Index of wetness is used to find the rainfall variation or deviation for a particular year and is given as,

Index of wetness = (Rainfall in a particular year at a place/Avg. Annual Rainfall) × 100

Rainfall Deficiency = 100 - Index of wetness

For example: If the index of wetness is “x” then the rainfall deficiency will be 100 - x.

Note:

If Rainfall deficiency is 30 - 45%, it is called large deficiency.

If Rainfall deficiency is 45 - 60%, it is called serious deficiency.

If Rainfall deficiency is > 60%, it is called disastrous deficiency.

Calculation:

Index of wetness = 50/75 × 100 = 66.67%