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Rain

April 06, 2023

Several terms redirect here. For other uses, see Rain (disambiguation), Rainy (disambiguation), Rainfall (disambiguation) and Rainwater (disambiguation).

Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems.

Heavy rainfall on a roof
Rain
Typical sound of rain with thunder
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Rain falling on a road

The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.

The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. Antarctica is the driest continent. The globally averaged annual precipitation over land is 715 mm (28.1 in), but over the whole Earth, it is much higher at 990 mm (39 in).[1] Climate classification systems such as the Köppen classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges. Rainfall amounts can be estimated by weather radar.

Rain is also known or suspected on other planets, where it may be composed of methane, neon, sulfuric acid, or even iron rather than water.

Formation

Water-saturated air

 
Rain falling on a field, in southern Estonia

Air contains water vapor, and the amount of water in a given mass of dry air, known as the mixing ratio, is measured in grams of water per kilogram of dry air (g/kg).[2][3] The amount of moisture in the air is also commonly reported as relative humidity; which is the percentage of the total water vapor air can hold at a particular air temperature.[4] How much water vapor a parcel of air can contain before it becomes saturated (100% relative humidity) and forms into a cloud (a group of visible and tiny water and ice particles suspended above the Earth's surface)[5] depends on its temperature. Warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it. The dew point is the temperature to which a parcel must be cooled in order to become saturated.[6]

 
Streets in Tampere, Finland watered by night rain.

There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, and evaporative cooling. Adiabatic cooling occurs when air rises and expands.[7] The air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain (orographic lift). Conductive cooling occurs when the air comes into contact with a colder surface,[8] usually by being blown from one surface to another, for example from a liquid water surface to colder land. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath.[9] Evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation.[10]

The main ways water vapor is added to the air are wind convergence into areas of upward motion,[11] precipitation or virga falling from above,[12] daytime heating evaporating water from the surface of oceans, water bodies or wet land,[13] transpiration from plants,[14] cool or dry air moving over warmer water,[15] and lifting air over mountains.[16] Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds. Elevated portions of weather fronts (which are three-dimensional in nature)[17] force broad areas of upward motion within the Earth's atmosphere which form clouds decks such as altostratus or cirrostratus.[18] Stratus is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. It can also form due to the lifting of advection fog during breezy conditions.[19]

Coalescence and fragmentation

 
The shape of raindrops depending upon their size

Coalescence occurs when water droplets fuse to create larger water droplets. Air resistance typically causes the water droplets in a cloud to remain stationary. When air turbulence occurs, water droplets collide, producing larger droplets.

 
Black Rain Clouds

As these larger water droplets descend, coalescence continues, so that drops become heavy enough to overcome air resistance and fall as rain. Coalescence generally happens most often in clouds above freezing and is also known as the warm rain process.[20] In clouds below freezing, when ice crystals gain enough mass they begin to fall. This generally requires more mass than coalescence when occurring between the crystal and neighboring water droplets. This process is temperature dependent, as supercooled water droplets only exist in a cloud that is below freezing. In addition, because of the great temperature difference between cloud and ground level, these ice crystals may melt as they fall and become rain.[21]

Raindrops have sizes ranging from 0.1 to 9 mm (0.0039 to 0.3543 in) mean diameter but develop a tendency to break up at larger sizes. Smaller drops are called cloud droplets, and their shape is spherical. As a raindrop increases in size, its shape becomes more oblate, with its largest cross-section facing the oncoming airflow. Large rain drops become increasingly flattened on the bottom, like hamburger buns; very large ones are shaped like parachutes.[22][23] Contrary to popular belief, their shape does not resemble a teardrop.[24] The biggest raindrops on Earth were recorded over Brazil and the Marshall Islands in 2004 — some of them were as large as 10 mm (0.39 in). The large size is explained by condensation on large smoke particles or by collisions between drops in small regions with particularly high content of liquid water.[25]

Raindrops associated with melting hail tend to be larger than other raindrops.[26]

 
A raindrop on a leaf

Intensity and duration of rainfall are usually inversely related, i.e., high-intensity storms are likely to be of short duration and low-intensity storms can have a long duration.[27][28]

Droplet size distribution

Main article: Raindrop size distribution

The final droplet size distribution is an exponential distribution. The number of droplets with diameter between   and   per unit volume of space is  . This is commonly referred to as the Marshall–Palmer law after the researchers who first characterized it.[23][29] The parameters are somewhat temperature-dependent,[30] and the slope also scales with the rate of rainfall   (d in centimeters and R in millimeters per hour).[23]

Deviations can occur for small droplets and during different rainfall conditions. The distribution tends to fit averaged rainfall, while instantaneous size spectra often deviate and have been modeled as gamma distributions.[31] The distribution has an upper limit due to droplet fragmentation.[23]

Raindrop impacts

Raindrops impact at their terminal velocity, which is greater for larger drops due to their larger mass-to-drag ratio. At sea level and without wind, 0.5 mm (0.020 in) drizzle impacts at 2 m/s (6.6 ft/s) or 7.2 km/h (4.5 mph), while large 5 mm (0.20 in) drops impact at around 9 m/s (30 ft/s) or 32 km/h (20 mph).[32]

Rain falling on loosely packed material such as newly fallen ash can produce dimples that can be fossilized, called raindrop impressions.[33] The air density dependence of the maximum raindrop diameter together with fossil raindrop imprints has been used to constrain the density of the air 2.7 billion years ago.[34]

The sound of raindrops hitting water is caused by bubbles of air oscillating underwater.[35][36]

The METAR code for rain is RA, while the coding for rain showers is SHRA.[37]

Virga

Main article: Virga

In certain conditions, precipitation may fall from a cloud but then evaporate or sublime before reaching the ground. This is termed virga and is more often seen in hot and dry climates.

Causes

Frontal activity

Main article: Weather fronts

Stratiform (a broad shield of precipitation with a relatively similar intensity) and dynamic precipitation (convective precipitation which is showery in nature with large changes in intensity over short distances) occur as a consequence of slow ascent of air in synoptic systems (on the order of cm/s), such as in the vicinity of cold fronts and near and poleward of surface warm fronts. Similar ascent is seen around tropical cyclones outside the eyewall, and in comma-head precipitation patterns around mid-latitude cyclones.[38] A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually, their passage is associated with a drying of the air mass. Occluded fronts usually form around mature low-pressure areas.[39] What separates rainfall from other precipitation types, such as ice pellets and snow, is the presence of a thick layer of air aloft which is above the melting point of water, which melts the frozen precipitation well before it reaches the ground. If there is a shallow near-surface layer that is below freezing, freezing rain (rain which freezes on contact with surfaces in subfreezing environments) will result.[40] Hail becomes an increasingly infrequent occurrence when the freezing level within the atmosphere exceeds 3,400 m (11,000 ft) above ground level.[41]

Convection

 
Convective precipitation
 
Orographic precipitation

Convective rain, or showery precipitation, occurs from convective clouds (e.g., cumulonimbus or cumulus congestus). It falls as showers with rapidly changing intensity. Convective precipitation falls over a certain area for a relatively short time, as convective clouds have limited horizontal extent. Most precipitation in the tropics appears to be convective; however, it has been suggested that stratiform precipitation also occurs.[38][42] Graupel and hail indicate convection.[43] In mid-latitudes, convective precipitation is intermittent and often associated with baroclinic boundaries such as cold fronts, squall lines, and warm fronts.[44]

Orographic effects

Main articles: Orographic lift, Precipitation types (meteorology), and United States rainfall climatology

Orographic precipitation occurs on the windward side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, resulting in adiabatic cooling and condensation. In mountainous parts of the world subjected to relatively consistent winds (for example, the trade winds), a more moist climate usually prevails on the windward side of a mountain than on the leeward or downwind side. Moisture is removed by orographic lift, leaving drier air (see katabatic wind) on the descending and generally warming, leeward side where a rain shadow is observed.[16]

In Hawaii, Mount Waiʻaleʻale, on the island of Kauai, is notable for its extreme rainfall, as it is amongst the places in the world with the highest levels of rainfall, with 9,500 mm (373 in).[45] Systems known as Kona storms affect the state with heavy rains between October and April.[46] Local climates vary considerably on each island due to their topography, divisible into windward (Koʻolau) and leeward (Kona) regions based upon location relative to the higher mountains. Windward sides face the east to northeast trade winds and receive much more rainfall; leeward sides are drier and sunnier, with less rain and less cloud cover.[47]

In South America, the Andes mountain range blocks Pacific moisture that arrives in that continent, resulting in a desert-like climate just downwind across western Argentina.[48] The Sierra Nevada range creates the same effect in North America forming the Great Basin and Mojave Deserts.[49][50]

Within the tropics

 
Rainfall distribution by month in Cairns showing the extent of the wet season at that location
See also: Monsoon and Tropical cyclone
Main article: Wet season

The wet, or rainy, season is the time of year, covering one or more months, when most of the average annual rainfall in a region falls.[51] The term green season is also sometimes used as a euphemism by tourist authorities.[52] Areas with wet seasons are dispersed across portions of the tropics and subtropics.[53] Savanna climates and areas with monsoon regimes have wet summers and dry winters. Tropical rainforests technically do not have dry or wet seasons, since their rainfall is equally distributed through the year.[54] Some areas with pronounced rainy seasons will see a break in rainfall mid-season when the intertropical convergence zone or monsoon trough move poleward of their location during the middle of the warm season.[27] When the wet season occurs during the warm season, or summer, rain falls mainly during the late afternoon and early evening hours. The wet season is a time when air quality improves,[55] freshwater quality improves,[56][57] and vegetation grows significantly.

