A few millimeters of rain is considered heavy, so learn about weather and geography.

Precipitation refers to the depth of liquid and solid (melted) precipitation that falls from the sky to the ground and accumulates on the horizontal surface without evaporation, infiltration and loss. Its unit is millimeters. In meteorology, precipitation amount is used to distinguish the intensity of precipitation. It can be divided into: light rain, moderate rain, heavy rain, heavy rain, heavy rain, etc.

Light rain: The raindrops are clearly visible and do not float; they do not splash on the ground; water accumulates slowly in depressions; the sound of rain on the house is weak, and there is only dripping water from the eaves; the precipitation within 12 hours is less than 5mm or the precipitation within 24 hours Rainfall process less than 10mm.

Moderate rain: The rain falls in lines, and the raindrops are difficult to distinguish; it falls on hard ground and splashes; water accumulates in depressions quickly; there is a rustling sound on the roof; the precipitation is 5 to 15mm in 12 hours or 5 to 15mm in 24 hours. Measure the rainfall process of 10~25mm.

Heavy rain: the rain falls like a downpour and blurs into flakes; water accumulates in depressions very quickly; there is a sound of rain on the roof; the precipitation is 15-30mm in 12 hours or the precipitation is 25-50mm in 24 hours process.

Heavy rain: Any rainfall process in which the precipitation exceeds 50mm within 24 hours is collectively called a heavy rain. According to the intensity of heavy rain, it can be divided into three types: heavy rain, heavy rain and extremely heavy rain. Heavy rain: a rainfall process with a rainfall of 30 to 70 mm within 12 hours or a rainfall of 50 to 100 mm within 24 hours. Heavy rainstorm: a rainfall process with a rainfall of 70 to 140 mm within 12 hours or a rainfall of 100 to 250 mm within 24 hours. Extremely heavy rain: a rainfall process in which the precipitation exceeds 140 mm within 12 hours or the precipitation exceeds 250 mm within 24 hours.

(Hope this helps you)