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The wet season (sometimes called the rainy season) is the time of year when most of a region's average annual
rainfall Rain is liquid water in the form of droplet Raindrops in a plant. A drop or droplet is a small column of liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechani ...

rainfall
occurs. Generally, the season lasts at least a month. The term ''green season'' is also sometimes used as a
euphemism A euphemism () is an innocuous word or expression used in place of one that is deemed offensive or suggests something unpleasant. Some euphemisms are intended to amuse, while others use bland, inoffensive terms for concepts that the user wishes to ...
by tourist authorities. Areas with wet seasons are dispersed across portions of the
tropics The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% i ...

tropics
and
subtropics The subtropical zones or subtropics are geographical Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country locat ...

subtropics
. Under the
Köppen climate classification The Köppen climate classification is one of the most widely used systems. It was first published by German-Russian (1846–1940) in 1884, with several later modifications by Köppen, notably in 1918 and 1936. Later, the climatologist (1894- ...
, for
tropical climate Tropical climate is one of the five major climate groups in the . Tropical climates are characterized by monthly average temperatures of 18 °C (64.4 °F) or higher year-round and feature hot temperatures. Annual precipitation is often ...
s, a wet season month is defined as a month where average precipitation is or more. In contrast to areas with
savanna A savanna or savannah is a mixed woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ' woods), a low-density forming open s with plenty of sunlight and li ...

savanna
climates and
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric ph ...

monsoon
regimes,
Mediterranean climate A Mediterranean climate or dry summer climate is characterized by dry summers and mild, wet winters. The climate Climate is the long-term pattern of weather Weather is the state of the atmosphere, describing for example the degre ...
s have wet winters and dry summers. Dry and rainy months are characteristic of
tropical seasonal forest The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S; these latitudes correspond to the ...
s: in contrast to
tropical rainforest Tropical rainforests are rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape ...

tropical rainforest
s, which do not have dry or wet seasons, since their rainfall is equally distributed throughout the year.Elisabeth M. Benders-Hyde (2003)
World Climates.
Blue Planet Biomes. Retrieved on 2008-12-27.
Some areas with pronounced rainy seasons will see a break in rainfall mid-season, when the intertropical convergence zone or
monsoon trough The monsoon trough is a portion of the Intertropical Convergence Zone in the Western Pacific,Bin WangThe Asian Monsoon.Retrieved 2008-05-03. as depicted by a line on a weather map 250px, A surface weather analysis for the United States on Oct ...
moves to higher latitudes in the middle of the warm season.J. S. 0guntoyinbo and F. 0. Akintola (1983)
Rainstorm characteristics affecting water availability for agriculture.
IAHS Publication Number 140. Retrieved on 2008-12-27.
When the wet season occurs during a warm season, or
summer Summer is the hottest of the four temperate In geography, the temperate climates of Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land ...

summer
,
precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...
falls mainly during the late afternoon and early evening. In the wet season,
air quality Air pollution is the presence of substances in the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gas ...
improves, fresh
water quality Water quality refers to the Chemical property, chemical, Physical property, physical, and Biology, biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against whi ...

water quality
improves, and vegetation grows substantially, leading to crop yields late in the season. Rivers overflow their banks, and some animals retreat to higher ground.
Soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms tha ...

Soil
nutrients diminish and erosion increases. The incidence of
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign fo ...

malaria
and dengue increases in areas where the rainy season coincides with high temperatures, particularly in tropical areas. Some animals have adaptation and survival strategies for the wet season. Often, the previous dry season leads to food shortages in the wet season, as the crops have yet to mature.


Character of the rainfall

In areas where the heavy rainfall is associated with a wind shift, the wet season is known as the monsoon season. Many tropical and subtropical climates experience monsoon rainfall patterns. Rainfall in the wet season is mainly due to daytime heating, which leads to diurnal thunderstorm activity within a pre-existing moist airmass , so the rain mainly falls in late afternoon and early evening in savannah and monsoon regions. Much of the total rainfall each day occurs in the first minutes of the downpour, before the storms mature into their stratiform stage. Most places have only one wet season, but areas of the tropics can have two wet seasons, because the monsoon trough, or Intertropical Convergence Zone, can pass over locations in the tropics twice per year. However, since rain forests have rainfall spread evenly through the year, they do not have a wet season.


Areas affected

Areas with a
savanna A savanna or savannah is a mixed woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ' woods), a low-density forming open s with plenty of sunlight and li ...

savanna
climate in
Sub-Saharan Africa Sub-Saharan Africa (commonly called Black Africa) is, geographically, the area of the continent of Africa that lies south of the Sahara. According to the United Nations, it consists of all list of sovereign states and dependent territories i ...

