What is urban runoff?

Urban runoff refers to rainwater that collects pollutants as it flows over impervious surfaces such as roads, sidewalks, and rooftops in urban environments. This runoff typically carries a variety of contaminants, including oil, heavy metals, pesticides, and other pollutants, which can have detrimental effects on local water bodies and ecosystems when it is discharged into them.

The characteristics of urban areas significantly contribute to this phenomenon. Unlike natural landscapes, urban areas often lack vegetation and have extensive hard surfaces, which prevent water from soaking into the ground. Instead, precipitation flows directly into storm drains or waterways, picking up pollutants along the way. This process poses significant challenges for water quality management, necessitating effective stormwater management practices to mitigate pollution from runoff.

In contrast, the other options do not accurately describe urban runoff. Water from industrial sources pertains to a specific type of discharge, while evaporation refers to water transitioning from liquid to vapor, which does not apply to runoff. Lastly, stormwater that is filtered through natural wetlands contributes to water quality improvement rather than defining what urban runoff specifically is.