Why Is Rain Measured in Mm

Rainfall is extremely variable, both over time and between different locations, which makes it very difficult to measure. A rain gauge basically collects water falling on it and records the change over time in the rainfall depth, which is usually expressed in mm.

Why is rainfall expressed in terms of depth mm and not by volume?

Because rainfall is highly spatially variable so it would make more sense to measure it as depth at a given point (x,y,z which is the location of the rain gauging station) rather than volume because volume implies a given application area (which is often unknown and can only be extrapolated by scrutinising rainfall …

Is rain measured in ml or MM?

Bob says rain is measured in a rain gauge its depth is measured in millimetres (mm). So 1 mm of rain = 1L per square M. “Millilitres of rain is probably what hydrologists and roof builders work with” says Bob.