Basic rainfall descriptors Pick the correct set of definitions relating to rainfall characteristics.

Introduction / Context:
Hydrologic design uses three basic rainfall descriptors: intensity, duration, and frequency. Understanding these terms underpins IDF (Intensity–Duration–Frequency) analysis and stormwater design.

Given Data / Assumptions:

• Standard meteorological definitions.
• Frequency often expressed via return period (e.g., 10-year event).

Concept / Approach:
Intensity is a rate (e.g., mm/h), duration is the time span over which that intensity is considered, and frequency/return period describes how often events of that magnitude are expected statistically.

Step-by-Step Solution:

Verification / Alternative check:
These form the axes and curves of IDF relationships used in drainage sizing and flood estimation.

Why Other Options Are Wrong:
Options a–c are individually correct; thus option d (“All of the above”) is the comprehensive correct answer.

Common Pitfalls:
Confusing frequency with duration or interpreting return period deterministically rather than probabilistically.

Final Answer:
All of the above