>>2666845Everything that is taught in American schools about climate is outdated, flat out wrong, or misleading. The old model in the 1800s was anywhere that didn't have forest was classed as a desert, this included plains areas that got up to 40 inches of annual precipitation. Statistically, the western US is less than 1/3rd truly arid climates, aridity is not classified by static arbitrary numbers (like under 20 inches is arid), it is determined by the local evaporation rate to precipitation rate and the precipitation spread. Most of the Mediterranean would be arid or semi-arid if you go by arbitrary numbers, yet when you consider the periodicity of the precipitation (a true Mediterranean climate receives almost no rain for almost half the year then gets a wet winter), you end up with a seasonally dry temperate climate, ie a Mediterranean climate. The western US has similar comparisons, about 1/3rd is actually arid, 1/4th humid, and 2/5ths semi arid. Evaporation rates are lower when temperatures are lower, and most of the west is colder than the east for their latitudes, a lot colder in fact, leading to non existent evaporation rates in its wettest season, which is winter (excepting parts of the SW which receive higher summer rainfall during the AZ monsoon). And as a result, colder climates need significantly less rainfall to be classed as temperate and humid. In the mountains of Arizona abive 7k ft, the evaporation rate is at or just under 20 inches, in Montana at 4k ft elevation it can be as low as 10 inches, in the desert of SW AZ amd SE CA it can be as high as 150 inches. The seasonal and duirnal variations in rainfall, temperature and humidiry lead to complex climate types, some not found elsewhere in the world. The total forested area of the western US is approximately 30-35% (similar to most of Europe), almost evenly spread, the least forested are NV and WY.
tl:dr - Climate, weather, topography, and biogeography are more complex than one assumes.
