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{{Other uses|Rain (disambiguation)|Rainy (disambiguation)}}
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[[File:FoggDam-NT.jpg|alt=Black storm clouds under which a grey sheet of rain is falling on grasslands.|thumb|right|upright=1.4|A rain shaft at the base of a [[thunderstorm]]]]
[[File:Rain-on-Thassos.jpg|thumb|upright=1.4|Torrential rain in [[Greece]].]]
{{Weather}}
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{{Listen|filename=Thunder.ogg|title=Rain|description=typical sound of rain with [[thunder]]|format=[[Ogg]]}}
'''Rain''' is liquid [[water]] in the form of [[droplet]]s that have [[condensation|condensed]] from [[atmosphere|atmospheric]] [[water vapor]] and then [[precipitation (meteorology)|precipitated]]—that is, become heavy enough to 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 suitable conditions for many types of [[ecosystem]], as well as water for [[hydroelectricity|hydroelectric power plants]] and crop [[irrigation]].
 
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 [[convection|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 [[wet season|rainy seasons]] to [[savannah]] [[clime]]s.
 
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.{{citation needed|date=January 2012}} Antarctica is the driest continent. The globally averaged annual precipitation over land is {{convert|715|mm|in|abbr=on}}, but over the whole Earth it is much higher at {{convert|990|mm|in|abbr=on}}.<ref>{{cite web|url=http://www.planetguide.net/book/chapter_2/water_cycle.html |title=The Water Cycle |publisher=Planetguide.net |date= |accessdate=2011-12-26}}</ref> [[Climate]] classification systems such as the [[Köppen climate classification]] system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using [[rain gauge]]s. 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===
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).<ref>{{cite web|author=Steve Kempler|year=2009|url=http://daac.gsfc.nasa.gov/PIP/shtml/atmospheric_water_vapor_or_humidity.shtml|title=Parameter information page|publisher=[[NASA]] [[Goddard Space Flight Center]]|accessdate=2008-12-27 |archiveurl = http://web.archive.org/web/20071126083414/http://daac.gsfc.nasa.gov/PIP/shtml/atmospheric_water_vapor_or_humidity.shtml |archivedate = November 26, 2007}}</ref><ref>{{cite book |url=http://www.atmos.washington.edu/~stoeling/WH-Ch03.pdf| page=80|accessdate=2010-01-30|date=2005-09-12|author=Mark Stoelinga|title=Atmospheric Thermodynamics|publisher=[[University of Washington]]}}</ref> The amount of moisture in 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.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=relative+humidity&submit=Search|author=Glossary of Meteorology|date=June 2000|accessdate=2010-01-29|publisher=[[American Meteorological Society]]|title=Relative Humidity}}</ref> How much water vapor a parcel of air can contain before it becomes saturated (100%&nbsp;relative humidity) and forms into a [[cloud]] (a group of visible and tiny water and ice particles suspended above the Earth's surface)<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=cloud1|author=Glossary of Meteorology|date=June 2000|accessdate=2010-01-29|publisher=[[American Meteorological Society]]|title=Cloud}}</ref> 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.<ref>{{cite web|author=Naval Meteorology and Oceanography Command|year=2007|url=http://www.navmetoccom.navy.mil/pao/Educate/WeatherTalk2/indexatmosp.htm|title=Atmospheric Moisture|publisher=[[United States Navy]]|accessdate=2008-12-27}} {{Dead link|date=September 2010|bot=H3llBot}}</ref>
 
There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, and evaporative cooling. [[Adiabatic lapse rate#Dry adiabatic lapse rate|Adiabatic cooling]] occurs when air rises and expands.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=adiabatic-process1|title=Adiabatic Process|publisher=[[American Meteorological Society]]|accessdate=2008-12-27}}</ref> 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,<ref>{{cite web|author=TE Technology, Inc|year=2009|url=http://www.tetech.com/Cold-Plate-Coolers.html|title=Peltier Cold Plate|accessdate=2008-12-27}}</ref> 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 [[Thermal radiation|infrared radiation]], either by the air or by the surface underneath.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=radiational+cooling&submit=Search|title=Radiational cooling|publisher=[[American Meteorological Society]]|accessdate=2008-12-27}}</ref> 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.<ref>{{cite web|author=Robert Fovell|year=2004|url=http://www.atmos.ucla.edu/~fovell/AS3downloads/saturation.pdf|title=Approaches to saturation|publisher=[[UCLA|University of California in Los Angelese]]|accessdate=2009-02-07}}</ref>
 
The main ways water vapor is added to the air are: wind convergence into areas of upward motion,<ref name="convection">{{cite book|author=Robert Penrose Pearce|year=2002|url=http://books.google.com/?id=QECy_UBdyrcC&pg=PA66&lpg=PA66&dq=ways+to+moisten+the+atmosphere|title=Meteorology at the Millennium|publisher=Academic Press|page=66|isbn=978-0-12-548035-2|accessdate=2009-01-02}}</ref> precipitation or virga falling from above,<ref>{{cite web|author=[[National Weather Service]] Office, Spokane, Washington|year=2009|url=http://www.wrh.noaa.gov/otx/outreach/ttalk/virga.php|title=Virga and Dry Thunderstorms|accessdate=2009-01-02}}</ref> daytime heating evaporating water from the surface of oceans, water bodies or wet land,<ref>{{cite web|author=Bart van den Hurk and Eleanor Blyth|year=2008|url=http://www.knmi.nl/~hurkvd/Loco_workshop/Workshop_report.pdf|title=Global maps of Local Land-Atmosphere coupling|publisher=KNMI|accessdate=2009-01-02}}</ref> transpiration from plants,<ref>{{cite web|author=Krishna Ramanujan and Brad Bohlander|year=2002|url=http://www.gsfc.nasa.gov/topstory/20020926landcover.html|title=Landcover changes may rival greenhouse gases as cause of climate change|publisher=[[National Aeronautics and Space Administration]] [[Goddard Space Flight Center]]|accessdate=2009-01-02 |archiveurl = http://web.archive.org/web/20080603022239/http://www.gsfc.nasa.gov/topstory/20020926landcover.html |archivedate = June 3, 2008}}</ref> cool or dry air moving over warmer water,<ref>{{cite web|author=[[National Weather Service]] JetStream|year=2008|url=http://www.srh.weather.gov/srh/jetstream/synoptic/airmass.htm|title=Air Masses|accessdate=2009-01-02}}</ref> and lifting air over mountains.<ref name="MT">{{cite web|author=Dr. Michael Pidwirny|year=2008|url=http://www.physicalgeography.net/fundamentals/8e.html|title=CHAPTER 8: Introduction to the Hydrosphere (e). Cloud Formation Processes|publisher=Physical Geography|accessdate=2009-01-01}}</ref> Water vapor normally begins to condense on [[Cloud condensation nuclei|condensation nuclei]] such as dust, ice, and salt in order to form clouds. Elevated portions of weather fronts (which are three-dimensional in nature)<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=front1|author=Glossary of Meteorology|date=June 2000|accessdate=2010-01-29|publisher=[[American Meteorological Society]]|title=Front}}</ref> force broad areas of upward motion within the Earth's atmosphere which form clouds decks such as [[altostratus]] or [[cirrostratus]].<ref name="DR">{{cite web|author=David Roth|title=Unified Surface Analysis Manual|year=|accessdate=2006-10-22|publisher=[[Hydrometeorological Prediction Center]]|url= http://www.wpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf}}</ref> [[Stratus cloud|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 [[Radiation fog|advection fog]] during breezy conditions.<ref>{{cite web|author=FMI|year=2007|url=http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?/docu/Manual/SatManu/CMs/FgStr/backgr.htm|title=Fog And Stratus - Meteorological Physical Background|publisher=Zentralanstalt für Meteorologie und Geodynamik|accessdate=2009-02-07}}</ref>
 
===Coalescence and fragmentation===
[[File:Raindrops sizes.svg|alt=Diagram showing that very small rain drops are almost spherical in shape. As drops become larger, they become flattened on the bottom, like a hamburger bun. Very large rain drops are split into smaller ones by air resistance which makes them increasingly unstable.|thumb|The shape of rain drops depend upon their size]]
[[Coalescence (meteorology)|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. 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.<ref>{{cite web|author=Glossary of Meteorology|date=June 2000|url=http://amsglossary.allenpress.com/glossary/search?id=warm-rain-process1|title=Warm Rain Process|accessdate=2010-01-15|publisher=[[American Meteorological Society]]}}</ref> 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.<ref>{{cite web|author=Paul Sirvatka|year=2003|url=http://weather.cod.edu/sirvatka/bergeron.html|title=Cloud Physics: Collision/Coalescence; The Bergeron Process|publisher=[[College of DuPage]]|accessdate=2009-01-01}}</ref>
 
Raindrops have sizes ranging from {{convert|0.1|to|9|mm|in|abbr=on}} mean diameter, above which they tend to break up. 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 [[parachute]]s.<ref>{{cite web |title = Bad Meteorology: Raindrops are shaped like teardrops. |url = http://www.ems.psu.edu/~fraser/Bad/BadRain.html |author = Alistair B. Fraser |accessdate = 2008-04-07|date=2003-01-15|publisher=[[Pennsylvania State University]]}}</ref><ref name="Villermaux" /> Contrary to popular belief, their shape does not resemble a teardrop.<ref>{{cite web|author=[[United States Geological Survey]]|year=2009|url=http://ga.water.usgs.gov/edu/raindropshape.html|title=Are raindrops tear shaped?|publisher=[[United States Department of the Interior]]|accessdate=2008-12-27}}</ref> The biggest raindrops on Earth were recorded over [[Brazil]] and the [[Marshall Islands]] in 2004&nbsp;— some of them were as large as {{convert|10|mm|in|abbr=on}}. 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.<ref>{{cite news | title = Monster raindrops delight experts | url = http://news.bbc.co.uk/2/hi/science/nature/3898305.stm | author = Paul Rincon |publisher=[[British Broadcasting Company]]|date=2004-07-16|accessdate = 2009-11-30
}}</ref>
 
