You have probably heard a TV weather person say we "had an inch of rain last night". When you think about it, this is an odd way to report the amount of water received. Normally, we measure liquids as volumes. At the store, you buy a gallon of milk, not eight inches worth.

Just how much water does "one inch" of rain represent? We can estimate this volume by making a few simple calculations. First, determine the size, in square meters, of the area shown on your Cumberland, MD topographic map. Do this by measuring the length and width of the mapped area with a ruler in centimeters. Convert these map distances to real distances by multiplication with the representative fraction. Change this number from cm. in meters by dividing by 100. Multiply the length of the map by the width to get the area in square meters.

What did you get? Answer

Now, to calculate the volume of water received over this region, multiply the area of the map (square meters) by the depth of water received during the rainstorm (in metric, an inch of rain is about 0.025 meters). The result is the volume of rain, in cubic meters, produced by this one rainstorm.

What did you get? Answer

Over an entire year, the rainfall for this area averages around 38.3 inches, or .97 meters. Having calculated the volume of water produced by an inch of rain, how much water (cubic meters) is received by this region over an entire year?

What did you get? Answer

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