Rainfall in Spain is measured in liters per square meters, l.m^-2.

1. How many mm of rain is equivalent to a rainfall of 1.0 l.m^-2?
2. What total volume of water falls on Real Madrid's home soccer pitch, which has an area of 0.50 ha, as a result of a 33 mm downpour?

Answer 1: 1.0 l = 1.0 x 10⁶ µl = 1.0 x 10⁶ mm³. A square with sides 1.0 m has an area of 1.0 m², which is 1.0 x 10⁶ mm². If such a square were to be covered by a layer of water 1.0 mm deep, the volume of water would be 1.0 mm x 1.0 x 10⁶ mm² = 1.0 x 10⁶ mm³, which is 1.0 l. So, a rainfall of 1.0 mm is equivalent to 1.0 l.m^-2.

Answer 2: We have shown that 1.0 l.m^-2 is equivalent to 1.0 mm of rain. So, 33 mm is equivalent to 33 l.m^-2. 1 ha is 1.0 x 10⁴ m², so 0.50 ha is 5.0 x 10³ m². Hence the total volume of water is 33 l.m^-2 x 5.0 x 10³ m², which is 165000 l, or 165 m³.