Rain drops associated with melting hail tend to be larger than other rain drops.<ref>{{cite web|author=Norman W. Junker|year=2008|url=http://www.wpc.ncep.noaa.gov/research/mcs_web_test_test_files/Page882.htm|title=An ingredients based methodology for forecasting precipitation associated with MCS’s|publisher=[[Hydrometeorological Prediction Center]]|accessdate=2009-02-07}}</ref>
 
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.<ref name="JS">{{cite web|author=J. S. Oguntoyinbo and F. O. Akintola|year=1983|url=http://www.cig.ensmp.fr/~iahs/redbooks/a140/iahs_140_0063.pdf|title=Rainstorm characteristics affecting water availability for agriculture|publisher=IAHS Publication Number 140|accessdate=2008-12-27}}</ref><ref>{{cite journal|author=Robert A. Houze Jr|url=http://ams.allenpress.com/archive/1520-0477/78/10/pdf/i1520-0477-78-10-2179.pdf|title=Stratiform Precipitation in Regions of Convection: A Meteorological Paradox?|journal=Bulletin of the [[American Meteorological Society]]|date=October 1997|volume=78|pages=2179–2196|accessdate=2008-12-27|issue=10|doi=10.1175/1520-0477(1997)078<2179:SPIROC>2.0.CO;2|issn=1520-0477|year=1997|bibcode = 1997BAMS...78.2179H }} {{Dead link|date=September 2010|bot=H3llBot}}</ref>
 
===Droplet size distribution===
The final droplet size distribution is an [[exponential distribution]]. The number of droplets with diameter between <math>d</math> and <math>D+dD</math> per unit volume of space is <math>n(d) = n_0 e^{-d/\langle d \rangle} dD</math>. This is commonly referred to as the Marshall–Palmer law after the researchers who first characterized it.<ref name="Villermaux">{{cite journal |author=Emmanuel Villermaux, Benjamin Bossa |title=Single-drop fragmentation distribution of raindrops. |url=https://www.irphe.fr/~fragmix/publis/VB2009.pdf |journal=Nature Physics |date=September 2009 |volume=5 |pages=697–702 |doi=10.1038/NPHYS1340 |laysummary=http://news.bbc.co.uk/2/hi/science/nature/8155883.stm |issue=9 |bibcode = 2009NatPh...5..697V }}</ref><ref>Marshall, J. S. & Palmer, W. M. The distribution of raindrops with size. J. Meteorol. 5, 165–166 (1948).</ref> The parameters are somewhat temperature-dependent,<ref>Houze, Robert A., Peter V. Hobbs, Paul H. Herzegh, David B. Parsons, 1979: Size Distributions of Precipitation Particles in Frontal Clouds. J. Atmos. Sci., 36, 156–162. doi: http://dx.doi.org/10.1175/1520-0469(1979)036<0156:SDOPPI>2.0.CO;2</ref> and the slope also scales with the rate of rainfall <math>\langle d \rangle^{-1}=41 R^{-0.21}</math> (d in centimeters and R in millimetres per hour).<ref name="Villermaux" />
 
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 distribution]]s.<ref>Niu, Shengjie, Xingcan Jia, Jianren Sang, Xiaoli Liu, Chunsong Lu, Yangang Liu, 2010: Distributions of Raindrop Sizes and Fall Velocities in a Semiarid Plateau Climate: Convective versus Stratiform Rains. J. Appl. Meteor. Climatol., 49, 632–645. doi: http://dx.doi.org/10.1175/2009JAMC2208.1</ref> The distribution has an upper limit due to droplet fragmentation.<ref name="Villermaux" />
 
===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, {{convert|0.5|mm|in|abbr=on}} [[drizzle]] impacts at {{convert|2|m/s|ft/s|abbr=on}} or {{convert|4.5|mph|km/h|abbr=on|disp=flip}}, while large {{convert|5|mm|in|abbr=on}} drops impact at around {{convert|9|m/s|ft/s|abbr=on}} or {{convert|20|mph|km/h|abbr=on|disp=flip}}.<ref>{{cite web |title = Falling raindrops hit 5 to 20 mph speeds |url = http://usatoday30.usatoday.com/news/science/wonderquest/2001-12-19-rain-drops.htm |publisher = USA Today |accessdate = 2013-12-22}}</ref>
 
Rain falling on loosely packed material such as newly fallen ash can produce dimples that can be fossilized.<ref>W.A. van der Westhuizen, N.J. Grobler, J.C. Loock, E.A.W. Tordiffe, Raindrop imprints in the Late Archaean-Early Proterozoic Ventersdorp Supergroup, South Africa, Sedimentary Geology, Volume 61, Issues 3–4, February 1989, Pages 303-309, ISSN 0037-0738, http://dx.doi.org/10.1016/0037-0738(89)90064-X. (http://www.sciencedirect.com/science/article/pii/003707388990064X)</ref> 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.<ref>Som, Sanjoy M., Catling, David C., Harnmeijer, Jelte P., Polivka, Peter M., Buick, Roger. Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints. Nature. 484: 7394 p. 359-362. http://dx.doi.org/10.1038/nature10890</ref>
 
The [[Droplet#Sound|sound of raindrops]] hitting water is caused by bubbles of air [[Minnaert resonance|oscillating underwater]].<ref>{{cite journal
| author = Andrea Prosperetti and Hasan N. Oguz
| authorlink = Andrea Prosperetti
| year = 1993
| title = The impact of drops on liquid surfaces and the underwater noise of rain
| journal = Annual Review of Fluid Mechanics
| volume = 25
| pages = 577–602
| doi = 10.1146/annurev.fl.25.010193.003045
| url = http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.fl.25.010193.003045
| format = PDF
| accessdate = 2006-12-09
| bibcode=1993AnRFM..25..577P
}}</ref><ref>{{cite web |url=http://ffden-2.phys.uaf.edu/311_fall2004.web.dir/Ryan_Rankin/bubble%20resonance.htm |title=Bubble Resonance |accessdate=2006-12-09 |author=Ryan C. Rankin |date=June 2005 |work=The Physics of Bubbles, Antibubbles, and all That}}</ref>
 
The [[METAR]] code for rain is RA, while the coding for rain showers is SHRA.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm|title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]]|accessdate=2009-08-29|date=2007-04-10}} {{Dead link|date=April 2012|bot=H3llBot}}</ref>
 
===Phantom rain===
Sometimes over the deserts heavy rainclouds are raining down, but because of the hot climate near surface, all rain evaporates before it reaches the ground. [[Edward Abbey]] describes it in ''[[Desert Solitaire]]'': "Sometimes it rains and still fails to moisten the desert – the falling water evaporates halfway down between cloud and earth. Then you see curtains of blue rain dangling out of reach in the sky while the living things wither below for want of water. Torture by tantalizing, hope without fulfillment. And the clouds disperse and dissipate into nothingness…” <ref>[http://thesustainablesoul.blogspot.fi/2010/07/desert-reflections-part-2-phantom-rain.html Desert Reflections Part 2: Phantom Rain and Ways of Being]</ref>
 
==Causes==
 
===Frontal activity===
{{Main|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 scale meteorology|synoptic systems]] (on the order of cm/s), such as in the vicinity of [[cold front]]s and near and poleward of surface [[warm front]]s. Similar ascent is seen around [[tropical cyclone]]s outside of the [[eye (cyclone)|eyewall]], and in comma-head precipitation patterns around [[mid-latitude cyclone]]s.<ref name="Geerts">{{cite web|author=B. Geerts|year=2002|url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/con_str.html|title=Convective and stratiform rainfall in the tropics|publisher=[[University of Wyoming]]|accessdate=2007-11-27}}</ref> 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.<ref name=autogenerated3>{{cite web|author=David Roth|title=Unified Surface Analysis Manual|year=2006|accessdate=2006-10-22|publisher=[[Hydrometeorological Prediction Center]]|url= http://www.wpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf}}</ref> 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.<ref>{{cite web|url=http://www.meted.ucar.edu/nwp/pcu3/cases/eta_05Dec02_ptype/page4.htm|title=Precipitation Type Forecasts in the Southeastern and Mid-Atlantic states|author=MetEd|date=2003-03-14|accessdate=2010-01-30|publisher=[[University Corporation for Atmospheric Research]]}}</ref> [[Hail]] becomes an increasingly infrequent occurrence when the freezing level within the atmosphere exceeds {{convert|11000|ft|m|abbr=on|disp=flip}} above ground level.<ref name="mesoanal">{{cite web|url=http://www.crh.noaa.gov/lmk/soo/docu/SvrWx_MesoGuide.pdf|title=Meso-Analyst Severe Weather Guide|accessdate=2013-12-22|publisher=[[National Oceanic and Atmospheric Administration]]}}</ref>
 
===Convection===
[[File:Konvektionsregen.jpg|alt=Diagram showing that as moist air becomes heated more than its surroundings, it moves upward, resulting in brief rain showers.|thumb|right|Convective precipitation]]
[[File:Steigungsregen.jpg|alt=Diagram showing how moist air over the ocean rises and flows over the land, causing cooling and rain as it hits mountain ridges.|thumb|right|Orographic precipitation]]
 
[[Convection rain|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.<ref name="Geerts" /><ref>{{cite journal |author=Robert Houze |date=October 1997 |title=Stratiform Precipitation in Regions of Convection: A Meteorological Paradox? |journal=Bulletin of the American Meteorological Society |volume=78 |issue=10 |page=2179 |accessdate= 2007-11-27 |doi=10.1175/1520-0477(1997)078<2179:SPIROC>2.0.CO;2 |issn=1520-0477|bibcode = 1997BAMS...78.2179H }}</ref> [[Graupel]] and [[hail]] indicate convection.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=graupel&submit=Search|title=Graupel|publisher=[[American Meteorological Society]]|accessdate=2009-01-02}}</ref> In mid-latitudes, convective precipitation is intermittent and often associated with baroclinic boundaries such as [[cold front]]s, [[squall line]]s, and warm fronts.<ref>{{cite book|author=Toby N. Carlson|year=1991|url=http://books.google.com/?id=2lIVAAAAIAAJ&pg=PA216&lpg=PA216&dq=where+convection+occurs+in+the+mid-latitudes|title=Mid-latitude Weather Systems|publisher=Routledge|page=216|isbn=978-0-04-551115-0|accessdate=2009-02-07}}</ref>
 
