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So there is a mountain range. It is about 3000 miles long, 500 miles wide and the average height is 5,000 m. Now there is still quite a lot of land and I don't want to make everything behind the mountains into a desert. Must a rain shadow create a desert?

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Yes and no. Rain shadows are caused by unidirectional blockers of weather systems in areas where the prevailing wind brings in most or all of the rain. This means that while the mountains creating the rain shadow may block all of, for example, the easterly trending storm systems in the area weather coming up from the south or down from the north won't be effected, much. A mountain range that blocks the prevailing winds and thus the primary weather systems of a particular region will always create a relatively dry zone behind the range. That area need not be a true desert if there are enough other weather systems that hit the area from other directions and dump enough rain (more than about 200mm annual rainfall depending on temporal distribution) during the year though.

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  • $\begingroup$ As a practical example, consider the Rocky Mountains. Not a lot of rain shadow effect north of the Canadian border, certainly not enough to create a large desert. Even south of the border, there's little if any actual desert east of the range, just dry plains becoming wetter as you go east. $\endgroup$
    – jamesqf
    Jun 24, 2018 at 17:56
  • $\begingroup$ Equally New Zealand's spinal range, especially in the North Island, creates a pronounced dry season on the East Coast but it remains wet enough to support year round agriculture, in fact it is some of the best land in the world for arable cropping. $\endgroup$
    – Ash
    Jun 24, 2018 at 18:28
  • $\begingroup$ Another example is the appalachians which has a mild but noticeable rain shadow effect, but no one would call Illinois desert. $\endgroup$
    – John
    Jun 24, 2018 at 20:35
  • $\begingroup$ @John: Though the Appalachians are nowhere near 5000 m :-) $\endgroup$
    – jamesqf
    Jun 25, 2018 at 20:21
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You can be dry but not be desert.

Costa Rica has an rain shadow ecosystem called a tropical dry forest.

enter image description heretropical dry forest

https://www.gdfcf.org/dry-forest

It is pretty cool! I guess the few months of rain are enough to carry the forest over during the long dry months.


Another option is a grassland or savannah. On the Big Island the rainshadow produces an area like this - grass with a few trees.

https://yourbigislandexperience.com/tag/kohala-coast/ enter image description here

https://www.climate.gov/news-features/featured-images/rain-shadows-summits-hawaii rainshadow on the big island

Kohala looks a lot browner in that second image than in the first.

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