WATER SOURCES Flashcards
outline global distribution of water sources
The water sources are the hydrosphere, cryosphere, lithosphere and atmosphere. The hydrosphere accounts for 96.5% of all water on earth and can be in the form of vapor, ice or liquid. The cryosphere accounts for 1.7% of the water on earth and includes ice bergs and glaciers. The lithosphere also accounts for 1.7% of all water on earth and captures water for the longest periods of time and can flow into underground aquifers takes the form of lakes, rivers and ponds. The atmosphere accounts for 0.001% of water on earth as water is stored temporarily as water vapour and condensation before being released back to earth as precipitation.
cryospheric water examples
- sea ice e.g. much of Arctic Ocean is frozen - grows in winter & shrinks in summer - frozen = sea ice - does not raise sea level as is made out of sea water
- Ice shelves form when ice sheets and glaciers move out into the oceans e.g. Antarctica and Greenland
- Icebergs = chunks of ice that break off glaciers and ice shelves and drift in the oceans - raise sea level when leave land and push in ocean but not when they melt
- Ice sheets - mass of glacial land ice e.g. Greenland & Antarctica - both contain more than 99% freshwater ice on earth - form in areas where snow falls in winter and doesn’t melt in summer - if Greenland ice sheet melter sea levels would rise around 6 metres
terrestrial water examples
4 categories: surface water, groundwater, soil water and biological water
surface water: free flowing water of rivers, ponds and lakes
groundwater: water that collects underground in the pore spaces of rock
soil water: held together with air in unsaturated upper weathered layers of the earth.
biological water: water stores in biomass
atmospheric water
gas: water vapour - absorbs and reflects incoming solar radiation - keeping atmosphere at a temperature that can maintain life - increase in water vapour = increase in atmospheric temperatures - positive feedback
- clouds
aquifers importance
Just over 30% of all freshwater is stored in rocks deep below the ground forming vast underground reservoirs called aquifers. These are crucial for providing water to people around the world. However, many aquifers are being exploited unsustainably as more water is extracted.
Aquifers most commonly form in porous (contain air pockets - pores) and permeable (allow water to pass through) rocks like chalk and sandstone. Water either enters the rocks directly, where they are exposed on the ground, or very slowly as water drains through the overlying soil.
what is the soil water budget?
The SWB outlines the changes in the soil water store over the course of a typical year. Soils vary enormously in their capacity to store and transfer water - this is the soil water budget. Porous, sandy soils hold little moisture as water is easily transferred through the pore spaces. Clay soils tend to store water, with very limited water transfer.
How long does water remain in the water cycle stores?
Water moves between these stores at different rates, and remains in storage for different periods of time - this is known as residence time.
Store with longest residence time and why
deep groundwater - it takes a long time to fill and empty a large reservoir
store with shortest residence time and why
atmospheric - it falls as rainfall
residence time more info - ice caps and sheets, oceans, surface sea and ocean water, atmosphere
Stores such as Ice caps and sheets have incredibly long residence times. Water gets “locked up” in these stores and has to travel through the cryospheric system or wait for changing climatic conditions before it is released again. The oceans also store water for long periods of time, water can be transferred to incredible depths and remains in the oceanic store for long periods of time. Surface sea and ocean water is recycled between stores more rapidly. In the atmosphere the residence time of water vapour relative to total evaporation is only about 10 days. Water is rapidly moved in and out of this store via various processes in the water cycle.
How does climate change drive the magnitude of water stores over time?
About 18 000 years ago we were at the peak of the last Ice Age, when a third of the Earth’s land area was covered by glaciers and ice sheets. With water ‘locked up’ as snow and ice, the magnitude of this store increased significantly. With less liquid water reaching the oceans, sea levels fell by over 100m compared to today.
Global warming could have significant impacts on sea level rise as the amount of water stored as snow and ice declines and more liquid water reachers the oceans.
How does Cloud formation drive the magnitude of water stores
Cloud formation, as a result of condensation, and subsequent precipitation varies considerably with time and space. The driving force behind global cloud formation and precipitation is the global atmospheric circulation model.
- At the Equator, high temperatures results in high rates of evaporation. This warm moist air rises, cools and condenses to form large banks of cloud and heavy rainfall.
- In the mid latitudes e.g. the UK, cloud formation is mostly the result of warm air from the Tropics meeting cold air from the Arctic. Where these two air masses meet, warm air is forced up forming clouds and rain. Winds drive these weather systems across the mid-latitudes, resulting in changeable conditions that we experience.
How do cryospheric processes drive the magnitude of water stores
After oceanic water, the largest stores of water on Earth are frozen water (ice). 95% is locked up in the world’s 2 great ice sheets covering Antarctica and Greenland. These have accumulated over hundreds of thousands of years.
On a shorter timescale, snow accumulated in winter adds to the mass of a glacier or ice sheet. In the summer, melting occurs. In recent decades the climate has warmed, meaning most glaciers are shrinking and retreating.
The melting (ablation) of freshwater ice has a profound impact on sea levels. There is a positive feedback where rising sea levels, triggers calving (ice breaking away) and further melting.
Permafrost is formed when air temperatures are so low that they freeze any soil and groundwater present.
The polar regions are not just an important store of water; they also contribute to the global circulation of water and transfer of heat around the world. A global conveyor belt circulates ocean water towards the poles where it cools, becomes denser and sinks. This is known as the thermohaline circulation and it drives the global water cycle.
What is the global conveyer belt
In the Earth’s polar regions ocean water gets very cold, forming sea ice. As a consequence the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. As the seawater gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep-ocean currents driving the global conveyer belt.
