How is the amount of rain measured? Do they just put a bucket outside? (If that’s the case, then we’ve gotten pver a foot here in southern CA’s latest storm…filled me dang bucket left outside.) I’m certain it has to be more technical than that.
Seriously, though, it’s hard to believe that after hours of rain just blanketing the area that it was “just” a half-inch (or in the case of Sunday, one tenth of an inch) of rain.
Yep, a bucket is pretty much how it’s done (as long as the bucket has straight sides like a coffee can). The idea is that any vessel with the same size bottom as it’s openning will acurately record rainfall for a particular place. You could very well have gotten a foot of rain in your backyard, especially if you live in the foothills like I do. The numbers given on the weather report are the average for the whole Los Angeles basin. Where you got a bucket’s worth of rain, someone in, say Cerritos, might have only gotten a thimble’s worth.
I remember when I was a kid, at my school we decided to study the weather for science, and we set up a little weather centre. So we marked down the high and low temperatures, and we read a little wind direction thingumajiggy.
But we also had a real rain gauge, which was a square-ish tube, that started out with a narrow vertical reservoir at the base, and flared up after an inch or so until it was about 8 inches high. And it had the usual measurements printed on the side in proper increments.
And that was the standard way to measure rainfall. Of course, it depends on where it’s placed. You can’t get runoff from a roof, for example. Or have it too likely to be sheltered from surrounding buildings. Another problem is, a hundred metres away might get half an inch more rain for some reason.
Your welcome, NickyLarson, but it was your link in the first place, I just got curious about why it didn’t work right.
I was at Home Depot today and they had rain gauges that were a tall tube with a funnel on top. I would assume to magnify the scale. As far as I know, any straight sided bucket, tube or anything else should give you a fairly accurate measurement of the rainfall, as long as it wasn’t in some sort of drip from a tree or roof.
But, I live within a stone’s throw of DFW airport, which is the official reporting site for the Dallas area. And, I have seen official rainfalls of 1/10 inch when the water level in the street was over the curb, and also, I’ve seen times when there was not even a spot on the walk when 1/2 inch of official rain was reported. Around here, the rainfall amount in one area may not even be close to the official amount.
Manduck said “What did your chemistry teacher think he was talking about when he said that? Because it makes no sense at all.”
whats so hard to understand. If you have a square tube and it is 1-cm in width and 1-cm in length, for every cm of rainfall that builds up in the tube that would equal one inch of rain.
Let’s put it another way - if you had a square tube that was ten meters in width and ten meters in length, every centimeter of rainfall that builds up in the tube would still be a centimeter of rain. The length/width of the tube isn’t relevant.
In both cases, you’d have to have an inch of water in the tube to equal an inch of rain.
WillGolfForFood said
"Let’s put it another way - if you had a square tube that was ten meters in width and ten meters in length, every centimeter of rainfall that builds up in the tube would still be a centimeter of rain. The length/width of the tube isn’t relevant.
In both cases, you’d have to have an inch of water in the tube to equal an inch of rain."
Siva’s response is:
Rainfall is a measurement of volume. Using your example you are saying that a lake 500 meters wide and 500 meters long but only 1 inch deep has a volume of 1 inch and the same volume as a lake that is 1000metersx1000metersx1 inch. Now think about it. The measurement of rainfall is all about volume in a given parameter. Another example of your example is that if
I have a cup that holds 32oz’s but it is only 5 1/4 inches tall and has a 4 1/2 inch circumference, that it would have the same volume as a cup that was 5 1/4 inches tall but a circumference of 5 inches. You’re reasoning–it’s the same heighth
What planet are you from? Rainfall is not a measure of volume, otherwise they’d have to say something like “The three square miles contained by the rhombus bordered by Mrs. Potts’ cornfield, Ralph Schmenkman’s cow pasture, Myrtle Wasserman’s junked Studebaker, and the town water tower received one inch of rain for a total of 3 inch-miles of rain today.”
When have you ever heard anything resembling this? Your lake example is totally bogus, because no matter how big a lake is if it is 1 inch deep, it is one inch deep. Rainfall is a measure of how deep the lake would be if all the water in the lake came from the rain indicated in the rainfall measurement. Lake or reservoir volume is given in acre-feet, just as rainfall would be if you were really concerned with volume.
What rainfall is actually measuring is how much rain fell in one tiny area. You need to have many measuring stations to get a clue as to how wide spread the rain is, and if you have two stations measuring one inch of rain you don’ suddenly say there was twice as much rain. If one tiny village gets one inch of rain it’s a lot less total rain than if the entire state gets one inch of rain, but if your rain guage is in that tiny village you can’t tell the difference.
I don’t know what you are talking about, siva. If you put a 16oz tin can a 720z coffee can and a 500 gallon inflatable pool out in the rain, they will all have an equal depth of water in them after the rain has passed. That depth is equal to the amount of rainfall.
A rain guage has a larger funnel-type opening and a narrower measuring tube. The markings on the tube are calibrated to take into account the discripency caused by having a larger openning than a bottom. The shape of the guage is simply a matter of convinence.
siva may be remembering her chemistry teacher incorrectly. Mine told me that 1g of water occupied a volume of 1 cubic centimeter.
The only way an inch of rain could equal one cubic centimeter is, as I believe has been stated here already (too lazy to look) is if the container were an inch long but had a total volume of ~.5 inch (1/2.54, to be exact). But if you’ve got a gram of water, no matter what kind of container you put it in, you’re gonna have 1cm^3 H2O.
The actual rain gauge from which most “official” readings originate are of the NWS “tipping bucket” style. A funnel collects rain so it drops one drip at a time through a small hole. Each drip lands in a “bucket,” which actually looks like a small see-saw with walls. When one side of the see-saw has 0.01" of rainfall in it, it tips over. The water runs out, and the other side of the see-saw is under the hole ready to collect drips.
Nice thing about this is that it is totally automated: a computer counts the number of bucket tips and that’s the number of hundreths of an inch of rainfall.
As mentioned by other posts, local rainfall may vary lots from the official site (usually an airport). Out where I work, we can watch the rain clouds that dumped “official” rainfall at the airport 5 miles away split as they hit the thermals coming off adjacent fields. Rain falls all around us and we get nary a drop. Very annoying.
Sure, I’m all for moderation – as long as it’s not excessive.