Dry season

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Dry season in Laos. Long shadow of a dead tree with its branches on the dry fields of Don Det, a sunny day with blue sky and white clouds, late afternoon. Long shadow of a dead tree with its branches on the dry fields of Laos - landscape.jpg
Dry season in Laos. Long shadow of a dead tree with its branches on the dry fields of Don Det, a sunny day with blue sky and white clouds, late afternoon.

The dry season is a yearly period of low rainfall, especially in the tropics. The weather in the tropics is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back over the course of the year. The temperate counterpart to the tropical dry season is summer.


Rain belt

The tropical rain belt lies in the southern hemisphere roughly from October to March; during that time the northern tropics have a dry season with sparser precipitation, and days are typically sunny throughout. From April to September, the rain belt lies in the northern hemisphere, and the southern tropics have their dry season. Under the Köppen climate classification, for tropical climates, a dry season month is defined as a month when average precipitation is below 60 millimetres (2.4 in). [1]

The rain belt reaches roughly as far north as the Tropic of Cancer and as far south as the Tropic of Capricorn. Near these latitudes, there is one wet season and one dry season annually. At the equator there are two wet and two dry seasons, as the rain belt passes over twice a year, once moving north and once moving south. Between the tropics and the equator, locations may experience a short wet and a long wet season; and a short dry and a long dry season. Local geography may substantially modify these climate patterns, however.


During the dry season, humidity is very low, causing some watering holes and rivers to dry up. This lack of water (and lack of food supply) may force many grazing animals to migrate to more fertile spots. Examples of such animals are: zebras, elephants, giraffe, rhinoceros, antelope and wildebeest, water buffalo, cape buffalo, gaur, tapir, emu, ostrich, rhea, and kangaroos. Because of the lack of water in the plants, bushfires (wildfires) are common. [2]


Data shows that in Africa the start of the dry season coincides with a rise in the cases of measles—which researchers believe might be attributed to the higher concentration of people in the dry season, as agricultural operations are all but impossible without irrigation. During this time, some farmers move into cities, creating hubs of higher population density, and allowing the disease to spread more easily. [3]


New data shows that in the seasonal parts of the South American Amazon rainforest, foliage growth and coverage varies between the dry and wet seasons—with about 25% more leaves and faster growth in the dry season. Researchers believe that the Amazon itself has an effect in bringing[ clarification needed ] the onset of the wet season: by growing more foliage, it evaporates more water. [4] However, this growth appears only in the undisturbed parts of the Amazon basin, where researchers believe roots can reach deeper and gather more rainwater. [5] It has also been shown that ozone levels are much higher in the dry than in the wet season in the Amazon basin. [6]

Related Research Articles

<span class="mw-page-title-main">Temperate climate</span> Main climate class

In geography, the temperate climates of Earth occur in the middle latitudes, which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout the year and more distinct seasonal changes compared to tropical climates, where such variations are often small and usually only have precipitation changes.

<span class="mw-page-title-main">Tropics</span> Region of Earth surrounding the Equator

The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at 23°26′10.8″ (or 23.43632°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′10.8″ (or 23.43632°) S; these latitudes correspond to the axial tilt of the Earth. The tropics are also referred to as the tropical zone and the torrid zone. The tropics also includes everywhere on Earth which is a subsolar point at least once during the solar year. Thus the maximum latitudes of the tropics have the same value positive and negative. Likewise, they approximate the angle of the Earth's axial tilt. The "angle" itself is not perfectly fixed due chiefly to the influence of the moon, but the limits of tropics are a geographic convention, being an averaged form, and the variance is very small.

<span class="mw-page-title-main">Tropic of Capricorn</span> Line of southernmost latitude at which the sun can be directly overhead

The Tropic of Capricorn is the circle of latitude that contains the subsolar point at the December solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reaches 90 degrees below the horizon at solar midnight on the June Solstice. Its northern equivalent is the Tropic of Cancer.

