# Precipitation

Under precipitate is understood in the meteorology water including its impurities, consisting of clouds , fog or haze (both clouds in contact with the soil) or water vapor- containing air ( humidity ) is derived and

• falls to earth in liquid or solid form as a result of gravity
• or the wind kicked up is
• or on the earth's surface deposits or flows
• or is deposited in solid form from (supercooled) water as icing on surfaces
• or settles directly on objects as fogging through condensation or resublimation .

## Emergence

Water vapor is released into the atmosphere through evaporation and sublimation . Clouds arise from condensation nuclei through condensation of moisture in the air. In order to be able to fall back on the earth's surface as precipitation, the size (or mass) of the condensed particles must exceed a certain value. The water cycle is closed by the precipitation .

## impact

The frequency and the average amount of precipitation are characteristic of the corresponding geographic areas. Precipitation is a factor that influences the local climate . It is particularly relevant for agriculture , since successful rain-fed agriculture is only possible after a certain amount of rainfall . A mean amount of precipitation can therefore usually be roughly deduced from an ecozone encountered .

In the case of condensation from humid air, heat of condensation is transferred , in the case of resublimation, resublimation heat is transferred from the water vapor, in the case of freezing, freezing heat is transferred from the water to the environment (air, water, vegetation, other surfaces). If supercooled fog freezes or supercooled rain, the heat transfer is low. When precipitation evaporates and sublimates , heat is withdrawn from the environment; this also has a cooling effect on the earth's surface and partially regulates the (small) climate .

## Examples of precipitation

### Liquid precipitation

falling blown up deposited
or
runoff
attached condensed
Rain
freezing rain
drops
Driving rain Rain puddle
rainwater
snowmelt
Fog eaves fog
dew
Dew
condensation

### Solid precipitation

falling blown up deposited deposited
(icing)
resublimed
Snow
sleet
hail
snow
pebbles ice grain
Snowstorm
snowstorm
blizzard
blowing snow
drifting snow
snowdrift
drifting snow
Snow
snowdrift
hoar
Wechte
slush
Hoar
frost Raufrost
Raueis
Eisblume
Eis
Clear ice Slippery
ice
Icicles
Ripe
flickering snow

## Specifications

rain
snow
hail
Hoar frost rain - thawing hoarfrost rains from trees
designation Art Final state description
rain falling liquid Water in the form of drops, other types: drizzle, freezing rain ( supercooled water that suddenly freezes when hit)
Fogging falling liquid Water in very small droplets, therefore very little rainfall
snow falling firmly loose, solid form (from around −12 ° C the water vapor condenses directly into small ice crystals (so-called resublimation - which meteorologists often just call sublimation ), which then clump together to form snowflakes ).
Sleet falling firmly Irregular, solid, very light (air-containing) shape (frozen granules of 2–5 mm in size, which can arise from strong updrafts on cold fronts , for example).
hail falling firmly Frozen raindrops (ice),> 5 mm in diameter, consisting of a condensation core and several frozen layers. There are also irregularly shaped or composed of several individual grains of hailstones. The formation takes place in showers and thunderstorms with very strong currents.
Polar snow falling firmly Ice needles that resublimate immediately from the water vapor of the air close to the ground in severe frost and then fall to the ground.
dew discontinued liquid Water vapor that condenses on objects into fine water droplets
Ripe discontinued firmly Water vapor that resublimates on objects into fine ice crystals and on extensive cold surfaces (snow or ice fields) up to 5 cm large ice crystals.

### Artificial precipitation

Precipitation can be generated artificially under certain meteorological constellations by applying a large amount of artificial ice nuclei, i.e. condensation nuclei (e.g. silver iodide ), to supercooled clouds; see Hagelflieger . From large-scale water vapor emissions originating Industrieschnee is as artificial precipitation which may arise due civilization.

### Demarcation

Artificial snow from snowmaking systems , artificial ice and black ice (frozen lake and sea water) are not counted as precipitation because the water does not come directly and mainly from clouds, fog or humidity. Relocated precipitation (e.g. snow displaced by the snow plow , spray plumes , roof avalanches , rainwater in flowing waters ) remains precipitation.

"Rain" from sprinkling systems is i. A. not counted as precipitation, but can lead to increased cloud formation and increased "general precipitation" due to the increased evaporation.

## Laws of the spatial distribution of precipitation

1. In the mountains, the amount of precipitation depends on the direction of the strike to the prevailing air flow (see windward and lee side ).
2. Mainland areas receive less rainfall than marine areas at the same geographical latitude (see maritime climate , continental climate ).
3. High sums of precipitation in the vicinity of the equator and in moderate latitudes alternate with low sums of precipitation in the extra-equatorial tropics and polar regions (see tropics , subtropics , temperate zone , polar climate ).
4. In the tropics, the eastern parts of the tropical seas are humid all year round, whereas the western parts are only humid in summer and autumn.

