hydrology

The study of that part of the water cycle that takes place on land. Precipitation falling on the land either infiltrates the soil and substrata, evaporates (whether or not it is first intercepted by vegetation), accumulates as standing water or flows across the surface as run-off into watercourses, lakes and the sea.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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