Question

Consider the following statements:
1. The normal annual rainfall of a station is obtained as the arithmetic average of the successive annual rainfall in the last 30 years.
2. The 'normal rainfall' is updated by deleting the needful number of oldest years data from the record and adding the needful number of most recent years data to the record.
3. The standard deviation computed for the rainfall of the same 30 years of rainfall data is taken as a measure of the variability of the rainfall during the same set of years.
4. If the observed rainfall in any year is less than the current normal annual rainfall, then that year is called a dry year.
Which of the above statements are correct?

• A. 1, 2, 3 and 4
• B. 1, 2 and 3 only
• C. 2 and 4 only
• D. 1, 3 and 4 only

Answer 1

The correct option is D 1, 3 and 4 only

The Normal rainfall is calculated as the average value of rainfall of a particular date, month or year over a specified period of 30 years. The 30 year normal rainfall is recomputed every decade to account for factors that may affect the amount of rainfall in that area like change in land use, environment etc.
The standard deviation shows the rainfall variability over a particular period.