Tropical cyclones, a source of very heavy rainfall, consist of large air masses several hundred miles across with low pressure at the centre and with winds blowing inward towards the centre in either a clockwise direction (southern hemisphere) or counterclockwise (northern hemisphere).[58] Although cyclones can take an enormous toll in lives and personal property, they may be important factors in the precipitation regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions.[59] Areas in their path can receive a year's worth of rainfall from a tropical cyclone passage.[60]

Human influence

 
Image of Atlanta, US showing temperature distribution, with blue showing cool temperatures, red warm, and hot areas appearing white.
 
Average surface air temperatures from 2011 to 2020 compared to the 1951–1980 average. Source: NASA
See also: Global warming and Urban heat island

The fine particulate matter produced by car exhaust and other human sources of pollution forms cloud condensation nuclei leads to the production of clouds and increases the likelihood of rain. As commuters and commercial traffic cause pollution to build up over the course of the week, the likelihood of rain increases: it peaks by Saturday, after five days of weekday pollution has been built up. In heavily populated areas that are near the coast, such as the United States' Eastern Seaboard, the effect can be dramatic: there is a 22% higher chance of rain on Saturdays than on Mondays.[61] The urban heat island effect warms cities 0.6 to 5.6 °C (1.1 to 10.1 °F) above surrounding suburbs and rural areas. This extra heat leads to greater upward motion, which can induce additional shower and thunderstorm activity. Rainfall rates downwind of cities are increased between 48% and 116%. Partly as a result of this warming, monthly rainfall is about 28% greater between 32 to 64 km (20 to 40 mi) downwind of cities, compared with upwind.[62] Some cities induce a total precipitation increase of 51%.[63]

Increasing temperatures tend to increase evaporation which can lead to more precipitation. Precipitation generally increased over land north of 30°N from 1900 through 2005 but has declined over the tropics since the 1970s. Globally there has been no statistically significant overall trend in precipitation over the past century, although trends have varied widely by region and over time. Eastern portions of North and South America, northern Europe, and northern and central Asia have become wetter. The Sahel, the Mediterranean, southern Africa and parts of southern Asia have become drier. There has been an increase in the number of heavy precipitation events over many areas during the past century, as well as an increase since the 1970s in the prevalence of droughts—especially in the tropics and subtropics. Changes in precipitation and evaporation over the oceans are suggested by the decreased salinity of mid- and high-latitude waters (implying more precipitation), along with increased salinity in lower latitudes (implying less precipitation and/or more evaporation). Over the contiguous United States, total annual precipitation increased at an average rate of 6.1 percent since 1900, with the greatest increases within the East North Central climate region (11.6 percent per century) and the South (11.1 percent). Hawaii was the only region to show a decrease (−9.25 percent).[64]

Analysis of 65 years of United States of America rainfall records show the lower 48 states have an increase in heavy downpours since 1950. The largest increases are in the Northeast and Midwest, which in the past decade, have seen 31 and 16 percent more heavy downpours compared to the 1950s. Rhode Island is the state with the largest increase, 104%. McAllen, Texas is the city with the largest increase, 700%. Heavy downpour in the analysis are the days where total precipitation exceeded the top one percent of all rain and snow days during the years 1950–2014.[65][66]

The most successful attempts at influencing weather involve cloud seeding, which include techniques used to increase winter precipitation over mountains and suppress hail.[67]

Characteristics

Patterns

 
Band of thunderstorms seen on a weather radar display
Main article: Rainband

Rainbands are cloud and precipitation areas which are significantly elongated. Rainbands can be stratiform or convective,[68] and are generated by differences in temperature. When noted on weather radar imagery, this precipitation elongation is referred to as banded structure.[69] Rainbands in advance of warm occluded fronts and warm fronts are associated with weak upward motion,[70] and tend to be wide and stratiform in nature.[71]

Rainbands spawned near and ahead of cold fronts can be squall lines which are able to produce tornadoes.[72] Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front's orientation due to the formation of a low-level barrier jet.[73] Bands of thunderstorms can form with sea breeze and land breeze boundaries if enough moisture is present. If sea breeze rainbands become active enough just ahead of a cold front, they can mask the location of the cold front itself.[74]

Once a cyclone occludes an occluded front (a trough of warm air aloft) will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately northwestern, periphery (also termed the warm conveyor belt), forcing a surface trough to continue into the cold sector on a similar curve to the occluded front. The front creates the portion of an occluded cyclone known as its comma head, due to the comma-like shape of the mid-tropospheric cloudiness that accompanies the feature. It can also be the focus of locally heavy precipitation, with thunderstorms possible if the atmosphere along the front is unstable enough for convection.[75] Banding within the comma head precipitation pattern of an extratropical cyclone can yield significant amounts of rain.[76] Behind extratropical cyclones during fall and winter, rainbands can form downwind of relative warm bodies of water such as the Great Lakes. Downwind of islands, bands of showers and thunderstorms can develop due to low-level wind convergence downwind of the island edges. Offshore California, this has been noted in the wake of cold fronts.[77]

Rainbands within tropical cyclones are curved in orientation. Tropical cyclone rainbands contain showers and thunderstorms that, together with the eyewall and the eye, constitute a hurricane or tropical storm. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.[78]

Acidity

 
Sources of acid rain
See also: Acid rain

The phrase acid rain was first used by Scottish chemist Robert Augus Smith in 1852.[79] The pH of rain varies, especially due to its origin. On America's East Coast, rain that is derived from the Atlantic Ocean typically has a pH of 5.0–5.6; rain that comes across the continental from the west has a pH of 3.8–4.8; and local thunderstorms can have a pH as low as 2.0.[80] Rain becomes acidic primarily due to the presence of two strong acids, sulfuric acid (H2SO4) and nitric acid (HNO3). Sulfuric acid is derived from natural sources such as volcanoes, and wetlands (sulfate-reducing bacteria); and anthropogenic sources such as the combustion of fossil fuels, and mining where H2S is present. Nitric acid is produced by natural sources such as lightning, soil bacteria, and natural fires; while also produced anthropogenically by the combustion of fossil fuels and from power plants. In the past 20 years, the concentrations of nitric and sulfuric acid has decreased in presence of rainwater, which may be due to the significant increase in ammonium (most likely as ammonia from livestock production), which acts as a buffer in acid rain and raises the pH.[81]

Köppen climate classification

 
Updated Köppen–Geiger climate map[82]
  Af
  Am
  Aw
  BWh
  BWk
  BSh
  BSk
  Csa
  Csb
  Cwa
  Cwb
  Cfa
  Cfb
  Cfc
  Dsa
  Dsb
  Dsc
  Dsd
  Dwa
  Dwb
  Dwc
  Dwd
  Dfa
  Dfb
  Dfc
  Dfd
  ET
  EF
Main article: Köppen climate classification

The Köppen classification depends on average monthly values of temperature and precipitation. The most commonly used form of the Köppen classification has five primary types labeled A through E. Specifically, the primary types are A, tropical; B, dry; C, mild mid-latitude; D, cold mid-latitude; and E, polar. The five primary classifications can be further divided into secondary classifications such as rain forest, monsoon, tropical savanna, humid subtropical, humid continental, oceanic climate, Mediterranean climate, steppe, subarctic climate, tundra, polar ice cap, and desert.

Rain forests are characterized by high rainfall, with definitions setting minimum normal annual rainfall between 1,750 and 2,000 mm (69 and 79 in).[83] A tropical savanna is a grassland biome located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes, with rainfall between 750 and 1,270 mm (30 and 50 in) a year. They are widespread on Africa, and are also found in India, the northern parts of South America, Malaysia, and Australia.[84] The humid subtropical climate zone is where winter rainfall is associated with large storms that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones.[85] Humid subtropical climates lie on the east side continents, roughly between latitudes 20° and 40° degrees away from the equator.[86]

An oceanic (or maritime) climate is typically found along the west coasts at the middle latitudes of all the world's continents, bordering cool oceans, as well as southeastern Australia, and is accompanied by plentiful precipitation year-round.[87] The Mediterranean climate regime resembles the climate of the lands in the Mediterranean Basin, parts of western North America, parts of Western and South Australia, in southwestern South Africa and in parts of central Chile. The climate is characterized by hot, dry summers and cool, wet winters.[88] A steppe is a dry grassland.[89] Subarctic climates are cold with continuous permafrost and little precipitation.[90]

Pollution

This section is an excerpt from Per- and polyfluoroalkyl substances § Prevalence in rainwater.[edit]
In 2022 it was found that levels of at least four perfluoroalkyl acids (PFAAs) in rainwater worldwide ubiquitously, and often greatly, exceeded the EPA's lifetime drinking water health advisories as well as comparable Danish, Dutch, and European Union safety standards, leading researchers to conclude that "the global spread of these four PFAAs in the atmosphere has led to the planetary boundary for chemical pollution being exceeded".[91] There are some moves to restrict and replace their use.[92]

