This didn't make sense to me at first because in California, where I live the western coast is the driest, but then over the eastern side of the Sierra Nevada mountain range, the climate is much drier.
In ecology this process is called the rain shadow effect, where storms as they come from the coast, dump all of their water as they approach the peaks, and then the area on the other side of the mountains is dry.
It wasn't until I looked at the jet stream maps of the world that I realized my confusion. In the Northern Hemisphere, where I have always lived, the jet steam goes from west to east, but in the Southern Hemisphere, where Namibia is, the jet stream pushes weather systems from east to west.
Go here to see animation of jet stream
This difference is explained by the Coriolis effect. So in Southern Africa, storms come from the east and dump all of their rains on the more eastern coast of the country then as they go over mountain ranges like the Great Escarpment they dump their water and are dry by the time the storm system gets to the Namib Desert, leaving it very arid.
Ref:
https://earth.nullschool.net/#current/wind/isobaric/10hPa/orthographic=352.43,9.10,297
https://upload.wikimedia.org/wikipedia/commons/9/9a/Rainshadow_copy.jpg
I wonder what effect this absence of precipitation next to the ocean has on marine life. Do you know anything about that? -- Romain Screve
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