Correct option is A
Methods used to convert point rainfall values at different rain gauge stations into an average value over a catchment area:
1. Arithmetical mean method
The arithmetical mean method is a very crude method and it is rarely used.
2. Thiessen Polygon method
Thiessen Polygon method is superior to the arithmetic average method as some weightage is given to various stations on a rational basis.
3. Isohyetal Method
The Isohyetal Method is considered as the best method as compared to the above two.
In the isohyetal method, precipitation values are plotted at their respective stations on a suitable base map, and isohyets are drawn to create an isohyet map.
Isohyets:
It is a line joining points of equal rainfall for a given interval.
Isohyets are contours of equal precipitation analogous to contour lines on a topographic map.