===Orographic effects===
{{Main|Orographic lift|Precipitation types (meteorology)|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 lapse rate|adiabatic]] cooling and condensation. In mountainous parts of the world subjected to relatively consistent winds (for example, the [[trade wind]]s), 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.<ref name="MT"/>
 
In [[Hawaii]], [[Mount Waiʻaleʻale]], on the island of Kauai, is notable for its extreme rainfall, as it has the second highest average annual rainfall on Earth, with {{convert|460|in|mm||abbr=on|disp=flip}}.<ref>{{cite web|author=Diana Leone|year=2002|url=http://starbulletin.com/2002/05/27/news/story3.html|title=Rain supreme|publisher=Honolulu Star-Bulletin|accessdate=2008-03-19}}</ref> Systems known as [[Kona storm]]s affect the state with heavy rains between October and April.<ref name="BIRCH">Steven Businger and Thomas Birchard, Jr. [http://www.soest.hawaii.edu/MET/Faculty/businger/PDF/BowEchoPPR.pdf A Bow Echo and Severe Weather Associated with a Kona Low in Hawaii.] Retrieved on 2007-05-22.</ref> Local climates vary considerably on each island due to their topography, divisible into windward (''Ko{{okina}}olau'') 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.<ref>{{cite web|author=Western Regional Climate Center|year=2002|url=http://www.wrcc.dri.edu/narratives/HAWAII.htm|title=Climate of Hawaii|accessdate=2008-03-19}}</ref>
 
In South America, the [[Andes]] mountain range blocks [[Pacific Ocean|Pacific]] moisture that arrives in that continent, resulting in a desertlike climate just downwind across western Argentina.<ref name="Andes">{{cite book|author=Paul E. Lydolph|year=1985|url=http://books.google.com/?id=bBjIuXHEgZ4C&pg=PA333&lpg=PA333&dq=effect+of+Andes+on+rainfall+in+Chile|title=The Climate of the Earth|publisher=Rowman & Littlefield|page=333|isbn=978-0-86598-119-5|accessdate=2009-01-02}}</ref> The [[Sierra Nevada (U.S.)|Sierra Nevada]] range creates the same effect in North America forming the [[Great Basin]] and [[Mojave Desert]]s.<ref>{{cite book|author=Michael A. Mares|year=1999|url=http://books.google.com/?id=g3CbqZtaF4oC&pg=PA252&lpg=PA252&dq=sierra+nevada+leads+to+great+basin+desert|title=Encyclopedia of Deserts|publisher=[[University of Oklahoma]] Press|page=252|isbn=978-0-8061-3146-7|accessdate=2009-01-02}}</ref><ref>{{cite web|author=Adam Ganson|year=2003|url=http://www.indiana.edu/~sierra/papers/2003/Ganson.html|title=Geology of Death Valley|publisher=[[Indiana University]]|accessdate=2009-02-07}}</ref>
 
===Within the tropics===
[[File:Cairns climate.svg|alt=Chart showing an Australian city with as much as 450 mm of rain in the winter months and less than 50 mm in the summer.|right|thumb|250 px|Rainfall distribution by month in [[Cairns]] showing the extent of the wet season at that location]]
{{See also|Monsoon|Tropical cyclone}}
{{Main|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.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=rainy-season1|title=Rainy season|publisher=[[American Meteorological Society]]|accessdate=2008-12-27}}</ref> The term ''green season'' is also sometimes used as a [[euphemism]] by tourist authorities.<ref>{{cite web|author=Costa Rica Guide|year=2005|url=http://costa-rica-guide.com/when.htm|title=When to Travel to Costa Rica|publisher=ToucanGuides|accessdate=2008-12-27}}</ref> Areas with wet seasons are dispersed across portions of the [[tropics]] and [[subtropics]].<ref>{{cite web|author=Michael Pidwirny|year=2008|url=http://www.physicalgeography.net/fundamentals/9k.html|title=CHAPTER 9: Introduction to the Biosphere|publisher=PhysicalGeography.net|accessdate=2008-12-27}}</ref> [[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.<ref name="Hyde">{{cite web|author=Elisabeth M. Benders-Hyde|year=2003|url=http://www.blueplanetbiomes.org/climate.htm|title=World Climates|publisher=Blue Planet Biomes|accessdate=2008-12-27}}</ref> 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.<ref name="JS" /> 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,<ref>{{cite web|author=Mei Zheng|year=2000|url=http://digitalcommons.uri.edu/dissertations/AAI9989458/|title=The sources and characteristics of atmospheric particulates during the wet and dry seasons in Hong Kong|publisher=[[University of Rhode Island]]|accessdate=2008-12-27}}</ref> [[freshwater]] quality improves,<ref>{{cite journal|author=S. I. Efe, F. E. Ogban, M. J. Horsfall, E. E. Akporhonor|year=2005|url=https://tspace.library.utoronto.ca/bitstream/1807/6445/1/ja05036.pdf|title=Seasonal Variations of Physico-chemical Characteristics in Water Resources Quality in Western Niger Delta Region, Nigeria|journal=Journal of Applied Scientific Environmental Management|accessdate=2008-12-27|issn=1119-8362|volume=9|pages=191–195|issue=1}}</ref><ref>{{cite book|author=C. D. Haynes, M. G. Ridpath, M. A. J. Williams|year=1991|url=http://books.google.com/?id=ZhvtSmJYuN4C&pg=PA91&lpg=PA91&dq=wet+season+characteristics|title=Monsoonal Australia|publisher=Taylor & Francis|page=90|isbn=978-90-6191-638-3|accessdate=2008-12-27}}</ref> and vegetation grows significantly.
 
[[Tropical cyclone]]s, 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 counter clockwise (northern hemisphere).<ref>{{cite web|author=[[Chris Landsea]]|year=2007|url=http://www.aoml.noaa.gov/hrd/tcfaq/D3.html|title=Subject: D3) Why do tropical cyclones' winds rotate counter-clockwise (clockwise) in the Northern (Southern) Hemisphere?|publisher=[[National Hurricane Center]]|accessdate=2009-01-02}}</ref> Although [[cyclone]]s 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.<ref name="2005 EPac outlook">{{cite web|author=[[Climate Prediction Center]]|year=2005|url=http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html|title=2005 Tropical Eastern North Pacific Hurricane Outlook|publisher=[[National Oceanic and Atmospheric Administration]]|accessdate=2006-05-02}}</ref> Areas in their path can receive a year's worth of rainfall from a tropical cyclone passage.<ref>{{cite news|author=Jack Williams|url=http://www.usatoday.com/weather/whhcalif.htm|title=Background: California's tropical storms|publisher=[[USA Today]]|accessdate=2009-02-07 | date=2005-05-17}}</ref>
 
===Human influence===
[[File:Atlanta thermal.jpg|thumb|right|200px|Image of [[Atlanta, Georgia]] showing temperature distribution, with blue showing cool temperatures, red warm, and hot areas appear white.]]
[[File:Global Warming Map.jpg|alt=World map of temperature distribution shows the northern hemisphere was warmer than the souther hemisphere during the periods compared.|thumb|right|200 px|Mean surface temperature anomalies during the period 1999 to 2008 with respect to the average temperatures from 1940 to 1980]]
 
{{See also|Global warming|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.<ref>{{cite journal|date=1998-08-06|author= R. S. Cerveny and R. C. Balling|title=Weekly cycles of air pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region|journal=Nature|volume=394|pages=561–563|doi=10.1038/29043|issue=6693|bibcode = 1998Natur.394..561C }}</ref> The urban heat island effect warms cities {{convert|0.6|C-change|1}} to {{convert|5.6|C-change|1}} 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 {{convert|20|to|40|mi|km|abbr=on|disp=flip}} downwind of cities, compared with upwind.<ref>{{cite news | title=Spain goes hi-tech to beat drought | author=Dale Fuchs | publisher=The Guardian | date=2005-06-28 | url=http://www.guardian.co.uk/weather/Story/0,2763,1516375,00.html | accessdate=2007-08-02 | location=London}}</ref> Some cities induce a total precipitation increase of 51%.<ref>{{cite web|url=http://www.gsfc.nasa.gov/topstory/20020613urbanrain.html|title=NASA Satellite Confirms Urban Heat Islands Increase Rainfall Around Cities|author=[[Goddard Space Flight Center]]|publisher=[[National Aeronautics and Space Administration]]|date=2002-06-18|accessdate=2009-07-17 |archiveurl = http://web.archive.org/web/20080612173654/http://www.gsfc.nasa.gov/topstory/20020613urbanrain.html |archivedate = June 12, 2008}}</ref>
 
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&nbsp;percent since 1900, with the greatest increases within the East North Central climate region (11.6 percent per century) and the South (11.1&nbsp;percent). Hawaii was the only region to show a decrease (−9.25&nbsp;percent).<ref>{{cite web|url=http://www.epa.gov/climatechange/science/recentpsc.html|title=Precipitation and Storm Changes|author=Climate Change Division|publisher=[[United States Environmental Protection Agency]]|date=2008-12-17|accessdate=2009-07-17}}</ref>
 
The most successful attempts at influencing [[weather]] involve [[cloud seeding]], which include techniques used to increase [[snow|winter precipitation]] over mountains and suppress [[hail]].<ref name="AMSmod">{{cite web|url=http://www.ametsoc.org/policy/wxmod98.html|author=American Meteorological Society|title=Planned and Inadvertent Weather Modification|date=1998-10-02|accessdate=2010-01-31}}</ref>
 
==Characteristics==
 
===Patterns===
[[File:Sturmfront auf Doppler-Radar-Schirm.jpg|200 px|thumb|right|Band of thunderstorms seen on a [[weather radar]] display]]
{{Main|Rainband}}
[[Rainband]]s are [[cloud]] and precipitation areas which are significantly elongated. Rainbands can be [[stratiform]] or [[atmospheric convection|convective]],<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?p=1&query=rainband&submit=Search Rainband.] Retrieved on 2008-12-24.</ref> and are generated by differences in temperature. When noted on [[weather radar]] imagery, this precipitation elongation is referred to as banded structure.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=banded-structure1 Banded structure.] Retrieved on 2008-12-24.</ref> Rainbands in advance of warm [[occluded front]]s and [[warm front]]s are associated with weak upward motion,<ref>Owen Hertzman (1988). [http://adsabs.harvard.edu/abs/1988PhDT.......110H Three-Dimensional Kinematics of Rainbands in Midlatitude Cyclones.] Retrieved on 2008-12-24</ref> and tend to be wide and stratiform in nature.<ref>Yuh-Lang Lin (2007). [http://books.google.com/books?id=4KXtnQ3bDeEC&pg=PA405&lpg=PA405&dq=sea+breeze+rainbands&source=bl&ots=CL5KD0HLAJ&sig=Gz5bwKi9yu8j25EbXLD3TVNNQ68&hl=en&sa=X&oi=book_result&resnum=10&ct=result Mesoscale Dynamics.] Retrieved on 2008-12-25.</ref>
 
