The Water Cycle

Water, Water Everywhere

What is the Water Cycle?• The earth has a limited amount of water. That water keeps going around

and around and around and around in what we call the "Water Cycle".• It is powered by solar energy, and aided by gravity. The water cycle includes

all the processes that shift water—both those that physically move water, and those that convert water between solid, liquid, and gaseous states.• This cycle is made up of a few main parts:• evaporation (and transpiration)• condensation• precipitation• collection

Where does the water cycle get energy to keep going?• There is the same amount of

water on the Earth now as there was when the Earth began. The water cycle is how the earth's water recycles itself. • Earth's water keeps changing

from liquid water to vapor and then back again. This cycle happens because of the sun's heat and gravity.

What does the sun provide during the water cycle?• The sun is what makes the water cycle work. • Wherever the sun shines on the ocean, evaporation creates fresh water vapor

out of salty seawater. Winds lift the moist air high into the atmosphere, and blow it about the globe. As air moves away from the warm ocean it starts to cool off. With sufficient cooling, water vapor changes into drops of liquid water— a process called condensation• The sun provides what almost everything on Earth needs to go—energy, or heat. • Heat causes liquid and frozen water to evaporate into water vapor gas, which

rises high in the sky to form clouds...clouds that move over the globe and drop rain and snow. • This process is a large part of the water cycle.

Where is the water?• The cycle also contains many reservoirs, where water accumulates.

The great majority of water—more than 97%—lies in the oceans. Just over 2% is frozen in glaciers and ice caps. • The rest—a meager half percent or so—is divided between the

atmosphere, lakes and streams, and the ground.

What is evaporation in the water cycle?• Wherever the sun shines on the

ocean, evaporation creates fresh water vapor out of salty seawater. • Evaporation is when the sun

heats up water in rivers or lakes or the ocean and turns it into vapor or steam. • The water vapor or steam leaves

the river, lake or ocean and goes into the air.

What is transpiration during the water cycle?• Water even evaporates from plants. • This is called transpiration. • Plants, such as trees, lose water out of their leaves after they have

absorbed water from the ground. • Transpiration helps keep plants cool in the same way that

perspiration keeps animals, such as humans, cool. • The rate at which water will evaporate or transpire from plants

depends on the temperature, wind, and humidity.

What is condensation during the water cycle?• Water vapor in the air gets cold

and changes back into liquid, forming clouds. This is called condensation. • Pour a glass of cold water on a hot

day and watch what happens. Water forms on the outside of the glass. That water didn't somehow leak through the glass! It actually came from the air. Water vapor in the warm air, turns back into liquid when it touches the cold glass.

Evaporation• Wherever the sun shines on the ocean, evaporation creates fresh

water vapor out of salty seawater. • Winds lift the moist air high into the atmosphere, and blow it about

the globe. • As air moves away from the warm ocean it starts to cool off. With

sufficient cooling, water vapor changes into drops of liquid water— a process called condensation.

What is precipitation during the water cycle?•Precipitation occurs

when so much water has condensed that the air cannot hold it anymore. • The clouds get heavy and

water falls back to the earth in the form of rain, hail, sleet or snow.

Precipitation• With continued condensation, tiny drops of water grow bigger and

bigger and gather into clouds. • The average airborne water molecule stays aloft for only 10 days or

so, until it joins a water droplet heavy enough to fall from the sky. • Most precipitation, be it rain, snow, sleet, or hail, drops right back

into the ocean. • There, the water circulates until evaporation claims it once again.

What is percolation during the water cycle?• The last step is percolation. • Percolation is when the water on

the surface of the Earth seeps down underground. • It later forms aquifers in the low

lying regions.

What is runoff in the water cycle?

• Runoff is the overflow of water from the land and into a body of water. • The water can overflow into a

stream, a river, or even an ocean. • It's caused when the soil can no

longer hold any more water.

Runoff• When ice and snow melt, or rain falls on land, water is pulled swiftly

downhill by gravity. • Some of it flows across the top of the ground, a process called runoff. • Surface water gathers into rivers pauses for a time in lakes, and rushes

down to the sea. • As it flows across the ground, running water cuts into the earth,

wearing down and reshaping the ground. • Moving water is the most powerful geologic force sculpting the

landscape.

Groundwater• Precipitation actually infiltrates, or soaks into, the earth than runs off. • More than 95% of the planet’s liquid fresh water is groundwater—

water held within the ground. • Some shallow groundwater doesn’t last long. • Evaporation directly from the soil, and transpiration through plants,

both transfer moisture back to the air. • The process of transpiration is part of plant metabolism. Liquid water

is absorbed by roots, and lifted to the leaves, where it is converted to vapor and lost to the sky.

Transpiration

• The process of transpiration is part of plant metabolism. • Liquid water is absorbed by roots, and lifted to the

leaves, where it is converted to vapor and lost to the sky.

How are evaporation and condensation similar and different?

•Similar•Both are changes in heat energy and are parts of the water cycle

• Different

• evaporation is the process by which water changes to gas but• condensation is the

process by which gas changes into water.

Global Impact• The water cycle is the most fundamental system operating on the surface of the earth. The varied

processes of the water cycle control the global climate, shape the landscape, and allow life to exist.• Evaporation powers vast weather systems like hurricanes and cyclones, while uneven precipitation

nourishes rainforests or parches deserts. Other weather events, such as floods, droughts, and blizzards, are all aspects of the water cycle.

• Runoff is unequalled in its ability to erode rock and soil, and reshape the face of the land. Mountains are worn low and canyons are carved deep, grain-by-grain from the relentless force of moving water.

• For mankind, perhaps the most immediate impact of the water cycle is its influence on the quantity and quality of fresh water.

• Because of the unequal distribution of water around the cycle, fresh water is relatively scarce—only 0.65% of Earth's total water supply is neither salty nor frozen.

• As groundwater infiltrates through the soil, it gathers up both mineral compounds and buried toxic chemicals.