Why is precipitation measured in millimeters


How much rain per hour is a lot?

A large amount of precipitation in a rather short period of time is referred to as heavy rain. A storm warning due to heavy rain is issued within an hour from a rainfall of 25 liters per square meter. Since the soil can usually not absorb these drastic amounts of water, such storms can lead to floods, flash floods or landslides.

The rainfall record from China is an unbelievable 401 liters per square meter.

What forms of precipitation are there?

There are different forms of precipitation. Liquid precipitation includes rain, freezing rain and drops. Solid precipitation includes hail, snow, sleet, snow pebbles and grains of ice.


Rain refers to liquid water that falls from the atmosphere to the earth due to gravity. It is the most common form of cloud precipitation. Other types of precipitation include water in its frozen state such as snow or hail.

How does rain come about?

Rain arises through the condensation of evaporated water from oceans, lakes or from land. These droplets form clouds and, as soon as a certain weight is reached, fall back to the earth as a result of gravity.

What types of rain are there?

A distinction is made between different forms of rain depending on the origin, duration, intensity, impact and geographic occurrence. Some examples are incline rain, heavy rain, continuous rain or tropical rain.

How can you measure the amount of rain?

A raindrop between 0.5 and 1.5 mm in size falls with one speed from approx. 20km / h.
Measuring the amount of rain or the intensity and duration is relatively easy. For this you need a rain gauge, which is available in both analogue and digital form.


hail is a form of solid Precipitationwhere balls of ice or lumps of ice fall from the atmosphere to the earth due to gravity. From a diameter of the balls of 0.5 cm one speaks of hailstones, everything below that is called Sleet.

How does hail come about?

Hail arises in Thunderclouds in which supercooled water droplets combine with so-called crystallization grains and form clumps. If there are few of these grains and thus a large excess of water, more and more water is deposited on a hailstone due to up and down movements by the wind. This allows the hailstones to grow to an impressive size before they are too heavy and fall from the cloud to the ground.

When can it hail?

Hail showers usually occur earlier warm season, in Germany more often in April. Since the thunderclouds extend up to a height of over 10km, the deep minus temperatures prevail here, which are necessary for the formation of ice.

What are the effects of hailstorms?

Depending on size and speed Hailstones can cause major damage to cars and glass panes, but also to people and animals. Hailstones can reach speeds of well over 150km / h. The largest hailstone was found in the United States and was 8 inches in diameter.

How can you measure the amount of hail?

In the case of hail, the size of the individual hailstones is often measured. To measure the amount of precipitation, the water equivalent of the melted hailstones can be measured in a rain gauge.


snow refers to fine ice crystals that fall from the atmosphere to the earth due to gravity. It is the most common form of solid precipitation. Other forms of solid precipitation are, for example, hail or sleet.

How is snow made?

Snow usually arises in high, cold layers of air as small water droplets freeze in the clouds at temperatures in the atmosphere of below minus 4 degrees. It can also Ice crystals Form directly from water vapor when it attaches to a so-called freezing core. Over time, the resulting ice crystals clump together to form larger flakes, which fall to the earth in the form of snow when they reach a certain weight.

Depending on the temperature and humidity, the shape and size vary greatly. Snowflakes are greatest at temperatures just below freezing and high humidity. At temperatures below -30 degrees in the high air layers, it hardly snows anymore because the air is often too dry.

Due to the special formation of snow, it only occurs in nature. Snow from the snow cannon, for example, has a much higher density. Snowflakes have a delicate structure and occur in many variations. Snow has a falling speed of approx. 4 km / h and is therefore much slower than rain or hail.

How can you measure the amount of snow?

This is usually measured here Snow depth and the Fresh snow in centimeters. Snow can also be measured in a molten state using a rain gauge. Due to the low density of snow, a comparatively large amount of snow can be achieved even with a small amount of water.