why is rain measured from drops rather than what is on the ground?

Answer 1

Rain falls in drops but you can't measure drops because some are bigger than others. However it is measured by the amount that falls.

Answer 2

There are several means by which rain is measured, the most accurate commonly used method is to use a collection canister with a diameter that is calibrated to a measuring stick graduated to the 1/100 of an inch. This is a measurement of what hits the ground at a particular location. In the case of standard National Weather Service cooperative observer program cans, it indicates what falls on a square foot surface area of the ground, and these are placed so there is no interference from rooftops, trees, etc. From this, how much total water precipitates can be estimated for larger areas. The duration of an event is also important, as this affects how much of this rain can be absorbed by the soil, and how much runs off as flood water. Effective rainfall is estimated from this and other factors. If we measured rain by measuring puddles on the ground, it would be difficult to know how much had already percolated into the soil, and each puddle area would have to be calculated before we had a total.
The short answer, we measure the way we do according to scientific principles for standardizaton of method and elimination of variables so every measuring point is collecting data the same way. This minimizes error and gives greater confidence in data.

Answer 3

Because once it hits the ground it either soaks in or pools so two places less than 10ft apart could get vastly different readings and therefore the measurement would be meaningless for comparison

Answer 4

its easier to put out a little jar and measure what falls into it than trying to pick up water drops on the ground and put them into the little jar to get a measuement.