Why are green roofs considered an effective BMP for stormwater management?

Green roofs are recognized as an effective Best Management Practice (BMP) for stormwater management primarily because they play a crucial role in absorbing rainwater and reducing overall runoff. The vegetation and substrate found in green roofs retain moisture by absorbing rainfall, which decreases the volume of water that would otherwise flow directly into storm drainage systems.

When it rains, green roofs act like sponges, soaking up rainwater and minimizing the speed at which stormwater enters the urban drainage system. This helps prevent issues related to urban flooding, erosion, and the overflow of sewer systems that can occur during heavy rain events. By promoting water retention and evaporation, they also help to mimic natural processes, reducing the burden on municipal stormwater systems.

While their energy cost reduction, provision of wildlife habitat, and air quality improvement are significant benefits, the key feature that establishes green roofs as effective BMPs specifically for stormwater management is their ability to absorb and mitigate runoff. This function aligns closely with the goals of stormwater management practices, which aim to control and manage the quantity and quality of runoff in urban areas.