# PRECIPITATION

## How is rainfall measured?

Agencies like the National Weather Service use very accurate devices that measure rainfall to the nearest one-hundredth of an inch. The devices, known as rain gauges or tipping-bucket gauges, collect rainwater, usually at a point unaffected by local buildings or trees that may interfere with the rain.

## How can I measure how much rain falls where I live?

Any container with a flat bottom and flat sides can measure rainfall. The width of the top of the container must be the same as at the bottom of the container, but the diameter does not matter. It could be a device purchased for measuring precipitation or something as simple as a coffee can.

## Where does it rain the most?

Mt. Waialeale, on the island Kauai in Hawaii, receives a whopping average of 472 inches (1,200 centimeters) of rain a year—that's over 39 feet [12 meters] of rain per year!

## Where does it rain the least?

Northern Sudan's Wadi Halfa (which is in the Sahara Desert) receives an average of less than one-tenth of an inch of rain per year. That's hardly a drop at the bottom of a bucket.

## How much water is in snow?

When about 10 inches (25 centimeters) of snow melts, it turns into about one inch of water. Snow has pockets of air between snowflakes when they are on the ground, so it takes 10 times the snow to make an equivalent amount of water.

## Where was the most snowfall ever recorded?

Washington State's Mt. Baker recorded the most snowfall in a single season: 1,140 inches (2,896 centimeters).

Do oceans get more rain than land?

The oceans receive just over their share, percentage-wise, of the world's precipitation, about 77 percent. The remaining 23 percent of precipitation falls on the continents. Some areas of the world receive far more precipitation than others. Some parts of equatorial South America, Africa, Southeast Asia, and nearby islands receive over 200 inches (500 centimeters) of rain a year, while some desert areas receive only a fraction of an inch of rain per year.

## What is the difference between snow and hail?

Snow is water vapor that freezes in clouds before falling to the Earth. Hail is water droplets (raindrops) that have turned to ice in clouds.

## How is hail formed?

Hail is ice that is formed in large thunderstorm clouds. Hail begins as droplets of water—normally destined to become raindrops—that are blown upward and subsequently freeze. They then fall lower within the cloud, where they collect more water, are blown upward again, and refreeze. The hailstone grows larger as it collects more and more ice, and eventually falls to the ground.

## How big was the largest hailstone?

In 2003, a hailstone was recovered near Aurora, Nebraska, with a diameter of 18.75 inches (47.63 centimeters). The previous record was in 1970, when people recovered a hailstone with a 17.5 inches (44.45 centimeters) diameter in Kansas.

# GLACIERS AND FJORDS

## What is a glacier?

A glacier is a mass of ice that stays frozen throughout the year and flows downhill. Glaciers are capable of carving rock with their weight and slow, steady movement. They are responsible for the stunning landscape of Yosemite National Park in California. Large glaciers that cover the land are also known as ice sheets.

## Are there still glaciers in the United States?

Yes, small glaciers exist throughout Alaska, within the Cascade Range of Washington state, sporadically across the Rocky Mountains, and also in the Sierra Nevadas of California.

## How old are glaciers?

Glaciers present today were created during the last stage of glaciations, the Pleistocene epoch, which lasted from 1.6 million years ago to about 10,000 years ago.

## Did glaciers create the Great Lakes?

Yes, the Great Lakes are the world's largest lakes formed by glaciers. During the Pleistocene epoch, glaciers inched over the Great Lakes area, moving weak rock out of their way and leaving behind huge, carved basins. As the glaciers began to melt, the basins filled with water and created the Great Lakes.

## Are glaciers only found in cold, northern places?

No, glaciers are found in all six continents.

## What is a tropical glacier?

Tropical glaciers are those found high in the mountains of tropical regions in the world. The Andes Mountains in South America contain 70 percent of the world's tropical glaciers.

## Is global warming causing the world's glaciers to melt?

Many scientists believe that greenhouse gases from human activities are directly causing glaciers in all parts of the world to melt and recede at an unprecedented rate. It is thought that by 2030 there will be no glaciers in Glacier National Park in Montana. In East Africa, Mt. Kenya's Lewis Glacier in Kenya has lost 40 percent of its size in just the last 25 years.

