Long_shadow_of_a_dead_tree_with_its_branches_on_the_dry_fields_of_Laos_-_landscape

The dry season is a yearly period of low rainfall, especially in the

tropics The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

. 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 In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

counterpart to the tropical dry season is summer or

winter Winter is the coldest and darkest season of the year in temperate and polar climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Dif ...

Rain belt

The tropical rain belt lies in the southern hemisphere roughly from November to March; during that time the northern tropics have a dry season with sparser

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

, and days are typically sunny throughout. From May to September, the rain belt lies in the northern hemisphere, and the southern tropics have their dry season. Under the

Köppen climate classification The Köppen climate classification divides Earth climates into five main climate groups, with each group being divided based on patterns of seasonal precipitation and temperature. The five main groups are ''A'' (tropical), ''B'' (arid), ''C'' (te ...

, for

tropical climate 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 or higher in the coolest month, featuring hot te ...

s, a dry season month is defined as a month when average precipitation is below . The rain belt reaches roughly as far north as the

Tropic of Cancer The Tropic of Cancer, also known as the Northern Tropic, is the Earth's northernmost circle of latitude where the Sun can be seen directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted toward the Sun ...

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 The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

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 or a long wet season; and a short dry or a long dry season. Local geography may substantially modify these climate patterns, however they can.

Drought

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,

elephant Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...

s, giraffes, hippos, rhinos,

antelope The term antelope refers to numerous extant or recently extinct species of the ruminant artiodactyl family Bovidae that are indigenous to most of Africa, India, the Middle East, Central Asia, and a small area of Eastern Europe. Antelopes do ...

s and wildebeest, wild water buffaloes, African buffaloes, gaur, tapirs, emus, ostriches, rheas, and kangaroos. Because of the lack of water in the plants, bushfires (wildfires) are common.

Diseases

Data shows that in Africa the start of the dry season coincides with a rise in the cases of

measles Measles (probably from Middle Dutch or Middle High German ''masel(e)'', meaning "blemish, blood blister") is a highly contagious, Vaccine-preventable diseases, vaccine-preventable infectious disease caused by Measles morbillivirus, measles v ...

—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.

Research

New data shows that in the seasonal parts of the

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Amazon rainforest The Amazon rainforest, also called the Amazon jungle or Amazonia, is a Tropical and subtropical moist broadleaf forests, moist broadleaf tropical rainforest in the Amazon biome that covers most of the Amazon basin of South America. This basin ...

, 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 the onset of the wet season: by growing more foliage, it evaporates more water. However, this growth appears only in the undisturbed parts of the Amazon basin, where researchers believe roots can reach deeper and gather more rainwater. It has also been shown that

ozone Ozone () (or trioxygen) is an Inorganic compound, inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , break ...

levels are much higher in the dry than in the wet season in the Amazon basin.

References

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