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U2 Lesson 3 Completed Guided Notes Precipitation

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Rain is the most common:

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Freezing Precipitation:  snow, sleet, freezing rain

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Freezing Precipitation:  snow, sleet, freezing rain

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What is hail How is hail formed and why does it happen Weather Wise S2E3

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rain gauge = a hollow tube with a measuring scale on the side that measures the amount of rain that falls

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rain gauge = a hollow tube with a measuring scale on the side that measures the amount of rain that falls

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Encyclopedic Entry Vocabulary

Precipitation is any type of water that forms in the Earth's atmosphere and then drops onto the surface of the Earth.

Water vapor, droplets of water suspended in the air, builds up in the Earth's atmosphere. Water vapor in the atmosphere is visible as clouds and fog. Water vapor collects with other materials, such as dust, in clouds.

Precipitation condenses, or forms, around these tiny pieces of material, called cloud condensation nuclei (CCN).

Clouds eventually get too full of water vapor, and the precipitation turns into a liquid ( rain) or a solid ( snow).

Precipitation is part of the water cycle. Precipitation falls to the ground as snow and rain. It eventually evaporates and rises back into the atmosphere as a gas. In clouds, it turns back into liquid or solid water, and it falls to Earth again. People rely on precipitation for fresh water to drink, bathe, and irrigate crops for food.

The most common types of precipitation are rain, hail, and snow.

Rain

Rain is precipitation that falls to the surface of the Earth as water droplets. Raindrops form around microscopic cloud condensation nuclei, such as a particle of dust or a molecule of pollution.

Rain that falls from clouds but freezes before it reaches the ground is called sleet or ice pellets.

Even though cartoon pictures of raindrops look like tears, real raindrops are actually spherical.

Hail

Hail forms in cold storm clouds. It forms when very cold water droplets freeze, or turn solid, as soon as they touch things like dust or dirt. The storm blows the hailstone s into the upper part of the cloud. More frozen water droplets are added to the hailstone before it falls.

Unlike sleet, which is liquid when it forms and freezes as it falls to Earth, hail falls as a stone of solid ice.

Hailstones are usually the size of small rocks, but they can get as large as 15 centimeters (6 inches) across and weigh more than a pound.

Snow

Snow is precipitation that falls in the form of ice crystals. Hail is also ice, but hailstones are just collections of frozen water droplets. Snow has a complex structure. The ice crystals are formed individually in clouds, but when they fall, they stick together in clusters of snowflakes.

Snowfall happens when many individual snowflakes fall from the clouds. Unlike a hail storm, snowfall is usually calm. Hailstones are hard, while snowflakes are soft.

Snowflakes develop different patterns, depending on the temperature and humidity of the air.

When snow falls in the form of a ball instead of soft flakes, it is called graupel. This happens when snow is melted and precipitation forms around the snow crystal.

Snow requires temperatures at the ground to be near or below freezing-less than 0 degrees Celsius (32-degrees Fahrenheit). Snow that falls on warmer ground melts on contact.

Other Types of Precipitation

Sometimes, different types of precipitation fall at the same time. During harsh winter storms, for instance, it is not unusual for sleet and rain to fall at the same time.

Other times, precipitation doesn't fall at all. Virga is a type of precipitation that begins to fall from a cloud, but evaporates before it reaches the surface of the Earth.

Human activity can create precipitation. Urban heat islands, which are areas around major cities that are much warmer than their surroundings, lead to increased and more intense rainfall near cities.

Global warming also causes changes in global precipitation. When the planet is hotter, more ice evaporates in the atmosphere. That eventually leads to more rainy precipitation. It usually means wetter weather in parts of North America, for example, and drier conditions in tropical areas that are usually humid.

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Writers

Kim Rutledge
Tara Ramroop
Diane Boudreau
Melissa McDaniel
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrators

Mary Crooks, National Geographic Society
Tim Gunther

Editors

Jeannie Evers, Emdash Editing
Kara West

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

Last Updated

Feb. 15, 2011

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This lists the logos of programs or partners of NG Education which have provided or contributed the content on this page. Powered by Encyclopedic Entry Vocabulary Precipitation is any type of water that forms in the Earth's atmosphere and then drops onto the surface of the Earth.

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Encyclopedic Entry Vocabulary

Rain is liquid precipitation: water falling from the sky. Raindrops fall to Earth when clouds become saturated, or filled, with water droplets. Millions of water droplets bump into each other as they gather in a cloud. When a small water droplet bumps into a bigger one, it condenses, or combines, with the larger one. As this continues to happen, the droplet gets heavier and heavier. When the water droplet becomes too heavy to continue floating around in the cloud, it falls to the ground.

