Hydrology is the science of the hydrologic cycle. The hydrologic cycle describes the circulation of water throughout our environment. This requires an understanding of the different processes and phases that water undergoes as it moves around our world. The major processes shown in the picture below are indicated by blue arrows.

There are many processes in the hydrologic cycle. Visible processes such as precipitation and runoff are examples of more familiar processes while; evaporation and groundwater flow may not be as familiar. However unfamiliar, they are still significant components of the hydrologic cycle. Water moves between these different processes under the influence of gravitational forces and energy from the sun. A phase change is often associated with a process, for example going from liquid to gas when it evaporates, or from liquid to solid when it freezes in the glaciers. Although water is always moving between these different processes and phases, it is also being stored in oceans, lakes, and aquifers.

Hydrology encompasses both surface and subsurface processes, with meteorology superimposed over the entire cycle. Because each of these sciences is relatively complex on their own, they are often subdivided into their specific areas of study. Hydrologists, primarily concern themselves with surface waters while hydrogeologists typically focus on subsurface water. The third main component is meteorology, which is the science of weather and climate. Because they are all so closely interlinked, a basic understanding of each of the components is required to interpret water quantity and the larger hydrologic cycle.

courtesy of NASA Earth Observatory http://earthobservatory.nasa.gov/

About 75% of the surface of the earth is covered by water, with the vast majority of this as oceans. In Alberta, lakes and rivers are the main sources of surface water. Some areas of the province seem to have an abundance of water and other areas seem quite dry. In reality, the water that can be seen is only a portion of the total fresh water that may be available, and an even smaller portion of the total water on the planet. The following chart illustrates the relative quantities and distribution of water.

Fresh water accounts for about 2.5% of the total water in the world. Of this 2.5%, less than 0.3% is actually on the surface in lakes and rivers. A much larger percentage of potentially available fresh water is stored in groundwater. Most of this groundwater is neither accessible nor cost effective to recover. The bulk of fresh water (69%) is locked in the polar ice caps and also not generally available for use. This means that although there is plenty of water on our planet, only a tiny fraction is potentially available for human use. The oceans are by far the most plentiful source of water but the saline water is not suitable for most of our needs and uses. The oceans do have a dominating role in creating and supplying the fresh water we need.

World Water Balance and Water Resources of the Earth, UNESCO, 1978.

A Water Balance from the Alberta Perspective

If you could look at the basic water balance of Alberta as a whole, here is what it would look like. As you can see, most of the rain and snow is returned to the atmosphere through evaporation and evapotranspiration. Only about 20% of the precipitation makes its way into our rivers and streams, and groundwater.

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The oceans make up about 96.5% of the water on earth and play an integral part in regulating global climate and the hydrologic cycle. The salty water in the oceans follows the cycle illustrated by the diagram, to become the fresh water that is vital for supporting and sustaining our environment.

Water begins the cycle in the oceans. The energy from the sun evaporates some of this water. Evaporation removes water molecules only, leaving the salts in the oceans. As the water vapor rises into the atmosphere it cools and condenses into clouds. The clouds are then pushed by the wind, and under the right conditions they will produce precipitation that collects to form lakes and rivers, and eventually infiltrates into the ground to become groundwater. The rivers of Alberta and the groundwater aquifers will eventually discharge back into the oceans, renewing the cycle.