Why are Deserts so dry?

SAHARA DESERT in North Africa Key places today… North Africa Sahara Desert Atlantic Ocean Canary Islands Morocco Atlas Mountains

1. Deserts are areas of permanent HIGH PRESSURE Air sinks 1. Air warms Moisture evaporates Clear blue skies and dry weather High PRESSURE or anticyclone

2. Deserts lie on the West side of continents…. In zones where the prevailing winds come from the east.

Saharan sand blown off to the west by easterly winds.

3. The cold ocean current : THE CANARY CURRENT

Canary Islands - fog

‘It was pretty cold and windy in the damp fog’

San Francisco coast California – Also gets fogs.

3. Moisture condenses out of the air over cold oceans

RELIEF RAINFALL and RAIN SHADOW Atlantic Ocean Atlas Mountains Sahara Desert

RAIN in Morocco Sahara Desert Rain near Equator

R E L I F A N

Rain Shadow effect here Sahara Desert Begins Relief Rainfall Here

Warm dry air sinks down into the Sahara… … making it a desert

The Relief Rainfall and the Rain Shadow happens in the dry SW USA too.