## What are the consequences when glaciers melt?

Glaciers that have melted in the Himalayas, home to the world's largest mountains, have filled up and burst the banks of nearby glacial lakes, filling rivers and causing widespread flooding and death to nearby populations downstream. Similar consequences will likely befall those now living near other glaciers around the world.

Athabasca Glacier is located in the Canadian Rockies, in Jasper National Park, outside of Edmonton, Alberta, Canada. Due to global warming, the glacier recedes at a rate of two to three meters per year (photo by Paul A. Tucci).

## What is a fjord?

During the ice ages, glaciers, which were prevalent at higher latitudes and elevations, became so large that gravity drove them to lower elevations, eventually all the way to the sea. On their way, glaciers would carve deep canyons in the surface of the Earth. At the end of the ice age, as the ice melted and the ocean level rose, these glacial troughs filled with seawater. These very dramatic-looking canyons with high cliffs hanging over a thin bay of water are known as fjords. Fjords are very common in Norway and Alaska.

## From where does the word "fjord" originate?

The word fjord comes from the Norse language and means "where you travel across." It is significant to early Norwegians as a place to travel across to get to the sea when there were no bridges available.

Norway is famous for its scenic fjords, such as Geiranger Fjord, pictured here.

## What is the highest fjord in Norway?

The highest fjord is Sognafjord, which begins at a depth of 4,291 feet (1,308 meters) in the ocean and rises to more than 3,280 feet (1,000 meters).

## Are all fjords found in Norway?

No. In fact, fjords are found throughout the world, wherever glaciers retreated and have cut into the earth, filling in and creating a huge valley of sea water. Notable fjords are found in Alaska and on New Zealand's South Island.

## Where is the longest fjord?

The longest fjord is in Greenland, Scoresby Dund. It stretches more than 217 miles (350 kilometers).

# CONTROLLING WATER

## What do dams do?

By blocking the flow of a river, a dam allows a reservoir of water to build up. Dams are built in order to minimize floods, to provide water for agriculture, and to provide water for recreational uses. Dams in the United States are somewhat controversial, as the Bureau of Reclamation and the Army's Corps of Engineers battle to build more dams and control more water in the western United States. Many outdoor enthusiasts and environmentalists feel that dams are not always necessary.

## What is the tallest dam in the world?

Tajikistan is home to the world's two tallest dams—Rogun and Nurek. Rogun is about 1,100 feet (335 meters) tall (about 100 stories!) and Nurek is about 985 feet tall (300 meters). The United States' tallest dam, Oroville (in Northern California), is sixteenth on the world list at 755 feet (230 meters).

## How do farmers water their crops?

The process of artificially watering crops is called irrigation. In some areas of the world, agriculture can rely on rainfall for all its water needs. In drier areas (usually those receiving less than 20 inches [51 centimeters] of rainfall per year), irrigation is required. Water is pumped from aquifers or delivered via an aqueduct to the fields where it flows through small channels between plants, or is sprayed through sprinklers. In very water-conservative regions such as Israel, water is scientifically dripped onto plants, thereby providing the exact amount of water necessary.

## How did the ancient Romans get water to their cities?

The ancient Romans and Mesopotamians built aqueducts to transport water between a source and areas where it was needed for agriculture or civilization. The Roman system was very extensive, and was constructed throughout its empire. Some portions of these ancient aqueducts are still in use. Today, modern concrete-lined channels transport water hundreds of miles. The most extensive aqueduct systems in the world today are those that bring water to Southern California from the Colorado River in the east and from the Sacramento River in the north.

## Were the Romans the only civilization to develop water resources in an advanced way?

No, recent excavations in Henan Province in China uncovered a network of clay pipes built during the Eastern Zhou Dynasty (1122 to 256 b.c.e.); the pipes were connected

Romans constructed this aqueduct in 22 B.C.E. near Caesarea, a town now located in Israel between Tel Aviv and Haifa (photo by Paul A. Tucci).

to many reservoirs around the cities. This use of technology may actually pre-date Roman water works.

## Where will the biggest dam in the world be located?

The Three Gorges Dam, which spans the Yangtze River in China's Hubei province, will be the biggest dam in the world once it is completed. It will be capable of generating 22,500 megawatts of power. Over 1,500,000 people will likely be displaced as result of living in the valleys above the dam. This fact, along with the potential loss of thousands of archaeological sites, has been a source of controversy since the project was conceived in the 1990s.