What role does runoff play in water cycle?
The variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. As it flows, the water may infiltrate into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses >>From Wikipedia<< Which basically means the process in which water may travel across land underground, that's how it gets to the rivers, lake, etc. and get evaporated.