Measurement

See also: Precipitation § Rate

Gauges

See also: Rain gauge, Disdrometer, and Snow gauge
 
Standard rain gauge

Rain is measured in units of length per unit time, typically in millimeters per hour,[93] or in countries where imperial units are more common, inches per hour.[94] The "length", or more accurately, "depth" being measured is the depth of rain water that would accumulate on a flat, horizontal and impermeable surface during a given amount of time, typically an hour.[95] One millimeter of rainfall is the equivalent of one liter of water per square meter.[96]

The standard way of measuring rainfall or snowfall is the standard rain gauge, which can be found in 100-mm (4-in) plastic and 200-mm (8-in) metal varieties.[97] The inner cylinder is filled by 25 mm (0.98 in) of rain, with overflow flowing into the outer cylinder. Plastic gauges have markings on the inner cylinder down to 0.25 mm (0.0098 in) resolution, while metal gauges require use of a stick designed with the appropriate 0.25 mm (0.0098 in) markings. After the inner cylinder is filled, the amount inside it is discarded, then filled with the remaining rainfall in the outer cylinder until all the fluid in the outer cylinder is gone, adding to the overall total until the outer cylinder is empty.[98] Other types of gauges include the popular wedge gauge (the cheapest rain gauge and most fragile), the tipping bucket rain gauge, and the weighing rain gauge.[99] For those looking to measure rainfall the most inexpensively, a can that is cylindrical with straight sides will act as a rain gauge if left out in the open, but its accuracy will depend on what ruler is used to measure the rain with. Any of the above rain gauges can be made at home, with enough know-how.[100]

When a precipitation measurement is made, various networks exist across the United States and elsewhere where rainfall measurements can be submitted through the Internet, such as CoCoRAHS or GLOBE.[101][102] If a network is not available in the area where one lives, the nearest local weather or met office will likely be interested in the measurement.[103]

Remote sensing

See also: Weather radar
 
Twenty-four-hour rainfall accumulation on the Val d'Irène radar in Eastern Canada. Zones without data in the east and southwest are caused by beam blocking from mountains. (Source: Environment Canada)

One of the main uses of weather radar is to be able to assess the amount of precipitations fallen over large basins for hydrological purposes.[104] For instance, river flood control, sewer management and dam construction are all areas where planners use rainfall accumulation data. Radar-derived rainfall estimates complement surface station data which can be used for calibration. To produce radar accumulations, rain rates over a point are estimated by using the value of reflectivity data at individual grid points. A radar equation is then used, which is

 
where Z represents the radar reflectivity, R represents the rainfall rate, and A and b are constants.[105] Satellite-derived rainfall estimates use passive microwave instruments aboard polar orbiting as well as geostationary weather satellites to indirectly measure rainfall rates.[106] If one wants an accumulated rainfall over a time period, one has to add up all the accumulations from each grid box within the images during that time.
1988 rain in the U.S. The heaviest rain is seen in reds and yellows.
1993 rain in the U.S.

Intensity

Heavy rain in Zapopan
 
Heavy rain in Glenshaw, Pennsylvania
The sound of heavy rainfall in a suburban neighborhood
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Rainfall intensity is classified according to the rate of precipitation, which depends on the considered time.[107] The following categories are used to classify rainfall intensity:

  • Light rain — when the precipitation rate is < 2.5 mm (0.098 in) per hour
  • Moderate rain — when the precipitation rate is between 2.5 mm (0.098 in) – 7.6 mm (0.30 in) or 10 mm (0.39 in) per hour[108][109]
  • Heavy rain — when the precipitation rate is > 7.6 mm (0.30 in) per hour,[108] or between 10 mm (0.39 in) and 50 mm (2.0 in) per hour[109]
  • Violent rain — when the precipitation rate is > 50 mm (2.0 in) per hour[109]

Euphemisms for a heavy or violent rain include gully washer, trash-mover and toad-strangler.[110] The intensity can also be expressed by rainfall erosivity R-factor[111] or in terms of the rainfall time-structure n-index.[107]

Return period

See also: 100-year flood

The average time between occurrences of an event with a specified intensity and duration is called the return period.[112] The intensity of a storm can be predicted for any return period and storm duration, from charts based on historic data for the location.[113] The return period is often expressed as an n-year event. For instance, a 10-year storm describes a rare rainfall event occurring on average once every 10 years. The rainfall will be greater and the flooding will be worse than the worst storm expected in any single year. A 100-year storm describes an extremely rare rainfall event occurring on average once in a century. The rainfall will be extreme and flooding worse than a 10-year event. The probability of an event in any year is the inverse of the return period (assuming the probability remains the same for each year).[112] For instance, a 10-year storm has a probability of occurring of 10 percent in any given year, and a 100-year storm occurs with a 1 percent probability in a year. As with all probability events, it is possible, though improbable, to have multiple 100-year storms in a single year.[114]

Forecasting

Main article: Quantitative precipitation forecast
 
Example of a five-day rainfall forecast from the Hydrometeorological Prediction Center

The Quantitative Precipitation Forecast (abbreviated QPF) is the expected amount of liquid precipitation accumulated over a specified time period over a specified area.[115] A QPF will be specified when a measurable precipitation type reaching a minimum threshold is forecast for any hour during a QPF valid period. Precipitation forecasts tend to be bound by synoptic hours such as 0000, 0600, 1200 and 1800 GMT. Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail.[116] Starting in the mid to late 1990s, QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States.[117]

Forecast models show significant sensitivity to humidity levels within the planetary boundary layer, or in the lowest levels of the atmosphere, which decreases with height.[118] QPF can be generated on a quantitative, forecasting amounts, or a qualitative, forecasting the probability of a specific amount, basis.[119] Radar imagery forecasting techniques show higher skill than model forecasts within 6 to 7 hours of the time of the radar image. The forecasts can be verified through use of rain gauge measurements, weather radar estimates, or a combination of both. Various skill scores can be determined to measure the value of the rainfall forecast.[120]

Impact

Agricultural

 
Rainfall estimates for southern Japan and the surrounding region from 20–27 July 2009.

Precipitation, especially rain, has a dramatic effect on agriculture. All plants need at least some water to survive, therefore rain (being the most effective means of watering) is important to agriculture. While a regular rain pattern is usually vital to healthy plants, too much or too little rainfall can be harmful, even devastating to crops. Drought can kill crops and increase erosion,[121] while overly wet weather can cause harmful fungus growth.[122] Plants need varying amounts of rainfall to survive. For example, certain cacti require small amounts of water,[123] while tropical plants may need up to hundreds of inches of rain per year to survive.

In areas with wet and dry seasons, soil nutrients diminish and erosion increases during the wet season.[27] Animals have adaptation and survival strategies for the wetter regime. The previous dry season leads to food shortages into the wet season, as the crops have yet to mature.[124] Developing countries have noted that their populations show seasonal weight fluctuations due to food shortages seen before the first harvest, which occurs late in the wet season.[125] Rain may be harvested through the use of rainwater tanks; treated to potable use or for non-potable use indoors or for irrigation.[126] Excessive rain during short periods of time can cause flash floods.[127]

Culture and religion

See also: List of rain deities
 
A rain dance being performed in Harar, Ethiopia

Cultural attitudes towards rain differ across the world. In temperate climates, people tend to be more stressed when the weather is unstable or cloudy, with its impact greater on men than women.[128] Rain can also bring joy, as some consider it to be soothing or enjoy the aesthetic appeal of it. In dry places, such as India,[129] or during periods of drought,[130] rain lifts people's moods. In Botswana, the Setswana word for rain, pula, is used as the name of the national currency, in recognition of the economic importance of rain in its country, since it has a desert climate.[131] Several cultures have developed means of dealing with rain and have developed numerous protection devices such as umbrellas and raincoats, and diversion devices such as gutters and storm drains that lead rains to sewers.[132] Many people find the scent during and immediately after rain pleasant or distinctive. The source of this scent is petrichor, an oil produced by plants, then absorbed by rocks and soil, and later released into the air during rainfall.[133]

 
Rain, depicted in the 1493 Nuremberg Chronicle

Rain holds an important religious significance in many cultures.[134] The ancient Sumerians believed that rain was the semen of the sky god An,[135] which fell from the heavens to inseminate his consort, the earth goddess Ki,[135] causing her to give birth to all the plants of the earth.[135] The Akkadians believed that the clouds were the breasts of Anu's consort Antu[135] and that rain was milk from her breasts.[135] According to Jewish tradition, in the first century BC, the Jewish miracle-worker Honi ha-M'agel ended a three-year drought in Judaea by drawing a circle in the sand and praying for rain, refusing to leave the circle until his prayer was granted.[136] In his Meditations, the Roman emperor Marcus Aurelius preserves a prayer for rain made by the Athenians to the Greek sky god Zeus.[134] Various Native American tribes are known to have historically conducted rain dances in effort to encourage rainfall.[134] Rainmaking rituals are also important in many African cultures.[137] In the present-day United States, various state governors have held Days of Prayer for rain, including the Days of Prayer for Rain in the State of Texas in 2011.[134]

Global climatology

See also: Earth rainfall climatology

Approximately 505,000 km3 (121,000 cu mi) of water falls as precipitation each year across the globe with 398,000 km3 (95,000 cu mi) of it over the oceans.[138] Given the Earth's surface area, that means the globally averaged annual precipitation is 990 mm (39 in). Deserts are defined as areas with an average annual precipitation of less than 250 mm (10 in) per year,[139][140] or as areas where more water is lost by evapotranspiration than falls as precipitation.[141]

Deserts

Main article: Desert
 
Largest deserts
 
Isolated towering vertical desert shower

The northern half of Africa is dominated by the world's most extensive hot, dry region, the Sahara Desert. Some deserts also occupy much of southern Africa: the Namib and the Kalahari. Across Asia, a large annual rainfall minimum, composed primarily of deserts, stretches from the Gobi Desert in Mongolia west-southwest through western Pakistan (Balochistan) and Iran into the Arabian Desert in Saudi Arabia. Most of Australia is semi-arid or desert,[142] making it the world's driest inhabited continent. In South America, the Andes mountain range blocks Pacific moisture that arrives in that continent, resulting in a desert-like climate just downwind across western Argentina.[48] The drier areas of the United States are regions where the Sonoran Desert overspreads the Desert Southwest, the Great Basin and central Wyoming.[143]

Polar deserts

Main articles: Polar desert and Polar climate

Since rain only falls as liquid, it rarely falls when surface temperatures are below freezing, unless there is a layer of warm air aloft, in which case it becomes freezing rain. Due to the entire atmosphere being below freezing most of the time, very cold climates see very little rainfall and are often known as polar deserts. A common biome in this area is the tundra which has a short summer thaw and a long frozen winter. Ice caps see no rain at all, making Antarctica the world's driest continent.

