White Sands National Monument, New Mexico, USA

Wadi Dhar, Yemen

Dead Vleii, Namib DesertDESERTINTRODUCTION

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 AfricaKalahari in Southern AfricaAtacama in South AmericaGobi in Central AsiaArabian in the Middle EastGreat Victoria and Great Sandy in

AustraliaMojave 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?

Sun heats

equator

Ground heats

air

Air rises and

cools in the

atmosphere

As air cools it can no longer

rise

Cold air sinks at

the Horse

Latitudes

WIND moves between high

and low pressure LOWHIGH

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.

Wind direction.

Cooler air.

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 oceanAtlanticAtacama DesertPatagonian DesertThe AndesS-E trade windsNorth 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=ZUsARF-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=olELJyQicvk