Evaporation is the process that changes liquid water to gaseous water (water vapor). Water moves from the Earth’s surface to the atmosphere via evaporation.
• Water Science School HOME • The Water Cycle •
Water cycle components » Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater lakes and rivers · Groundwater flow · Groundwater storage · Ice and snow · Infiltration · Oceans · Precipitation · Snowmelt · Springs · Streamflow · Sublimation · Surface runoff
Credit: Alan Cressler, USGS
What is evaporation and why does it occur?
Evaporation is the process that changes liquid water to gaseous water (water vapor). Water moves from the Earth’s surface to the atmosphere via evaporation.
Evaporation occurs when energy (heat) forces the bonds that hold water molecules together to break. When you’re boiling water on the stove, you’re adding heat to liquid water. This added heat breaks the bonds, causing the water to shift from its liquid state to its gaseous state (water vapor), which we know as steam.
Water easily evaporates at its boiling point (212° F, 100° C) but evaporates much more slowly at its freezing point because of the heat energy required to evaporate the water.
The opposite of evaporation is condensation. Condensation is the process of water vapor turning back into liquid water. Condensation occurs when saturated air is cooled, such as on the outside of a glass of ice water.
Evaporation drives the water cycle
Most of the moisture in the atmosphere (about 90%) came from water evaporating from oceans, seas, lakes, and rivers. (And because over 70% of Earth’s surface is covered by oceans, they contribute a lot to the overall volume of water evaporating into the atmosphere.) The rest of the moisture in the atmosphere came from plant transpiration and (a very small amount) from sublimation.
On a global scale, the amount of water evaporating is about the same as the amount of water delivered to the Earth as precipitation.
This does vary geographically, though. Evaporation is more prevalent over the oceans than precipitation, while over the land, precipitation routinely exceeds evaporation. Most of the water that evaporates from the oceans falls back into the oceans as precipitation. Only about 10 percent of the water evaporated from the oceans is transported over land and falls as precipitation. Once evaporated, a water molecule spends about 10 days in the air. The process of evaporation is so great that without precipitation runoff, and groundwater discharge from aquifers, oceans would become nearly empty.
People make use of evaporation
One way to produce table salt is to evaporate saline water in evaporation ponds, a technique used by people for thousands of years.
Seawater contains other valuable minerals that are easily obtained due to evaporation. Water from the Dead Sea is ideal for the extraction of not only table salt, but also magnesium, potash, and bromine. The Dead Sea is actually a lake, located in the Middle East within a closed watershed and without any means of outflow. This closed basin system is abnormal for most lakes. Water primarily leaves the lake by evaporating, resulting in upwards of 1,300 - 1,600 millimeters of evaporated water per year in this desert area! The result is that the waters of the Dead Sea have the highest salinity and density of any sea in the world, too high to support life.
(Source: Overview of Middle East Water Resources, Middle East Water Data Banks Project).
Evaporative cooling: Cheap air conditioning!
Because energy is required to break the bonds holding water molecules together, evaporation removes heat from the environment, leading to a net cooling. Think of when a physician wipes an alcohol pad on your arm before giving you an injection – your arm feels cold. That’s because the alcohol rapidly evaporates from the surface of your skin, and with it some heat from the surface of your arm.
In climates where the humidity is low and the temperatures are hot, an evaporative cooler can lower the air temperature by 20 degrees F., while it increases humidity. As this map shows, evaporative coolers work best in the dry areas of the United States (red areas marked A) and can work somewhat in the blue areas marked B. But in section C, in the humid eastern U.S., normal air conditioners must be used.
Evaporative coolers are really quite simple devices, at least compared to air conditioners, because they pull in the dry, hot outdoor air and pass it through an evaporative pad that is kept wet by a supply of water. In a home device, a fan draws the air through the pad causing the water in the pad to evaporate, resulting in cooler air which is then pumped through the house. Much less energy is used as compared to an air conditioner.
Credit: California Energy Commission
Below are other science topics associated with the water cycle.
