# data[].attributes.attachment_link.description
The water cycle is the endless process that connects all of the water on Earth.

# data[].attributes.body
What is condensation?

# data[].attributes.attachment_link.title
WATER CYCLE💧| The water cycle process | Easy science video

# data[].attributes.body
How do you think evaporation and transpiration are similar?

# data[].attributes.attachment_link.title
Learn the Water Cycle to Blank Space by Taylor Swift

# data[].attributes.body
What did you learn about evaporation?

# data[].attributes.attachment_link.readable_text
Evaporation happens when a liquid turns into a gas. It can be easily visualized when rain puddles "disappear" on a hot day or when wet clothes dry in the sun. In these examples, the liquid water is not actually vanishing-it is evaporating into a gas, called water vapor.

Evaporation happens on a global scale. Alongside condensation and precipitation, evaporation is one of the three main steps in the Earth's water cycle. Evaporation accounts for 90 percent of the moisture in the Earth's atmosphere; the other 10 percent is due to plant transpiration.

Substances can exist in three main states: solid, liquid, and gas. Evaporation is just one way a substance, like water, can change between these states. Melting and freezing are two other ways. When liquid water reaches a low enough temperature, it freezes and becomes a solid-ice. When solid water is exposed to enough heat, it will melt and return to a liquid. As that liquid water is further heated, it evaporates and becomes a gas-water vapor.

These changes between states (melting, freezing, and evaporating) happen because as the temperature either increases or decreases, the molecules in a substance begin to speed up or slow down. In a solid, the molecules are tightly packed and only vibrate against each other. In a liquid, the molecules move freely, but stay close together. In a gas, they move around wildly and have a great deal of space between them.

In the water cycle, evaporation occurs when sunlight warms the surface of the water. The heat from the sun makes the water molecules move faster and faster, until they move so fast they escape as a gas. Once evaporated, a molecule of water vapor spends about ten days in the air.

As water vapor rises higher in the atmosphere, it begins to cool back down. When it is cool enough, the water vapor condenses and returns to liquid water. These water droplets eventually gather to form clouds and precipitation.

Evaporation from the oceans is vital to the production of fresh water. Because more than 70 percent of Earth's surface is covered by oceans, they are the major source of water in the atmosphere. When that water evaporates, the salt is left behind. The freshwater vapor then condenses into clouds, many of which drift over land. Precipitation from those clouds fills lakes, rivers, and streams with fresh water.

# data[].attributes.attachment_link.description
Evaporation is the process by which a liquid turns into a gas. It is also one of the three main steps in the global water cycle.

# data[].attributes.body
What are some other examples of evaporation?

# data[].attributes.body
What did you learn about condensation?

# data[].attributes.attachment_link.description
Condensation is the process where water vapor becomes liquid

# data[].attributes.attachment_caption
water becoming a layer of fog on a window

# data[].attributes.body
What are some other examples of condensation?

# data[].attributes.body
What did you learn about precipitation?

# data[].attributes.attachment_link.readable_text
Image

Photograph by _ultraforma_

Precipitation is any liquid or frozen water that forms in the atmosphere and falls back to the earth. It comes in many forms, like rain, sleet, and snow. Along with evaporation and condensation, precipitation is one of the three major parts of the global water cycle.

Precipitation forms in the clouds when water vapor condenses into bigger and bigger droplets of water. When the drops are heavy enough, they fall to the earth. If a cloud is colder, like it would be at higher altitudes, the water droplets may freeze to form ice. These ice crystals then fall to the earth as snow, hail, or rain, depending on the temperature within the cloud and at Earth's surface. Most rain actually begins as snow high in the clouds. As the snowflakes fall through warmer air, they become raindrops.

Particles of dust or smoke in the atmosphere are essential for precipitation. These particles, called "condensation nuclei," provide a surface for water vapor to condense upon. This helps water droplets gather together and become large enough to fall to the earth.

A common misconception is that when raindrops fall, they have a teardrop shape. In fact, smaller raindrops (ones that are approximately one millimeter (0.039 inches) across) are almost perfectly spherical. Larger raindrops (two to three millimeters (0.078-0.118 inches) across) are also round, but with a small indent on their bottom side. They look more like kidney beans when falling. Very large rain drops (larger than 4.5 millimeters (0.177 inches)) have a huge indent and look more like a parachute. These extra-large drops usually end up splitting into two smaller droplets. The indents on raindrops are caused by air resistance.

