Water Cycle Flashcards
just __ % of the Earth’s total freshwater, is accessible to humans
0.9
Why is water stored unevenly
because of the uneven spread of land to sea and permeable or porous rock which enable aquifers to form
what are the major stores of water
Most water is stored as saline water in oceans and freshwater as ice or within aquifers (groundwater stores)
Frozen water in the cryosphere = 68.7%
Liquid water in the hydrosphere = 1%
Water vapour in the atmosphere = 0.2%
Groundwater in the lithosphere = 30.1%
is the water cycle a closed or open system
closed
define the hydrological cycle
the continuous movement of water on, above and below Earth’s surface
what are the processes in the hydrological cycle
Evaporation - the sun evaporates surface water into vapour
Condensation - water vapour condenses and precipitates
Flows - water runs off the surface into streams and reservoirs or beneath the surface as ground flow
how does the hydrological cycle involve energy exchange
As water evaporates, it uses energy from its surrounding to perform this process
This effectively cools the environment
The reverse happens when water condenses (heat is released)
This heat exchange influences the local climate
Stores are…
those places where water is held for a period of time
examples of non-groundwater stores
Water in the atmosphere in the form of water vapour or water droplets in clouds
Surface stores such as puddles, lakes, rivers and reservoirs
Interception is how precipitation is prevented from reaching the ground, usually by being caught on leaves or branches
Ice and snow
Seas and oceans
examples of groundwater stores
Not all rocks can store or transport water
An impermeable but porous rock such as clay, can store water but not transfer water
Un-weathered granite cannot store or transfer water as it has no spaces between rock particles
Sandstone is both porous and permeable and is able to store and transport water
A rock which stores water is called an aquifer and is the most unpolluted source of reliable water when managed carefully
how is an aquifer formed
Formed extremely slowly over a very long time. Water infiltrates underground and collects in the pore spaces of porous rock. the interconnected pore spaces become saturated with water.
Pore spaces can be openings between grains or fractures in the rock or even caverns
Porosity is not enough to form an aquifer, pores must connect with each other to allow water to flow/transfer from one space to another . The flow through an aquifer is very slow
What are the two types of aquifiers
Unconfined - where porous rock is open to surface water and is directly recharged by precipitation
Confined - where there are thick layers/beds of rock over the aquifer, known as the confining beds; these contain the aquifer from the Earth’s surface or other rocks
The size of the stores of water along with water residence time is dictated by:
Flows/transfers such as evaporation
Global factors such as climate change
Local factors such as human activity on a hillslope
define Groundwater Flow
Also called baseflow and is water that has infiltrated and percolated into the bedrock and below the water table
how does Climate change drive change
During the last Ice Age (approx. 18,000 yrs ago), roughly a third of Earth’s surface was covered in ice sheets and glaciers
This increased the magnitude (size) of the cryosphere’s stores
But, it lowered the hydrosphere’s store (no flow of liquid water) and sea levels were over 100 m lower than present day
how do clouds and precipitation drive change
The global atmospheric circulation drives the formation of clouds and types of precipitation
The Equator receives more insolation, resulting in higher temperatures which cause high rates of evaporation
As the warm, moist air rises, it cools, condenses and forms banks of towering clouds with heavy rainfall
This area is a low-pressure zone known as the Inter-Tropical Convergence Zone (ITCZ)
The ITCZ (also called the ‘thermal equator’) tracks with the seasonal movement of the Sun, north and south of the equator bringing intense low-pressure rain/monsoon conditions with the movement
(Global scale)
how do Cryospheric processes drive change
The second largest store of water is ice and 95% is locked as the ice sheets of Antarctica and Greenland
Any changes to the size (magnitude) of these sheets impact globally
The total melting of the ice sheets could result in a 60 m sea level rise, which is a lot of stored water
Melting of the ice sheets adds water to the hydrosphere store of the oceans
Ice shelves are further destabilised, which triggers ice calving, these icebergs subsequently melt; adding to the hydrosphere store and rising sea levels
This is a positive feedback loop
Farming practices impact stores:
Ditches drain the land and increase water flow away from the land
The interception by vegetation can prevent as much as 40% of precipitation from reaching the surface
Over-abstraction of groundwater for irrigation removes stores of water
how does Deforestation reduce interception and infiltration
The interception by leaves stems and branches not only reduce the amount that reaches the ground but also slows the passage of water to the surface, allowing infiltration into the subsurface to occur
Deforestation affects surface stores as natural depression stores such as puddles, ponds and soil are removed
Roots help to break up the soil, increasing the rate of infiltration and groundwater recharge
