1. What is a Recurrence Interval Calculator (ARI)?

Definition: This calculator determines the average recurrence interval (ARI) of an event based on its probability of occurrence.

Purpose: It helps hydrologists, engineers, and risk assessors understand how often an event of a given probability is expected to occur.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( ARI \) — Average recurrence interval (years)
• \( P \) — Probability of event occurrence (0 to 1)

Explanation: The reciprocal of the probability gives the average time between occurrences of events with that probability.

3. Importance of Recurrence Interval Calculation

Details: ARI is crucial for flood risk assessment, infrastructure design, and understanding extreme weather event frequencies.

4. Using the Calculator

Tips: Enter the probability of the event (between 0 and 1). For example, for a 1% chance, enter 0.01.

5. Frequently Asked Questions (FAQ)

Q1: What does ARI mean?
A: ARI (Average Recurrence Interval) is the average time between occurrences of an event with a given probability.

Q2: How is probability related to ARI?
A: A 10% probability event (P=0.1) has an ARI of 10 years, meaning it's expected to occur on average once every 10 years.

Q3: What's a 100-year flood?
A: It's a flood with a 1% annual probability (P=0.01), giving an ARI of 100 years. This doesn't mean it happens exactly every 100 years.

Q4: Can probability be greater than 1?
A: No, probability values must be between 0 (never happens) and 1 (always happens).

Q5: How is this used in engineering?
A: Engineers use ARI to design structures to withstand events of specific probabilities (e.g., designing bridges for 50-year flood events).