not confuse rainfall recurrence with flood recurrence.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
Quick reference
| Scenario | Recurrence interval (years) | Annual exceedance probability |
|---|---|---|
| Worked example | 100 | 1 % |
| Half the amounts | 50 | 2 % |
| Double the amounts | 200 | 0.5 % |
Need the full picture? Get the detailed PDF report with charts, tables, formulas and working steps.
Reviewed 2026-10-18 · Next review 2027-04-18
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