Rainforests

See also: Rainforest

Rainforests are areas of the world with very high rainfall. Both tropical and temperate rainforests exist. Tropical rainforests occupy a large band of the planet mostly along the equator. Most temperate rainforests are located on mountainous west coasts between 45 and 55 degrees latitude, but they are often found in other areas.

Around 40–75% of all biotic life is found in rainforests. Rainforests are also responsible for 28% of the world's oxygen turnover.

Monsoons

See also: Monsoon and Monsoon trough

The equatorial region near the Intertropical Convergence Zone (ITCZ), or monsoon trough, is the wettest portion of the world's continents. Annually, the rain belt within the tropics marches northward by August, then moves back southward into the Southern Hemisphere by February and March.[144] Within Asia, rainfall is favored across its southern portion from India east and northeast across the Philippines and southern China into Japan due to the monsoon advecting moisture primarily from the Indian Ocean into the region.[145] The monsoon trough can reach as far north as the 40th parallel in East Asia during August before moving southward thereafter. Its poleward progression is accelerated by the onset of the summer monsoon which is characterized by the development of lower air pressure (a thermal low) over the warmest part of Asia.[146][147] Similar, but weaker, monsoon circulations are present over North America and Australia.[148][149] During the summer, the Southwest monsoon combined with Gulf of California and Gulf of Mexico moisture moving around the subtropical ridge in the Atlantic Ocean bring the promise of afternoon and evening thunderstorms to the southern tier of the United States as well as the Great Plains.[150] The eastern half of the contiguous United States east of the 98th meridian, the mountains of the Pacific Northwest, and the Sierra Nevada range are the wetter portions of the nation, with average rainfall exceeding 760 mm (30 in) per year.[151] Tropical cyclones enhance precipitation across southern sections of the United States,[152] as well as Puerto Rico, the United States Virgin Islands,[153] the Northern Mariana Islands,[154] Guam, and American Samoa.

Impact of the Westerlies

See also: Westerlies
 
Long-term mean precipitation by month

Westerly flow from the mild north Atlantic leads to wetness across western Europe, in particular Ireland and the United Kingdom, where the western coasts can receive between 1,000 mm (39 in), at sea level and 2,500 mm (98 in), on the mountains of rain per year. Bergen, Norway is one of the more famous European rain-cities with its yearly precipitation of 2,250 mm (89 in) on average. During the fall, winter, and spring, Pacific storm systems bring most of Hawaii and the western United States much of their precipitation.[150] Over the top of the ridge, the jet stream brings a summer precipitation maximum to the Great Lakes. Large thunderstorm areas known as mesoscale convective complexes move through the Plains, Midwest, and Great Lakes during the warm season, contributing up to 10% of the annual precipitation to the region.[155]

The El Niño-Southern Oscillation affects the precipitation distribution, by altering rainfall patterns across the western United States,[156] Midwest,[157][158] the Southeast,[159] and throughout the tropics. There is also evidence that global warming is leading to increased precipitation to the eastern portions of North America, while droughts are becoming more frequent in the tropics and subtropics.

Wettest known locations

Cherrapunji, situated on the southern slopes of the Eastern Himalaya in Shillong, India is the confirmed wettest place on Earth, with an average annual rainfall of 11,430 mm (450 in). The highest recorded rainfall in a single year was 22,987 mm (905.0 in) in 1861. The 38-year average at nearby Mawsynram, Meghalaya, India is 11,873 mm (467.4 in).[160] The wettest spot in Australia is Mount Bellenden Ker in the north-east of the country which records an average of 8,000 mm (310 in) per year, with over 12,200 mm (480.3 in) of rain recorded during 2000.[161] The Big Bog on the island of Maui has the highest average annual rainfall in the Hawaiian Islands, at 10,300 mm (404 in).[162] Mount Waiʻaleʻale on the island of Kauaʻi achieves similar torrential rains, while slightly lower than that of the Big Bog, at 9,500 mm (373 in)[163] of rain per year over the last 32 years, with a record 17,340 mm (683 in) in 1982. Its summit is considered one of the rainiest spots on earth, with a reported 350 days of rain per year.

Lloró, a town situated in Chocó, Colombia, is probably the place with the largest rainfall in the world, averaging 13,300 mm (523.6 in) per year.[164] The Department of Chocó is extraordinarily humid. Tutunendaó, a small town situated in the same department, is one of the wettest estimated places on Earth, averaging 11,394 mm (448.6 in) per year; in 1974 the town received 26,303 mm (86 ft 3.6 in), the largest annual rainfall measured in Colombia. Unlike Cherrapunji, which receives most of its rainfall between April and September, Tutunendaó receives rain almost uniformly distributed throughout the year.[165] Quibdó, the capital of Chocó, receives the most rain in the world among cities with over 100,000 inhabitants: 9,000 mm (354 in) per year.[164] Storms in Chocó can drop 500 mm (20 in) of rainfall in a day. This amount is more than what falls in many cities in a year's time.

Continent Highest average Place Elevation Years of record
in mm ft m
 South America  523.6 13,299   Lloró, Colombia (estimated)[a][b]  520 158[c]   29 
 Asia  467.4 11,872   Mawsynram, India[a][d]  4,597 1,401   39 
 Africa  405.0 10,287   Debundscha, Cameroon  30 9.1   32 
 Oceania  404.3 10,269   Big Bog, Maui, Hawaii (USA)[a]  5,148 1,569   30 
 South America  354.0 8,992   Quibdo, Colombia  120 36.6   16 
 Australia  340.0 8,636   Mount Bellenden Ker, Queensland  5,102 1,555   9 
 North America  256.0 6,502   Hucuktlis Lake, British Columbia  12 3.66   14 
 Europe  183.0 4,648   Crkvice, Montenegro  3,337 1,017   22 
Source (without conversions): Global Measured Extremes of Temperature and Precipitation, National Climatic Data Center. 9 August 2004.[166]
Continent Place Highest rainfall
in mm
Highest average annual rainfall[167]  Asia  Mawsynram, India 467.4 11,870 
Highest in one year[167]  Asia  Cherrapunji, India 1,042 26,470 
Highest in one calendar month[168]  Asia  Cherrapunji, India 366 9,296
Highest in 24 hours[167]  Indian Ocean  Foc Foc, La Réunion 71.8 1,820
Highest in 12 hours[167]  Indian Ocean  Foc Foc, La Réunion 45.0 1,140
Highest in one minute[167]  North America  Unionville, Maryland, USA 1.23 31.2

Outside Earth

Rainfalls of diamonds have been suggested to occur on the gas giant planets, Jupiter and Saturn,[169] as well as on the ice giant planets, Uranus and Neptune.[170] There is likely to be rain of various compositions in the upper atmospheres of the gas giants, as well as precipitation of liquid neon in the deep atmospheres.[171][172] On Titan, Saturn's largest natural satellite, infrequent methane rain is thought to carve the moon's numerous surface channels.[173] On Venus, sulfuric acid virga evaporates 25 km (16 mi) from the surface.[174] Extrasolar planet OGLE-TR-56b in the constellation Sagittarius is hypothesized to have iron rain.[175] Accordingly, research carried out by the European Southern Observatory shows that WASP-76b can produce showers of burning liquid iron droplets once temperature decreases during the planet's night hours.[176] There is evidence from samples of basalt brought back by the Apollo missions that the Moon has been subject to lava rain.[177]

See also

Notes

  • a b c The value given is the continent's highest, and possibly the world's, depending on measurement practices, procedures and period of record variations.
  • ^ The official greatest average annual precipitation for South America is 900 cm (354 in) at Quibdó, Colombia. The 1,330 cm (523.6 in) average at Lloró [23 km (14 mi) SE and at a higher elevation than Quibdó] is an estimated amount.
  • ^ Approximate elevation.
  • ^ Recognized as "The Wettest place on Earth" by the Guinness Book of World Records.[178]
  • ^ This is the highest figure for which records are available. The summit of Mount Snowdon, about 500 yards (460 m) from Glaslyn, is estimated to have at least 200.0 inches (5,080 mm) per year.

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External links

 
Wikiquote has quotations related to Rain.
 