<span class="mw-page-title-main">Tropical and subtropical moist broadleaf forests</span> Habitat type defined by the World Wide Fund for Nature

Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature.

<span class="mw-page-title-main">Precipitation</span> Product of the condensation of atmospheric water vapor that falls under gravity

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation but colloids, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers.

<span class="mw-page-title-main">Subtropics</span> Geographic and climate zone

The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from 23°26′10.8″ (or 23.43632°) to approximately 35° north and south. The horse latitudes lie within this range.

<span class="mw-page-title-main">Tropical climate</span> One of the five major climate groups in the Köppen climate classification

Tropical climate is the first of the five major climate groups in the Köppen climate classification identified with the letter A. Tropical climates are defined by a monthly average temperature of 18 °C (64.4 °F) or higher in the coolest month, and feature hot temperatures all year-round. Annual precipitation is often abundant in tropical climates, and shows a seasonal rhythm but may have seasonal dryness to varying degrees. There are normally only two seasons in tropical climates, a wet season and a dry season. The annual temperature range in tropical climates is normally very small. Sunlight is intense in these climates.

<span class="mw-page-title-main">Köppen climate classification</span> Climate classification system

The Köppen climate classification is one of the most widely used climate classification systems. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notably in 1918 and 1936. Later, the climatologist Rudolf Geiger (1894–1981) introduced some changes to the classification system, which is thus sometimes called the Köppen–Geiger climate classification system.

<span class="mw-page-title-main">Tropical rainforest</span> Forest in areas with heavy rainfall in the tropics

Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as lowland equatorial evergreen rainforest. True rainforests are typically found between 10 degrees north and south of the equator ; they are a sub-set of the tropical forest biome that occurs roughly within the 28-degree latitudes. Within the World Wildlife Fund's biome classification, tropical rainforests are a type of tropical moist broadleaf forest that also includes the more extensive seasonal tropical forests.

Rainfall and the tropical climate dominate the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year, roughly following the solar equator. The tropical rain belt is an area of active rain that is positioned mostly around the tropics.

<span class="mw-page-title-main">Climate of Peru</span> Diverse climates of this large South American country

Climate of Peru describes the diverse climates of this large South American country with an area of 1,285,216 km2 (496,225 sq mi). Peru is located entirely in the tropics but features desert and mountain climates as well as tropical rainforests. Elevations above sea level in the country range from −37 to 6,778 m and precipitation ranges from less than 20 mm (0.79 in) annually to more than 8,000 mm (310 in). There are three main climatic regions: the Pacific Ocean coast is one of the driest deserts in the world but with some unique features; the high Andes mountains have a variety of microclimates depending on elevation and exposure and with temperatures and precipitation from temperate to polar and wet to dry; and the Amazon basin has tropical climates, mostly with abundant precipitation, along with sub-tropical climates in elevations above 1,550 m (5,090 ft).

<span class="mw-page-title-main">Hadley cell</span> Equatorial atmospheric phenomenon

The Hadley cell, named after George Hadley, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward at a height of 10 to 15 kilometers above the earth's surface, descending in the subtropics, and then returning equatorward near the surface. This circulation creates the trade winds, tropical rain-belts and hurricanes, subtropical deserts and the jet streams. A Hadley cell's relatively low-altitude overturning circulation has air sinking at roughly 30 degrees latitude after traveling from near the equator.

A tropical marine climate is a tropical climate that is primarily influenced by the ocean. It is usually experienced by islands and coastal areas 10° to 20° north and south of the equator. There are two main seasons in a tropical marine climate: the wet season and the dry season. The annual rainfall is 1000 to over 1500 mm. The temperature ranges from 20 °C to 35 °C. The trade winds blow all year round and are moist, as they pass over warm seas. These climatic conditions are found, for example, across the Caribbean; the eastern coasts of Brazil, Madagascar and Queensland; and many islands in tropical waters.

