>>2679254Same way most deserts form. Blocking windward mountain ranges with high orthographic lifting effect and jet stream positions. Jet streams play a huge role, mountains less so but are still important. An example of the jet stream overcoming mountains is the western US where lowlands can get as little as 1 inch of average precipitation a year, while inland mountains can get up to 60-100 average inches of precipitation a year, coastal mountains get up to 300 inches, and parts of Hawaii up to 500 inches. An example of mountains more successfully rerouting a predominant jetstream is inland china, Gansu province and inner Mongolia and surrounds, average winter temp is -18c and areas will get less than 4 inches of annual precipitation while to the north and east the Siberian high and Pacific jetstream dump up to 1000 inches of winter snow on Japan and 250 inches in Siberian mountains, both similar amounts to every western US state and western Canadian province. During the ice age the Sahara was actually almost completely green due to the jet stream being at a much lower latitude. There are more than a few rabbit holes when you begin deep studying the climate. The Iberian peninsula deserts are still moderately productive to agriculture in river and drainage dales, similar to the lower elevation deserts of Arizona, California, New Mexico, and Utah (all of which like Spain also have expansive temperate forests, and snowy mountain ranges, albeit the US ones are up to 5-10 times snowier in totals, like putting the snowiest Austrian ski mountain in central or southern Spain at its least, but in AZ and NM).
