Runoff — Science definition

Water flowing across the surface to streams and rivers instead of soaking in; how much depends on the surface.

Where it is taught

In use

Evaporation lifts it from surfaces to the air; transpiration does the same through the pores of plant leaves, and in a forest that is a large fraction of the total; condensation turns vapour back to liquid as air cools, forming cloud; precipitation returns it; and runoff carries it across the surface to rivers and the sea, while some soaks into the ground.

Carbon, Water & Cycling Matter

Questions using runoff

Problem 1

Illustrative pond interval: rain adds 40 L; runoff adds 20 L; evaporation removes 25 L; outflow removes 15 L. Other pathways are excluded. Calculate storage change, label inputs and outputs, and explain the conservation distinction.
Answer and explanation

The modeled pond gains 20 L. Rain and runoff are inputs, while evaporation and outflow cross outward. The changing pond amount is consistent with matter conservation because the pond is only one boundary. The result assumes the stated pathways are complete for the interval and does not predict future weather or every real pond exchange.

Inputs: 40+20=60 L.

Outputs: 25+15=40 L.

Change: 60−40=+20 L.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

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