Rainbands spawned near and ahead of [[cold front]]s can be [[squall line]]s which are able to produce [[tornado]]es.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=prefrontal-squall-line1 Prefrontal squall line.] Retrieved on 2008-12-24.</ref> 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]].<ref>J. D. Doyle (1997). [http://cat.inist.fr/?aModele=afficheN&cpsidt=2721180 The influence of mesoscale orography on a coastal jet and rainband.] Retrieved on 2008-12-25.</ref> 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.<ref>A. Rodin (1995). [http://cat.inist.fr/?aModele=afficheN&cpsidt=3570629 Interaction of a cold front with a sea-breeze front numerical simulations.] Retrieved on 2008-12-25.</ref>
 
Once a cyclone occludes, a '''tr'''ough '''o'''f '''w'''arm air '''al'''oft, or "[[trowal]]" for short, will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately northwestern, periphery (also known as the warm conveyor belt), forcing a surface trough to continue into the cold sector on a similar curve to the occluded front. The trowal creates the portion of an occluded cyclone known as its comma head, due to the [[comma (punctuation)|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 trowal is unstable enough for convection.<ref name="TROW">{{cite web
| title = What is a TROWAL? via the Internet Wayback Machine
| author = [[St. Louis University]]
| date = 2003-08-04
| url = http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm
| accessdate = 2006-11-02 |archiveurl = http://web.archive.org/web/20060916052440/http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm |archivedate = 2006-09-16}}</ref> Banding within the comma head precipitation pattern of an [[extratropical cyclone]] can yield significant amounts of rain.<ref>David R. Novak, Lance F. Bosart, Daniel Keyser, and Jeff S. Waldstreicher (2002). [http://cstar.cestm.albany.edu/CAP_Projects/Project4/Banded%20Precip/novakWAF.pdf A Climatological and composite study of cold season banded precipitation in the Northeast United States.] Retrieved on 2008-12-26.</ref> 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.<ref>Ivory J. Small (1999). [http://www.wrh.noaa.gov/wrh/99TAs/9918/index.html An observation study of island effect bands: precipitation producers in Southern California.] Retrieved on 2008-12-26.</ref>
 
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 [[tropical cyclone|hurricane or tropical storm]]. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.<ref name="ODT">[[University of Wisconsin–Madison]] (1998).[http://cimss.ssec.wisc.edu/tropic/research/products/dvorak/odt.html Objective Dvorak Technique.] Retrieved on 2006-05-29.</ref>
 
===Acidity===
[[File:Origins of acid rain.svg|thumb|right]]
{{See also|Acid rain}}
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.<ref>{{cite web|url=http://pubs.acs.org/doi/abs/10.1021/es00166a003|title=Effect of storm type on rainwater composition in southeastern North Carolina|author=Joan D. Willey|publisher=Environmental Science & Technology|date=January 1988}}</ref> Rain becomes acidic primarily due to the presence of two strong acids, [[sulfuric acid]] (H<sub>2</sub>SO<sub>4</sub>) and [[nitric acid]] (HNO<sub>3</sub>). 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 H<sub>2</sub>S 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 solution|buffer]] in acid rain and raises the pH.<ref>{{cite web|url=http://pubs.acs.org/doi/abs/10.1021/es060638w?prevSearch=%255Bauthor%253A%2BWilley%252C%2BJoan%2BD.%255D&searchHistoryKey=|title=Changing Chemical Composition of Precipitation in Wilmington, North Carolina, U.S.A.: Implications for the Continental U.S.A|author=Joan D. Willey|publisher=Environmental Science & Technology|date=2006-08-19}}</ref>
 
===Köppen climate classification===
[[File:World Koppen Map.png|thumb|right|400px|Updated Köppen-Geiger climate map<ref>{{cite journal | author=Peel, M. C. and Finlayson, B. L. and McMahon, T. A. |year=2007 | title= Updated world map of the Köppen-Geiger climate classification | journal=Hydrol. Earth Syst. Sci. | volume=11 | pages=1633–1644 |url=http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.html | doi = 10.5194/hess-11-1633-2007 | issn = 1027-5606}} ''(direct:[http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf Final Revised Paper])''</ref>
{|
|- valign=top |
|
{{legend|#0000FE|[[equatorial climate|Af]]}}
{{legend|#0077FF|[[monsoon|Am]]}}
{{legend|#46A9FA|[[tropical savanna climate|Aw]]}}
| width=5 |
|
{{legend|#FE0000|[[desert climate|BWh]]}}
{{legend|#FE9695|[[desert climate|BWk]]}}
{{legend|#F5A301|[[semi-arid climate|BSh]]}}
{{legend|#FFDB63|[[semi-arid climate|BSk]]}}
| width=5 |
|
{{legend|#FFFF00|[[mediterranean climate|Csa]]}}
{{legend|#C6C700|[[mediterranean climate|Csb]]}}
| width=5 |
|
{{legend|#96FF96|[[humid subtropical climate|Cwa]]}}
{{legend|#63C764|[[oceanic climate|Cwb]]}}
| width=5 |
|
{{legend|#C6FF4E|[[Humid subtropical climate|Cfa]]}}
{{legend|#66FF33|[[oceanic climate|Cfb]]}}
{{legend|#33C701|[[oceanic climate|Cfc]]}}
| width=5 |
|
{{legend|#FF00FE|[[continental climate|Dsa]]}}
{{legend|#C600C7|[[continental climate|Dsb]]}}
{{legend|#963295|[[continental climate|Dsc]]}}
{{legend|#966495|[[continental climate|Dsd]]}}
| width=5 |
|
{{legend|#ABB1FF|[[humid continental climate|Dwa]]}}
{{legend|#5A77DB|[[humid continental climate|Dwb]]}}
{{legend|#4C51B5|[[subarctic climate|Dwc]]}}
{{legend|#320087|[[subarctic climate|Dwd]]}}
| width=5 |
|
{{legend|#00FFFF|[[humid continental climate|Dfa]]}}
{{legend|#38C7FF|[[humid continental climate|Dfb]]}}
{{legend|#007E7D|[[subarctic climate|Dfc]]}}
{{legend|#00455E|[[subarctic climate|Dfd]]}}
| width=5 |
|
{{legend|#B2B2B2|[[tundra climate|ET]]}}
{{legend|#686868|[[ice cap climate|EF]]}}
|}
]]
 
{{Main|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 {{convert|1750|and|2000|mm|in|abbr=on}}.<ref>{{cite web|author=Susan Woodward|url=http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/rainforest/rainfrst.html|title=Tropical Broadleaf Evergreen Forest: The Rainforest|date=1997-10-29|accessdate=2008-03-14|publisher=[[Radford University]]}}</ref> A tropical savanna is a [[grassland]] [[biome]] located in [[semi-arid]] to semi-[[humid]] climate regions of [[subtropical]] and [[tropical]] [[latitudes]], with rainfall between {{convert|750|and|1270|mm|in|abbr=on}} a year. They are widespread on [[Africa]], and are also found in [[India]], the northern parts of [[South America]], [[Malaysia]], and [[Australia]].<ref name="SAVWOOD">{{cite web|author=Susan Woodward|url=http://www.radford.edu/~swoodwar/CLASSES/GEOG235/biomes/savanna/savanna.html|title=Tropical Savannas|date=2005-02-02|accessdate=2008-03-16|publisher=[[Radford University]]}}</ref> The humid subtropical climate zone where winter rainfall is associated with large [[storm]]s that the [[westerlies]] steer from west to east. Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones.<ref>{{cite encyclopedia | title = Humid subtropical climate | encyclopedia = [[Encyclopædia Britannica]] | publisher = Encyclopædia Britannica Online | year = 2008 | url = http://www.britannica.com/eb/article-53358/climate | accessdate = 2008-05-14 }}</ref> Humid subtropical climates lie on the east side continents, roughly between [[latitude]]s 20° and 40° degrees away from the equator.<ref>{{cite web|author=Michael Ritter|url=http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/humid_subtropical.html|date=2008-12-24|publisher=[[University of Wisconsin–Stevens Point]]|title=Humid Subtropical Climate|accessdate=2008-03-16}}</ref>
 
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.<ref>{{cite book|author=Lauren Springer Ogden|title=Plant-Driven Design|page=78|isbn=978-0-88192-877-8|publisher=Timber Press|year=2008|accessdate=2009-07-19}}</ref> The Mediterranean climate regime resembles the climate of the lands in the [[Mediterranean Basin]], parts of western [[North America]], parts of [[Western Australia|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.<ref>{{cite web|author=Michael Ritter|url=http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/mediterranean.html|title=Mediterranean or Dry Summer Subtropical Climate|accessdate=2009-07-17|date=2008-12-24|publisher=[[University of Wisconsin–Stevens Point]]}}</ref> A steppe is a dry [[grassland]].<ref>{{cite web|author=Brynn Schaffner and Kenneth Robinson|url=http://www.blueplanetbiomes.org/steppe_climate_page.htm|title=Steppe Climate|date=2003-06-06|accessdate=2008-04-15|publisher=West Tisbury Elementary School}}</ref> Subarctic climates are cold with continuous [[permafrost]] and little precipitation.<ref name="subritter">{{cite web|author=Michael Ritter|url=http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/subarctic.html|title=Subarctic Climate|accessdate=2008-04-16|publisher=[[University of Wisconsin–Stevens Point]]|date=2008-12-24}}</ref>
 
==Measurement==
 
===Gauges===
[[File:250mm Rain Gauge.jpg|thumb|upright|left|125 px|Standard rain gauge]]
 
