Hydrologic Cycle

The hydrologic cycle is a term that describes the natural movement of water between land and air driven by the sun and gravity. The cycle can be broken down into its major processes; precipitation, infiltration, runoff, evaporation, condensation and groundwater flow.

Precipitation

Precipitation begins after water vapour, which has condensed in the atmosphere, becomes too heavy to remain in the atmosphere air currents and falls. Sometimes precipitation evaporates before it reaches the surface. Most often, however, falling precipitation reaches the surface and is subject to one of the following.

Infiltration

Infiltration is the process of precipitation seeping into the ground. This is largely a function of the permeability of the ground and the moisture content of the soils. The more permeable a soil and the higher the moisture content, the more precipitation seeps into the ground.

Runoff

Precipitation that does not infiltrate the ground surface runs overland to lower elevations, which are occupied by surface water bodies. Runoff can also come from melted snow and ice.

Evaporation

Evaporation is the change of liquid water to a vapour. Sunlight aids this process as it raises the temperature of liquid water in oceans and lakes. As the liquid heats, molecules are released and change into a gas. Warm air rises up into the atmosphere and becomes the vapour involved in condensation. Evaporation is often considered jointly with the process of transpiration.

Transpiration

Transpiration is the process by which plants take in water through their roots and release it through their leaves. Water can be cleaned because contaminants and pollutants are removed. Of the transpired water passing through a plant only 1 % is used in the growth process. Transpiration also transports nutrients from the soil into the roots and carries them to the various cells of the plant and is used to keep tissues from becoming overheated.

Condensation

Condensation is the process of water changing from vapour to liquid phase. Water vapour in the air rises mostly by convection. This means warm, humid air will rise, while cooler air will move downward. Ad the warmer air rises, the water vapour will lose energy, causing temperature to drop. The water vapour then changes state into liquid or ice.

Groundwater

Infiltrating water that is not taken up by plants or stored as soil moisture serves to recharge groundwater systems. Groundwater is stored in and flows through units referred to as aquifers. Ultimately, groundwater is discharged to the ground surface in springs, rivers, lakes or oceans to complete the hydrologic cycle.