50 Fun Facts About Water Cycle

Roughly what share of global evaporation comes from the ocean?

The ocean also holds 97% of the planet's water and receives 78% of global precipitation.

What powers the water cycle?

Solar energy heats water in oceans, lakes and rivers until it evaporates; heat transfers between phases keep the cycle turning.

After evaporating, about how long does water typically stay in the atmosphere?

That short residence time contrasts with groundwater, which can sit underground for more than 10,000 years.

Groundwater can remain beneath the surface for more than how long before leaving?

Aquifers refill slowly, which is why 'fossil' groundwater in arid regions is not treated as a renewable supply.

About how much water falls as precipitation worldwide each year?

Nearly 398,000 km³ of that lands on the oceans; the same volume, 505,000 km³, returns to the air as evapotranspiration.

Saltwater makes up roughly what percentage of all the water on Earth?

That leaves only 2.5% as fresh water, and most of that is frozen or underground rather than in lakes and rivers.

Of the fresh water sitting on Earth's surface in liquid form, what share is in lakes?

Swamps hold 11% and rivers a mere 2%, even though rivers carry most of the water we actually see moving.

Glaciers and ice sheets hold about what fraction of the world's fresh water?

Glacial ice is the largest freshwater reservoir on the planet, with the Antarctic ice sheet alone holding about 61%.

Roughly what percentage of the world's readily available fresh water is groundwater?

In the United States groundwater is the largest source of usable water storage, and California pumps more of it than any other state.

Evaporation removes energy from the remaining liquid, producing which effect?

Molecules near the surface that absorb enough energy escape as gas, leaving the remaining liquid cooler. Sweat works the same way.

Condensation is the reverse of which process?

Gas turns back to liquid on a surface or on cloud condensation nuclei, which is how droplets, dew and clouds form.

Sublimation is the change from a solid directly into what?

Dry ice at room temperature is the classic example; snow and ice can also sublimate away without melting.

Evapotranspiration combines evaporation with which other process?

Transpiration from vegetation plus evaporation from open water and bare soil together make up evapotranspiration, which is measured to plan irrigation.

Plants release water vapour through small leaf pores called what?

Guard cells open and close each pore; plants shut them when roots cannot keep up with water loss, which also slows photosynthesis.

What percentage of water taken up by a plant is released back through its leaves?

Only a tiny fraction is used for growth and metabolism; the rest passes straight through on its way back to the atmosphere.

The dew point is the temperature at which relative humidity reaches what level?

Air cooled to its dew point is saturated; the dew point equals the air temperature only when the air is already saturated.

Cloud condensation nuclei are tiny particles about how big?

That is about one hundredth the size of a cloud droplet; a typical raindrop is about 2 mm across.

Whose 1802 cloud nomenclature gave us Latin names like cumulus and stratus?

His system became the basis of today's international scheme of five physical forms and ten basic genera.

Thunderstorms and hail are produced by which type of cloud?

Its flat anvil top forms where the rising air hits the tropopause; peaks often reach about 12,000 metres.

By definition, fog reduces visibility to less than what distance?

Mist impairs visibility less; fog is essentially a stratus cloud sitting on the ground.

Dew forms most easily on grass, car roofs and bridges because those surfaces do what?

As a surface cools by radiating heat, moisture condenses on it faster than it can evaporate, and droplets form.

Snowflake arms grow with six-fold symmetry because of which property of ice?

The six arms grow independently from the corners of a hexagon, but in nearly identical conditions, so they tend to match.

Who began photographing thousands of snowflakes through a microscope in 1885?

Bentley's search for identical flakes revealed their huge variety; Nakaya later linked crystal shape to temperature and moisture.

Compared with liquid water, ice at atmospheric pressure is about how much lighter by volume?

That is a volumetric expansion of about 9%, which is why ice floats and why frozen pipes burst.

Since January 2010, US hail is classed as 'severe' above what diameter?

The National Weather Service raised the threshold from 0.75 inch; stronger updrafts keep larger stones aloft longer.