{{See also|Rain gauge|Disdrometer|Snow gauge}}
 
Rain is measured in units of length per unit time, typically in millimeters per hour,<ref>http://www.wmo.int/pages/prog/www/IMOP/publications/CIMO-Guide/CIMO%20Guide%207th%20Edition,%202008/Part%20I/Chapter%206.pdf</ref> or in countries where [[imperial units]] are more common, inches per hour.<ref>{{cite web|url=http://training.fema.gov/EMIWeb/edu/docs/fem/Chapter 5 - Principal Hazards in U.S.doc |title=Chapter 5 - Principal Hazards in U.S.doc|page=128}}</ref> 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.<ref>[http://www.newton.dep.anl.gov/askasci/gen99/gen99115.htm Rain gauge and cubic inches<!-- Bot generated title -->]</ref> One millimeter of rainfall is the equivalent of one liter of water per square meter.<ref>{{cite web|url=http://www.fao.org/docrep/r4082e/r4082e05.htm |title=FAO.org |publisher=FAO.org |date= |accessdate=2011-12-26}}</ref>
 
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.<ref>{{cite web|author=[[National Weather Service]] Office, Northern Indiana|year=2009|url=http://www.crh.noaa.gov/iwx/program_areas/coop/8inch.php|title=8 Inch Non-Recording Standard Rain Gauge|accessdate=2009-01-02}}</ref> The inner cylinder is filled by {{convert|25|mm|in|abbr=on}} of rain, with overflow flowing into the outer cylinder. Plastic gauges have markings on the inner cylinder down to {{convert|0.25|mm|in|abbr=on}} resolution, while metal gauges require use of a stick designed with the appropriate {{convert|0.25|mm|in|abbr=on}} 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.<ref>{{cite web|author=Chris Lehmann|year=2009|url=http://nadp.sws.uiuc.edu/CAL/2000_reminders-4thQ.htm|title=10/00|publisher=Central Analytical Laboratory|accessdate=2009-01-02}}</ref> 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.<ref>{{cite web|author=[[National Weather Service]]|year=2009|url=http://www.weather.gov/glossary/index.php?letter=w|title=Glossary: W|accessdate=2009-01-01}}</ref> 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.<ref>{{cite web|author=Discovery School|year=2009|url=http://school.discovery.com/lessonplans/activities/weatherstation/itsrainingitspouring.html|title=Build Your Own Weather Station|publisher=Discovery Education|accessdate=2009-01-02|archiveurl=http://web.archive.org/web/20081226022910/http://school.discovery.com/lessonplans/activities/weatherstation/itsrainingitspouring.html <!--Added by H3llBot-->|archivedate=2008-12-26}}</ref>
 
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 [[Community Collaborative Rain, Hail and Snow network|CoCoRAHS]] or GLOBE.<ref>{{cite web|url=http://cocorahs.org |title=Community Collaborative Rain, Hail & Snow Network Main Page|publisher=Colorado Climate Center|year=2009|accessdate=2009-01-02}}</ref><ref>{{cite web|title=Global Learning and Observations to Benefit the Environment Program |url=http://www.globe.gov/fsl/welcome/welcomeobject.pl |author=The Globe Program|year=2009|accessdate=2009-01-02}}</ref> 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.<ref>{{cite web|author=[[National Weather Service]]|year=2009|url=http://www.nws.noaa.gov|title=NOAA's National Weather Service Main Page|accessdate=2009-01-01}}</ref>
 
===Remote sensing===
{{See also|Weather radar}}
[[File:Radar-accumulations eng.png|right|thumb|200px|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 [[hydrology|hydrological]] purposes.<ref>{{cite journal|url=http://www.springerlink.com/content/g5447473427jl6w1/|title=Radar Rainfall Estimates for Hydrologic and Landslide Modeling|author=Kang-Tsung Chang, Jr-Chuan Huang, Shuh-Ji Kao, and Shou-Hao Chiang|doi=10.1007/978-3-540-71056-1_6|isbn=978-3-540-71056-1|journal=Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications|year=2009|accessdate=2010-01-15|pages=127–145}}</ref> For instance, river flood control, sewer management and dam construction are all areas where planners use rainfall accumulation data. Radar-derived rainfall estimates compliment 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,
:<math> Z = A R^b </math>,
 
where Z represents the radar reflectivity, R represents the rainfall rate, and A and b are constants.<ref>{{cite web|url=http://ecommons.library.cornell.edu/bitstream/1813/2115/1/pdfthesis.pdf|publisher=[[Cornell University]]|author=Eric Chay Ware|title=Corrections to Radar-Estimated Precipitation Using Observed Rain Gauge Data: A Thesis|date=August 2005|page=1|accessdate=2010-01-02}}</ref> Satellite derived rainfall estimates use passive [[microwave]] instruments aboard [[polar orbit]]ing as well as [[geostationary orbit|geostationary]] [[weather satellite]]s to indirectly measure rainfall rates.<ref>{{cite web|url=http://www.isac.cnr.it/~ipwg/meetings/melbourne/papers/Mngadi.pdf|title=Southern Africa Satellite Derived Rainfall Estimates Validation|author=Pearl Mngadi, Petrus JM Visser, and Elizabeth Ebert|page=1|publisher=International Precipitation Working Group|date=October 2006|accessdate=2010-01-05}}</ref> 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.
 
{{multiple image
| align = left
| direction = horizontal
| image1 = 1988 US Rain.ogv
| width1 = 300
| alt1 =
| caption1 = 1988 Rain in the U.S. The heaviest rain is seen in reds and yellows.
| image2 = 1993 US Rain.ogv
| width2 = 300
| alt2 =
| caption2 = 1993 Rain in the U.S.
}}
{{-}}
 
===Intensity===
{{listen
| filename = Heavy rain in Glenshaw, PA.ogg
| title = Heavy rain in Glenshaw, PA
| description = The sound of a heavy rain fall in suburban neighborhood
}}
 
Rainfall intensity is classified according to the rate of precipitation:
* Light rain — when the precipitation rate is < {{convert|2.5|mm|in|abbr=on}} per hour
* Moderate rain — when the precipitation rate is between {{convert|2.5|mm|in|abbr=on}} - {{convert|7.6|mm|in|abbr=on}} or {{convert|10|mm|in|abbr=on}} per hour<ref name="rainint"/><ref name="UKint">{{cite web|page=6|url=http://www.metoffice.gov.uk/media/pdf/4/1/No._03_-_Water_in_the_Atmosphere.pdf
|title=Fact Sheet No. 3: Water in the Atmosphere|publisher=Crown Copyright|date=August 2007|author=Met Office|accessdate=2011-05-12}}</ref>
* Heavy rain — when the precipitation rate is > {{convert|7.6|mm|in|abbr=on}} per hour,<ref name="rainint">{{cite web|date=June 2000|url=http://amsglossary.allenpress.com/glossary/search?id=rain1|author=Glossary of Meteorology|title=Rain|publisher=[[American Meteorological Society]]|accessdate=2010-01-15}}</ref> or between {{convert|10|mm|in|abbr=on}} and {{convert|50|mm|in|abbr=on}} per hour<ref name="UKint"/>
* Violent rain — when the precipitation rate is > {{convert|50|mm|in|abbr=on}} per hour<ref name="UKint"/>
 
Euphemisms for a heavy or violent rain include gully washer, trash-mover and toad-strangler.<ref>[http://dictionary.reference.com/browse/gullywasher Gullywasher | Define Gullywasher at Dictionary.com<!-- Bot generated title -->]</ref><ref>[http://en.wiktionary.org/wiki/toad-strangler toad-strangler - Wiktionary<!-- Bot generated title -->]</ref>
 
{{clear}}
 
===Return period===
{{See also|100-year flood}}
The likelihood or probability of an event with a specified intensity and duration, is called the [[return period]] or frequency.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?id=return-period1|title=Return period|publisher=[[American Meteorological Society]]|accessdate=2009-01-02}}</ref> The intensity of a storm can be predicted for any return period and storm duration, from charts based on historic data for the location.<ref>{{cite web|author=Glossary of Meteorology|year=2009|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=return+period&submit=Search|title=Rainfall intensity return period|publisher=[[American Meteorological Society]]|accessdate=2009-01-02}}</ref> The term ''1 in 10&nbsp;year storm'' describes a rainfall event which is rare and is only likely to occur once every 10&nbsp;years, so it has a 10&nbsp;percent likelihood any given year. The rainfall will be greater and the flooding will be worse than the worst storm expected in any single year. The term ''1 in 100&nbsp;year storm'' describes a rainfall event which is extremely rare and which will occur with a likelihood of only once in a century, so has a 1&nbsp;percent likelihood in any given year. The rainfall will be extreme and flooding to be worse than a 1 in 10&nbsp;year event. As with all probability events, it is possible, though improbable, to have multiple "1 in 100&nbsp;Year Storms" in a single year.<ref>{{cite web|author=Boulder Area Sustainability Information Network|year=2005|url=http://bcn.boulder.co.us/basin/watershed/flood.html|title=What is a 100 year flood?|publisher=Boulder Community Network|accessdate=2009-01-02}}</ref>
 
