Surface Runoff and Precipitation

Precipitation brings water from the atmosphere to the ground, while surface runoff is the movement of that water across the land towards larger water bodies.  Surface runoff and precipitation are both key components of the water cycle:

 

Precipitation  -  This is the process by which water in the atmosphere, in the form of water vapor, condenses into liquid or solid forms and falls to the Earth's surface.  Common forms of precipitation include rain, snow, sleet, and hail.  Precipitation is a primary way that water from the atmosphere reaches the ground, replenishing rivers, lakes, and groundwater.

Surface Runoff  -  This occurs when water from precipitation flows over the land's surface and eventually makes its way into bodies of water like rivers, lakes, and oceans.  Surface runoff happens when the ground cannot absorb all the water, either because the soil is saturated, frozen, or impermeable, or because the precipitation is too intense for infiltration to occur.  Runoff can also occur from melting snow or ice.