# Find the Intensity of Rainfall When the duration of Rainfall is Given

## Find the intensity of Rainfall When the duration of Rainfall is Given

First of all, we need to know the formula used to determine rainfall intensity. There are three types of empirical formulas –

a) For storm duration of 5 to 20 minutes $i = \frac{672}{t+10}$

b) For storm duration of 20 to 100 minutes $i = \frac{1020}{t+10}$

c) Where rainfall is frequent $i = \frac{3430}{t+18}$

Here, i = Intensity of rainfall in mm/hr, t = duration of the storm in minutes.

Following are the two mathematical examples for the determination of rainfall intensity

### Mathematical Problem: 1

Find the intensity of rainfall when the storm continues for a period of 75 minutes.

Solution:

As the duration of rainfall is in between 20 to 100 minutes, so, the formula will be $i = \frac{1020}{t+10}$
The intensity of rainfall, $i = \frac{1020}{75+10}$ $Or, i = \frac{1020}{85} = 12 mm/hr$

### Mathematical Problem: 2

Find the intensity of rainfall when the rainfall occurs frequently and the total duration of rainfall is 115 minutes:

Solution:

As the rainfall occurs frequently, we will use 3rd formula, $i = \frac{3430}{t+18}$
So, the intensity of rainfall is $i = \frac{3430}{115+18}$ $Or, i = \frac{3430}{133} = 25.78 mm/hr$