Question

A rainy day as defined by the India Meteorological Department is a day when the rainfall at a point received is ................... in 24 hours

• A. $>$2.5 mm
• B. $>$2.0 mm
• C. $>$3.5 mm
• D. $>$2.25 mm

Hint:

Remember the threshold: 2.5 mm is the key value.
Any 24-hour rainfall measurement equal to or greater than 2.5 mm qualifies as a rainy day under IMD standards.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The India Meteorological Department (IMD) defines standardized terminology for recording daily precipitation to maintain consistency in meteorological, hydrological, and agricultural records.

Step 2: Detailed Explanation:
Meteorological stations measure total rainfall accumulated over a 24-hour period (usually from 08:30 hours IST of the previous day to 08:30 hours IST of the current day).
The classifications used by the IMD are as follows:
- Rainy Day: A day is officially recorded as a "rainy day" if the total rainfall received at a station during those 24 hours is 2.5 mm or more (\( \ge 2.5 \) mm, which is commonly represented as \( > 2.5 \) mm in multiple-choice questions to distinguish it from smaller traces).
- Standard Day Dry Day: If the rainfall is less than 2.5 mm, it is not classified as a rainy day, as such minor precipitation typically evaporates quickly and does not contribute significantly to surface runoff or agricultural soil moisture.
Thus, the threshold of \( > 2.5 \) mm is the established scientific standard.

Step 3: Final Answer:
A rainy day is defined as a day with rainfall \( > 2.5 \) mm in 24 hours.