Example 11.1.1. Average rainfall.
A rainfall gauge is essentially a graduated cylinder that collects rain as it falls. But instead of being marked with volume measurements, it is marked with height measurements.
With rain in the forecast, you decide to set out a rain gauge at 10 oβclock in the evening, even though it is not currently raining. You check on the rain gauge at 8 oβclock the next morning, and find that it has collected an amount of water so that the gauge reads 4 mm. This measurement means that if the ground was perfectly flat and impermeable so that the rain could neither run off nor be absorbed by the ground, youβd be standing in a large puddle 4 mm deep.
So the average rate of accumulation over those 10 hours was 0.4 mmβh.