The amount of rain is measured by pluviometer. In this device, rain is collected by a funnel on top of a drum and measured in a graduated cylinder.
The amount of rainfall is measured in the rain gauge in millimeters: one millimeter of rain corresponds to 1 liter of water per square meter. When it is said, for example, that yesterday the rainfall, or rainfall, was 5 millimeters in the city of Porto Alegre, it means that if the rainwater had been collected in a swimming pool or any closed container, a layer would have formed. 5 mm high.
Forecasters say rain is light when it is less than 0.5mm in an hour; It is strong when it exceeds 4mm.
Atmospheric pressure is related to air humidity. The drier the air, the higher the value of this pressure.
Decreasing atmospheric pressure indicates increased air humidity, which in turn indicates the possibility of rain. Atmospheric pressure is measured by barometer.