Human life depends on rain. Rain is the source of freshwater for many cultures where rivers, lakes, or aquifers are not easily accessible. Rain makes modern life possible by providing water for agriculture, industry, hygiene, and electrical energy. Governments, groups, and individuals collect rain for personal and public use.

Raindrops condense around microscopic pieces of material called cloud condensation nuclei (CCN). CCN can be particles of dust, salt, smoke, or pollution. Brightly colored CCN, such as red dust or green algae, can cause colored rain. Because CCN are so tiny, however, color is rarely visible.

When rain forms around certain types of pollutants, such as sulfur dioxide and nitrogen oxide, the CCN react with water to make the rain acidic. This is called acid rain. Acid can harm plants, aquatic animals like fish and frogs, and the soil. Sulfur dioxide and nitrogen oxide can be released into the atmosphere naturally, such as through a volcanic eruption. These pollutants can also be released by human activity, such as the burning of fossil fuels.

Burning fossil fuels can influence rain patterns. In urban areas, where many vehicles are on the road at once, rainfall is more likely during the weekend than during the week. This is because during the week, millions of cars release exhaust into the atmosphere, creating billions of CCN in the clouds. By the end of the week, clouds are much more likely to be saturated with moisture and CCN.

Scientists have developed a process called cloud seeding to "plant" CCNs in clouds to cause rain. Cloud seeding would reduce drought, although there is very little evidence that it works yet.

Although most people think raindrops look like teardrops, they actually look more like chocolate chip cookies. Like raw balls of dough dropped on a cookie sheet, the smallest raindrops, up to 1 millimeter in diameter, are actually spherical. At 2 millimeters raindrops start to flatten, because of the air pressure pushing up on them as they fall to Earth. This effect is increased at 3 millimeters, and depressions form on the bottom of the drops as the air pushes up on the drops harder. At 4 millimeters raindrops actually distort into a shape that looks like a parachute. When they get to be about 4.5 millimeters in diameter, raindrops are so big that they break apart into two or more separate drops.

Raindrops measure 0.5 millimeter (.02 inches) in diameter or larger. Drizzle, which is smaller than rain, consists of drops smaller than 0.5 millimeter. Most of Earth's precipitation falls as rain.

Raindrops often begin as snowflakes, but melt as they fall through the atmosphere. Snow forms in the same way rain does, but in colder conditions.

Rain falls at different rates in different parts of the world. Dry desert regions can get less than a centimeter (0.4 inches) of rain every year, while tropical rain forest s receive more than a meter (3.2 feet). The world record for the most rain in a single year was recorded in Cherrapunji, India, in 1861, when 2,296 centimeters (905 inches) of rain fell.

(sodium chloride, NaCl) crystalline mineral often used as a seasoning or preservative for food.

Articles & Profiles

Maps

Websites

Credits

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Writers

Kim Rutledge
Tara Ramroop
Diane Boudreau
Melissa McDaniel
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrators

Mary Crooks, National Geographic Society
Tim Gunther

Editors

Jeannie Evers, Emdash Editing
Kara West

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

Last Updated

May 12, 2011

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For information on user permissions, please read our Terms of Service. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. She or he will best know the preferred format. When you reach out to him or her, you will need the page title, URL, and the date you accessed the resource.

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Nancy Wynne

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This lists the logos of programs or partners of NG Education which have provided or contributed the content on this page. Powered by Encyclopedic Entry Vocabulary Rain is liquid precipitation: water falling from the sky. Raindrops fall to Earth when clouds become saturated, or filled, with water droplets.

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Globally, rain is the main source of fresh water for plants and animals rainfall is essential for life across Earth's landscapes. In addition to moving tremendous amounts of water through Earth's atmosphere, rain clouds also move tremendous amounts of energy. When water evaporates from the surface and rises as vapor into the atmosphere, it carries heat from the sun-warmed surface with it. Later, when the water vapor condenses to form cloud droplets and rain, the heat is released into the atmosphere. This heating is a major part of Earth's energy budget and climate.

The rainfall maps show total monthly rainfall in millimeters as recorded by NASA's Tropical Rainfall Measuring Mission ( TRMM) satellite, which is a joint mission between NASA and the Japanese Space Agency. High rain totals are represented in dark blue, while small rainfall totals are shown in white. TRMM measures rainfall in the tropics. High-latitude regions, where TRMM does not record rainfall, are gray.

