The hydrological cycle describes the movement and storage of water between the four spheres of the system: atmosphere, biosphere, lithosphere and hydrosphere (see Strahler and Strahler, 1998, for more information on the four spheres). It involves both the vertical and horizontal transfer of water in different forms. The cycle also reflects the interactions of environmental processes between these spheres. See Figure 2 for the Hydrological Cycle, Click >> HERE.

Key hydrological terms

• Interception – water absorbed by vegetation. This includes wetted leaves surfaces which is further lost through evaporation and stemflow.
• Infiltration – the process whereby water is absorbed by the soil or land surface.
• Surface runoff (or Overland flow) – the portion of precipitation that flows over the land surface
• Subsurface flow (Throughflow) - includes water stored in soil, regolith or bedrock beneath the land surface.

A hydrograph is a graph which shows the variations in river discharge at a particular point over a period of time. It measures the speed at which rainfall falling on a drainage basin reaches the river channel. The important components of a hydrograph include discharge, time, lag time, rainfall, rising limb, peak discharge, storm runoff, baseflow and descending (recession) limb.