In most of the continental US, only a third of runoff transfers the continental surplus to balance the deficit of the ocean's fraction of annual precipitation.
<h3>Water Cycle and Surface Runoff</h3>
The physical geology and topography of the ground as well as meteorological conditions all have an impact on surface runoff.
Only approximately a third of precipitation that falls on land drains into rivers and streams before being dumped back into the ocean.
The remaining two-thirds either evaporate, transpire, or soak into the earth (infiltrate). Humans have the ability to redirect surface runoff for their own purposes.
More and more of the natural environment is being replaced by impermeable surfaces, such as roads, homes, parking lots, and buildings, which decrease groundwater infiltration and hasten runoff to ditches and streams as more people inhabit the planet and as development and urbanization increase.
