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Bob Harrington · May 31st 04, 11:22 AM posted to alt.talk.weather

wrote:
I am having a dispute with a friend over rain gauges. He has one of
those commercial ones that are about a one inch clear plastic cylinder
with inches painted on the side. I however, simply keep a 5 gallon
plastic pail outside on the lawn, away from trees and the roof, etc.

He claims that a pail is not accurate, and only his commercial one is.
I think that as long as my pail has straight sides and a flat bottom,
it is just as accurate, and possibly even a little more accurate,
because it's sampling a larger area of space. After all, rain does
not fall evenly, so wouldn't a larger cylinder or container be more
accurate, simply because it's more representative of an average in my
yard?

He lives several miles away, so there is no way to compare amounts,
although I am tempted to buy one of those "rain gauges" and compare
the results to my pail.

I should mention that I glued the end off an old broken tape measure
to the inside of my pail.

Does anyone know the answer?

All else being the same, I would think that your pail might be less
accurate in that the greater surface area vs. volume of collected water
would result in greater evaporation between measurements which would
skew your readings downward compared to the narrower collection tube.

Better still are the rain gauges that consist of a larger cylinder
topped with a funnel that concentrates the rainfall into an inner
cylinder that has 1/10 the cross sectional area of the collection
funnel. This allows more accurate measurement of rainfall since the
graduations on the inner tube are exaggerated by a factor of ten; an
overflow hole near the top of the inner cylinder lets excessive rainfall
collect in the outer cylinder to be poured into the inner cylinder at
measuring time if necessary. The funnel and narrow inner tube help keep
evaporation to a minimum.

Bob ^,,^