## Precipitation measurement

### Measuring devices, units of measurement and methods of measurement

Two different types of measuring devices are used to measure :

• non-registering precipitation gauges (rain gauges)
• recording precipitation gauges (precipitation recorder, pluviograph)

Most precipitation gauges collect the precipitation as point precipitation measurements in a measuring vessel. One millimeter (unit of measurement) corresponds to the water height (precipitation height) of 1 mm, which would result if no water ran off or evaporated. Alternatively, the amount of water (amount of precipitation) is often given in (flat surface). One millimeter is equal to one liter per square meter. Those parts that do not occur in the form of liquid water are either converted into the corresponding amount of the same (if the density is known) or, in the case of snow and hail , converted into water by slight heating to reduce evaporation and measurement errors. ${\ displaystyle \ mathrm {l} / \ mathrm {m} ^ {2}}$

In addition to the direct calculation on site, precipitation intensities can also be determined by radar measurements . For this purpose, the radar reflectivity , which depends on the strength of the rain , is used. The fallen quantities can now also be estimated across the board using precipitation radars. This is particularly important in the field of flood management ( verify or calibrate point measured values ). In addition to the amount or amount of precipitation, the intensity and duration of precipitation are also important.

Long-term ( climatological ) precipitation measurements allow statistical calculations to indicate the average frequency of different precipitation events (especially heavy rain events ) that relate intensity and duration to one another.

### Amount of precipitation

In meteorology, the amount of precipitation is usually given in millimeters (water height) for rain and in centimeters for frozen precipitation . It in turn provides information about the amount of precipitation.

If the amount of precipitation or the resulting amount of precipitation cannot be measured, it is given as "less than 0.1 mm". In case of snowfall, hail or sleet, it is given in (centimeters). A conversion into the amount of precipitation in liters or into the water-equivalent amount of precipitation per square meter can only be made after determining the density, as there can be large differences with frozen precipitation. ${\ displaystyle \ mathrm {cm}}$

• For snow, for example, the density is between (dry, loose fresh snow) and (heavily bound fresh snow): New snow has about 110 (up to 115 - 130 ) the density of water, but settles quite quickly (within hours, especially due to the weight of the layers that have snowed over it) to roughly 13 , so that 1 meter of fresh snow and 30 cm of set snow correspond to about 100 mm of rain.${\ displaystyle 30 \, \ mathrm {kg} / \ mathrm {m} ^ {3}}$${\ displaystyle 200 \, \ mathrm {kg} / \ mathrm {m} ^ {3}}$
• In the case of hail, the indication of the amount of precipitation only relates to the duration of an event and mostly only to the height of the hail layer on the ground (the amount of precipitation in the form of rain is specified separately). It is converted into water volume according to the conversions for loose fillings .

### Rainfall

One looks at the liquid water (precipitation water), which collects in the event of precipitation (rain, snow, hail, fog, etc.) in a defined period of time (see also precipitation intensity) in a vessel that is only open at the top and has a defined horizontal opening. The amount of precipitation is the volume of the liquid in relation to the area of ​​the opening and is given in liters per square meter (1 liter is 1  cubic decimeter ). With the conversion

${\ displaystyle 1 \, {\ frac {\ text {liters}} {\ text {square meters}}} = 1 \, {\ frac {\ mathrm {dm} ^ {3}} {\ mathrm {m} ^ { 2}}} = {\ frac {(0 {,} 1 \, \ mathrm {m}) ^ {3}} {\ mathrm {m} ^ {2}}} = 0 {,} 001 {\ frac { \ mathrm {m} ^ {3}} {\ mathrm {m} ^ {2}}} = 1 \, \ mathrm {mm}}$

it is only numerically equal to the amount of precipitation in millimeters. If you want to calculate the amount of precipitation in liters from the millimeter specification, the number of millimeters must be multiplied by the horizontally projected collection area in square meters: millimeters × square meters = liters.

The usual measurement interval (it must always be specified) is 24 hours (1 day), but also 48 or 72 hours and so on for longer heavy rain events, for driving rain also 1 hour and correspondingly more, but also up to 5 minutes (e.g. as a dimensioning for drainage facilities on buildings) as well as a month, a season and the whole year for climatological considerations. In those cases in which several standard intervals are added, one also speaks of the total precipitation .

Factors such as evaporation , soil infiltration or runoff are not taken into account in the measurement.

### Precipitation duration

The term precipitation duration stands for the duration of a single precipitation event. On the basis of the duration of the precipitation, a distinction is made between continuous precipitation and showers . It is also necessary for the definition of return intervals for heavy rain events and flood scenarios.

