Processes in the Water
Evaporation -
For the water cycle to work, water has to get from the Earth's surface back up into the skies so it can rain back down and ruin your parade or water your crops or yard. It is the invisible process of evaporation that changes liquid and frozen water into water-vapor gas, which then floats up into the skies to become clouds.
The need for heat: As usual, you can thank the sun for keeping evaporation going. The sun's energy breaks the bonds that hold liquid water's molecules together. Thus, it makes sense that water evaporates more easily in hot conditions, such as in the desert, rather than on a cloudy winter day.
Humidity: The amount of water vapor in the air is known as "humidity", often mentioned in the weather reports on the local news. When warm air containing a lot of water vapor (high humidity) moves into colder temperatures (either high in the atmosphere or even on the outside of your glass of iced tea), the colder temperatures cause water vapor to condense into a liquid. The colder temperatures cause water vapor to condense into water droplets and can result in fog.
Condensation -
All air contains water molecules in the form of water vapor, which is invisible. Since the water cycle is all about water changing forms all the time, how does the water vapor turn from a gas back into a liquid and become rain?
The word is "condensation". Water vapor gas condenses back into liquid water and ice, which you mainly see as clouds and then as rain and snow.
Condensation happens because of temperature changes. Warmer air can contain more water vapor than colder air, so when air rises up from the heated earth's surface high into the sky (warm air rises, of course), to where the temperatures are much colder, condensation happens. Some of the water vapor in the cold air high in the sky just cannot stay a gas, and condenses into tiny liquid water droplets—the clouds you see every day. Give it time, the liquid water comes down as rain.
Precipitation -
The air is full of water, even if you can't see it. Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets—clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail....all forms of precipitation.
The amount of precipitation that falls is different all around the world. In deserts, such as in Chile, it may only rain one inch per year, while on some mountains in Hawaii and in India, it can rain more than 600 inches per year. That is almost 2 inches every day!
Some locations get rain all year long, and many other places have rainy and dry seasons, and only get significant rainfall during certain months of the year. Some places, such as Antarctica, really don't get rain, but they sure get a lot of snow, which accumulates as ice-fields and glaciers.
Precipitation is the "exit ramp" back to earth from the superhighway in the atmosphere that is moving water vapor and clouds all around the globe.
Transpiration / Evapotranspiration-
Take a breath and breathe out—you just participated in the global water cycle. Your breath contains water—breathe on a glass pane to see it appear. When a person breathes, the term is called "respiration".
All the plants around you are "breathing" and releasing water, too. The term is called "transpiration", and although a Brussels sprout doesn't have a mouth, it has tiny holes in its leaves that allow water to leave the leaf, via evaporation, and go into the air. So, plants "transpire" water while humans "respire" water.
Evaporation -
For the water cycle to work, water has to get from the Earth's surface back up into the skies so it can rain back down and ruin your parade or water your crops or yard. It is the invisible process of evaporation that changes liquid and frozen water into water-vapor gas, which then floats up into the skies to become clouds.
The need for heat: As usual, you can thank the sun for keeping evaporation going. The sun's energy breaks the bonds that hold liquid water's molecules together. Thus, it makes sense that water evaporates more easily in hot conditions, such as in the desert, rather than on a cloudy winter day.
Humidity: The amount of water vapor in the air is known as "humidity", often mentioned in the weather reports on the local news. When warm air containing a lot of water vapor (high humidity) moves into colder temperatures (either high in the atmosphere or even on the outside of your glass of iced tea), the colder temperatures cause water vapor to condense into a liquid. The colder temperatures cause water vapor to condense into water droplets and can result in fog.
Condensation -
All air contains water molecules in the form of water vapor, which is invisible. Since the water cycle is all about water changing forms all the time, how does the water vapor turn from a gas back into a liquid and become rain?
The word is "condensation". Water vapor gas condenses back into liquid water and ice, which you mainly see as clouds and then as rain and snow.