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  • BBC article on the weekend rain effect
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  • BBC article on the mathematics of running in the rain
  • What are clouds, and why does it rain?

April 06, 2023
rain, several, terms, redirect, here, other, uses, disambiguation, disambiguation, fall, disambiguation, water, disambiguation, water, droplets, that, have, condensed, from, atmospheric, water, vapor, then, fall, under, gravity, major, component, water, cycle,. Several terms redirect here For other uses see Rain disambiguation Rainy disambiguation Rainfall disambiguation and Rainwater disambiguation Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth It provides water for hydroelectric power plants crop irrigation and suitable conditions for many types of ecosystems Heavy rainfall on a roof Rain source source Typical sound of rain with thunder Problems playing this file See media help source source source source source source source source source source source source source source Rain falling on a road The major cause of rain production is moisture moving along three dimensional zones of temperature and moisture contrasts known as weather fronts If enough moisture and upward motion is present precipitation falls from convective clouds those with strong upward vertical motion such as cumulonimbus thunder clouds which can organize into narrow rainbands In mountainous areas heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains On the leeward side of mountains desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass The movement of the monsoon trough or intertropical convergence zone brings rainy seasons to savannah climes The urban heat island effect leads to increased rainfall both in amounts and intensity downwind of cities Global warming is also causing changes in the precipitation pattern globally including wetter conditions across eastern North America and drier conditions in the tropics Antarctica is the driest continent The globally averaged annual precipitation over land is 715 mm 28 1 in but over the whole Earth it is much higher at 990 mm 39 in 1 Climate classification systems such as the Koppen classification system use average annual rainfall to help differentiate between differing climate regimes Rainfall is measured using rain gauges Rainfall amounts can be estimated by weather radar Rain is also known or suspected on other planets where it may be composed of methane neon sulfuric acid or even iron rather than water Contents 1 Formation 1 1 Water saturated air 1 2 Coalescence and fragmentation 1 3 Droplet size distribution 1 4 Raindrop impacts 1 5 Virga 2 Causes 2 1 Frontal activity 2 2 Convection 2 3 Orographic effects 2 4 Within the tropics 2 5 Human influence 3 Characteristics 3 1 Patterns 3 2 Acidity 3 3 Koppen climate classification 3 4 Pollution 4 Measurement 4 1 Gauges 4 2 Remote sensing 4 3 Intensity 4 4 Return period 5 Forecasting 6 Impact 6 1 Agricultural 6 2 Culture and religion 7 Global climatology 7 1 Deserts 7 2 Polar deserts 7 3 Rainforests 7 4 Monsoons 7 5 Impact of the Westerlies 7 6 Wettest known locations 8 Outside Earth 9 See also 10 Notes 11 References 12 External linksFormationWater saturated air Rain falling on a field in southern Estonia Air contains water vapor and the amount of water in a given mass of dry air known as the mixing ratio is measured in grams of water per kilogram of dry air g kg 2 3 The amount of moisture in the air is also commonly reported as relative humidity which is the percentage of the total water vapor air can hold at a particular air temperature 4 How much water vapor a parcel of air can contain before it becomes saturated 100 relative humidity and forms into a cloud a group of visible and tiny water and ice particles suspended above the Earth s surface 5 depends on its temperature Warmer air can contain more water vapor than cooler air before becoming saturated Therefore one way to saturate a parcel of air is to cool it The dew point is the temperature to which a parcel must be cooled in order to become saturated 6 Streets in Tampere Finland watered by night rain There are four main mechanisms for cooling the air to its dew point adiabatic cooling conductive cooling radiational cooling and evaporative cooling Adiabatic cooling occurs when air rises and expands 7 The air can rise due to convection large scale atmospheric motions or a physical barrier such as a mountain orographic lift Conductive cooling occurs when the air comes into contact with a colder surface 8 usually by being blown from one surface to another for example from a liquid water surface to colder land Radiational cooling occurs due to the emission of infrared radiation either by the air or by the surface underneath 9 Evaporative cooling occurs when moisture is added to the air through evaporation which forces the air temperature to cool to its wet bulb temperature or until it reaches saturation 10 The main ways water vapor is added to the air are wind convergence into areas of upward motion 11 precipitation or virga falling from above 12 daytime heating evaporating water from the surface of oceans water bodies or wet land 13 transpiration from plants 14 cool or dry air moving over warmer water 15 and lifting air over mountains 16 Water vapor normally begins to condense on condensation nuclei such as dust ice and salt in order to form clouds Elevated portions of weather fronts which are three dimensional in nature 17 force broad areas of upward motion within the Earth s atmosphere which form clouds decks such as altostratus or cirrostratus 18 Stratus is a stable cloud deck which tends to form when a cool stable air mass is trapped underneath a warm air mass It can also form due to the lifting of advection fog during breezy conditions 19 Coalescence and fragmentation The shape of raindrops depending upon their size Coalescence occurs when water droplets fuse to create larger water droplets Air resistance typically causes the water droplets in a cloud to remain stationary When air turbulence occurs water droplets collide producing larger droplets Black Rain Clouds As these larger water droplets descend coalescence continues so that drops become heavy enough to overcome air resistance and fall as rain Coalescence generally happens most often in clouds above freezing and is also known as the warm rain process 20 In clouds below freezing when ice crystals gain enough mass they begin to fall This generally requires more mass than coalescence when occurring between the crystal and neighboring water droplets This process is temperature dependent as supercooled water droplets only exist in a cloud that is below freezing In addition because of the great temperature difference between cloud and ground level these ice crystals may melt as they fall and become rain 21 Raindrops have sizes ranging from 0 1 to 9 mm 0 0039 to 0 3543 in mean diameter but develop a tendency to break up at larger sizes Smaller drops are called cloud droplets and their shape is spherical As a raindrop increases in size its shape becomes more oblate with its largest cross section facing the oncoming airflow Large rain drops become increasingly flattened on the bottom like hamburger buns very large ones are shaped like parachutes 22 23 Contrary to popular belief their shape does not resemble a teardrop 24 The biggest raindrops on Earth were recorded over Brazil and the Marshall Islands in 2004 some of them were as large as 10 mm 0 39 in The large size is explained by condensation on large smoke particles or by collisions between drops in small regions with particularly high content of liquid water 25 Raindrops associated with melting hail tend to be larger than other raindrops 26 A raindrop on a leaf Intensity and duration of rainfall are usually inversely related i e high intensity storms are likely to be of short duration and low intensity storms can have a long duration 27 28 Droplet size distribution Main article Raindrop size distribution The final droplet size distribution is an exponential distribution The number of droplets with diameter between d displaystyle d and D d D displaystyle D dD per unit volume of space is n d n 0 e d d d D displaystyle n d n 0 e d langle d rangle dD This is commonly referred to as the Marshall Palmer law after the researchers who first characterized it 23 29 The parameters are somewhat temperature dependent 30 and the slope also scales with the rate of rainfall d 1 41 R 0 21 displaystyle langle d rangle 1 41R 0 21 d in centimeters and R in millimeters per hour 23 Deviations can occur for small droplets and during different rainfall conditions The distribution tends to fit averaged rainfall while instantaneous size spectra often deviate and have been modeled as gamma distributions 31 The distribution has an upper limit due to droplet fragmentation 23 Raindrop impacts Raindrops impact at their terminal velocity which is greater for larger drops due to their larger mass to drag ratio At sea level and without wind 0 5 mm 0 020 in drizzle impacts at 2 m s 6 6 ft s or 7 2 km h 4 5 mph while large 5 mm 0 20 in drops impact at around 9 m s 30 ft s or 32 km h 20 mph 32 Rain falling on loosely packed material such as newly fallen ash can produce dimples that can be fossilized called raindrop impressions 33 The air density dependence of the maximum raindrop diameter together with fossil raindrop imprints has been used to constrain the density of the air 2 7 billion years ago 34 The sound of raindrops hitting water is caused by bubbles of air oscillating underwater 35 36 The METAR code for rain is RA while the coding for rain showers is SHRA 37 Virga Main article Virga In certain conditions precipitation may fall from a cloud but then evaporate or sublime before reaching the ground This is termed virga and is more often seen in hot and dry climates CausesFrontal activity Main article Weather fronts Stratiform a broad shield of precipitation with a relatively similar intensity and dynamic precipitation convective precipitation which is showery in nature with large changes in intensity over short distances occur as a consequence of slow ascent of air in synoptic systems on the order of cm s such as in the vicinity of cold fronts and near and poleward of surface warm fronts Similar ascent is seen around tropical cyclones outside the eyewall and in comma head precipitation patterns around mid latitude cyclones 38 A wide variety of weather can be found along an occluded front with thunderstorms possible but usually their passage is associated with a drying of the air mass Occluded fronts usually form around mature low pressure areas 39 What separates rainfall from other precipitation types such as ice pellets and snow is the presence of a thick layer of air aloft which is above the melting point of water which melts the frozen precipitation well before it reaches the ground If there is a shallow near surface layer that is below freezing freezing rain rain which freezes on contact with surfaces in subfreezing environments will result 40 Hail becomes an increasingly infrequent occurrence when the freezing level within the atmosphere exceeds 3 400 m 11 000 ft above ground level 41 Convection Convective precipitation Orographic precipitation Convective rain or showery precipitation occurs from convective clouds e g cumulonimbus or cumulus congestus It falls as showers