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
how does urbanisation effect stores
Development of the slope creates impermeable surfaces which effectively removes natural depression stores
Impermeable surfaces also reduce infiltration, impacting groundwater stores
Surface runoff is increased and river channel stores are increased - which may lead to flooding
how does industrialisation effect stores
Burning of fossil fuels generates CO2 in the atmosphere enhancing the greenhouse effect and global warming
This in turn affects precipitation rates and intensities of fall, affecting magnitude of stores
Industrial output can produce acid rain, which destroys vegetation and interception rates, affecting water stores
difference between Throughfall and Throughflow
Throughfall is above ground and is where water transfers through the canopy of trees etc. to the ground without any interception.
Throughflow occurs below ground and is the transfer of water laterally below the surface after infiltration.
define a drainage basin
An area of land drained by a river and its tributaries. A drainage basin can also be called a ‘catchment’
Nile River basin drainage area facts
more than 3 million km2 over 12 countries
are drainage basins open or closed systems
open, drains all the water which lands on the Earth’s surface
Is the atmosphere a store or transfer
the atmosphere can be both a store and a transfer – clouds store but also move water around the planet
Inputs and outputs in drainage basins
Inputs are the addition of water to a drainage basin through precipitation
Inputs vary throughout the year (rain, sleet, snow, location etc) and intensities (flood, drought, temperature etc) and frequency (seasonal, monsoon etc
Outputs are the losses of water from a drainage basin in various forms
River discharge is the volume of water passing a point in the river channel at a given unit of time and expressed as cubic metres per second or ‘cumecs’ (m3/sec)
why is interception important for a drainage basin system
It slows the passage of water to the surface and reduces the amount that reaches the ground – some or all will evaporate and the rest will take a longer route over leaves, trees etc.
This is important, as it reduces the amount available for overland/surface flow and therefore, there is a reduction in soil erosion and flooding
The interception by vegetation and buildings can prevent as much as __% of precipitation from reaching the ground
40
Stores in a drainage basin system
Soil stores – water retained within the pore spaces of the soil called interstices
Groundwater stores water that has percolated and is held in rocks below the top of the water table
above ground flows in a drainage basin systems
Throughfall is precipitation that makes it to the ground without interception by the plant canopy
Drip flow is water that flows off leaves and drips to the ground. Some leaves have developed drip tips and waxy surfaces
Trunk and stem: the flow of water down the stems of plants or trunks of trees
Overland surface flow is when water flows over the land surface. Two types: channel and sheet flow
below ground flows in drainage basins
Infiltration is where water enters small openings and pores in the ground from the surface.
Vegetation cover increases infiltration rates as they slow the rate of flow allowing infiltration to occur, and their roots break up the soil increasing potential pore spaces and channels
Throughflow is the lateral (sideways) movement of water through the upper soil, along lines of seepage called percaline
Percolation is where water flows down through the soil layers and underlying rock is pulled down through gravity. The rate of travel is determined through porosity (soil) and permeability (rock)
Baseflow / Groundwater flow: water that has infiltrated and percolated into the bedrock and below the water, table to feed springs, river channels and recharge aquifers (recharge will only occur when there is an excess of water)
types of overland flow
Channel flow is where water flows in small channels or rills (<30cm width or depth) in a defined stream pattern
Sheet flow is a layer of water on the surface, either due to excess surface flow from increased precipitation or water cannot infiltrate quickly enough
Hortonian overland flow describes the tendency of water to flow horizontally across land surfaces when rainfall has exceeded infiltration capacity and depression storage capacity. The water cannot enter the ground, so it runs straight off the surface.
what is drainage density
The number of tributaries in a drainage basin
how drainage density effects basins
Drainage basins with lots of tributaries have a high drainage density
Drainage basins with few tributaries have a low drainage density
Drainage density affects the magnitude of stores
Key points to mention when describing hydrographs:
Steepness of the rising and falling limb
The value of the peak discharge
The lag time (period of time between peak rainfall and peak discharge)
Time is taken to return to normal
what factors affect drainage basin runoff
precipitation type and intensity
The geology of the drainage basin affects runoff - permeable rocks allow precipitation to be lost or stored
Climate - higher temperatures allow for more evapotranspiration to occur
Vegetation type affects infiltration rates and can slow runoff
Drainage basin relief - steeper relief allows for faster runoff
Size of the basin - the larger the basin, the more water it can store before discharge
what natural impacts effect the water cycle
Natural climate change - the impact of ice ages or interglacial periods will change the availability of water within the system
Extreme climatic events, such as drought, impact the water cycle by reducing the amount available within the system
Ecosystem changes - plant succession may alter the dominant vegetation in an area, which can alter interception rates. Animal burrowing leaves tiny voids which water can infiltrate instead of transferring to groundwater
Seasonal changes- wet and dry seasons change the availability of water within the system
how does precipitation Seasonally Impact on the Water Cycle
winter: Usually greater levels of precipitation, snow will delay the availability of water until melted
summer: Usually, precipitation is less, however, summer storms can bring flash flooding
how does evaporation Seasonally Impact on the Water Cycle
winter: Lower temps reduce the rate
summer: Higher temps increase the rate
how does soil moisture Seasonally Impact on the Water Cycle
winter: Saturated soils lead to increased overland flow and loss of water within the cycle
summer: Soils may dry out, reducing the availability of water, although any rain infiltrates quickly. Hard, the baked ground is initially impermeable
how does vegetation Seasonally Impact on the Water Cycle
winter: Vegetation dies back, reducing interception and transpiration
summer: Vegetation grows, increasing rates of transpiration and interception
how does river channel flow Seasonally Impact on the Water Cycle
winter: Higher discharge rates are usual with winter storms
summer: Lower discharge rates as levels of precipitation drop
what human factors impact the water cycle
Climate change
Farming practices
Deforestation
Land use change
Water abstraction
how does climate change affect the water cycle
Increasing global temperatures reduce mountain glacial ice and the availability of freshwater for communities dependent on this water
how does water abstraction affect the water cycle
The growth of the global population has increased the demand for water supplies. Excessive removal of aquifer water means that recharge cannot keep up and stores are depleted. This can allow seawater ingress if the water table drops below sea water or salinisation if the water table rises and evaporation leaves natural salt concentrations behind
how does Land use change affect the water cycle
Changes to an urbanised landscape increase impermeable surfaces, leading to increased runoff and reduced infiltration. City drainage systems remove water quickly but can lead to flooding when river channels cannot discharge excess runoff quickly
how does Deforestation affect the water cycle
Vegetation removal for agriculture, urbanisation or firewood for fuel supply, impacts an important water storage and transfer capability. Soil moisture is reduced, transpiration declines and less precipitation occurs at a local level which can lead to a dry river system
how does Farming practices affect the water cycle