The most obvious pattern in the total rainfall maps is seasonal change. A band of heavy rain moves north and south of the Equator seasonally. In fact, about two-thirds of all rain falls along or near the equator, and countries in those latitudes often have several months of near-daily rain followed by months of dryness as the rain band moves north and south. The Asian monsoon brings rain to China, Southeast Asia, and India between April and September. From October through May, South America goes through a rainy season, but even parts of the Amazon Rainforest goes a few months each year without significant rain.

View, download, or analyze more of these data from NASA Earth Observations (NEO):
Total Rainfall

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Globally, rain is the main source of fresh water for plants and animals rainfall is essential for life across Earth's landscapes. In addition to moving tremendous amounts of water through Earth's atmosphere, rain clouds also move tremendous amounts of energy.

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floods = an overflowing of water in a normally dry area caused by too much precipitation that can have devastating effects on organisms and the environment.  Hurricanes can cause flooding

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floods = an overflowing of water in a normally dry area caused by too much precipitation that can have devastating effects on organisms and the environment.  Hurricanes can cause flooding

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dams - across or through water

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levees - natural or artificial banks

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drought = this occurs when there is little to no precipitation over a long period of time.  Lakes and rivers as well as ground water can be reduced causing shortages for organisms and people.

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drought = this occurs when there is little to no precipitation over a long period of time.  Lakes and rivers as well as ground water can be reduced causing shortages for organisms and people.

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The South Fork Dam in Pennsylvania collapses on May 31, 1889, causing the Johnstown Flood, killing more than 2,200 people.

Johnstown is 60 miles east of Pittsburgh in a valley near the Allegheny, Little Conemaugh and Stony Creek Rivers. It is located on a floodplain that has been subject to frequent disasters. A dam was built in 1840 on the Little Conemaugh River, 14 miles upstream from Johnstown. Nine hundred feet by 72 feet, it was the largest earth dam (made of dirt and rock, rather than steel and concrete) in the United States and it created the largest man-made lake of the time, Lake Conemaugh. The dam was part of an extensive canal system that became obsolete as the railroads replaced the canal as a means of transporting goods. As the canal system fell into disuse, maintenance on the dam was neglected.
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In 1889, Johnstown was home to 30,000 people, many of whom worked in the steel industry. On May 31, the residents were unaware of the danger that steady rain over the course of the previous day had caused. A spillway at the dam became clogged with debris that could not be dislodged. An engineer at the dam saw warning signs of an impending disaster and rode a horse to the village of South Fork to warn the residents. However, the telegraph lines were down and the warning did not reach Johnstown. At 3:10 p.m., the dam collapsed, causing a roar that could be heard for miles. All of the water from Lake Conemaugh rushed forward at 40 miles per hour, sweeping away everything in its path.
READ MORE: How America's Most Powerful Men Caused America's Deadliest Flood
People in the path of the rushing flood waters were often crushed as their homes and other structures were swept away. Thirty-three train engines were pulled into the raging waters, creating more hazards. Some people in Johnstown were able to make it to the top floors of the few tall buildings in town. However, whirlpools brought down many of these taller buildings. A bridge downstream from the town caught much of the debris and then proceeded to catch fire. Some people who had survived by floating on top of debris were burned to death in the fire. Reportedly, one baby survived on the floor of a house as it floated 75 miles from Johnstown.

One of the American Red Cross's first major relief efforts took place in the aftermath of the Johnstown flood. Clara Barton arrived five days later to lead the relief. It took five years to rebuild Johnstown, which again endured deadly floods in 1936 and 1977.
READ MORE: The Deadliest Natural Disasters in US History

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The South Fork Dam in Pennsylvania collapses on May 31, 1889, causing the Johnstown Flood, killing more than 2,200 people. Johnstown is 60 miles east of Pittsburgh in a valley near the Allegheny, Little Conemaugh and Stony Creek Rivers. It is located on a floodplain that has been subject to frequent disasters.

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Hurricane Katrina flooded New Orleans.. this is a story of what the city did to reduce its risk

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Hurricane Katrina flooded New Orleans.. this is a story of what the city did to reduce its risk

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Fifteen years after Hurricane Katrina exposed the New Orleans area's levee system as a "system in name only," its redesign and reconstruction - at a cost of $14.6 billion - is finally almost complete, with only a few stretches of armoring still under construction, a senior U.S. Army Corps of Engineers official said this week.

