Transcript desert-introduction

White Sands National
Monument, New Mexico,
USA
Wadi Dhar, Yemen
DESERT
INTRODUCTION
Dead Vleii, Namib Desert

Describe the characteristics and
distribution of the two ecosystems
listed in the syllabus (tropical rainforest
and tropical desert).
• Explain the relationship in each
ecosystem of natural vegetation,
wildlife and climate.
DISTRIBUTION OF DESERTS
Annual precipitation in deserts is less than 250mm and less
than 100mm in extreme deserts. Deserts have large diurnal
temperature ranges.

Deserts are located near the tropics
(Tropic of Cancer and the Tropic of
Capricorn). Some of the world's most
famous deserts include:
Sahara in Northern Africa
 Kalahari in Southern Africa
 Atacama in South America
 Gobi in Central Asia
 Arabian in the Middle East
 Great Victoria and Great Sandy in
Australia
 Mojave and Chihuahuan of North
America


Antarctica is sometimes classified as a
desert because it actually has very low
levels of precipitation. However, when
we talk about deserts in this section of
the desert we mean sandy deserts.
Types of Deserts

Desert Types
 There are 5 main types of deserts
1.Subtropical Deserts – 30o n/s
2.Rain shadow deserts on Leeward side of
major Mountain ranges
3.Continental Interior Deserts- center of
continents far from ocean 35-50 N
4.Coastal desert- prevailing onshore wind
cooled by cold ocean current
5. Polar deserts- extremely cold and dry
Atmospheric Convection and Subtropical Deserts
World Wind and Pressure Belts
How is a Hadley Cell Formed?
As air
cools it
Air rises
can no
and cools
Coldlonger
air
in the
sinks rise
at
atmosph
the Horse
Ground
ere
Latitudes
WIND moves heats air
between high
and low pressure
HIGH
LOW
Sun
heats
equator
Subtropical Deserts or Trade wind
deserts

Sahara

The trade winds in two belts on the
equatorial sides of the Horse Latitudes heat
up as they move toward the Equator. These
dry winds dissipate cloud cover, allowing
more sunlight to heat the land. Most of the
major deserts of the world lie in areas
crossed by the trade winds. The world's
largest desert, the Sahara of North Africa,
which has experienced temperatures as high
as 57° C, is a trade wind desert.
2. Rain-Shadow Desert
Relief Rainfall.
Cooler air.
Wind direction.
Warmer air.
Orographic deserts - deserts that receive little
moisture due to the "rain shadow" effect of
nearby mountains, e.g., Basin and Range of
Nevada and eastern Oregon's deserts.

Rain shadow deserts are formed
because tall mountain ranges prevent
moisture-rich clouds from reaching
areas on the lee, or protected side, of
the range. As air rises over the
mountain, water is precipitated and the
air loses its moisture content. A desert
is formed in the leeside "shadow" of
the range.
Latitude: -45 / Longitude: -73

Image showing the impact of the
Andes Mountains on rainfall and
vegetation. At left is southermost Chile,
which appears quite lush, while
Argentina (Patagonia) appears dry and
brown. Bright turquoise lakes are the
result of extremely fine sediment
ground up by mountain glaciers and
deposited in the lakes.
The rainshadow effect S.America
Pacific ocean
 Atlantic
 Atacama Desert
 Patagonian Desert
 The Andes
 S-E trade winds
 North Westerlies

Midlatitude deserts

These deserts are in interior drainage
far from oceans and have a wide range
of annual temperatures.
4. Coastal or Ocean-Current Desert

Coastal deserts where cold oceans lie
next to hot coastal regions - most of
the precipitation falls over the oceans
before it gets to the land, e.g., Atacama
and Kalahari deserts.
Hot
Desert
Climates
Describe and explain the desert
climate.

Deserts are extremely dry (arid)
places. True deserts normally have
less than 250mm a year, although
some deserts like the Atacama to the
right can go years without any water.
Deserts are very dry because the air
that descends over them is very dry.

The air is dry because most of the
moisture has fallen as precipitation
over the Equator (tropical rainforests)
before being pushed out and falling
near the tropics. The air is also very
dry because the air travelling from the
equator to the tropics travels over land
and not the sea.

This means that no additional moisture
is picked up. Because there is no
moisture in the air, there are very few
clouds in deserts which means desert
areas are exposed to high levels of
incoming radiation from the sun. This
means that daytime temperatures in
the desert are very high.

However, the lack of cloud cover also
means that a lot of outgoing radiation is
able to escape, making desert
temperatures very cold at night. So
even though the annual temperature
range in deserts is very low, the daily
temperature range is very high. The
daily temperature range is known as
the diurnal temperature range.
Rock desert or
hamada
Sand desert
or erg
Stony desert
Basins of inland
drainage called
playas or shotts
Dry ravines or
wadis or
arroyos
Alluvial fans
can join
together to
form a bajada
DESERT
VEGETATION
Fish out of Water.

https://www.youtube.com/watch?v=ZU
sARF-CBcI
This xerophytic or drought resistant vegetation has adapted
to living in dry conditions by having small, twisted leaves
with stomata which only open at night to allow respiration.
Perennials, such as ocotillo, become dormant between the
rains. Once all moisture has evaporated from the soil, the
plant drops its leaves and temporarily stops growing.
Instead of thorns, the creosote bush relies for
protection on a smell and taste that wildlife find
unpleasant. Creosote has an extensive double
root system -- both radial and deep -- to
accumulate water from both surface and ground
water.
Cactus, xerophytic adaptations of the rose family,
are among the most drought-resistant plants on
the planet due to their absence of leaves, shallow
root systems, ability to store water in their
stems, spines for shade and waxy skin to seal in
moisture.
Desert plants must act quickly
when heat, moisture and light
inform them it's time to
bloom. Ephemerals are the
sprinters of the plant world,
sending flower stalks jetting
out in a few days. The peak of
this bloom may last for just
days or many weeks,
depending on the weather and
difference in elevation.
The Living Planet.

http://www.youtube.com/watch?v=olEL
JyQicvk