Yearly period of low rainfall, especially in the tropics
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
or
winter
.
Rain belt
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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
, 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
Koppen 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 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
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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
,
giraffes
,
hippos
,
rhinos
,
antelopes
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.
[2]
Diseases
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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]
Research
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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]
References
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