with rapidly changing intensity Convective precipitation falls over a certain area for a relatively short time as convective clouds have limited horizontal extent Most precipitation in the tropics appears to be convective however it has been suggested that stratiform precipitation also occurs 38 42 Graupel and hail indicate convection 43 In mid latitudes convective precipitation is intermittent and often associated with baroclinic boundaries such as cold fronts squall lines and warm fronts 44 Orographic effects Main articles Orographic lift Precipitation types meteorology and United States rainfall climatology Orographic precipitation occurs on the windward side of mountains and is caused by the rising air motion of a large scale flow of moist air across the mountain ridge resulting in adiabatic cooling and condensation In mountainous parts of the world subjected to relatively consistent winds for example the trade winds a more moist climate usually prevails on the windward side of a mountain than on the leeward or downwind side Moisture is removed by orographic lift leaving drier air see katabatic wind on the descending and generally warming leeward side where a rain shadow is observed 16 In Hawaii Mount Waiʻaleʻale on the island of Kauai is notable for its extreme rainfall as it is amongst the places in the world with the highest levels of rainfall with 9 500 mm 373 in 45 Systems known as Kona storms affect the state with heavy rains between October and April 46 Local climates vary considerably on each island due to their topography divisible into windward Koʻolau and leeward Kona regions based upon location relative to the higher mountains Windward sides face the east to northeast trade winds and receive much more rainfall leeward sides are drier and sunnier with less rain and less cloud cover 47 In South America the Andes mountain range blocks Pacific moisture that arrives in that continent resulting in a desert like climate just downwind across western Argentina 48 The Sierra Nevada range creates the same effect in North America forming the Great Basin and Mojave Deserts 49 50 Within the tropics Rainfall distribution by month in Cairns showing the extent of the wet season at that location See also Monsoon and Tropical cyclone Main article Wet season The wet or rainy season is the time of year covering one or more months when most of the average annual rainfall in a region falls 51 The term green season is also sometimes used as a euphemism by tourist authorities 52 Areas with wet seasons are dispersed across portions of the tropics and subtropics 53 Savanna climates and areas with monsoon regimes have wet summers and dry winters Tropical rainforests technically do not have dry or wet seasons since their rainfall is equally distributed through the year 54 Some areas with pronounced rainy seasons will see a break in rainfall mid season when the intertropical convergence zone or monsoon trough move poleward of their location during the middle of the warm season 27 When the wet season occurs during the warm season or summer rain falls mainly during the late afternoon and early evening hours The wet season is a time when air quality improves 55 freshwater quality improves 56 57 and vegetation grows significantly Tropical cyclones a source of very heavy rainfall consist of large air masses several hundred miles across with low pressure at the centre and with winds blowing inward towards the centre in either a clockwise direction southern hemisphere or counterclockwise northern hemisphere 58 Although cyclones can take an enormous toll in lives and personal property they may be important factors in the precipitation regimes of places they impact as they may bring much needed precipitation to otherwise dry regions 59 Areas in their path can receive a year s worth of rainfall from a tropical cyclone passage 60 Human influence Image of Atlanta US showing temperature distribution with blue showing cool temperatures red warm and hot areas appearing white Average surface air temperatures from 2011 to 2020 compared to the 1951 1980 average Source NASA See also Global warming and Urban heat island The fine particulate matter produced by car exhaust and other human sources of pollution forms cloud condensation nuclei leads to the production of clouds and increases the likelihood of rain As commuters and commercial traffic cause pollution to build up over the course of the week the likelihood of rain increases it peaks by Saturday after five days of weekday pollution has been built up In heavily populated areas that are near the coast such as the United States Eastern Seaboard the effect can be dramatic there is a 22 higher chance of rain on Saturdays than on Mondays 61 The urban heat island effect warms cities 0 6 to 5 6 C 1 1 to 10 1 F above surrounding suburbs and rural areas This extra heat leads to greater upward motion which can induce additional shower and thunderstorm activity Rainfall rates downwind of cities are increased between 48 and 116 Partly as a result of this warming monthly rainfall is about 28 greater between 32 to 64 km 20 to 40 mi downwind of cities compared with upwind 62 Some cities induce a total precipitation increase of 51 63 Increasing temperatures tend to increase evaporation which can lead to more precipitation Precipitation generally increased over land north of 30 N from 1900 through 2005 but has declined over the tropics since the 1970s Globally there has been no statistically significant overall trend in precipitation over the past century although trends have varied widely by region and over time Eastern portions of North and South America northern Europe and northern and central Asia have become wetter The Sahel the Mediterranean southern Africa and parts of southern Asia have become drier There has been an increase in the number of heavy precipitation events over many areas during the past century as well as an increase since the 1970s in the prevalence of droughts especially in the tropics and subtropics Changes in precipitation and evaporation over the oceans are suggested by the decreased salinity of mid and high latitude waters implying more precipitation along with increased salinity in lower latitudes implying less precipitation and or more evaporation Over the contiguous United States total annual precipitation increased at an average rate of 6 1 percent since 1900 with the greatest increases within the East North Central climate region 11 6 percent per century and the South 11 1 percent Hawaii was the only region to show a decrease 9 25 percent 64 Analysis of 65 years of United States of America rainfall records show the lower 48 states have an increase in heavy downpours since 1950 The largest increases are in the Northeast and Midwest which in the past decade have seen 31 and 16 percent more heavy downpours compared to the 1950s Rhode Island is the state with the largest increase 104 McAllen Texas is the city with the largest increase 700 Heavy downpour in the analysis are the days where total precipitation exceeded the top one percent of all rain and snow days during the years 1950 2014 65 66 The most successful attempts at influencing weather involve cloud seeding which include techniques used to increase winter precipitation over mountains and suppress hail 67 CharacteristicsPatterns Band of thunderstorms seen on a weather radar display Main article Rainband Rainbands are cloud and precipitation areas which are significantly elongated Rainbands can be stratiform or convective 68 and are generated by differences in temperature When noted on weather radar imagery this precipitation elongation is referred to as banded structure 69 Rainbands in advance of warm occluded fronts and warm fronts are associated with weak upward motion 70 and tend to be wide and stratiform in nature 71 Rainbands spawned near and ahead of cold fronts can be squall lines which are able to produce tornadoes 72 Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front s orientation due to the formation of a low level barrier jet 73 Bands of thunderstorms can form with sea breeze and land breeze boundaries if enough moisture is present If sea breeze rainbands become active enough just ahead of a cold front they can mask the location of the cold front itself 74 Once a cyclone occludes an occluded front a trough of warm air aloft will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast and ultimately northwestern periphery also termed the warm conveyor belt forcing a surface trough to continue into the cold sector on a similar curve to the occluded front The front creates the portion of an occluded cyclone known as its comma head due to the comma like shape of the mid tropospheric cloudiness that accompanies the feature It can also be the focus of locally heavy precipitation with thunderstorms possible if the atmosphere along the front is unstable enough for convection 75 Banding within the comma head precipitation pattern of an extratropical cyclone can yield significant amounts of rain 76 Behind extratropical cyclones during fall and winter rainbands can form downwind of relative warm bodies of water such as the Great Lakes Downwind of islands bands of showers and thunderstorms can develop due to low level wind convergence downwind of the island edges Offshore California this has been noted in the wake of cold fronts 77 Rainbands within tropical cyclones are curved in orientation Tropical cyclone rainbands contain showers and thunderstorms that together with the eyewall and the eye constitute a hurricane or tropical storm The extent of rainbands around a tropical cyclone can help determine the cyclone s intensity 78 Acidity Sources of acid rain See also Acid rain The phrase acid rain was first used by Scottish chemist Robert Augus Smith in 1852 79 The pH of rain varies especially due to its origin On America s East Coast rain that is derived from the Atlantic Ocean typically has a pH of 5 0 5 6 rain that comes across the continental from the west has a pH of 3 8 4 8 and local thunderstorms can have a pH as low as 2 0 80 Rain becomes acidic primarily due to the presence of two strong acids sulfuric acid H2SO4 and nitric acid HNO3 Sulfuric acid is derived from natural sources such as volcanoes and wetlands sulfate reducing bacteria and anthropogenic sources such as the combustion of fossil fuels and mining where H2S is present Nitric acid is produced by natural sources such as lightning soil bacteria and natural fires while also produced anthropogenically by the combustion of fossil fuels and from power plants In the past 20 years the concentrations of nitric and sulfuric acid has decreased in presence of rainwater which may be due to the significant increase in ammonium most likely as ammonia from livestock production which acts as a buffer in acid rain and raises the pH 81 Koppen climate classification Updated Koppen Geiger climate map 82 Af Am Aw BWh BWk BSh BSk Csa Csb Cwa Cwb Cfa Cfb Cfc Dsa Dsb Dsc Dsd Dwa Dwb Dwc Dwd Dfa Dfb Dfc Dfd ET EF Main article Koppen climate classification The Koppen classification depends on average monthly values of temperature and precipitation The most commonly used form of the Koppen classification has five primary types labeled A through E Specifically the primary types are A tropical B dry C mild mid latitude D cold mid latitude and E polar The five primary classifications can be further divided into