The annual average rainfall in a tropical city is 200 mm. On a particular rainy day (24-hour period), the cumulative rai...

Question

The annual average rainfall in a tropical city is 200 mm. On a particular rainy day (24-hour period), the cumulative rainfall experienced by the city is shown in the graph below. Over the 24-hour period, 50% of the rainfall falling on a rooftop, which had an obstruction-free area of 50 m^2, was harvested into a tank. What is the total volume of water collected in the tank (in litres)?

A. 25,000  B. 18,750  C. 7,500  D. 3,125

Accepted Answer

Total volume of water collected = 7,500 litres A rooftop of area 50 m^2 catches rain during a 24-hour storm. Only 50% of the rain that falls is collected into a tank; the rest is lost. The cumulative rainfall graph shows how much rain has fallen by any given hour. Reading the graph at the 24-hour mark gives the total depth of rain that fell. Multiplying depth × area × efficiency converts this to a volume in cubic metres, and 1 m^3 = 1,000 litres.