Precipitation is always fresh water, even when the water originated from the ocean. This is because sea salt does not evaporate with water. However, in some cases, pollutants in the atmosphere can contaminate water droplets before they fall to the ground. The precipitation that results from this is called acid rain. Acid rain does not harm humans directly, but it can make lakes and streams more acidic. This harms aquatic ecosystems because plants and animals often cannot adapt to the acidity.

National Geographic Society

January 12, 2023

# data[].attributes.attachment_link.description
Image Photograph by _ultraforma_ Precipitation is any liquid or frozen water that forms in the atmosphere and falls back to the earth. It comes in many forms, like rain, sleet, and snow. Along with evaporation and condensation, precipitation is one of the three major parts of the global water cycle.

# data[].attributes.body
What are some other examples of precipitation?

# data[].attributes.body
What did you learn about runoff?

# data[].attributes.attachment_link.readable_text
Runoff occurs when there is more water than land can absorb. The excess liquid flows across the surface of the land and into nearby creeks, streams, or ponds. Runoff can come from both natural processes and human activity.

The most familiar type of natural runoff is snowmelt. Mountains that cannot absorb water from heavy snowfalls produce runoff that turns into streams, rivers, and lakes. Glaciers, snow, and rain all contribute to this natural runoff.

Runoff also occurs naturally as soil is eroded and carried to various bodies of water. Even toxic chemicals enter waterways through natural processes, such as volcanic eruptions. Toxic gases released by volcanoes eventually return to the water or soil as precipitation.

Runoff from human activity comes from two places: point sources and nonpoint sources. Point source pollution is any source that empties directly into a waterway. This might include a pipe from specific sewage treatment plant, factory, or even a home. Regulations determine what type of runoff, and how much, industries are allowed to release. These regulations vary by region, state, and nation.

Nonpoint source pollution is any source where runoff does not go directly into a waterway. Nonpoint sources of runoff can be large urban, suburban, or rural areas. In these areas, rainwater and irrigation wash chemicals into local streams. Runoff from nonpoint sources includes lawn fertilizer, car exhaust, and even spilled gasoline from a car. Farms are a huge nonpoint source of runoff, as rainwater and irrigation drain fertilizers and pesticides into bodies of water.

Impervious surfaces, or surfaces that can't absorb water, increase runoff. Roads, sidewalks, and parking lots are impervious surfaces. Materials as diverse as car-washing soaps, litter, and spilled gas from a gas station all become runoff.

Reducing Runoff

Runoff is a major source of water pollution. As the water runs along a surface, it picks up litter, petroleum, chemicals, fertilizers, and other toxic substances. From California to New Jersey, beaches in the U.S. are regularly closed after heavy rainfall because of runoff that includes sewage and medical waste.

These chemical pollutants can harm not just a beach, but an entire ecosystem. Tiny microbes, such as plankton or algae, absorb pollutants in the runoff. Fish or shellfish consume the microbes or absorb the pollutants directly. Animals such as birds consume the fish, increasing the level of pollutants in their own bodies. This process in which the concentration of a substance increases as it passes up the food chain is called biomagnification.

Biomagnification means organisms high on the food chain, including people, have a higher concentration of pollutants in their bodies than organisms such as seagrass or algae. As people eat foods such as oysters, they may be ingesting runoff from farms, sewage treatment plants, and city streets.

Runoff is an economic threat, as well as an environmental one. Agribusiness loses millions of dollars to runoff every year. In the process of erosion, runoff can carry away the fertile layer of topsoil. Farmers rely on topsoil to grow crops. Tons of topsoil are lost to runoff every year.

People can limit runoff pollution in many ways. Farmers and gardeners can reduce the amount of fertilizer they use.

Urban areas can reduce the number of impervious surfaces. Soil acts as a natural sponge, filtering and absorbing many harmful chemicals.

Communities can plant native vegetation. Shrubs and other plants prevent erosion and runoff from going into waterways.

# data[].attributes.attachment_link.description
Runoff occurs when there is more water than land can absorb.

# data[].attributes.body
Collection is the process of water (from precipitation) gathering and being stored in bodies of water - oceans, lakes, rivers, etc...this is the second step as runoff leads to collection