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I am trying to calculate total daily rainfall based on data from a tipping bucket rain gauge which is calibrated to a tip of 0.2mm. I have data giving the exact time that a tip is recorded and have summed the number of tips per day.

I am getting myself confused when converting between mm and ml. I understand that the rainfall height is simply 0.2mm x the number of tips in a 24 hour period. Where I am getting confused is converting this number to total daily rainfall in ml. I am interested in looking at variations in runoff generation for some field-scale runoff plots. I have the area measurement for the rain gauge (214 cm²). Do I need to convert for the field area where the gauge is situated as well when calculating the total daily rainfall? I feel like it can't be as simple as whatever the rainfall height is (in mm) converted to ml.

Thanks

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  • $\begingroup$ See also What does a mm of rain mean?... as the other inputs says, to get a volume, you need to consider what area you want the volume of rainfall for. 10 mm of rain puts down more volume if it is a wide storm over a whole city versus a small-scale peak over a small field. $\endgroup$ Nov 25 at 22:51
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You are on the right track. Rain gauges measure rainfall as a linear measure. Consequently, 2 mm of rainfall is the same as saying that the measured depth of water that would have accrued due to rainfall is 2 mm. You do not need to convert the rain gauge area because the rain gauge has been calibrated to give you the correct measured depth of rainfall as a linear measure, in this case, in mm.

So you have this rain gauge in a field, say an agricultural field, of a known specific area. The volume of the rainfall is simply the depth times the area. To keep the units consistent, convert 2 mm to meters, and do the math. Here is an example for a field 300 m by 200 m, using a 2 mm rainfall measured with your tipping bucket rain gauge -

  • Field area 300 m x 200 m or 30000 sq meters
  • rainfall 2/1000 meters
  • Volume rainfall 30000 m x 2/1000 m = $60 m^3$

This was a great question!

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  • $\begingroup$ This is great-thanks for explaining it! $\endgroup$
    – eH156683
    Nov 26 at 11:59

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