==Forecasting==
{{Main|Quantitative precipitation forecast}}
[[File:Rita5dayqpf.gif|thumb|left|200px|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.<ref name="SERFC">{{cite web|author=Jack S. Bushong|year=1999|url=http://cms.ce.gatech.edu/gwri/uploads/proceedings/1999/BushongJ-99.pdf|title=Quantitative Precipitation Forecast: Its Generation and Verification at the Southeast River Forecast Center|publisher=[[University of Georgia]]|accessdate=2008-12-31}}</ref> 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&nbsp;[[GMT]]. Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail.<ref>{{cite web|author=Daniel Weygand|year=2008|url=http://www.wrh.noaa.gov/wrh/talite0821.pdf|title=Optimizing Output From QPF Helper|publisher=[[National Weather Service]] Western Region|accessdate=2008-12-31}}</ref> Starting in the mid to late 1990s, QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States.<ref>{{cite web|author=Noreen O. Schwein|year=2009|url=http://ams.confex.com/ams/89annual/techprogram/paper_149707.htm|title=Optimization of quantitative precipitation forecast time horizons used in river forecasts|publisher=[[American Meteorological Society]]|accessdate=2008-12-31}}</ref> [[Numerical weather prediction|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.<ref>{{cite journal|author=Christian Keil, Andreas Röpnack, George C. Craig, and Ulrich Schumann|url=http://www.agu.org/pubs/crossref/2008/2008GL033657.shtml|title=Sensitivity of quantitative precipitation forecast to height dependent changes in humidity|journal=Geophysical Research Letters|volume=35|doi=10.1029/2008GL033657|date=2008-12-31|pages=L09812|bibcode=2008GeoRL..3509812K|issue=9}}</ref> QPF can be generated on a quantitative, forecasting amounts, or a qualitative, forecasting the probability of a specific amount, basis.<ref>{{cite journal|author=P. Reggiani and A. H. Weerts|year=2007|url=http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F2007JHM858.1&ct=1|title=Probabilistic Quantitative Precipitation Forecast for Flood Prediction: An Application|journal=Journal of Hydrometeorology|date=February 2008|pages=76–95|volume=9|issue=1|accessdate=2008-12-31|doi=10.1175/2007JHM858.1|bibcode = 2008JHyMe...9...76R }}</ref> Radar imagery forecasting techniques show higher [[Forecast skill|skill]] than model forecasts within 6 to 7&nbsp;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.<ref name="Canada">{{cite web|author=Charles Lin|year=2005|url=http://www.actif-ec.net/Workshop2/Presentations/ACTIF_P_S1_02.pdf|title=Quantitative Precipitation Forecast (QPF) from Weather Prediction Models and Radar Nowcasts, and Atmospheric Hydrological Modelling for Flood Simulation|publisher=Achieving Technological Innovation in Flood Forecasting Project|accessdate=2009-01-01}}</ref>
 
==Impact==
 
===Effect on agriculture===
[[File:Heavy Rains in Southern Japan.gif|thumb|Rainfall estimates for southern [[Japan]] and the surrounding region from July 20–27, 2009.]]
Precipitation, especially rain, has a dramatic effect on [[agriculture]]. All [[plant]]s 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 [[plant]]s, too much or too little rainfall can be harmful, even devastating to [[crops]]. [[Drought]] can kill crops and increase erosion,<ref>{{cite web|url=http://www.bom.gov.au/climate/drought/livedrought.shtml|title=Living With Drought|author=[[Bureau of Meteorology]]|publisher=Commonwealth of Australia|year=2010|accessdate=2010-01-15}}</ref> while overly wet weather can cause harmful [[fungus]] growth.<ref>{{cite web|url=http://agnewsarchive.tamu.edu/dailynews/stories/CROP/Jun0607a.htm|title=Texas Crop and Weather|date=2007-06-06|author=Robert Burns|publisher=[[Texas A&M University]]|accessdate=2010-01-15}}</ref> Plants need varying amounts of rainfall to survive. For example, certain [[cactus|cacti]] require small amounts of water,<ref>{{cite web|url=http://www.sbs.utexas.edu/mauseth/researchoncacti/|title=Mauseth Research: Cacti|author=James D. Mauseth|publisher=[[University of Texas]]|date=2006-07-07|accessdate=2010-01-15}}</ref> 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.<ref name="JS"/> 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.<ref>[[A. Roberto Frisancho]] (1993). [http://books.google.com/books?id=-K_SYHBo42MC&pg=PA388&lpg=PA388&dq=wet+season+characteristics&source=web&ots=QSA_t3uuZU&sig=iin9pzOynVHyA7x4wMYEkApeCV8&hl=en&sa=X&oi=book_result&resnum=5&ct=result Human Adaptation and Accommodation.] University of Michigan Press, pp. 388. ISBN 978-0-472-09511-7. Retrieved on 2008-12-27.</ref> 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.<ref>{{cite journal|author=Marti J. Van Liere, Eric-Alain D. Ategbo, Jan Hoorweg, Adel P. Den Hartog, and Joseph G. A. J. Hautvast|title=The significance of socio-economic characteristics for adult seasonal body-weight fluctuations: a study in north-western Benin|journal=British Journal of Nutrition|publisher=Cambridge University Press|year=1994|volume=72|pages=479–488|url=http://journals.cambridge.org/download.php?file=%2FBJN%2FBJN72_03%2FS0007114594000504a.pdf&code=40a3bcb87f8abc243d961c531b3262e2|doi=10.1079/BJN19940049|pmid=7947661|issue=3}}</ref> Rain may be [[Rainwater harvesting|harvested]] through the use of [[rainwater tank]]s; treated to potable use or for non-potable use indoors or for irrigation.<ref>{{cite web|url=http://rainwaterharvesting.tamu.edu/drinking/gi-366_2021994.pdf|title=Harvesting, Storing, and Treating Rainwater for Domestic Indoor Use|author=Texas Department of Environmental Quality|publisher=[[Texas A&M University]]|date=2008-01-16|accessdate=2010-01-15}}</ref> Excessive rain during short periods of time can cause flash [[flood]]s.<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=flash+flood&submit=Search|title=Flash Flood|author=Glossary of Meteorology|publisher=[[American Meteorological Society]]|date=June 2000|accessdate=2010-01-15}}</ref>
 
===In culture===
Cultural attitudes towards rain differ across the world. In [[temperate]] [[climate]]s, people tend to be more stressed when the [[weather]] is unstable or cloudy, with its impact greater on men than women.<ref>{{cite journal|title=The effect of weather on mood, productivity, and frequency of emotional crisis in a temperate continental climate|journal=International Journal of Biometeorology|url=http://www.springerlink.com/content/j6687l0q639541p3/|doi=10.1007/BF01044907|volume=32|date=1986-12-10|accessdate=2010-01-15|author=A. G. Barnston|pages=134–143|issue=4|bibcode = 1988IJBm...32..134B }}</ref> 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]],<ref>{{cite web|url=http://www.thaindian.com/newsportal/enviornment/sudden-spell-of-rain-lifts-mood-in-delhi_100172192.html|publisher=Thaindian news|title=Sudden spell of rain lifts mood in Delhi|date=2009-03-23|accessdate=2010-01-15|author=IANS}}</ref> or during periods of [[drought]],<ref>{{cite web|url=http://www.mysanantonio.com/business/Rain_lifts_mood_of_farmers.html|title=Rain lifts moods of farmers|date=2009-09-11|accessdate=2010-01-15|author=William Pack|publisher=[[San Antonio Express-News]]}}</ref> rain lifts people's moods. In [[Botswana]], the [[Setswana]] word for rain, ''pula'', is used as [[Botswana pula|the name of the national currency]], in recognition of the economic importance of rain in this desert country.<ref>{{cite web|url=http://www.pulapulapula.co.uk/Glossary.html|title=Glossary of Setswana and Other Words|author=Robyn Cox|year=2007|accessdate=2010-01-15}}</ref> Several cultures have developed means of dealing with rain and have developed numerous protection devices such as [[umbrella]]s and [[raincoat]]s, and diversion devices such as [[rain gutter|gutters]] and [[storm drain]]s that lead rains to sewers.<ref>{{cite book|url=http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/chp1.pdf|page=4|year=2002|author=Allen Burton and Robert Pitt|title=Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers|publisher=CRC Press, LLC|accessdate=2010-01-15}}</ref> 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.<ref name="Bear1964">{{Cite journal
| volume = 201
| issue = 4923
| pages = 993–995
| last = Bear
| first = I.J.
| coauthors = R.G. Thomas
| title = Nature of argillaceous odour
| journal = Nature
| date = March 1964
| doi = 10.1038/201993a0
|bibcode = 1964Natur.201..993B }}</ref>
 
==Global climatology==
{{See also|Earth rainfall climatology}}
Approximately {{convert|505000|km3|mi3|abbr=on}} of water falls as precipitation each year across the globe with {{convert|398000|km3|mi3|abbr=on}} of it over the [[ocean]]s.<ref name="chow">{{cite web|author=Dr. Chowdhury's Guide to Planet Earth|year=2005|url=http://www.planetguide.net/book/chapter_2/water_cycle.html|title=The Water Cycle|publisher=WestEd|accessdate=2006-10-24}}</ref> Given the Earth's surface area, that means the globally averaged annual precipitation is {{convert|990|mm|in|abbr=on}}. Deserts are defined as areas with an average annual precipitation of less than {{convert|250|mm|0|abbr=on}} per year,<ref name="usgsdesert">{{cite web|url=http://pubs.usgs.gov/gip/deserts/what/|title=What is a desert?|author=Publications Service Center|publisher=[[United States Geologic Survey]]|accessdate=2010-01-15|date=2001-12-18}}</ref><ref>According to [http://pubs.usgs.gov/gip/deserts/what/ What is a desert?], the 250 mm threshold definition is attributed to [[Peveril Meigs]].</ref> or as areas where more water is lost by [[evapotranspiration]] than falls as precipitation.<ref name="brittanica" >{{cite web | url = http://www.britannica.com/eb/article-70815/desert | title = desert | accessdate = 2008-02-09 | work = Encyclopædia Britannica online}}</ref>
 
===Deserts===
{{Main|Desert}}
[[File:deserts.png|thumb|300px|Largest deserts]]
The northern half of Africa is primarily [[desert]] or [[arid]], containing the [[Sahara]]. 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,<ref>{{cite web
| url = http://www.deh.gov.au/biodiversity/about-biodiversity.html
| title = About Biodiversity
| accessdate = 2007-09-18
| publisher = Department of the Environment and Heritage
| archiveurl = http://web.archive.org/web/20070205015628/www.environment.gov.au/biodiversity/about-biodiversity.html
| archivedate = 2007-02-05
}}
</ref> making it the world's driest inhabited [[continent]]. In South America, the [[Andes]] mountain range blocks [[Pacific Ocean|Pacific]] moisture that arrives in that continent, resulting in a desertlike climate just downwind across western Argentina.<ref name="Andes"/> The drier areas of the United States are regions where the [[Sonoran desert]] overspreads the Desert Southwest, the Great Basin and central Wyoming.<ref name="USatl">{{cite web|date=2009-09-17|author=NationalAtlas.gov|publisher=[[United States Department of the Interior]]|url=http://www.nationalatlas.gov/printable/precipitation.html|title=Precipitation of the Individual States and of the Conterminous States|accessdate=2010-01-15}}</ref>
 
