What is runoff and what factors affect it?

Runoff is the portion of precipitation that flows over the land surface to streams and rivers instead of infiltrating into soil. Factors affecting runoff include: rainfall intensity and duration, soil type and moisture content, land slope, vegetation cover, land use (urbanization increases runoff), and catchment shape and size. Runoff coefficient is the ratio of runoff to rainfall, ranging from 0.1 for forests to 0.9 for paved areas.