The Science of Hydrology

What is hydrology?

Hydrology is the study of water in the environment.

Hydrology has evolved as a science to try and understand the complex water systems of the Earth, to study and predict how water will behave under different circumstances as it moves through the land phase of the water cycle.

Water is one of the most important natural resources and although plentiful, is not always in the right place at the right time or of the right quality. An overall aim of hydrologists is to apply scientific knowledge and mathematical principles to mitigate water-related problems in society and environmental protection. This may mean working out the best use of water supplies for cities or for irrigation, controlling river flooding or soil erosion, protecting or cleaning up pollution, planning long-term water storage reservoirs, flood risk assessment and flood/drought warning.

The water cycle

There is a continuous movement of water on, above or below the surface of the Earth. Water changes its physical state – liquid, vapour or solid – at various points within the water cycle.

Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go, in and out of the atmosphere. Water moves from one reservoir to another, from river to ocean or from the ocean or land surface to the atmosphere and back again by the physical processes of evaporation, condensation, precipitation, infiltration, runoff and subsurface flow.  

The Water Cycle

As the Earth’s surface water evaporates, winds move water in the air from the sea to the land, increasing the amount of freshwater on land. Water vapour is converted to clouds that bring fresh water to land in the form of rain or snow. Precipitation falls to the ground but what happens to that water depends greatly on the geography of the land at any particular place.