Elements of the water cycle Important terms: Condensation, Evaporation, Transpiration, Groundwater, Precipitation, Surface Runoff, Water Table

Evaporation Evaporation is the process by which water is converted from its liquid form to its vapor form. In water vapor form, it moves into the atmosphere (air). Evaporation from the oceans accounts for 80% of the water delivered as precipitation (rain, snow, sleet, or hail).

Condensation Condensation is the change of water from its gaseous form (water vapor) into liquid water. Condensation generally occurs in the atmosphere when warm air rises, cools and loses its capacity to hold water vapor. As a result, excess water vapor condenses to form cloud droplets.

Precipitation When cloud particles become too heavy to remain suspended in the air, they fall to the earth as precipitation. Precipitation occurs in a variety of forms; hail, rain, freezing rain, sleet or snow.

Transpiration Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves.

Water Table The saturated zone: The rock and soil in which all the open spaces are filled with water is called the saturated (or saturation) zone. As the top of the saturated zone rises toward the surface, it reaches a level of equilibrium with the overlying unsaturated zone. The unsaturated zone: The unsaturated zone (or zone of aeration) is the rock and sediment in which pore spaces contain mostly air and some water and therefore are not saturated. The unsaturated zone typically starts at the surface and extends downward to the saturated zone. The contact between the saturated and unsaturated zones is called the water table.

Surface Runoff Surface runoff is water, from rain, snowmelt, or other sources, that flows over the land surface, and is a major component of the water cycle.

Groundwater Groundwater is water that exists in the pore spaces and fractures in rock and sediment beneath the Earth's surface. It originates as rainfall or snow, and then moves through the soil into the groundwater system, where it eventually makes its way back to surface streams, lakes, or oceans.