secondary classifications such as rain forest monsoon tropical savanna humid subtropical humid continental oceanic climate Mediterranean climate steppe subarctic climate tundra polar ice cap and desert Rain forests are characterized by high rainfall with definitions setting minimum normal annual rainfall between 1 750 and 2 000 mm 69 and 79 in 83 A tropical savanna is a grassland biome located in semi arid to semi humid climate regions of subtropical and tropical latitudes with rainfall between 750 and 1 270 mm 30 and 50 in a year They are widespread on Africa and are also found in India the northern parts of South America Malaysia and Australia 84 The humid subtropical climate zone is where winter rainfall is associated with large storms that the westerlies steer from west to east Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones 85 Humid subtropical climates lie on the east side continents roughly between latitudes 20 and 40 degrees away from the equator 86 An oceanic or maritime climate is typically found along the west coasts at the middle latitudes of all the world s continents bordering cool oceans as well as southeastern Australia and is accompanied by plentiful precipitation year round 87 The Mediterranean climate regime resembles the climate of the lands in the Mediterranean Basin parts of western North America parts of Western and South Australia in southwestern South Africa and in parts of central Chile The climate is characterized by hot dry summers and cool wet winters 88 A steppe is a dry grassland 89 Subarctic climates are cold with continuous permafrost and little precipitation 90 Pollution This section needs expansion You can help by adding to it October 2022 This section is an excerpt from Per and polyfluoroalkyl substances Prevalence in rainwater edit In 2022 it was found that levels of at least four perfluoroalkyl acids PFAAs in rainwater worldwide ubiquitously and often greatly exceeded the EPA s lifetime drinking water health advisories as well as comparable Danish Dutch and European Union safety standards leading researchers to conclude that the global spread of these four PFAAs in the atmosphere has led to the planetary boundary for chemical pollution being exceeded 91 There are some moves to restrict and replace their use 92 MeasurementSee also Precipitation Rate Gauges See also Rain gauge Disdrometer and Snow gauge Standard rain gauge Rain is measured in units of length per unit time typically in millimeters per hour 93 or in countries where imperial units are more common inches per hour 94 The length or more accurately depth being measured is the depth of rain water that would accumulate on a flat horizontal and impermeable surface during a given amount of time typically an hour 95 One millimeter of rainfall is the equivalent of one liter of water per square meter 96 The standard way of measuring rainfall or snowfall is the standard rain gauge which can be found in 100 mm 4 in plastic and 200 mm 8 in metal varieties 97 The inner cylinder is filled by 25 mm 0 98 in of rain with overflow flowing into the outer cylinder Plastic gauges have markings on the inner cylinder down to 0 25 mm 0 0098 in resolution while metal gauges require use of a stick designed with the appropriate 0 25 mm 0 0098 in markings After the inner cylinder is filled the amount inside it is discarded then filled with the remaining rainfall in the outer cylinder until all the fluid in the outer cylinder is gone adding to the overall total until the outer cylinder is empty 98 Other types of gauges include the popular wedge gauge the cheapest rain gauge and most fragile the tipping bucket rain gauge and the weighing rain gauge 99 For those looking to measure rainfall the most inexpensively a can that is cylindrical with straight sides will act as a rain gauge if left out in the open but its accuracy will depend on what ruler is used to measure the rain with Any of the above rain gauges can be made at home with enough know how 100 When a precipitation measurement is made various networks exist across the United States and elsewhere where rainfall measurements can be submitted through the Internet such as CoCoRAHS or GLOBE 101 102 If a network is not available in the area where one lives the nearest local weather or met office will likely be interested in the measurement 103 Remote sensing See also Weather radar Twenty four hour rainfall accumulation on the Val d Irene radar in Eastern Canada Zones without data in the east and southwest are caused by beam blocking from mountains Source Environment Canada One of the main uses of weather radar is to be able to assess the amount of precipitations fallen over large basins for hydrological purposes 104 For instance river flood control sewer management and dam construction are all areas where planners use rainfall accumulation data Radar derived rainfall estimates complement surface station data which can be used for calibration To produce radar accumulations rain rates over a point are estimated by using the value of reflectivity data at individual grid points A radar equation is then used which isZ A R b displaystyle Z AR b where Z represents the radar reflectivity R represents the rainfall rate and A and b are constants 105 Satellite derived rainfall estimates use passive microwave instruments aboard polar orbiting as well as geostationary weather satellites to indirectly measure rainfall rates 106 If one wants an accumulated rainfall over a time period one has to add up all the accumulations from each grid box within the images during that time source source source source source source source source source source 1988 rain in the U S The heaviest rain is seen in reds and yellows source source source source source source source source source source 1993 rain in the U S Intensity source source source source source source source source source source source source source source Heavy rain in Zapopan Heavy rain in Glenshaw Pennsylvania source source The sound of heavy rainfall in a suburban neighborhood Problems playing this file See media help Rainfall intensity is classified according to the rate of precipitation which depends on the considered time 107 The following categories are used to classify rainfall intensity Light rain when the precipitation rate is lt 2 5 mm 0 098 in per hour Moderate rain when the precipitation rate is between 2 5 mm 0 098 in 7 6 mm 0 30 in or 10 mm 0 39 in per hour 108 109 Heavy rain when the precipitation rate is gt 7 6 mm 0 30 in per hour 108 or between 10 mm 0 39 in and 50 mm 2 0 in per hour 109 Violent rain when the precipitation rate is gt 50 mm 2 0 in per hour 109 Euphemisms for a heavy or violent rain include gully washer trash mover and toad strangler 110 The intensity can also be expressed by rainfall erosivity R factor 111 or in terms of the rainfall time structure n index 107 Return period See also 100 year flood The average time between occurrences of an event with a specified intensity and duration is called the return period 112 The intensity of a storm can be predicted for any return period and storm duration from charts based on historic data for the location 113 The return period is often expressed as an n year event For instance a 10 year storm describes a rare rainfall event occurring on average once every 10 years The rainfall will be greater and the flooding will be worse than the worst storm expected in any single year A 100 year storm describes an extremely rare rainfall event occurring on average once in a century The rainfall will be extreme and flooding worse than a 10 year event The probability of an event in any year is the inverse of the return period assuming the probability remains the same for each year 112 For instance a 10 year storm has a probability of occurring of 10 percent in any given year and a 100 year storm occurs with a 1 percent probability in a year As with all probability events it is possible though improbable to have multiple 100 year storms in a single year 114 ForecastingMain article Quantitative precipitation forecast Example of a five day rainfall forecast from the Hydrometeorological Prediction Center The Quantitative Precipitation Forecast abbreviated QPF is the expected amount of liquid precipitation accumulated over a specified time period over a specified area 115 A QPF will be specified when a measurable precipitation type reaching a minimum threshold is forecast for any hour during a QPF valid period Precipitation forecasts tend to be bound by synoptic hours such as 0000 0600 1200 and 1800 GMT Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail 116 Starting in the mid to late 1990s QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States 117 Forecast models show significant sensitivity to humidity levels within the planetary boundary layer or in the lowest levels of the atmosphere which decreases with height 118 QPF can be generated on a quantitative forecasting amounts or a qualitative forecasting the probability of a specific amount basis 119 Radar imagery forecasting techniques show higher skill than model forecasts within 6 to 7 hours of the time of the radar image The forecasts can be verified through use of rain gauge measurements weather radar estimates or a combination of both Various skill scores can be determined to measure the value of the rainfall forecast 120 ImpactAgricultural Rainfall estimates for southern Japan and the surrounding region from 20 27 July 2009 Precipitation especially rain has a dramatic effect on agriculture All plants need at least some water to survive therefore rain being the most effective means of watering is important to agriculture While a regular rain pattern is usually vital to healthy plants too much or too little rainfall can be harmful even devastating to crops Drought can kill crops and increase erosion 121 while overly wet weather can cause harmful fungus growth 122 Plants need varying amounts of rainfall to survive For example certain cacti require small amounts of water 123 while tropical plants may need up to hundreds of inches of rain per year to survive In areas with wet and dry seasons soil nutrients diminish and erosion increases during the wet season 27 Animals have adaptation and survival strategies for the wetter regime The previous dry season leads to food shortages into the wet season as the crops have yet to mature 124 Developing countries have noted that their populations show seasonal weight fluctuations due to food shortages seen before the first harvest which occurs late in the wet season 125 Rain may be harvested through the use of rainwater tanks treated to potable use or for non potable use indoors or for irrigation 126 Excessive rain during short periods of time can cause flash floods 127 Culture and religion See also List of rain deities A rain dance being performed in Harar Ethiopia Cultural attitudes towards rain differ across the world In temperate climates people tend to be more stressed when the weather is unstable or cloudy with its impact greater on men than women 128 Rain can also bring joy as some consider it to be soothing or enjoy the aesthetic appeal of it In dry places such as India 129 or during periods of drought 130 rain lifts people s moods In Botswana the Setswana word for rain pula is used as the name of the national currency in recognition of the economic importance of rain in its country since it has a desert climate 131 