Why does one inch in an official rain gauge actually only one - tenth of an inch of rain?

Answer 1

An official rain gauge typically has a larger diameter opening compared to a standard measuring device, which allows for more accurate measurement of rainfall. The calibration of the gauge takes into account the surface area of the opening, so that one inch of rain collected in the gauge is equivalent to a larger amount of rainfall over a standard area. This calibration factor is typically 1:10, meaning that one inch of rain in the gauge represents one-tenth of an inch of actual rainfall over the standard area.

Answer 2

If the rain gauge has a 10:1 ratio as described, then the funnel on top has an area that is 10 times the cross-sectional area of the glass tube. Suppose you had a can, that has the same area opening as the funnel, then if it rains 0.5 inch that day, there will be 0.5 inches of water in the can, but if you take the water in that can and pour it into the rain gauge (with cross sectional area 1/10 of the can), that same volume of water will fill up the gauge by 5 inches.

They do this so that it is easier to read the amount of rain. If you did not have the funnel on top, it'd be harder to read how much rain there was (was it 0.1 inches or 0.15 inches for example), plus statistically a smaller opening has less of a chance of 'catching' a raindrop than the wider opening.

Answer 3

The inner cylinder in an official rain gauge has a larger diameter than one inch, so the volume it collects is actually equal to one-tenth of an inch of rainfall. This design allows for more accurate measurement of smaller amounts of rainfall.