A large 5 mm raindrop hits the ground at roughly what speed?

Drops fall at terminal velocity, so bigger drops fall faster; 0.5 mm drizzle lands at only about 2 m/s.

Infiltration is the process by which surface water does what?

Its maximum rate is the infiltration capacity; when rain beats that rate, the excess becomes surface runoff.

Surface runoff in cities is worsened by impervious areas such as what?

Hard surfaces stop water soaking in, making runoff a primary cause of urban flooding and flooded basements.

The water table is the upper surface of which underground zone?

Below it the pores and fractures in the ground are full of groundwater, whether fresh, saline or brackish.

A rock unit that yields a usable quantity of water is called what?

An aquitard is a low-permeability bed alongside it; an aquiclude is fully impermeable and can confine an aquifer under pressure.

A shallow water-table formation beneath the Great Plains spans parts of how many US states?

It covers about 174,000 square miles beneath the Great Plains, from South Dakota down to Texas and New Mexico.

Geothermally heated groundwater that emerges at the surface is called what?

Karst springs instead emerge from networks of cracks and caves in soluble rock.

Permafrost is ground that stays below 0 °C for at least how long?

The oldest permafrost has stayed frozen for around 700,000 years, and the deepest extends more than 1,500 metres down.

In North America, a drainage basin is commonly called what?

Elsewhere 'watershed' keeps its original meaning: the ridge line dividing one basin from the next.

A 'Pineapple Express' is an atmospheric river carrying moisture from where?

These narrow plumes of water vapour hit western North America from California up to British Columbia and southeast Alaska.

Which chemical is most commonly used in cloud seeding to trigger ice crystals?

Its crystal structure resembles ice; dry ice and potassium iodide are also used, and hygroscopic salts are gaining ground.

The first standardized rain gauge, the Cheugugi, was invented in 1441 in which country?

It dates from the reign of Sejong the Great of the Joseon dynasty.

Mawsynram, reportedly the wettest place on Earth, is in which Indian state?

It averages about 11,872 mm of rain a year and recorded 1,003 mm in a single day in June 2022.

The Atacama, the driest non-polar desert, sits in a rain shadow between the Andes and what?

Two mountain chains block moisture from both the Pacific and the Atlantic; some weather stations there have never recorded rain.

A rain shadow forms on which side of a mountain range?

Air drops its moisture climbing the windward slope, then warms and dries as it descends, producing Foehn winds.

Hydrology takes its name from the Greek húdōr, meaning what?

Pierre Perrault helped found the modern science by showing rainfall alone could account for the flow of the Seine.

Which 17th-century pioneer showed that rainfall was enough to explain the Seine's flow?

He measured rainfall, runoff and drainage area; Edme Mariotte and Edmund Halley were fellow founders of modern hydrology.

How does the density of water vapour compare with that of dry air?

Moist air rises, cools and condenses, which is how convection builds clouds; water vapour is also the biggest greenhouse gas.

A monsoon is traditionally defined as what?

The term entered English in British India for the southwest winds off the Bay of Bengal and Arabian Sea that bring heavy rain.

Which of the three major categories of dry spell is defined simply by a lack of precipitation?

Hydrological drought concerns low streamflow, reservoir and groundwater storage, further along the water cycle.

The Great Lakes hold more than what share of the world's surface fresh water by volume?

They are the largest group of freshwater lakes by area; Lake Baikal alone holds 22 to 23% by volume.

Which body of water is the deepest in the world, at 1,642 metres?

Its depth makes it the largest freshwater lake by volume, holding more water than all the Great Lakes combined.

Which river has the largest discharge volume of any in the world?

It pushes out around 215,000 cubic metres per second, more than the next seven largest independent rivers combined.

How does the Dead Sea’s saltiness compare with the ocean’s?

Its 34.2% salinity gives a density of 1.24 kg per litre, which is why swimmers float so easily.

The Antarctic ice sheet holds about what share of all fresh water on Earth?

It covers 98% of the continent with ice averaging more than 2 km thick, some 26.5 million cubic kilometres in all.