Several cultures have developed means of dealing with rain and have developed numerous protection devices such as umbrellas and raincoats and diversion devices such as gutters and storm drains that lead rains to sewers 132 Many people find the scent during and immediately after rain pleasant or distinctive The source of this scent is petrichor an oil produced by plants then absorbed by rocks and soil and later released into the air during rainfall 133 Rain depicted in the 1493 Nuremberg Chronicle Rain holds an important religious significance in many cultures 134 The ancient Sumerians believed that rain was the semen of the sky god An 135 which fell from the heavens to inseminate his consort the earth goddess Ki 135 causing her to give birth to all the plants of the earth 135 The Akkadians believed that the clouds were the breasts of Anu s consort Antu 135 and that rain was milk from her breasts 135 According to Jewish tradition in the first century BC the Jewish miracle worker Honi ha M agel ended a three year drought in Judaea by drawing a circle in the sand and praying for rain refusing to leave the circle until his prayer was granted 136 In his Meditations the Roman emperor Marcus Aurelius preserves a prayer for rain made by the Athenians to the Greek sky god Zeus 134 Various Native American tribes are known to have historically conducted rain dances in effort to encourage rainfall 134 Rainmaking rituals are also important in many African cultures 137 In the present day United States various state governors have held Days of Prayer for rain including the Days of Prayer for Rain in the State of Texas in 2011 134 Global climatologySee also Earth rainfall climatology Approximately 505 000 km3 121 000 cu mi of water falls as precipitation each year across the globe with 398 000 km3 95 000 cu mi of it over the oceans 138 Given the Earth s surface area that means the globally averaged annual precipitation is 990 mm 39 in Deserts are defined as areas with an average annual precipitation of less than 250 mm 10 in per year 139 140 or as areas where more water is lost by evapotranspiration than falls as precipitation 141 Deserts Main article Desert Largest deserts Isolated towering vertical desert shower The northern half of Africa is dominated by the world s most extensive hot dry region the Sahara Desert Some deserts also occupy much of southern Africa the Namib and the Kalahari Across Asia a large annual rainfall minimum composed primarily of deserts stretches from the Gobi Desert in Mongolia west southwest through western Pakistan Balochistan and Iran into the Arabian Desert in Saudi Arabia Most of Australia is semi arid or desert 142 making it the world s driest inhabited continent In South America the Andes mountain range blocks Pacific moisture that arrives in that continent resulting in a desert like climate just downwind across western Argentina 48 The drier areas of the United States are regions where the Sonoran Desert overspreads the Desert Southwest the Great Basin and central Wyoming 143 Polar deserts Main articles Polar desert and Polar climate Since rain only falls as liquid it rarely falls when surface temperatures are below freezing unless there is a layer of warm air aloft in which case it becomes freezing rain Due to the entire atmosphere being below freezing most of the time very cold climates see very little rainfall and are often known as polar deserts A common biome in this area is the tundra which has a short summer thaw and a long frozen winter Ice caps see no rain at all making Antarctica the world s driest continent Rainforests See also Rainforest Rainforests are areas of the world with very high rainfall Both tropical and temperate rainforests exist Tropical rainforests occupy a large band of the planet mostly along the equator Most temperate rainforests are located on mountainous west coasts between 45 and 55 degrees latitude but they are often found in other areas Around 40 75 of all biotic life is found in rainforests Rainforests are also responsible for 28 of the world s oxygen turnover Monsoons See also Monsoon and Monsoon trough The equatorial region near the Intertropical Convergence Zone ITCZ or monsoon trough is the wettest portion of the world s continents Annually the rain belt within the tropics marches northward by August then moves back southward into the Southern Hemisphere by February and March 144 Within Asia rainfall is favored across its southern portion from India east and northeast across the Philippines and southern China into Japan due to the monsoon advecting moisture primarily from the Indian Ocean into the region 145 The monsoon trough can reach as far north as the 40th parallel in East Asia during August before moving southward thereafter Its poleward progression is accelerated by the onset of the summer monsoon which is characterized by the development of lower air pressure a thermal low over the warmest part of Asia 146 147 Similar but weaker monsoon circulations are present over North America and Australia 148 149 During the summer the Southwest monsoon combined with Gulf of California and Gulf of Mexico moisture moving around the subtropical ridge in the Atlantic Ocean bring the promise of afternoon and evening thunderstorms to the southern tier of the United States as well as the Great Plains 150 The eastern half of the contiguous United States east of the 98th meridian the mountains of the Pacific Northwest and the Sierra Nevada range are the wetter portions of the nation with average rainfall exceeding 760 mm 30 in per year 151 Tropical cyclones enhance precipitation across southern sections of the United States 152 as well as Puerto Rico the United States Virgin Islands 153 the Northern Mariana Islands 154 Guam and American Samoa Impact of the Westerlies See also Westerlies Long term mean precipitation by month Westerly flow from the mild north Atlantic leads to wetness across western Europe in particular Ireland and the United Kingdom where the western coasts can receive between 1 000 mm 39 in at sea level and 2 500 mm 98 in on the mountains of rain per year Bergen Norway is one of the more famous European rain cities with its yearly precipitation of 2 250 mm 89 in on average During the fall winter and spring Pacific storm systems bring most of Hawaii and the western United States much of their precipitation 150 Over the top of the ridge the jet stream brings a summer precipitation maximum to the Great Lakes Large thunderstorm areas known as mesoscale convective complexes move through the Plains Midwest and Great Lakes during the warm season contributing up to 10 of the annual precipitation to the region 155 The El Nino Southern Oscillation affects the precipitation distribution by altering rainfall patterns across the western United States 156 Midwest 157 158 the Southeast 159 and throughout the tropics There is also evidence that global warming is leading to increased precipitation to the eastern portions of North America while droughts are becoming more frequent in the tropics and subtropics Wettest known locations Cherrapunji situated on the southern slopes of the Eastern Himalaya in Shillong India is the confirmed wettest place on Earth with an average annual rainfall of 11 430 mm 450 in The highest recorded rainfall in a single year was 22 987 mm 905 0 in in 1861 The 38 year average at nearby Mawsynram Meghalaya India is 11 873 mm 467 4 in 160 The wettest spot in Australia is Mount Bellenden Ker in the north east of the country which records an average of 8 000 mm 310 in per year with over 12 200 mm 480 3 in of rain recorded during 2000 161 The Big Bog on the island of Maui has the highest average annual rainfall in the Hawaiian Islands at 10 300 mm 404 in 162 Mount Waiʻaleʻale on the island of Kauaʻi achieves similar torrential rains while slightly lower than that of the Big Bog at 9 500 mm 373 in 163 of rain per year over the last 32 years with a record 17 340 mm 683 in in 1982 Its summit is considered one of the rainiest spots on earth with a reported 350 days of rain per year Lloro a town situated in Choco Colombia is probably the place with the largest rainfall in the world averaging 13 300 mm 523 6 in per year 164 The Department of Choco is extraordinarily humid Tutunendao a small town situated in the same department is one of the wettest estimated places on Earth averaging 11 394 mm 448 6 in per year in 1974 the town received 26 303 mm 86 ft 3 6 in the largest annual rainfall measured in Colombia Unlike Cherrapunji which receives most of its rainfall between April and September Tutunendao receives rain almost uniformly distributed throughout the year 165 Quibdo the capital of Choco receives the most rain in the world among cities with over 100 000 inhabitants 9 000 mm 354 in per year 164 Storms in Choco can drop 500 mm 20 in of rainfall in a day This amount is more than what falls in many cities in a year s time Continent Highest average Place Elevation Years of recordin mm ft m South America 523 6 13 299 Lloro Colombia estimated a b 520 158 c 29 Asia 467 4 11 872 Mawsynram India a d 4 597 1 401 39 Africa 405 0 10 287 Debundscha Cameroon 30 9 1 32 Oceania 404 3 10 269 Big Bog Maui Hawaii USA a 5 148 1 569 30 South America 354 0 8 992 Quibdo Colombia 120 36 6 16 Australia 340 0 8 636 Mount Bellenden Ker Queensland 5 102 1 555 9 North America 256 0 6 502 Hucuktlis Lake British Columbia 12 3 66 14 Europe 183 0 4 648 Crkvice Montenegro 3 337 1 017 22 Source without conversions Global Measured Extremes of Temperature and Precipitation National Climatic Data Center 9 August 2004 166 Continent Place Highest rainfallin mmHighest average annual rainfall 167 Asia Mawsynram India 467 4 11 870 Highest in one year 167 Asia Cherrapunji India 1 042 26 470 Highest in one calendar month 168 Asia Cherrapunji India 366 9 296Highest in 24 hours 167 Indian Ocean Foc Foc La Reunion 71 8 1 820Highest in 12 hours 167 Indian Ocean Foc Foc La Reunion 45 0 1 140Highest in one minute 167 North America Unionville Maryland USA 1 23 31 2Outside EarthRainfalls of diamonds have been suggested to occur on the gas giant planets Jupiter and Saturn 169 as well as on the ice giant planets Uranus and Neptune 170 There is likely to be rain of various compositions in the upper atmospheres of the gas giants as well as precipitation of liquid neon in the deep atmospheres 171 172 On Titan Saturn s largest natural satellite infrequent methane rain is thought to carve the moon s numerous surface channels 173 On Venus sulfuric acid virga evaporates 25 km 16 mi from the surface 174 Extrasolar planet OGLE TR 56b in the constellation Sagittarius is hypothesized to have iron rain 175 Accordingly research carried out by the European Southern Observatory shows that WASP 76b can produce showers of burning liquid iron droplets once temperature decreases during the planet s night hours 176 There is evidence from samples of basalt brought back by the Apollo missions that the Moon has been subject to lava rain 177 See also Ecology portal Environment portal Water portal Weather portalAtmospheric river Hydropower Intensity duration frequency curve Precipitation types Rain dust Rain sensor Rain water harvesting Rainbow Raining animals Red rain in Kerala Petrichor the cause of the scent during and after rain Sanitary sewer overflow Sediment precipitation Water resources Weather Rainmaking 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