"On the other hand, if you get more than 20 inches of rain annually, (90% of the US does) then consider this:"
Can you try to post the facts. According to the National Climate Data Center ( a division of NOAA) you are 100% completely wrong. The US is broken down into 9 regions. From 1961-1990 3 of those regions composed of NE, ND, SD, MT, WY, UT, CO, AZ, NM, CA, AND NV received anywhere from 13.62 to 16.92 inches of rain per year. I calculated the land mass area of these 3 regions and they compose appx 30% of the entire US. That means on the average appx 30% of the US receives LESS than 17 inches of rain per year. Where did you get the figure that 90% of the US receives 20" or more of rain per year. You just made it up didn't you. Come on admit it you were guessing. You didn't think someone would ACTUALLY research it out did you. Just the facts dude... just the facts.