Agronomists often need to turn a rainfall reading in millimeters into an actual volume of water so they can plan irrigation, and this question tests whether that conversion is done correctly.
- 1 cm of rainfall = 1 liter per square meter: Wrong, since 1 cm is a depth of 0.01 meter, and over 1 square meter that works out to 0.01 cubic meter, which is 10 liters, not 1 liter.
- 1 mm of rainfall = 10 liters per square meter: Wrong, since 1 mm is a depth of 0.001 meter, and over 1 square meter that gives 0.001 cubic meter, which is only 1 liter, not 10.
- 1 mm of rainfall = 1 liter per square meter: Right. This is the standard conversion used across agriculture and meteorology: a 1 millimeter rain event delivers 1 liter of water on every square meter of ground, or equivalently 10,000 liters on a hectare.
- 1 cm of rainfall = 10 liters per square meter: This is numerically consistent too, since 1 cm is simply 10 mm, so it scales to 10 liters, but it is the same underlying fact restated at a different unit rather than the standard way the relationship is quoted.
Since 1 mm depth of water over 1 square meter always works out to exactly 1 liter by direct volume calculation, and this is the form the relationship is conventionally taught in, the millimeter based statement is taken as the intended correct answer.
Let's summarize:
- Multiply rainfall depth in meters by area in square meters and by 1000 to get liters.
- 1 mm over 1 square meter gives 1 liter, and 1 cm over 1 square meter gives 10 liters.
So option 3, one millimeter of rainfall equals one liter of water per square meter, is the correct statement.