falling on the land can be in solid or liquid form. Solid precipitation—snow, sleet,
ice pellets, and hail—remain in storage on the surface for various lengths of time.
Some solid precipitation will immediately melt while some falls at high altitude or
high latitude and becomes part of a year-round snow cover. In some cases the snow
falls, is compressed by snowfall after snowfall over a course of many years, and
metamorphoses into glacial ice. Glaciers represent storage in the hydrologic cycle.
Water may be stored in large glaciers for over 400,000 years. Eventually, glacier
ice returns water directly to the ocean by melting in contact with the ocean, melt-
ing into a stream, or evaporating and sublimating into the air. Ironically, glaciers
and snow account for 78 percent of the world’s freshwater supply, making much
of it not readily available for the benefit of life.
In places where there are seasonally warm temperatures, there is summer melt
from the ice and snow and much of this passes along streams. The American
Southwest is arid at low elevations but experiences significant snowfall at high ele-
vations. The winter snowpack provides summer stream flow so human concerns
such as hydroelectric generation and irrigation are closely tied to the nature of
the snowpack.
Liquid and solid precipitation falling on the ground and vegetation might follow
several paths. The simplest is that rain will run via gravity over land and into
streams. Most streams are organized into drainage basins connected to the ocean
and this is the simplest completion of the hydrologic cycle. Yet, streams comprise
only about .0001 of a percent of planetary water. The water in a stream might not
reach the ocean directly. There is loss into the groundwater supply, evaporation182 Hydrologic Cycle
Water molecules are continuously changing physical state and location, moving between solid,
liquid, and gas phases. This hydrologic cycle affects climate, ecosystems, and geomorphology.
(ABC-CLIO)