Sub-Saharan Africa
, such as
Ghana Ghana (), officially the Republic of Ghana, is a country in West Africa West Africa or Western Africa is the westernmost region of . The defines Western Africa as the 17 countries of , , , , , , , , , , , , , , , and as well as .Paul R. ...

Ghana
,
Burkina Faso Burkina Faso (, ; ) is a landlocked country in West Africa that covers an area of around and is bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to the south, and the Ivory Coast to the southwe ...

Burkina Faso
,
Darfur Darfur ( ; ar, دار فور, Dār Fūr, lit=Realm of the Fur Fur is a thick growth of hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The hu ...

Darfur
,
Eritrea Eritrea ( ), officially the State of Eritrea, is a country in the Horn of Africa region of East Africa, Eastern Africa, with its capital (and largest city) at Asmara. It is bordered by Ethiopia in the south, Sudan in the west, and Djibouti ...

Eritrea
,
Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea and Djibouti to the north, Somaliland to the northeast, Somalia to the east, Kenya to the sout ...

Ethiopia
, and
Botswana Botswana (, also ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label=Setswana; Kalanga language, Kalanga: ''Hango yeBotswana''), is a landlocked country in Southern Africa. Botswana is topographically flat, with up to 70 ...

Botswana
have a distinct rainy season. Also subtropical areas like
Florida Florida is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia (U.S. state), Geor ...

Florida
,
South South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic language, Proto-Germa ...
and
Southeast The points of the compass are the vectors by which planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity ...
Texas, and southern
Louisiana Louisiana (Standard French Standard French (in French: ''le français standard'', ''le français normé'', ''le français neutre'' eutral Frenchor ''le français international'' nternational French is an unofficial term for a standard ...

Louisiana
have a rainy season. Monsoon regions include the Indian subcontinent,
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern subregion of Asia, consisting of the regions ...

Southeast Asia
(including
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...

Indonesia
and
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

Philippines
), northern sections of
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
's North,
Polynesia Polynesia (, ; from grc, πολύς "many" and grc, νῆσος "island") ( to, Faka-Polinisia; mi, Porinihia; haw, Polenekia; fj, Kai-Polinesia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia) is a ...

Polynesia
,
Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or ...

Central America
, western and southern
Mexico Mexico, officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the south and west by the Pacific Ocean; to ...

Mexico
, the Desert Southwest of the United States,J. Horel (2006)
Normal Monthly Precipitation, Inches.
University of Utah. Retrieved on 2008-03-19.
southern
Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be ...

Guyana
,Horace Burton (2006)
The climate of Guyana.
Caribbean Institute for Meteorology and Hydrology. The Outfield, August 2006, pp. 3. Retrieved on 2009-02-08.
and northeast
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
.James Brian Elsner (1988)
Analysis of Wet Season Rainfall Over the Nordeste of Brazil, South America.
University Of Wisconsin-Milwaukee. Retrieved on 2009-02-06.
Northern
Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be ...

Guyana
has two wet seasons: one in early spring and the other in early winter. In western Africa, there are two rainy seasons across southern sections, but only one across the north. Within the Mediterranean climate regime, the west coast of the United States, the southwest coast of Australia and South Africa, the
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...
coastline of Italy, Spain, Greece, Lebanon, Syria, Algeria, Morocco, Tunisia, Israel and Turkey, as well as areas further inland in Western Asia which include Jordan, Northern Iraq and most parts of Iran, experience a wet season in the winter months. Similarly, the wet season in the
Negev desert The Negev or Negeb (; he, הַנֶּגֶב, ha-Négev; ar, ٱلنَّقَب, an-Naqab) is a desert and semidesert region of southern Israel. The region's largest city and administrative capital is Beersheba (pop. ), in the north. At its southe ...

Negev desert
of
Israel Israel (; he, יִשְׂרָאֵל, translit=Yīsrāʾēl; ar, إِسْرَائِيل, translit=ʾIsrāʾīl), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a ...

Israel
extends from October through May. At the boundary between the Mediterranean and monsoon climates lies the
Sonoran desert The Sonoran Desert ( es, Desierto de Sonora) is a North American desert and ecoregion An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically Ecology (from el, οἶκος, "house" and el, -λογία, label=n ...

Sonoran desert
, which receives the two rainy seasons associated with each climate regime. The wet season is known by many different local names throughout the world. For example, in Mexico it is known as "storm season". Different names are given to the various short "seasons" of the year by the Aboriginal tribes of
Northern Australia The unofficial geographic term Northern Australia includes those parts of Queensland Queensland ( ,) is a state situated in northeastern Australia, and is the States and territories of Australia, second-largest and third-most populous Aust ...