===Polar desert===
{{main|Polar desert|Polar climate}}
Since rain only falls as liquid, in frozen temperatures, rain can not fall. As a result, very cold climates see very little rainfall and are often known as [[polar desert]]s. 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 rainforest|tropical]] and [[Temperate rainforest|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|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.<ref>{{cite web|url=http://jisao.washington.edu/data/ud/africa/|publisher=[[University of Washington]]|title=Africa Rainfall Climatology|author=Todd Mitchell|date=October 2001|accessdate=2010-01-02}}</ref> 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.<ref>{{cite journal|url=http://airsea-www.jpl.nasa.gov/publication/paper/CARRS-ms5.pdf|title=Monsoon, Orography, and Human Influence on Asian Rainfall|journal=Proceedings of the First International Symposium in Cloud-prone & Rainy Areas Remote Sensing (CARRS), Chinese University of Hong Kong|author=W. Timothy Liu, Xiaosu Xie, and Wenqing Tang|publisher=[[National Aeronautic and Space Administration]] [[Jet Propulsion Laboratory]]|year=2006|accessdate=2010-01-04}}</ref> The monsoon trough can reach as far north as the [[40th parallel north|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.<ref name="NCFMRF">{{cite web|author=National Centre for Medium Range Forecasting|date=2004-10-23|url=http://www.ncmrwf.gov.in/Chapter-II.pdf|title=Chapter-II Monsoon-2004: Onset, Advancement and Circulation Features|publisher=India Ministry of Earth Sciences|accessdate=2008-05-03}}</ref><ref>{{cite web|author=[[Australian Broadcasting Corporation]]|date=1999-08-11|url=http://www.abc.net.au/storm/monsoon/print.htm|title=Monsoon|accessdate=2008-05-03}}</ref> Similar, but weaker, monsoon circulations are present over [[North America]] and [[Australia]].<ref>{{cite journal|author=David J. Gochis, Luis Brito-Castillo, and W. James Shuttleworth|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6C-4GX0CS2-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1155477058&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=39b2d61a04776e3b1b2b56071cdb5b2a|title=Hydroclimatology of the North American Monsoon region in northwest Mexico|doi=10.1016/j.jhydrol.2005.04.021|date=2006-01-10|pages=53–70|volume=316|journal=[[Journal of Hydrology]]|accessdate=2010-01-05|issue=1–4|bibcode = 2006JHyd..316...53G }}</ref><ref>[[Bureau of Meteorology]]. [http://www.bom.gov.au/weather/sa/giles/climate.shtml Climate of Giles.] Retrieved on 2008-05-03.</ref> 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]].<ref name="JHorel"/> The eastern half of the contiguous United States east of the [[98th meridian west|98th meridian]], the mountains of the [[Pacific Northwest]], and the [[Sierra Nevada (U.S.)|Sierra Nevada]] range are the wetter portions of the nation, with average rainfall exceeding {{convert|30|in|mm|abbr=on|disp=flip}} per year.<ref name=autogenerated1>NationalAtlas.gov [http://www.nationalatlas.gov/printable/precipitation.html Precipitation of the Individual States and of the Conterminous States.] Retrieved on 2008-03-09.</ref> [[Tropical cyclone]]s enhance precipitation across southern sections of the United States,<ref>{{cite journal|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=21888982|title=The Contribution of Eastern North Pacific Tropical Cyclones to the Rainfall Climatology of the Southwest United States|author=Kristen L. Corbosiero, Michael J. Dickinson, and Lance F. Bosart|journal=[[Monthly Weather Review]]|issn=0027-0644|volume=137|pages=2415–2435|publisher=[[American Meteorological Society]]|issue=8|doi=10.1175/2009MWR2768.1|year=2009|bibcode = 2009MWRv..137.2415C }}</ref> as well as [[Puerto Rico]], the [[United States Virgin Islands]],<ref>[[Central Intelligence Agency]]. [https://www.cia.gov/library/publications/the-world-factbook/geos/vq.html The World Factbook – Virgin Islands.] Retrieved on 2008-03-19.</ref> the [[Northern Mariana Islands]],<ref>[[BBC]]. [http://www.bbc.co.uk/weather/world/country_guides/results.shtml?tt=TT004880 Weather Centre - World Weather - Country Guides - Northern Mariana Islands.] Retrieved on 2008-03-19.</ref> [[Guam]], and [[American Samoa]].
 
===Impact of the Westerlies===
[[File:MeanMonthlyP.gif|thumb|right|340px|Long-term mean precipitation by month]]
{{See also|Westerlies}}
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 {{convert|1000|mm|in|abbr=on}}, at sea-level and {{convert|2500|mm|in|abbr=on}}, on the mountains of rain per year. [[Bergen]], Norway is one of the more famous European rain-cities with its yearly precipitation of {{convert|2250|mm|in|abbr=on}} on average. During the fall, winter, and [[spring (season)|spring]], Pacific storm systems bring most of [[Hawaii]] and the western United States much of their precipitation.<ref name="JHorel">J. Horel. [http://www.met.utah.edu/jhorel/html/wx/climate/normrain.html Normal Monthly Precipitation, Inches.] Retrieved on 2008-03-19.</ref> 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 Complex|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.<ref name="Walker">Walker S. Ashley, Thomas L. Mote, P. Grady Dixon, Sharon L. Trotter, Emily J. Powell, Joshua D. Durkee, and Andrew J. Grundstein. [http://ams.allenpress.com/archive/1520-0493/131/12/pdf/i1520-0493-131-12-3003.pdf Distribution of Mesoscale Convective Complex Rainfall in the United States.] Retrieved on 2008-03-02.</ref>
 
The [[El Niño-Southern Oscillation]] affects the precipitation distribution, by altering rainfall patterns across the western United States,<ref>John Monteverdi and Jan Null. [http://tornado.sfsu.edu/geosciences/elnino/elnino.html Western Region Technical Attachment NO. 97-37 November 21, 1997: El Niño and California Precipitation.] Retrieved on 2008-02-28.</ref> Midwest,<ref>{{cite web|author=Southeast Climate Consortium|date=2007-12-20|url=http://www.agclimate.org/Development/apps/agClimate/controller/perl/agClimate.pl/agClimate.pl?function=climforecast/outlook.html&location=local&type |title=SECC Winter Climate Outlook|accessdate=2008-02-29 |archiveurl = http://web.archive.org/web/20080304212445/http://www.agclimate.org/Development/apps/agClimate/controller/perl/agClimate.pl/agClimate.pl?function=climforecast/outlook.html&location=local&type |archivedate = 2008-03-04}}</ref><ref>{{cite web|author=Reuters|date=2007-02-16|url=http://www.reuters.com/article/domesticNews/idUSN1619766420070216|title=La Nina could mean dry summer in Midwest and Plains|accessdate=2008-02-29}}</ref> the Southeast,<ref>[[Climate Prediction Center]]. [http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensorain.shtml El Niño (ENSO) Related Rainfall Patterns Over the Tropical Pacific.] Retrieved on 2008-02-28.</ref> 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 [[Himalaya|Eastern Himalaya]] in [[Shillong]], [[India]] is the confirmed wettest place on Earth, with an average annual rainfall of {{convert|11430|mm|in|abbr=on}}. The highest recorded rainfall in a single year was {{convert|22987|mm|in|abbr=on}} in 1861. The 38-year average at nearby [[Mawsynram]], [[Meghalaya]], [[India]] is {{convert|11873|mm|in|abbr=on}}.<ref>{{cite web|url=http://www.clas.ufl.edu/users/jsouthwo/web/6-per-page-Wettest-Mawsynram-in-India.pdf|title=Mawsynram in India|author=A. J. Philip|publisher=[[Tribune News Service]]|date=2004-10-12|accessdate=2010-01-05}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> The wettest spot in Australia is [[Mount Bellenden Ker]] in the north-east of the country which records an average of {{convert|8000|mm|in|abbr=on}} per year, with over {{convert|12200|mm|in|1|abbr=on}} of rain recorded during 2000.<ref>{{cite web |title = Significant Weather - December 2000 (Rainfall) |url = http://www.bom.gov.au/inside/services_policy/public/sigwxsum/sigw1200.shtml#rain |publisher = Commonwealth of Australia|author=[[Bureau of Meteorology]] |year=2010|accessdate = 2010-01-15}}</ref> [[Mount Waialeale|Mount Waiʻaleʻale]] on the island of [[Kauaʻi]] in the [[Hawaiian Islands]] averages more than {{convert|460|in|mm|abbr=on|disp=flip}}<ref name="NCDCxrain">{{cite web|url=http://www.ncdc.noaa.gov/oa/climate/globalextremes.html|title=Global Measured Extremes of Temperature and Precipitation|author=[[National Climatic Data Center]]|date=2005-08-09|accessdate=2007-01-18|publisher=[[National Oceanic and Atmospheric Administration]]}}</ref> of rain per year over the last 32 years, with a record {{convert|17340|mm|in|abbr=on}} in 1982.{{Citation needed|reason=Searching the web one can find different amounts|date=December 2013}} Its summit is considered one of the rainiest spots on earth. It has been promoted in tourist literature for many years as the wettest spot in the world.<ref>{{cite web |title = USGS 220427159300201 1047.0 Mt. Waialeale rain gauge nr Lihue, Kauai, HI |url = http://waterdata.usgs.gov/hi/nwis/uv?site_no=220427159300201&PARAmeter_cd=00045 |publisher = USGS Real-time rainfall data at Wai{{okina}}ale{{okina}}ale Raingauge |accessdate = 2008-12-11}}</ref>{{Failed verification|date=December 2013}} [[Lloró]], a town situated in [[Chocó Department|Chocó]], [[Colombia]], is probably the place with the largest rainfall in the world, averaging {{convert|523.6|in|mm|abbr=on|disp=flip}} per year.<ref name="NCDCxrain" /> 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 {{convert|11394|mm|in|abbr=on}} per year; in 1974 the town received {{convert|26303|mm|ftin|abbr=on}},{{citation needed|date=December 2013}} 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.<ref>{{cite web |title = Tutunendaó, Choco: la ciudad colombiana es muy lluviosa |url = http://www.elperiodico.com/default.asp?idpublicacio_PK=46&idioma=CAS&idnoticia_PK=523370&idseccio_PK=1038 |publisher = El Periódico.com |author=Alfred Rodríguez Picódate|date=2008-02-07|accessdate = 2008-12-11}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> [[Quibdó]], the capital of Chocó, receives the most rain in the world among cities with over 100,000 inhabitants: {{convert|354|in|mm|abbr=on|disp=flip}} per year.<ref name="NCDCxrain"/> Storms in Chocó can drop {{convert|500|mm|in|abbr=on}} of rainfall in a day. This amount is more than falls in many cities in a year's time.
 