Precipitation and the Water Cycle
Streamflow and the Water Cycle
Snowmelt Runoff and the Water Cycle
The Atmosphere and the Water Cycle
Condensation and the Water Cycle
Infiltration and the Water Cycle
Surface Runoff and the Water Cycle
Springs and the Water Cycle
Sublimation and the Water Cycle
Ice, Snow, and Glaciers and the Water Cycle
Groundwater Flow and the Water Cycle
Groundwater Storage and the Water Cycle
- Overview
Evaporation is the process that changes liquid water to gaseous water (water vapor). Water moves from the Earth’s surface to the atmosphere via evaporation.
• Water Science School HOME • The Water Cycle •
Water cycle components » Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater lakes and rivers · Groundwater flow · Groundwater storage · Ice and snow · Infiltration · Oceans · Precipitation · Snowmelt · Springs · Streamflow · Sublimation · Surface runoff
Sources/Usage: Public Domain.Cooling towers at a power-production facility. The equipment at power-production facilities produces a lot of waste heat energy as a by-product. Facilities use water to cool the equipment, and then need to release the water back into the environment. Releasing hot water back into rivers would harm the ecology, so many power plants have tremendous cooling towers, where hot water is sprayed inside and evaporation is used to cool the release water before it goes back into the environment.
Credit: Alan Cressler, USGSWhat is evaporation and why does it occur?
Evaporation is the process that changes liquid water to gaseous water (water vapor). Water moves from the Earth’s surface to the atmosphere via evaporation.
Evaporation occurs when energy (heat) forces the bonds that hold water molecules together to break. When you’re boiling water on the stove, you’re adding heat to liquid water. This added heat breaks the bonds, causing the water to shift from its liquid state to its gaseous state (water vapor), which we know as steam.
Water easily evaporates at its boiling point (212° F, 100° C) but evaporates much more slowly at its freezing point because of the heat energy required to evaporate the water.
The opposite of evaporation is condensation. Condensation is the process of water vapor turning back into liquid water. Condensation occurs when saturated air is cooled, such as on the outside of a glass of ice water.
Sources/Usage: Public Domain.Hey, I'm Drippy! Did you know that on a global scale, the amount of water evaporating is about the same as the amount of water precipitating? Evaporation drives the water cycle
Most of the moisture in the atmosphere (about 90%) came from water evaporating from oceans, seas, lakes, and rivers. (And because over 70% of Earth’s surface is covered by oceans, they contribute a lot to the overall volume of water evaporating into the atmosphere.) The rest of the moisture in the atmosphere came from plant transpiration and (a very small amount) from sublimation.
On a global scale, the amount of water evaporating is about the same as the amount of water delivered to the Earth as precipitation.
This does vary geographically, though. Evaporation is more prevalent over the oceans than precipitation, while over the land, precipitation routinely exceeds evaporation. Most of the water that evaporates from the oceans falls back into the oceans as precipitation. Only about 10 percent of the water evaporated from the oceans is transported over land and falls as precipitation. Once evaporated, a water molecule spends about 10 days in the air. The process of evaporation is so great that without precipitation runoff, and groundwater discharge from aquifers, oceans would become nearly empty.
Sources/Usage: Public Domain.Hi, I'm Salty, Drippy's saline counterpart! Did you know that one way to produce table salt is to evaporate saline water in evaporation ponds, a technique used by people for thousands of years? People make use of evaporation
One way to produce table salt is to evaporate saline water in evaporation ponds, a technique used by people for thousands of years.
Seawater contains other valuable minerals that are easily obtained due to evaporation. Water from the Dead Sea is ideal for the extraction of not only table salt, but also magnesium, potash, and bromine. The Dead Sea is actually a lake, located in the Middle East within a closed watershed and without any means of outflow. This closed basin system is abnormal for most lakes. Water primarily leaves the lake by evaporating, resulting in upwards of 1,300 - 1,600 millimeters of evaporated water per year in this desert area! The result is that the waters of the Dead Sea have the highest salinity and density of any sea in the world, too high to support life.
(Source: Overview of Middle East Water Resources, Middle East Water Data Banks Project).
