(Reblogged from Nathen’s Miraculous Escape, from February 21, 2012.)
Reanna is from the Pacific northwest and I grew up in Joshua Tree, CA, where we are currently living. We have an ongoing conversation about humidity here because having grown up in a wet climate, she is vigilant for the ways that moisture in the air decomposes things. “If we don’t keep it warm in here, won’t condensation damage the books?” No, it won’t, and probably wouldn’t even if we had a constantly boiling pot of water. The only place I’ve ever seen mildew in Joshua Tree is in one of our bathrooms which, until very recently, had no windows and no fan. This was not aggressive mildew either, just noticeable every once in a while. “If the roof of the trailer has leaks, won’t there be tons of mold in the walls?” No, not likely, because even if rain was pouring right through the trailer, it would be completely dry again within hours.
I have never tracked humidity levels before, so while I knew that Joshua Tree was dry, I didn’t know what level of humidity qualified as dry. I also didn’t fully understand the different measurements of humidity that are floating around out there. The short version of that story is that there are three units of humidity: absolute, specific, and relative humidity. Absolute humidity is grams of water per kilogram of moist air and specific humidity is kilograms of dry air. Relative humidity is more complicated. If I understand correctly (if incompletely) it is the ratio between 1) the pressure that the water vapor in a given amount of air would exert on the insides of a container, should it somehow be trapped there without its accompanying dry air, and 2) the pressure below which water would start condensing out of the air. Relative humidity is the measure of humidity that you usually see in weather reports, partly because it takes into account temperature–at lower temperatures, air holds less water.
Here are some cities with different levels of relative humidity, to give a sense of where we are in Joshua Tree. I’ll also include precipitation. (Data is from Weather Underground unless otherwise noted.)
Seattle, WA, 2011: High 99%, Low 34%, Average 82%, Precipitation 12.92 inches
Honolulu, HI, 2011: High 96%, Low 18%, Average, 65.6% Precipitation 23.82 inches
Joshua Tree humidity, 2011: High = 83%, Low = 10%, Average = 30.7%, Precipitation 1.53 inches
Las Vegas, NV, 2011 (the driest city in the US): High 98%, Low 2%, Average 28.7%, Precipitation about 2.5 inches (precipitation according to climatestations.com)
Kolkata, India one of the most humid cities in the world, on July 15, 2011: High 94%, Low 64%, Average 84%, Precipitation 0.0 inches
And Kartoum, Sudan (Sahara desert), on January 4, 2011: High 43 %, Low 10%, Average 24%, Precipitation .51 inches