{| class="wikitable" cellpadding="5" style="margin:auto;"
|-
!rowspan=2| Continent
!colspan=2| Highest average
!rowspan=2| Place
!colspan=2| Elevation
!rowspan=2| Years of Record
|-
!in!!mm
!ft!!m
|-
| &nbsp;[[South America]]&nbsp;
| {{convert|523.6|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Lloró]], [[Colombia]] (estimated){{ref label|a|a|a}}{{ref label|b|b|none}}&nbsp;
| {{convert|520|ft|m|0|disp=table}}{{ref label|c|c|none}}&nbsp;
| &nbsp;29&nbsp;
|-
| &nbsp;[[Asia]]&nbsp;
|{{convert|467.4|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Mawsynram]], [[India]]{{ref label|a|a|b}}{{ref label|d|d|none}}&nbsp;
| {{convert|4597|ft|m|0|disp=table}}&nbsp; || &nbsp;39&nbsp;
|-
| &nbsp;[[Oceania]]&nbsp;
| {{convert|460.0|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Mount Waialeale|Mount Waiʻaleʻale]], [[Kauai]], [[Hawaii Islands|Hawaii (USA)]]{{ref label|a|a|c}}&nbsp;
| {{convert|5148|ft|m|0|disp=table}}&nbsp;
| &nbsp;30&nbsp;
|-
| &nbsp;[[Africa]]&nbsp;
|{{convert|405.0|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Debundscha]], [[Cameroon]]&nbsp;
| {{convert|30|ft|m|1|disp=table}}&nbsp; || &nbsp;32&nbsp;
|-
| &nbsp;South America&nbsp;
|{{convert|354.0|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Quibdo]], Colombia&nbsp;
| {{convert|120|ft|m|1|disp=table}}&nbsp;
| &nbsp;16&nbsp;
|-
| &nbsp;[[Australia (continent)|Australia]]&nbsp;
| {{convert|340.0|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Mount Bellenden Ker]], [[Queensland]]&nbsp;
| {{convert|5102|ft|m|0|disp=table}}&nbsp;
| &nbsp;9&nbsp;
|-
| &nbsp;[[North America]]&nbsp;
| {{convert|256.0|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Henderson Lake (British Columbia)|Henderson Lake]], [[British Columbia]]&nbsp;
| {{convert|12|ft|m|2|disp=table}}&nbsp;
| &nbsp;14&nbsp;
|-
| &nbsp;[[Europe]]&nbsp;
| {{convert|183.0|in|mm|0|disp=table}}&nbsp;
| &nbsp;[[Crkvice]], [[Montenegro]]&nbsp;
| {{convert|3337|ft|m|0|disp=table}}&nbsp;
| &nbsp;22&nbsp;
|-
| colspan=7 style="text-align:center;"|'''Source''' (without conversions): ''Global Measured Extremes of Temperature and Precipitation'', [[National Climatic Data Center]]. August 9, 2004.<ref>{{cite web|title=Global Measured Extremes of Temperature and Precipitation#Highest Average Annual Precipitation Extremes|url=http://www.ncdc.noaa.gov/oa/climate/globalextremes.html#highpre|publisher=[[National Climatic Data Center]]|date=August 9, 2004}}</ref>
|}
 
{| class="wikitable" cellpadding="5" style="margin:auto;"
|-
!rowspan=2|
!rowspan=2| Continent
!rowspan=2| Place
!colspan=2| Highest rainfall
|-
!in!!mm
|-
! Highest average annual rainfall<ref name="Global extremes"/>
| &nbsp;Asia
| &nbsp;[[Mawsynram, India]]
| {{convert|467.4|in|mm|-1|disp=table}}&nbsp;
|-
! Highest in one year<ref name="Global extremes">{{cite web |url= http://wmo.asu.edu/#global |title= Global Weather & Climate Extremes |publisher= World Meteorological Organization |date= |accessdate= 2013-04-18}}</ref>
| &nbsp;Asia
| &nbsp;[[Cherrapunji, India]]
| {{convert|1,042|in|mm|-1|disp=table}}&nbsp;
|-
! Highest in one Calendar month<ref name="extremes">{{cite web|url=http://members.iinet.net.au/~jacob/worldrf.html |title=World Rainfall Extremes |publisher=Members.iinet.net.au |date=2004-03-02 |accessdate=2011-12-26}}</ref>
| &nbsp;Asia
| &nbsp;Cherrapunji, India
| {{convert|366|in|mm|0|disp=table}}
|-
! Highest in 24 hours<ref name="Global extremes"/>
| &nbsp;[[Indian Ocean]]
| &nbsp;Foc Foc, [[La Reunion Island]]
| {{convert|71.8|in|mm|-1|disp=table}}
|-
! Highest in 12 hours<ref name="Global extremes"/>
| &nbsp;Indian Ocean
| &nbsp;Foc Foc, La Reunion Island
| {{convert|45.0|in|mm|-1|disp=table}}
|-
! Highest in one minute<ref name="Global extremes"/>
| &nbsp;North America
| &nbsp;[[Unionville, Talbot County, Maryland|Unionville, Maryland]], USA
| {{convert|1.23|in|mm|1|disp=table}}
|}
 
==Outside of Earth==
On [[Titan (moon)|Titan]], [[Saturn]]'s largest moon, infrequent methane rain is thought to carve the moon's numerous surface channels.<ref name="planetary-Arizona_Icebox">{{cite news |url=http://www.planetary.org/news/2005/huygens_science-results_0121.html |title=Titan: Arizona in an Icebox? |author=Emily Lakdawalla |date=2004-01-21 |publisher=The Planetary Society |accessdate=2005-03-28 |archiveurl=http://web.archive.org/web/20050124004404/http://www.planetary.org/news/2005/huygens_science-results_0121.html |archivedate=2005-01-14}}</ref> On [[Venus]], sulfuric acid [[virga]] evaporates {{convert|25|km|mi|abbr=on}} from the surface.<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/4335628.stm|author=Paul Rincon|accessdate=2010-01-25|title=Planet Venus: Earth's 'evil twin'|publisher=BBC News|date=2005-11-07}}</ref> There is likely to be rain of various compositions in the upper atmospheres of the [[gas giant]]s, as well as precipitation of liquid neon in the deep atmospheres.<ref name="galileo_ms">{{cite web
|author=Paul Mahaffy
|url = http://ael.gsfc.nasa.gov/jupiterHighlights.shtml
|title = Highlights of the Galileo Probe Mass Spectrometer Investigation
|publisher = NASA Goddard Space Flight Center, Atmospheric Experiments Laboratory
|accessdate = 2007-06-06}}</ref><ref>{{cite journal
|author = Katharina Lodders
|title=Jupiter Formed with More Tar than Ice
|journal=The Astrophysical Journal
|year=2004|volume=611|issue=1|pages=587–597
|url=http://www.journals.uchicago.edu/doi/full/10.1086/421970
| doi = 10.1086/421970
|accessdate=2007-07-03|bibcode=2004ApJ...611..587L}}</ref> Extrasolar planet [[OGLE-TR-56b]] in the constellation [[Sagittarius (constellation)|Sagittarius]] is hypothesized to have iron rain.<ref>{{cite journal|url=http://www.astrobio.net/pressrelease/352/new-world-of-iron-rain|title=New World of Iron Rain|author=[[Harvard University]] and [[Smithsonian Institution]]|journal=Astrobiology Magazine|date=2003-01-08|accessdate=2010-01-25}}</ref>
 
==See also==
{{portal|Environment|Ecology}}
{{div col|colwidth=30em}}
* [[Johad]]
* [[John Rainwater]] (pseudonymous mathematician)
* [[Rain dancing]]
* [[Rain dust]]
* [[Rain sensor]]
* [[Rainbow]]
* [[Raining animals]]
* [[Red rain in Kerala]]
* [[Sanitary sewer overflow]]
* [[Sediment precipitation]]
* [[Water resources]]
* [[Weather]]
{{div col end}}
 
==Notes==
* {{note label|a|a|a}}{{note label|a|a|b}}{{note label|a|a|c}} The value given is continent's highest and possibly the world's depending on measurement practices, procedures and period of record variations.
* {{note label|b|b|none}} The official greatest average annual precipitation for South America is {{convert|354|in|cm|disp=flip|abbr=on}} at Quibdó, Colombia. The {{convert|523.6|in|cm|disp=flip|abbr=on}} average at Lloró [{{convert|14|mi|km|disp=flip|abbr=on}} SE and at a higher elevation than Quibdó] is an estimated amount.
* {{note label|c|c|none}} Approximate elevation.
* {{note label|d|d|none}} Recognized as "The Wettest place on Earth" by the ''[[Guinness Book of World Records]]''.<ref name="wett">[http://www.clas.ufl.edu/users/jsouthwo/web/6-per-page-Wettest-Mawsynram-in-India.pdf UFL - Dispute between Mawsynram and Cherrapunji for the rainiest place in the world]{{dead link|date=December 2011}}</ref>
 
==References==
{{reflist|2}}
 
==External links==
{{wikiquote}}
{{commons|Rain}}
* [http://www.geography-site.co.uk/pages/physical/climate/why%20does%20it%20rain.html What are clouds, and why does it rain?]
* [http://news.bbc.co.uk/2/hi/sci/tech/146120.stm BBC article on the weekend rain effect]
* [http://news.bbc.co.uk/2/hi/asia-pacific/3893671.stm BBC article on rain-making]
* [http://news.bbc.co.uk/1/hi/magazine/4562132.stm BBC article on the mathematics of running in the rain]
{{good article}}
 
[[Category:Precipitation]]
 
{{Link GA|de}}
{{Link GA|eo}}
{{Link GA|id}}

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