Question

An accurate estimate of average rainfall in a particular catchment area can be obtained by

• A. arithmetic mean method
• B. isohyetal method
• C. normal ratio method
• D. Thiessen method

Answer 1

The correct option is B isohyetal method

Normal ratio method is used for estimating missing annual precipitation value at a station when the annual precipitation and normal annual precipitation at neighbouring stations are known. In calculating average rainfall in a catchment area arithmetic mean method is a very crude method and it is rarely used. Thiessen-polygon method of calculating the average precipitation is superior to the arithmetic average method as some weightage is given to the various stations on a rational basis. The isohyetal method is superior to other methods (arithmetic mean and thiessen) when stations are large in number.