Dynamic and complex: the global water cycle

Transcript

Water storage in the atmosphere

There is always water in the atmosphere – it’s like the superhighway that moves water around the globe – but that’s only 0.001% of the Earth’s total water.

Acknowledgement: Aerospaceweb.org

Water storage in ice and snow

Almost 70% of the Earth’s freshwater is stored in ice caps, glaciers and permanent snow. Most of this is in Antarctica – the Greenland ice cap contains just 10% of the total global ice mass.

Acknowledgement: US Geological Survey/Public domain

Sublimation

Snowfall that’s converted to ice in glaciers may run off through melting, but it can also transform directly from a solid (ice) to a gas (water vapour) – this is called sublimation.

Acknowledgement: OCWO, licensed through 123RF.com

Precipitation

All forms of water that fall from the air to the Earth’s surface are called precipitation. Whether it is snow, rain, sleet or hail depends on the temperature of the air that the water falls through.

Acknowledgement: Sergey Minaev, licenced through 123RF.com

Infiltration

Dr Louis Schipper

When you look at the soil, it’s not like concrete with no holes or anything like that, it is continuously reworked by animals that live in the soil, by the plant roots, by drying and wetting up, or freezing and thawing, it sort of breaks the soil up, so the water can get into that soil through pores at the surface.

Spring

A spring discharges groundwater on the land surface because the natural flow of groundwater to the place exceeds the flow from it. Springs are ephemeral, discharging intermittently, or permanent, discharging constantly.

Acknowledgement: Graeme Churchard, Creative Commons 2.0

Freshwater storage

Prof David Hamilton

Water can be stored in a lake anywhere from a matter of a day or two, up to in some cases perhaps 10 years, even maybe 100 years in the very deepest of lakes. Lake Taupo, for example, has water stored in it for over 10 years.

Water storage in oceans

Prof Keith Hunter

The role the oceans play in water storage is the dominant one because they contain virtually all the earths water – 98.5%.

Evaporation

Dr Dave Campbell

Wherever there is liquid water – whether it’s in the oceans or whether it’s in the soil as soil water, or in a river, or in a lake, or within plants – that liquid water can be turned to water vapour, and those water vapour molecules can move into the atmosphere.

Groundwater discharge

Groundwater exiting the land surface, usually through a spring, is called groundwater discharge.

Acknowledgement: Pierre Andrea Leclercq, Creative Commons 4.0 International

Groundwater storage

Large amounts of water are stored in the ground in pores, cracks and spaces between rock particles. Most of this groundwater storage comes from precipitation that infiltrates into the land surface.

Acknowledgement: USGS

Snow melt run-off to streams

When temperatures rise above the freezing point of water, snow starts to melt and runs off into streams. This event occurs seasonally in spring or when temperatures rise.

Acknowledgement: Thomas Neumann, NASA GSFC, Creative Commons 2.0

Surface run-off

Rainwater that does not infiltrate the ground and gradually collects in streams and rivers and eventually flows into the ocean is called surface run-off.

Acknowledgement: Whanganui District Council

Interception loss

After it has rained, plants ‘intercept’ the pathway for water by temporarily storing water on leaves and stems and evaporating it as the vegetation surfaces dry out.

Acknowledgement: Public domain

Transpiration

Transpiration is where plants evaporate water through the openings in their leaves. The rate of transpiration depends on leaf shape, size, pores (stomata) and waxiness of the leaf surface.

Acknowledgement: MTU/Tech Alive

Condensation

Condensation is the change of water from its gaseous form (water vapour) into liquid water. It generally occurs in the atmosphere when warm air rises, cools and loses its capacity to hold water vapour.

Acknowledgement: University of Waikato

Evaporation

Evaporation is the process by which water changes from a liquid to a gas or vapour. Large amounts of water are released back into the water cycle due to evaporation from lakes, rivers and oceans.

Acknowledgement: Michael Shake, licensed through 123RF Ltd