Condensation happens because of temperature changes. Warmer air can contain more water vapor than colder air, so when air rises up from the heated earth's surface high into the sky (warm air rises, of course), to where the temperatures are much colder, condensation happens. Some of the water vapor in the cold air high in the sky just cannot stay a gas, and condenses into tiny liquid water droplets—the clouds you see every day. Give it time, the liquid water comes down as rain.
Precipitation -
The air is full of water, even if you can't see it. Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets—clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail....all forms of precipitation.
The amount of precipitation that falls is different all around the world. In deserts, such as in Chile, it may only rain one inch per year, while on some mountains in Hawaii and in India, it can rain more than 600 inches per year. That is almost 2 inches every day!
Some locations get rain all year long, and many other places have rainy and dry seasons, and only get significant rainfall during certain months of the year. Some places, such as Antarctica, really don't get rain, but they sure get a lot of snow, which accumulates as ice-fields and glaciers.
Precipitation is the "exit ramp" back to earth from the superhighway in the atmosphere that is moving water vapor and clouds all around the globe.
Transpiration / Evapotranspiration-
Take a breath and breathe out—you just participated in the global water cycle. Your breath contains water—breathe on a glass pane to see it appear. When a person breathes, the term is called "respiration".
All the plants around you are "breathing" and releasing water, too. The term is called "transpiration", and although a Brussels sprout doesn't have a mouth, it has tiny holes in its leaves that allow water to leave the leaf, via evaporation, and go into the air. So, plants "transpire" water while humans "respire" water.
A large tree can transpire many thousands of gallons during the growing season. If you click the picture to the right, you can see leaf transpiration in action.
But the big word is "Evapotranspiration", which is just a combination of "evaporation" plus "transpiration". This just means that not only are plants transpiring water from their leaves, water is evaporating from the soil all around them, too. |
Runoff -
Runoff is nothing more than water "running off" the land surface. Just as the water you wash your car with runs off down the driveway as you work, the rain that Mother Nature covers the landscape with runs off downhill, too (due to gravity).
Even though some rainfall soaks into the ground, most of it flows over the land surface, going downhill. This runoff water reaches rivers, lakes, and the oceans, keeping the water cycle going.
Runoff is also important because as it flows over the land, some of it soaks into the ground, thus "recharging" groundwater, providing plants with water for their roots to take up so they can create the delicious beets and spinach you like so much, and keeps underground aquifers (areas underground full of water) full so people can drill a well and pull the water out for their own purposes.
Runoff is nothing more than water "running off" the land surface. Just as the water you wash your car with runs off down the driveway as you work, the rain that Mother Nature covers the landscape with runs off downhill, too (due to gravity).
Even though some rainfall soaks into the ground, most of it flows over the land surface, going downhill. This runoff water reaches rivers, lakes, and the oceans, keeping the water cycle going.
Runoff is also important because as it flows over the land, some of it soaks into the ground, thus "recharging" groundwater, providing plants with water for their roots to take up so they can create the delicious beets and spinach you like so much, and keeps underground aquifers (areas underground full of water) full so people can drill a well and pull the water out for their own purposes.
Infiltration -
You can't see it, but a large portion of the world's freshwater lies underground. It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts. Water in the ground keeps all plant life alive and serves peoples' needs, too.
How much rainfall infiltrates the ground depends on many things and varies a lot all over the world. But infiltration works everywhere, and pretty much anywhere in the world you are, there is some water at some depth below your feet, courtesy of infiltration.
Infiltration recharges groundwater: Just like a rechargeable battery, aquifers in the ground are "recharged" by water infiltrating from the surface. And because water underground often flows sideways, water in the ground can be recharged by rainfall hundreds of miles away.
You can't see it, but a large portion of the world's freshwater lies underground. It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts. Water in the ground keeps all plant life alive and serves peoples' needs, too.
How much rainfall infiltrates the ground depends on many things and varies a lot all over the world. But infiltration works everywhere, and pretty much anywhere in the world you are, there is some water at some depth below your feet, courtesy of infiltration.
Infiltration recharges groundwater: Just like a rechargeable battery, aquifers in the ground are "recharged" by water infiltrating from the surface. And because water underground often flows sideways, water in the ground can be recharged by rainfall hundreds of miles away.