We got a couple of inches of rain here in Philly last night and this morning – on top of the couple of inches we got last week and the week before. We keep getting the tail end of the systems that have been socking the West so hard with snow (and yes we’re damned grateful it’s too warm for it to be snowing).
My question is – how much water is in these storms? We’re talking a couple of inches of rain (or the equivalent of snow) over X number of thousand square miles – that seems like a hell of a lot of water. Is there a way to calculate it?
A few things to remember:
-There are 5280 feet in a linear mile, so 63360 inches in a lin. mile
-There are 63360*63360=4,014,489,600 square. inches in a sq. mi.,
-There are 231 cubic inches in a gallon.
Though this is not the only way to do this, it should be easy to explain this
all if we just convert everything to inches. Let’s convert the land
area to square inches and then multiple by however many inches of water
thickness we have to get total volume in cubic inches. We can convert
this to gallons.
X square miles = X4014489600 sq. inches
This layer is Y inches thick, so make that YX4014489600 cubic inches of water
Now, the volume of a gallon of water is 231 cubic inches, so we’re
talking about YX4014489600/231 gallons, or about
**YX17378743 gallons of water**
so let’s say we’re talking about an area 500 miles by 500 miles covered
by 4 inches of water, that’d be, X=500500=250000, Y=4,
Gallons of water = 250000417378743 = 17,378,743,000,000
So, with the numbers I used, we’re talking about 17 trillion gallons of water.
Now, I think Olympic swimming pools are 25m50m2m, which makes about 660,000 gallons.
So, using the numbers from before, that’s 26,331,429 olympic swimming pools.
Yeah, but it’s not easy to write out math here. I get that one inch of rain over just one square mile is about 2.32 million cubic feet of water. You can start from that. Google converts units for you; for instance you would search for one inch in feet to do the first step in my calculations.
Keep in mind that the water being dumped by the storm in Philadelphia is not the same water that was being dumped on the West Coast. The water being dumped on Philly came from the Gulf of Mexico, and was funneled up by the front (it may also have drawn upon Atlantic Ocean waters). The water being dumped on Seattle is from the Pacific Ocean.
As a general rule, the water in a storm is but a miniscule portion of the water on the planet. That’s why sea levels don’t go plunging down just because a hurricane dumps massive amounts of water inland.
It is still a lot of water. I wasn’t liking driving home on the Pa Tpk. last night.
One thing you should remember about the precipitation total in Seattle is that much of it comes from mist or light drizzle. Even a few days of mist won’t total much in the rain gauge, but it sure takes a toll on ones psyche.
Take a look at a chart which shows “Precipitation Days” a year and Seattle will probably beat Philadelphia.
[aside]
All you antimetricists, observe post #2 and tell me that estimating via metric isn’t simpler:
Let’s say we’re talking about an area 800 km by 800 km covered by 10 cm.
In metres, this is 800,000 m x 800,000 m x 0.1 m = 64,000,000,000 m[sup]3[/sup]
Now, I think Olympic swimming pools are 25 m x 50 m x 2 m = 2,500 m[sup]3[/sup]
64,000,000,000 / 2,500 = 25,600,000 pools
Pretty much the same answer, but with about 10 less steps. Also, since we know that 1 m[sup]3[/sup] weighs roughly a tonne, then we roughly know the weight too.
[/aside]
Yep, rain measured in millimetres is a lot easier to calculate. In most of Europe they actually measure in “litres/m[sup]2[/sup]” which is in fact the same unit by a different name, and even easier to fathom. (Or should I say, “easier to 1.8288 metres” )
(1 litre = 1,000cm[sup]3[/sup] = 0.001m[sup]3[/sup]. So 1 litre/m[sup]2[/sup] = 0.001m, or 1mm.)
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