# Is my rain gauge lying to me? **URL:** \ **Category:** Factual Questions\ **Created:** [July 30, 2005, 5:01am UTC](https://boards.straightdope.com/t/is-my-rain-gauge-lying-to-me/314853 "2005-07-30T05:01:42Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![goddessodd](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@goddessodd](https://boards.straightdope.com/u/goddessodd)\ **Post date:** [July 30, 2005, 5:01am UTC](https://boards.straightdope.com/t/is-my-rain-gauge-lying-to-me/314853/1 "2005-07-30T05:01:42Z")
Call me paranoid, but now I think my rain gauge is fibbing. This afternoon we had a short but intense thunderstorm. When I went out to check the rain gauge afterwards, I noticed that I had inadvertently dropped a clear plastic container about 3 inches away from my gauge. Both were on level ground, with no overhanging limbs or cover of any kind, nor was runoff an issue. The container in question was rectangular, about 3"x4". The funnel of the rain gauge is about 2x2". My rain gauge measured 1.5" of rain, but the box had 2.5". I measured both depths again, twice, using the same ruler, so I know that the gauge is accurately marked. Why the discrepancy? Is there a standard rain gauge size? I realize the surface areas are very different, but it still seems to me that surface area should not make much difference, it is **rain** , falling **everywhere** at a more or less steady rate. Could a smarter person explain this to me please. 😕 ---
**Author:** ![Waterman](https://avatars.discourse-cdn.com/v4/letter/w/b2d939/32.png) [@Waterman](https://boards.straightdope.com/u/Waterman)\ **Post date:** [July 30, 2005, 5:23am UTC](https://boards.straightdope.com/t/is-my-rain-gauge-lying-to-me/314853/2 "2005-07-30T05:23:50Z")
IMHO, the first question I would ask is how much time elapsed between the rain event and your reading the guage. For one thing, any container used for measuring rainfall would be subject to losses due to evaporation. Another might be the location of the container relative to wind direction, etc and other factors that could affect measured amount. Not enough of a “controlled experiment”. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [July 30, 2005, 6:02am UTC](https://boards.straightdope.com/t/is-my-rain-gauge-lying-to-me/314853/3 "2005-07-30T06:02:52Z")
How tall are the rain gauge and box? If the top of the container is too close to the ground, it’ll pick up water from the sky, _and_ water that splashes when raindrops hit nearby. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [July 30, 2005, 6:10am UTC](https://boards.straightdope.com/t/is-my-rain-gauge-lying-to-me/314853/4 "2005-07-30T06:10:11Z")
Does the 3" x 4" box have tapered sides? Is there any chance that the box actually had water in it (either from a previous rain, a water sprinkler, or some other cause) so that the 1.5" of recorded rain were added to existing water? If the sides of the box are tapered, there is a greater “collection” area for the rainfall and the box will fill faster. (In fact, some rain gauges are actually made with a taper and the markings are exaggerated to compensate. This allows the scale on the side to be marked in farther separated increments for easier reading.) Your description does not seem to indicate that this is true of yours if a ruler placed alongside shows the same gradients as the scale on the gauge. In general, I would say that evaporation would _not_ be the problem. A smaller, deeper container (such as the gauge) should permit less evaporation than a wider, shallower container and you stated that the larger box appeared to hold more water. ---
**Author:** ![goddessodd](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@goddessodd](https://boards.straightdope.com/u/goddessodd)\ **Post date:** [July 30, 2005, 10:51pm UTC](https://boards.straightdope.com/t/is-my-rain-gauge-lying-to-me/314853/5 "2005-07-30T22:51:27Z")
> [@tomndebb](#): > > Does the 3" x 4" box have tapered sides? Is there any chance that the box actually had water in it (either from a previous rain, a water sprinkler, or some other cause) so that the 1.5" of recorded rain were added to existing water? > > If the sides of the box are tapered, there is a greater “collection” area for the rainfall and the box will fill faster. (In fact, some rain gauges are actually made with a taper and the markings are exaggerated to compensate. This allows the scale on the side to be marked in farther separated increments for easier reading.) Your description does not seem to indicate that this is true of yours if a ruler placed alongside shows the same gradients as the scale on the gauge. > > In general, I would say that evaporation would _not_ be the problem. A smaller, deeper container (such as the gauge) should permit less evaporation than a wider, shallower container and you stated that the larger box appeared to hold more water. Neither container has tapered sides. Both containers were empty immediately before the rain (I left the box there when I went out to empty the rain gauge in anticipation of the coming rain) and checked immediately after the storm. The plastic box is 4" deep, so I suppose splash back might be a factor, and is something I had not thought about. I am now thinking about going to round up some aquariums of varying sizes, set them side by side and measuring the results. I base my irrigation needs on this rain gauge, so I am wondering how accurate they are in general. Interestingly, I spoke with a very close neighbor, who said his gauge measured 2" of rain from the same storm, so now I am really confused. At least 2" is right in the middle of my 2 measures!