Water in the Earth system is influencing all aspects of life on Earth. Pathways, storage, transfers and transformations have an effect on the global climate and human welfare. Within this interactive 4 scientists talk about some of the complex aspects of the water cycle.
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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.
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
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
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
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.
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
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%.
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 exiting the land surface, usually through a spring, is called groundwater discharge.
Acknowledgement: Pierre Andrea Leclercq, Creative Commons 4.0 International
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.
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
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
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 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 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 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