mm/h
millimeter per hour
Speedexact by definition
The millimetre per hour is a speed, and it is how rainfall intensity is reported: a depth of water accumulating per unit time over a horizontal surface. Light rain is under 2.5 mm/h, heavy rain over 10, and the design storms that size a drainage system run to 50 or 100 mm/h for short durations.
Watch out: An intensity in mm/h is not a total. A 100 mm/h burst lasting six minutes delivers 10 mm of rain, and a storm reported at that intensity for the full hour would be an extreme event almost anywhere. Rational-method drainage design multiplies intensity by catchment area, so the duration used has to match the catchment's time of concentration.
| 1 mm/h | 2.7777778e-07 m/s |
Solvers that use speed