processes of the water cycle


Plants and animals depend on water to live. They also play a role in the water cycle. Plants take up water from the soil and release large amounts of water vapor into the air through their leaves (Figure 1.3), a process known as transpiration.

human uses

People also depend on water as a natural resource. Not content to get water directly from streams or ponds, humans create canals, aqueducts, dams, and wells to collect water and direct it to where they want it (Figure 1.4). Clouds form above the Amazon Rainfor- est even in the dry season because of moisture from plant transpiration. Pont du Gard in France is an ancient aqueduct and bridge that was part of of a well-developed system that supplied wa- ter around the Roman empire. Click image to the left or use the URL below. URL:




Water changes from a liquid to a gas by evaporation to become water vapor. The Suns energy can evaporate water from the ocean surface or from lakes, streams, or puddles on land. Only the water molecules evaporate; the salts remain in the ocean or a fresh water reservoir. The water vapor remains in the atmosphere until it undergoes condensation to become tiny droplets of liquid. The droplets gather in clouds, which are blown about the globe by wind. As the water droplets in the clouds collide and grow, they fall from the sky as precipitation. Precipitation can be rain, sleet, hail, or snow. Sometimes precipitation falls back into the ocean and sometimes it falls onto the land surface.

streams and lakes

When water falls from the sky as rain it may enter streams and rivers that flow downward to oceans and lakes. Water that falls as snow may sit on a mountain for several months. Snow may become part of the ice in a glacier, where it may remain for hundreds or thousands of years. Snow and ice may go directly back into the air by sublimation, the process in which a solid changes directly into a gas without first becoming a liquid. Although you probably have not seen water vapor undergoing sublimation from a glacier, you may have seen dry ice sublimate in air. Snow and ice slowly melt over time to become liquid water, which provides a steady flow of fresh water to streams, rivers, and lakes below. A water droplet falling as rain could also become part of a stream or a lake. At the surface, the water may eventually evaporate and reenter the atmosphere.


A significant amount of water infiltrates into the ground. Soil moisture is an important reservoir for water (Figure The moisture content of soil in the United States varies greatly.



Water may seep through dirt and rock below the soil and then through pores infiltrating the ground to go into Earths groundwater system. Groundwater enters aquifers that may store fresh water for centuries. Alternatively, the water may come to the surface through springs or find its way back to the oceans.

the water cycle

The movement of water around Earths surface is the hydrological (water) cycle (Figure 1.1). Water inhabits reservoirs within the cycle, such as ponds, oceans, or the atmosphere. The molecules move between these reservoirs by certain processes, including condensation and precipitation. There are only so many water molecules and these molecules cycle around. If climate cools and glaciers and ice caps grow, there is less water for the oceans and sea level will fall. The reverse can also happen. The following section looks at the reservoirs and the processes that move water between them.

solar energy

The Sun, many millions of kilometers away, provides the energy that drives the water cycle. Our nearest star directly impacts the water cycle by supplying the energy needed for evaporation.


Most of Earths water is stored in the oceans, where it can remain for hundreds or thousands of years.


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this drives the water cycle.

a) the ocean

-->  b) the sun

c) the core

d) the air

when water changes from a liquid to a gas.

a) precipitation

b) condensation

-->  c) evaporation

d) hydration

rain, sleet, hail, or snow are examples of this.

-->  a) precipitation

b) condensation

c) evaporation

d) hydration

which of these is an example of sublimation?

a) ice changing to water

b) water changing to ice

c) water vapor changing to a cloud

-->  d) snow changing into a gas

plants do this process where water vapor can go into the air through the leaves.

a) sublimation

b) condensation

-->  c) transpiration

d) precipitation

another name for the water cycle is this.

a) atmospheric cycle

b) lithospheric cycle

c) biospheric cycle

-->  d) hydrological cycle

the only reason plants can grow in arid regions is that there is a lot of water trapped in the soil.

a) true

-->  b) false

when atmospheric temperature rises sea level _ because _.

-->  a) rises; ice caps and glaciers melt

b) falls; ice caps and glaciers grow

c) rises; ice caps and glaciers grow

d) falls; ice caps and glaciers melt

water can be stored for future use in snow and ice.

-->  a) true

b) false

as far back as the roman empire, humans diverted water to suit their own needs.

-->  a) true

b) false

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