Evaporative cooling: Cheap air conditioning!
Because energy is required to break the bonds holding water molecules together, evaporation removes heat from the environment, leading to a net cooling. Think of when a physician wipes an alcohol pad on your arm before giving you an injection – your arm feels cold. That’s because the alcohol rapidly evaporates from the surface of your skin, and with it some heat from the surface of your arm.
In climates where the humidity is low and the temperatures are hot, an evaporative cooler can lower the air temperature by 20 degrees F., while it increases humidity. As this map shows, evaporative coolers work best in the dry areas of the United States (red areas marked A) and can work somewhat in the blue areas marked B. But in section C, in the humid eastern U.S., normal air conditioners must be used.
Evaporative coolers are really quite simple devices, at least compared to air conditioners, because they pull in the dry, hot outdoor air and pass it through an evaporative pad that is kept wet by a supply of water. In a home device, a fan draws the air through the pad causing the water in the pad to evaporate, resulting in cooler air which is then pumped through the house. Much less energy is used as compared to an air conditioner.
Sources/Usage: Public Domain.Map showing where evaporative coolers are most effective in the United States. Evaporative coolers work best in the dry areas of the United States (red areas marked A) and can work somewhat in the blue areas marked B. But in section C, in the humid eastern U.S., normal air conditioners must be used.
Credit: California Energy Commission - Science
Below are other science topics associated with the water cycle.
Filter Total Items: 15Precipitation and the Water Cycle
Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. Precipitation is the main way atmospheric water returns to the surface of the Earth. Most precipitation falls as rain.Streamflow and the Water Cycle
What is streamflow? How do streams get their water? To learn about streamflow and its role in the water cycle, continue reading.Snowmelt Runoff and the Water Cycle
Perhaps you've never seen snow. Or, perhaps you built a snowman this very afternoon and perhaps you saw your snowman begin to melt. Regardless of your experience with snow and associated snowmelt, runoff from snowmelt is an important component of the global movement of water, possibly even if you live where it never snows. Note: This section of the Water Science School discusses the Earth's...The Atmosphere and the Water Cycle
The atmosphere is the superhighway in the sky that moves water everywhere over the Earth. Water at the Earth's surface evaporates into water vapor, then rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.Condensation and the Water Cycle
Condensation is the process of gaseous water (water vapor) turning into liquid water. Have you ever seen water on the outside of a cold glass on a humid day? That’s condensation.Infiltration and the Water Cycle
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.Surface Runoff and the Water Cycle
When water "runs off" the land surface, that’s runoff! Due to gravity, the water you wash your car with runs down the driveway as you work, and rain runs downhill. Runoff is an important component of the water cycle.Springs and the Water Cycle
A spring is a place where water moving underground finds an opening to the land surface and emerges, sometimes as just a trickle, maybe only after a rain, and sometimes in a continuous flow. Spring water can also emerge from heated rock underground, giving rise to hot springs.Sublimation and the Water Cycle
Solid, liquid, and gas - the three states of water. We see water freeze, transforming into a solid form such as ice, and we see water evaporate, turning into gas, but... have you ever seen ice transform directly to gas? This process is called sublimation and you can read all about it below.Ice, Snow, and Glaciers and the Water Cycle
The water stored in ice and glaciers moves slowly through are part of the water cycle, even though the water in them moves very slowly. Did you know? Ice caps influence the weather, too. The color white reflects sunlight (heat) more than darker colors, and as ice is so white, sunlight is reflected back out to the sky, which helps to create weather patterns.Groundwater Flow and the Water Cycle
Yes, water below your feet is moving all the time, but not like rivers flowing below ground. It's more like water in a sponge. Gravity and pressure move water downward and sideways underground through spaces between rocks. Eventually it emerges back to the land surface, into rivers, and into the oceans to keep the water cycle going.Groundwater Storage and the Water Cycle
The ground stores huge amounts of water and it exists to some degree no matter where on Earth you are. Lucky for people, in many places the water exists in quantities and at depths that wells can be drilled into the water-bearing aquifers and withdrawn to server the many needs people have.