### Rainfall intensity

As precipitation intensity refers to the ratio of precipitation amount or quantity and time. For rain it is usually given in millimeters per hour or liters per square meter (and hour, which is often not mentioned), for snow in centimeters per hour.

• Rain: 1 liter per square meter and hour results in 1 mm of rain height / amount in one hour (mm / h)
• Snow: average snow depth in centimeters per hour (cm / h)

Other information for statistical purposes can be millimeters (centimeters for snow) per day, week, month or year.

A moderate rain shower in Central Europe has an intensity of 5 mm / h, a heavy rain of 30 mm / h or a heavy rain of 5 mm / 5 min. During a violent storm, the amount of rain can increase to 50 mm / h and more. Precipitation amounts of a few 100 mm in a few days (about 300 mm / 4 d), even if they are extensive, lead to severe flood events on the large rivers. Tropical storms reach values ​​of 130 mm / h and well above.

### Long-term amounts of precipitation (mean precipitation, accumulated precipitation)

The following meteorological - climatological expressions exist for the average amount of precipitation in the course of a certain period at a defined location or in a certain region .

• Monthly precipitation , or monthly mean precipitation, is the total amount of precipitation for a specific month averaged over a specific number of years (usually 30 years), with the mean over this specific month. The information is given in millimeters per month and is used in various climate diagrams . If you only refer to a specific month, the information includes the year.
• Annual precipitation , or annual mean precipitation, is the total amount of precipitation a year averaged over a certain number of years (usually 30 years). The information is given in millimeters per year and is used in various climate diagrams. If you only refer to a very specific year, this is indicated separately.

For the characteristics of a specific year, the measured precipitation is added up (accumulated) and then compared with the mean precipitation for the same assessment period: In this way, a statement can be made as to whether a month or year is "too wet" or "too dry", a winter " snowy ", or that in a heavy rain event" the normal precipitation of a month fell in three days ". Likewise, climate and season characteristics can be compared, for example “dry in winter”, “maximum precipitation in late summer”.

## Precipitation records

Rain, positive records

Time interval Amount (mm) place year
1 minute 38 Barot, Guadeloupe 1970
1 hour 401 Shangdi, China 1947
12 hours 1,144 Foc-Foc , Reunion 1966
24 hours 1,825 Foc-Foc, Reunion 1966
1 week 5,003 Commerson crater , Reunion 1980
1 month 9,300 Cherrapunji , Meghalaya ( India ) 07/1861
12 months 26,461 Cherrapunji, India 08 / 1860-07 / 1861

Regionally limited extreme precipitation can also be significantly higher. For example, for the rain event on June 2, 2008 in the Killer and Starzeltal in Baden-Württemberg, precipitation of around 240 millimeters was determined in one hour.

Rain, negative records

Time interval Amount (mm) place year
14.4 years (173 months) 0 Arica , Chile 10 / 1903–01 / 1918
19 years (228 months) 0 Wadi Halfa , Sudan

## literature

• Peter Bauer, Peter Schlüssel: Global precipitation recording with satellite data. In: The Geosciences . Vol. 11, No. 12, 1993, pp. 413-418. doi : 10.2312 / geosciences . 1993.11.413 .

Wiktionary: Precipitation  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

1. Ernst Erhard Schmid (editor): Ground plan of the meteorology . Verlag von Leopold Voss, Leipzig 1862 ( limited preview in Google book search).
2. Helmut Kraus: The atmosphere of the earth. An Introduction to Meteorology, 3rd Edition . Springer, Berlin Heidelberg New York 2004, ISBN 3-540-20656-6 ( limited preview in the Google book search).
3. Weather lexicon of the German Weather Service ( Memento of the original from December 16, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .
4. ↑ More rain than ever before. In: Hamburger Abendblatt. August 3, 2002.
5. ^ A b WMO - World Meteorological Organization: Annual Report of the World Meteorological Organization 1994. 1995, ISBN 92-63-10824-2 .
6. Precipitation. University of Freiburg, archived from the original on February 18, 2009 ; accessed on August 25, 2019 .
7. Weather records. Wupperverband, archived from the original on November 8, 2009 ; Retrieved January 29, 2009 .
8. Jürg Luterbacher: Flood disasters in Central Europe - Experienced history and scenarios for the future. ( Memento of December 14, 2012 in the Internet Archive ) (PDF; 435 kB) 2003.
9. Climate data Ostwestfalen-Lippe (status 2000).
10. Assessment of the flood risk and determination of the areas with a significant flood risk in Baden-Württemberg, 2011 Archived copy ( Memento from February 22, 2014 in the Internet Archive ) (PDF; 2.5 MB).