Even though the system isn't quite complete, it's already in need of shoring up: The Corps plans on requesting $3.2 billion from Congress in fall 2021 to assure the new levees, already sinking, will continue to provide their present 100-year level of hurricane protection through 2073.

Meanwhile, state and local officials say, as they have since Katrina, that 100-year protection is not nearly good enough in an era marked by rising sea levels and more intense hurricanes fueled by global warming. They note that nearly $2 billion of assets and more than 1 million people are protected by those levees.

They're joined in their concerns by Robert Bea and Edward Link, two internationally recognized civil engineering experts who played key roles after Katrina in leading separate forensic studies, backed by the Defense Department and the National Science Foundation, of the engineering failures exposed by the storm. Those studies helped guide levee reconstruction efforts.

The Corps is proud of those efforts. Mark Wingate, deputy district engineer for the Corps' New Orleans District office, told the state Coastal Protection and Restoration Authority this week that there's no question the new levees represent a dramatic improvement in the area's flood protection.

The decision by Congress to quickly rebuild the east bank system and to finish the never-completed west bank system, combined with a decision by the Corps and White House to fast-track the project by streamlining environmental approvals allowed the vast majority of the system to be dramatically elevated by June 2011, Wingate said.

Having the entire $14.6 billion available at the beginning of the project marked a dramatic change from the previous 40 years, which saw individual levees and floodwall projects built in fits and starts, Wingate said. The system was designed and built to block overtopping by storm surges caused by a hurricane with a 1% chance of occurring in any year, the so-called 100-year storm.

Katrina "changed the way we do business," Wingate said. Among the major changes: Engineering standards for earthen levees were strengthened, requiring the use of quality clay. New standards for floodwalls resulted in the use of upside-down, T-shaped walls supported by much deeper pilings. Combined floodgates and pump stations were built at the ends of drainage canals in New Orleans to block surge from challenging weaker interior floodwalls - an Achilles heel in Katrina.

On the west bank, the West Closure Complex now includes the world's largest pump station, able to move an Olympic-sized swimming pool of rainwater into Barataria Bay every 5 seconds, even as the connected floodgate keeps storm surge from the Gulf of Mexico out of residential communities. And along the northwestern edge of Lake Borgne on the east bank, a 2-mile-long, 26-foot-high floodwall represents the largest individual construction project built by the Corps, Wingate said.

In fall 2021, the Corps will give final approval to its $3.2 billion, 50-year plan to assure the levees will continue to provide protection at their current level in 2023, when the levees have to be recertified as providing the 100-year surge protection required by the National Flood Insurance Program.

The levee system will continue to be upgraded as segments subside or otherwise fail to meet 100-year standards. And even when overtopped by surges from a larger hurricane, such as Katrina, the present designs will ensure levees remain in place after the storm moves on, which will dramatically reduce interior flooding, Wingate said.

In completing its draft report earlier this year, the Corps turned down a request by state and local officials to consider increasing protection to at least a 200-year level, or to a 500-year level of protection. It wasn't justified, officials said.

"While the 200-year level of risk reduction alternative was competitive, its net benefits were lower than that of the 100-year level of risk reduction," said Ricky Boyett, a Corps spokesperson. "Because of the lower net benefits, the 200-year level of risk reduction was not selected as the recommended plan."

Such a cost-benefit analysis is part of a federal standard that compares reductions in property damages, emergency costs and the avoidance of economic losses from flooding against construction costs.

A draft report said improvements to east bank levees would reduce expected annual damage from overtopping to $30 million a year, which the Corps estimated would result in a 2.3 to 1 benefit-to-cost ratio. The west bank report produced a similarly positive ratio.

While the Corps defends the new 100-year hurricane protection system, the agency in 2018 announced that it and the river levees running through the city were classified as "high risk," the second-worst rating the Corps bestows. The rating owes largely to the potentially dire consequences if levees are overtopped or fail.

The decision to use the traditional benefit-cost analysis to determine the type of levee protection for the area, rather than basing designs on potential worst-case disasters is a mistake, according to Bea and Link, who played key roles in identifying failures during Katrina and helped guide the rebuilding process.

"We're stuck on a record with a glitch in it. We're stuck in this one place in the soundtrack, and we can't get by it," said Link, a senior research engineer at the University of Maryland. Link served as director of the Interagency Performance Evaluation Task Force, which conducted the forensic assessment of levee failures for the Defense Department after Katrina.

