Precipitation is the amount of rainwater that falls in a given time period, assuming that water does not escape by evaporation or drainage.


You may see rainfall amounts such as "10 mm/h" indicated in weather forecasts on the daily news. In this case, it refers to the intensity of rain that causes 10 mm of water to fall on the ground surface in one hour.


Also, there is a slight difference between rainfall and precipitation. Rainfall refers to the amount of pure rainfall only, while precipitation refers to the amount of water that has fallen, including snow, hail, and hail in addition to rainwater.


How to Choose Rain Chains Based on the Amount of Precipitation

In recent years, strong rainfall has been increasing throughout various parts of the world, and it is necessary to estimate the appropriate maximum rainfall for each region and consider how the rainwater flowing on the roof can be handled accordingly to avoid any problems.

In addition to rain intensity, another important factor is roof area. The larger the roof area, the greater the amount of water that must be drained and the higher the drainage capacity required for the drainage downspouts involved. The formula for the amount of water that must be drained can be calculated by the following formula:

Roof area (m2) x precipitation (mm/h) = amount of water that falls on the building (l)

To quickly calculate the amount of water that accumulates on a roof, the following can be applied: 10 mm/hour of rain falling on 1 m2 is considered to be 10 L, and 100 mm of rain falling on 100 m2 is considered to be 100 L. Multiply this by the roof area, and you can easily estimate the amount of water that will accumulate on the roof. 


In addition, the roof area is called the "projected roof area," which is the area of the building viewed from directly above, and the exact amount of water can be calculated by multiplying the projected roof area by the amount of precipitation.