Hydrological cycle

The hydrologic cycle describes the continuous re-circulating transport of the waters of the earth, linking atmosphere, land and oceans.

Water evaporates from the ocean surface, driven by energy from the Sun, and joins the atmosphere, moving inland as clouds. Once inland, atmospheric conditions act to condense and precipitate water onto the land surface, where, driven by gravitational forces, it returns to the ocean through river and streams.

The process is quite complex, containing many sub-cycles.

Engineering Hydrology takes a quantitative view of the hydrologic cycle.

The quantification of the hydrologic cycle which is an open system can be represented by a mass balance equation, where inputs minus outputs are equal to the change in storage.

It is a basic Hydro-logic Principle or equation that may be applied either on global or

regional scale.

I-O=ΔS