Arid & Semi-Arid Environments Environments between 0 – 500mm of Rainfall a year.

Classification and Distribution Arid Environments- 0 – 250mm of rainfall a year. Semi-Arid Environments- 250 – 500mm of rainfall a year. Usually located between 20˚ and 35˚ of Latitude.

Causes Isolation means surface heat is able to build up easily. Air that is heated around the equator, it then rises through the equator to roughly 10-15km above the surface. This generates thunderstorms. It then starts to sink as it moves polewards because it starts to cool. Cold ocean currents.

Processes Salt weathering Freeze-thaw weathering Insolation Weathering Aeolian processes- these are processes which are made by the wind. Fluvial- processes that involves water as a major part.

Features Formed Yardangs- wind eroded ridges, usually 10m high and100m long. They are mostly aligned with the prevailing wind. Ventifacts – These are small cobbles that are eroded by sediment that has been blown by the wind. Desert Pavement- Deflation lowers the lands surface with sediments getting smaller as it moves along.

Continued... Ripples- these are small-scale features formed by Aeolian processes. They develop at right angles to the wind.

Fluvial Features Alluvial Fans-these are cones of sediment that are deposited by rivers. Playas- where a river brains into a shallow basin and makes a small lake called a playa. Pediments- there are gently sloping rock platforms. Canyons- this is where a river buts through and leaves a near vertical valley.

Dunes Linear Dune- these are a long straight dune, that stretches across long distances. They often stretch around 100km along the Arid environment. Star dunes- these are dunes with many faces, where the top all comes up to one longish jagged ridge. Parabolic- these are u-shaped, that have convex shapes.

Continued... Crescentic– these are the most common, these are smallish dunes with only one slip face that appears on the concave side.

Ecosystems Due to the extreme conditions in Arid and Semi-Arid environments all plants and animals that are to live there must adapt to the conditions.

Adaptations Plants and animals must adapt to high temperatures, drought, unpredictable rainfall etc. Plants- changed physical structure to survive droughts, they can now store a lot more water, they have it so that seeds plant after rain. Animals-