The ratio of actual rainfall in a year at a place to the normal annual rainfall of that place is called
- ARainfall coefficient
- BIndex of wetnessCorrect
- CRunoff coefficient
- DDegree of precipitation
Solution
Concept
The Index of Wetness is a ratio used to compare the actual rainfall of a specific year to the long-term average (normal) rainfall of that place.
Formula
Index of Wetness = (Actual rainfall in a year / Normal annual rainfall) × 100
Step-by-step solution
1. Identify the given ratio: Actual rainfall in a year divided by the Normal annual rainfall. 2. In hydrology, this specific ratio is defined as the 'Index of Wetness'. 3. It is usually expressed as a percentage to show how 'wet' or 'dry' a year was compared to the average. 4. For example, if the ratio is 1.0 (or 100%), the rainfall was exactly normal. Answer: (B) Index of wetness
Explanation
The Index of Wetness tells us how much the rainfall of a particular year deviates from the normal rainfall. A value less than 100% indicates a 'dry' year or a rainfall deficiency. It helps engineers understand drought conditions in a region.
Why the other options are wrong
A: Rainfall coefficient is not a standard term for this specific ratio. C: Runoff coefficient is the ratio of runoff to the total rainfall. D: Degree of precipitation is a general term and not a technical ratio used in hydrology.
Shortcut
Remember: Wetness = How much rain we actually got vs. what we usually get.
Common mistake
Students often confuse this with 'Runoff coefficient', which relates rainfall to the water that flows into rivers.
Correct answer: B) Index of wetness