The problem, he said, is that the Corps is creating standards on which levee designs are based that are not based on local decisions about how much risk a community can live with. Instead, they're based on past storm losses or on expected costs facing the National Flood Insurance Program.

In an era where global warming is causing more intense storms, higher storm surges and more rainfall, using such "legacy" factors is inadequate, he said.

Link said the Corps hasn't been able to make the overall risk associated with a levee structure the primary focus of its designs and decisionmaking, largely because Congress, through bills like the Water Resources Development Act, forces it to use what he calls "legacy standards," the traditional methods like determining a levee protects against existing 100-year overtopping standards, or by using the net economic benefits of building the structure as a guide. That's not the same as "tolerable risk," he said, a study of what losses the public actually will accept, in terms of the economic, cultural and human life losses that could occur from rarer worst-case accidents.

"Until the law or appropriate policy stipulates 'tolerable risk,' we are stuck on the 'broken record' of the past," he said.

The continued reliance on the 100-year protection standard represents an organizational failure by the Corps and Congress, which are still tailoring their responses to the last disaster, said Bea, an emeritus civil engineering professor at the University of California-Berkeley who led an independent forensic analysis of the levee failures after Katrina underwritten by the National Science Foundation.

Bea said the failure results in bad math in a simple "A plus B equals C" equation for dealing with risk: The A stands for natural hazards, such as tropical storms or hurricanes and global climate change. B stands for the organizational hazards, such as the continued reliance on the 100-year standard and the hidebound attitudes of organizations that refuse to change such standards.

"At the top of the list is hubris, followed by arrogance, corruption, incompetence, indolence," he said. "This is the equation that continues to be working in this country, and A plus B equals C - major disasters, sooner or later."

Still, both Link and Bea agree that the present levee system is generations better than its predecessor.

For the east bank levees, overseen by the Southeast Louisiana Flood Protection System-East, the improvements include 182 miles of levee and floodwalls, including 244 land-based gates, eight navigation floodgates, plus three combined floodgates and pump stations at the Lake Pontchartrain end of the city's drainage canals, said authority chief executive Derek Boese.

The east bank system has property tax millages in place that will provide it with enough money to maintain the system in the future, with one exception - the interior drainage in St. Bernard Parish.

Parish voters on Aug. 16 voted down a 10-year tax renewal that would have been used by the parish to pay for its drainage system, which has for years been operated by the Lake Borgne Basin Levee District, now part of the levee authority.

Last year, the authority and parish agreed - after four years of arguments and three failed tax elections - for the authority to turn over the interior drainage features, including several pump stations, to the parish.

As part of that deal, the state agreed to invest $4 million in pump station improvements. The levee authority agreed to pay the parish $4.9 million in January and another $1.9 million in January 2021, the equivalent of more than three years of the cost of operating the drainage system.

The plan was to turn over the drainage assets to the parish on Jan. 1, but the parish notified the authority it would not move forward with the deal, and the authority filed a lawsuit in Civil District Court to enforce the agreement.

With the failure of the millage vote, authority president Herb Miller announced Thursday that the authority will move forward with its lawsuit.

On the west bank, the Southeast Louisiana Flood Protection Authority has been successful in gaining voter approval in Algiers and Jefferson Parish for taxes needed to pay the authority's share of elevating portions of the earthen levee system. That has to happen before the installation of fabric mats that protect against erosion if the levees are overtopped, said executive director John Monzon.

The Corps continues to work on a new extension of east bank levees into St. John the Baptist and St. James parishes along the edge of Lake Maurepas and swampy areas to the west. The $760 million West Shore Lake Pontchartrain levee should be completed in 2024, Wingate said.

The Corps also has just signed an $8.9 million contract to build permanent and movable floodwalls along the Mississippi River at its headquarters building in New Orleans to deal with potential overtopping during hurricanes. The levees there are about 5 feet too low - a notable and oddly placed vulnerability in the system.

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15 years after Katrina, New Orleans levees are in the best shape ever. Experts say it's not enough.

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Fifteen years after Hurricane Katrina exposed the New Orleans area's levee system as a "system in name only," its redesign and reconstruction - at a cost of $14.6 billion - is finally almost complete, with only a few stretches of armoring still under construction, a senior U.S.

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Home | NASA Global Precipitation Measurement Mission

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NASA's Global Precipitation Measurement Mission (GPM) uses satellites to measure Earth's rain and snowfall for the benefit of mankind. Launched by NASA and JAXA on Feb. 27th, 2014, GPM is an international mission that sets the standard for spaceborne precipitation measurements.