What's a desert? Not something sweet after dinner, but a landscape or region that receives almost no rain. Deserts are areas with an average annual precipitation of less than 250 millimetres (10 inches) per year.
Here is the recent rainfall history for downtown San Diego:
2004-2005 22.49 inches
2005-2006 5.42
2006-2007 3.85
2007-2008 7.25
2008-2009 9.15
The average over 20 years is 10.77, so actually that's a bit MORE than a desert would receive, but you can see that 2004-2005 was a BIT high.
It seems to me that it rains more here, but I keep seeing this quote No Measurable Precipitation in the paper and on the television. What is measurable precipitation anyway?
Is this rain?
Not according to our weatherman, it's not.
But if you ask a picnic-bound family, it is.
Is this rain?
Not according to our weatherman!
I was loading and off-loading the truck.
I was soaking wet!
It seemed like rain to me!
Surely this is rain, you can see the drops.
Yes, this was rain.
One-third of an inch fell on this date.
These constrasting opinions led me to ask how do we measure precipitation?
With a rain gauge [A before the U, please!] also known as a pluviometer from Latin pluvia, which means rain. It's a graduated cylinder that collects the falling rain.
Of course there are many types - one measures the weight of the water then infers the rainfall, one is completely electronic and spots the raindrops whizzing by, another counts them as they fall on a flat surface, one has a tipping bucket which sends a signal when it fills (then empties itself), etc.
Everyone uses the same sort of rain gauge, so results measured in one part of the country will be comparable to others. Of course, here in the desert, we have to worry about the water evaporating before we get out there to check the results, and in other parts of the country like Hawaii, you have to check frequently because of overflow.
Why all this concern about measuring rain? you might ask.
No, it's not raining today in San Diego. I guess I just have water on my mind.
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