Which option correctly describes a green roof's stormwater benefit?

• A. It helps manage stormwater
• B. It increases runoff
• C. It has no effect
• D. It increases evaporation causing more rainfall

Answer: (B)

Green roofs reduce stormwater by storing rainwater in the soil layer and returning some of it to the atmosphere through evapotranspiration. This means less water runs off the roof immediately and the drainage is slowed, lowering peak flows and helping the drainage system cope with rain events. By capturing and delaying runoff, green roofs also improve water quality through filtration as water passes through the vegetation and substrate. So, they help manage stormwater by reducing and delaying runoff. The idea that they increase runoff isn’t how a green roof behaves, and green roofs do have a real effect—evaporation doesn’t create more rainfall; it returns water to the air, reducing the portion that leaves as runoff.