<span class="mw-page-title-main">Climate of Colombia</span> Tropical and isothermal

The Climate of Colombia is determined for geographic and atmospheric elements: temperature, precipitations, solar radiation, wind, latitude, altitude, atmospheric. This generate a large number of climate variants in Colombia, from more hottest, until the more cold with temperatures of 0 °C in high mountains. Generally is tropical and temperate as a result of its geographical location near the Equator presenting variations within five natural regions and depending on the altitude, being all isothermal. Because it has a very low latitude, there are no four seasons.

<span class="mw-page-title-main">Tropical savanna climate</span> Climate subtype

Tropical savanna climate or tropical wet and dry climate is a tropical climate sub-type that corresponds to the Köppen climate classification categories Aw and As. The driest month has less than 60 mm (2.4 in) of precipitation and also less than mm of precipitation.

<span class="mw-page-title-main">Tropical rainforest climate</span> Type of tropical climate in which there is no dry season

A tropical rainforest climate, humid tropical climate or equatorial climate is a tropical climate sub-type usually found within 10 to 15 degrees latitude of the equator. There are some other areas at higher latitudes, such as the coast of southeast Florida, USA, and Okinawa, Japan that fall into the tropical rainforest climate category. They experience high mean annual temperatures, small temperature ranges, and rain that falls throughout the year. Regions with this climate are typically designated Af by the Köppen climate classification. A tropical rainforest climate is typically hot, very humid, and wet.

<span class="mw-page-title-main">Rain</span> Precipitation in the form of water droplets

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

<span class="mw-page-title-main">Tropical monsoon climate</span> Climate subtype in the Köppen climate classification system

An area of tropical monsoon climate is a tropical climate sub-type that corresponds to the Köppen climate classification category Am. Tropical monsoon climates have monthly mean temperatures above 18 °C (64 °F) in every month of the year and a dry season. Tropical monsoon climates is the intermediate climate between the wet Af and the drier Aw.

<span class="mw-page-title-main">Seasonal tropical forest</span> Type of tropical forest

Seasonal tropical forest, also known as moist deciduous, semi-evergreen seasonal, tropical mixed or monsoon forests, typically contain a range of tree species: only some of which drop some or all of their leaves during the dry season. This tropical forest is classified under the Walter system as (ii) tropical climate with high overall rainfall concentrated in the summer wet season and dry season: representing a range of habitats influenced by monsoon (Am) or tropical wet savannah (Aw) climates. Drier forests in the Aw climate zone are typically deciduous and placed in the Tropical dry forest biome: with further transitional zones (ecotones) of savannah woodland then tropical and subtropical grasslands, savannas, and shrublands.

<span class="mw-page-title-main">Highland temperate climate</span>

The highland temperate climates are a temperate climate sub-type, although located in tropical zone, isothermal and with characteristics different from others temperate climates like oceanic or mediterranean where they are often are included without proper differentiation.


  1. "Updated world Köppen-Geiger climate classification map" (PDF).
  2. "Wet & Dry Seasons". Archived from the original on 2012-03-20. Retrieved 2008-04-21.
  3. "Dry Season Brings On Measles In Sub-Saharan Africa". ScienceDaily. February 7, 2008.
  4. "Amazon rainforest does have rainy and dry seasons". mongabay.com. March 12, 2007. Archived from the original on June 4, 2008.
  5. "Amazon rainforest greens up in the dry season".
  6. V. W. J. H. Kirchhoff, I. M. O. Da Silva, E. V. Browell (1990). "Ozone measurements in Amazonia: Dry season versus wet season". Journal of Geophysical Research. 95 (D10): 16913. Bibcode:1990JGR....9516913K. doi:10.1029/jd095id10p16913. Archived from the original on 2011-06-06. Retrieved 2008-04-21.{{cite journal}}: CS1 maint: multiple names: authors list (link)