Northern Australia
: the wet season typically experienced there from December to March is called ''Gudjewg''. The precise meaning of the word is disputed, although it is widely accepted to relate to the severe thunderstorms, flooding, and abundant vegetation growth commonly experienced at this time.


Effects

In tropical areas, when the monsoon arrives, high daytime high temperatures drop and overnight low temperatures increase, thus reducing
diurnal temperature variation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progr ...
. During the wet season, a combination of heavy rainfall and, in some places such as
Hong Kong Hong Kong (; , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (HKSAR), is a List of cities in China, city and Special administrative regions of China, special administrative region of China on the ...

Hong Kong
, an onshore wind, improve
air quality Air pollution is the presence of substances in the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gas ...
. In Brazil, the wet season is correlated with weaker
trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere The Northern Hemisphere is the half of Ear ...
off the ocean. The level of water becomes more balanced due to the charging of local
aquifer An aquifer is an underground layer of -bearing , rock fractures or unconsolidated materials (, , or ). can be extracted using a water . The study of water flow in aquifers and the characterization of aquifers is called . Related terms include a ...

aquifer
s during the wet season. Water also softens, as the concentration of dissolved materials reduces during the rainy season. Erosion is also increased during rainy periods. Arroyos that are dry at other times of the year fill with runoff, in some cases with water as deep as .United States War Department (1909)
Road Notes, Cuba. 1909.
United States Department of War. Retrieved on 2009-01-16.
Leaching of soils during periods of heavy rainfall depletes nutrients. The higher runoff from land masses affects nearby ocean areas, which are more
stratified Stratification may refer to: In mathematics: * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Stratified sampling , Data stratification in statistics In earth sciences: * Stable and unstable stratificati ...
, or less mixed, due to stronger surface currents forced by the heavy rainfall runoff.


Floods

High rainfall can cause widespread flooding, which can lead to landslides and mudflows in mountainous areas. Such floods cause rivers to burst their banks and submerge homes. The
Ghaggar-Hakra River The Ghaggar-Hakra River is an intermittent river Intermittent, temporary, or seasonal rivers and streams cease to flow every year or at least twice every five years.(Tzoraki et al., 2007) Such rivers drain large arid and semi-arid areas, co ...
, which only flows during India's monsoon season, can flood and severely damage local crops. Floods can be exacerbated by fires that occurred during the previous dry season, which cause soils which are sandy or composed of
loam Loam (in geology and soil science) is soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matt ...
to become hydrophobic, or water repellent. In various ways governments may help people deal with wet season floods. Flood plain mapping identifies which areas are more prone to flooding. Instructions on controlling erosion through outreach are also provided by telephone or the internet.


Life adaptations


Humans

The wet season is the main period of vegetation growth within the Savanna climate regime. However, this also means that wet season is a time for food shortages before crops reach their full maturity. This causes seasonal weight changes for people in developing countries, with a drop occurring during the wet season until the time of the first harvest, when weights rebound. Malaria incidence increases during periods of high temperature and heavy rainfall.


Animals

Cows calve, or give birth, at the beginning of the wet season. The onset of the rainy season signals the departure of the
monarch butterfly The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. It ...
from Mexico. Tropical species of
butterflies Butterflies are insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latiu ...

butterflies
show larger dot markings on their wings to fend off possible predators and are more active during the wet season than the
dry season The dry season is a yearly period of low rainfall, especially in the tropics The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of ...
. Within the tropics and warmer areas of the subtropics, decreased salinity of near shore wetlands due to the rains causes an increase in crocodile nesting. Other species, such as the
arroyo toad The arroyo toad (''Anaxyrus californicus'') is a species of true toads in the family Bufonidae{{Cat main, Toad This Wikipedia:Category, category contains both species commonly called toads, and the true toads from the family Bufonidae. Animals by ...

arroyo toad
, spawn within the couple of months after the seasonal rains.
Armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order (biology), order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving family (biology), families in the order, which is part of ...

Armadillo
s and
rattlesnake Rattlesnakes are a group of venomous snakes of the genera '' Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). The scientific name ''Crotalus'' is derived from the Greek language, Greek κρόταλον, meaning "castan ...

rattlesnake
s seek higher ground.Linda Deuver (1978)
Dry season, wet season.
Audubon Magazine, November 1978, pp. 120–130. Retrieved on 2009-02-06.


See also

* Akhet *
East Asian rainy season The East Asian rainy season, commonly called the plum rain (), is caused by precipitation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus ...
*
Dry season The dry season is a yearly period of low rainfall, especially in the tropics The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of ...


References

{{Authority control Seasons Rain