Question: We've been hearing a lot about Victoria's record rainfall of about 280 mm this November (1998), but what does that mean? I assume it refers to a depth of 280 mm having fallen, but over what surface area is it measured?
Answer: Rainfall amount is determined simply by putting out a bucket for the rain to fall in and measuring how deep the total rain collected in it is after some period of time, usually daily. Total monthly rainfall is the sum of all daily rainfall measurements that fell during a given month.
Now what does that mean. If the rain did not evaporate, run off the surface, or absorb into the surface, you would have had a puddle 280 mm deep across Victoria (British Columbia) by the end of the month. Of course, rainfall varies over an area, particularly in a mountainous region like Victoria where rain in the city can be much less than in the surrounding highlands. In the city the annual rainfall is about a third of that measured in the highlands. So be careful about how far you spread that puddle from the point of measurement.
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