Wednesday, February 17, 2010


In theory, Andalucía has a fairly dry climate. In theory. We have been lucky enough to be here for the wettest recorded winter in Córdoba's history. According to the newspaper, the measured rainfall since September (about 4 ½ months) has been 25% higher than what Córdoba normally sees in an entire year. Now, this is still nothing like a Portland winter. But…but….but….here you notice it more. There’s a lot more street life, and nothing puts a damper on street life like a heavy rain. And when you have to walk or take a bus to all of your destinations, you find yourself taking careful note of the weather. I even passed on a hike near Granada last weekend, because I wasn’t interested in braving the rain and snow.

I have made an interesting observation regarding rainfall measurement. In the USA, of course, we measure rainfall in inches. In Spain (and probably in all of Europe), rainfall is measured in l/m2 (liters per square meter...sorry, the blog doesn't seem to support superscripts). Now, if you think about it, the European measurement of volume of rain per unit area makes a lot of sense. Using units of inches for rain is dependent on the measurement method (the depth of water in a vertical-sided container), but volume of rain per unit area is independent of how you measure it.

But, how do you compare l/m2 with inches? Here is where the glory of the metric system becomes obvious. There is a straightforward relationship between units of length, area, volume, and weight that just doesn’t exist in the English system. For instance, one liter of volume is a cube with sides of 10cm (or 0.1 meters). Therefore, one liter per square meter is

(0.1m)3/(1m)2 = .001m

which is simply one millimeter. Therefore, a measurement in l/m2 can be thought of simply as millimeters of rain (comparable to inches of rain).

Sadly, this simple relationship doesn’t exist in the English system. How many inches of rain would correspond to one gallon of rain per square foot? Of course you can calculate it, but it would be a bit ugly.

So why does America continue to struggle against the metric system?


ascot said...

It's Reagan's fault. Carter set us on the way towards having a rational system of weights and measures and Reagan shut it down withing two years after taking office.

Took the solar panels off the White House, too.


Dimple said...

I can see the difficulty in calculating haw many gallons of water you have from a given number of inches of rainfall, but I don't really care. An inch of rain is an inch of water that has fallen from the sky. If it didn't soak in, run off, or evaporate, there would be a layer of water one inch deep in the given area. And if we have an inch of rainfall on our property, I don't have to water the yard!