3.5 Arid climates

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3.5 Arid climates

Learning objectives

After studying this section, you will be able to:

• Describe two different arid climates;
• Explain why the world’s deserts are arid.

Arid climates

Arid = Dry.

Desert climate (BW) = Climate zone with very little to no precipitation and high evaporation.

Steppe climate (BS) = Climate zone with some precipitation during the wet season, nearly balanced with evaporation rate.

Deserts

Daily maximum and minimum temperatures vary wildly in some deserts: there are no clouds to reflect sunlight during the day or function as “insulation” during the night.

Climate graph for Cairo, Egypt (BW).

Climate graph for Dakar, Senegal (BS).

Steppe landscape

• It has more vegetation than a desert landscape. 
• This semi-arid climate remains too dry for most tree species to grow. 
• Dominated by grasses and shrubs, but less than in the savannah climate.

The steppe landscape in the Sahel (Senegal).

The Great Green Wall is an initiative designed to stop the desertification of the semi-arid Sahel region in Africa.

Talking point

What problems do humans face when they live in a desert climate?

Atmospheric circulation and prevailing wind directions.

Atmospheric circulation

Subtropical high

Area of high atmospheric pressure located in the subtropics; the air mass descends.

Polar high / maximum

Area of high atmospheric pressure located in the polar regions; the air mass descends.

Polar front / subpolar minimum

Area of low atmospheric pressure located in the middle latitudes; the air mass rises.

Plurals of words with a Latin root

‘Minimum’, ‘maximum’ and ‘cactus’ are words that come from Latin. In Latin, a singular word that ends on ‘-um’, takes ‘-a’ in the plural, while singular words that end in ‘-us’, take ‘-i’ in the plural. So, ‘maximum’ becomes ‘maxima’ and ‘cactus’ becomes ‘cacti’. However, following normal English grammar you can instead add ‘-s’ or ‘-es’ to form a plural: ‘maximums’ and ‘cactuses’. The English language is shifting and both plural forms are now considered correct. For the word ‘maximum’, the Latin version ‘maxima’ is still preferred in science, but in less formal English usage, ‘maximums’ has become the norm.

Prevailing wind direction = most common wind direction.

Prevailing wind direction

Westerlies

Most common wind direction in the middle latitudes; a wind that blows from west to east.

Sea currents

Important factor in the location of deserts:

• Cold water evaporates less easily than warm water;
• Wind blowing from the sea to the land carries less moisture with it.

The northern Atacama Desert is located in the rain shadow of the Andes Mountains.

Essence

Arid areas exist in very different parts of the world and can be both hot and cold. Köppen differentiated between the desert climate and the steppe climate. The steppe climate is located on the edge of a desert climate. Deserts can form due to zones of high air pressure, the rain shadow created by mountain ranges, prevailing wind direction and cold ocean currents.

Havo: Look at the planner in Teams for the exercises you have to do.

Vwo: Look at the planner in Teams for the exercises you have to do.