The Water Cycle Flashcards
The Earth and its subsystems
Cryosphere - where its cold enough to freeze water eg glacial landscapes
Lithosphere - outermost part of the earth including the crust and upper mantle
Biosphere - living parts of Earth
Hydrosphere - includes all of the water on Earth in solid liquid or gas form
Atmosphere - layer of gas between Earths surface and space held by gravity
Water distribution
96.5% of the total global water is found in oceans which is bad for humans as it is salty so needs to be filtered. This leaves 2.5% of freshwater and 0.9% saline water. Within the freshwater 68.7% of this is trapped in ice and glaciers which is hard to access. the other 30.1% is in groundwater storage which can be economically hard to extract and to access
The global hydrological cycle
Water is continuously cycled between stores. It is a closed system as there are no inputs or outputs of water
Magnitude of stores vary over time and in space - EVAPORATION
Evaporation occurs when liquid turns to gas and becomes water vapour and gains energy from solar radiation. This increases the amount of water stored in the atmosphere
The magnitude of the evaporation flow varies by location and season. If there is lots of solar radiation, a large supply of water and warm dry air then the amount of evaporation will be high. If the opposite it will be low.
Magnitude of stores vary over time and in space - CONDENSATION
Condensation occurs when water vapour changes to a liquid and it loses energy to the surroundings and it happens when air containing water vapour cools to dew point
Water droplets can stay in the atmosphere or flow to other subsystems such as dew formed on leaves and other surfaces decreasing the water stored in the atmosphere
The magnitude of the condensation flow depends on the amount of water vapour in the atmosphere and the temperature. If there is lots of water vapour in the air and there’s a rapid drop in temperature then condensation will be high
Magnitude of stores vary over time and in space - CLOUD FORMATION AND PRECIPITATION
Essential parts of the water cycle. Precipitation main flow of water from atmosphere to ground.
Clouds form when warm air rises and cools causing water vapour to condense into water droplets which gather as clouds. When droplets get big enough they fall as precipitation. Topography, Convection and other air masses can cause warm air to cool.
Cloud formation and precipitation can vary seasonally as in the UK more rainfall in the inter than in the summer and by location as precipitation is generally higher in the tropics
Magnitude of stores vary over time and in space - CRYOSPHERIC PROCESSES
Such as accumulation and ablation change amount of water stored as ice in cryosphere. The balance varies with temperature.
During cold periods inputs are higher than output as water is transferred to it as snow and less water is transferred away due to melting. During periods of warmer global temperatures the magnitude of the cryosphere store reduces as losses due to melting are larger than the inputs of snow.
Variations happen over different timescales as well as changes in global temperature that occur over thousands of years . The can also occur over shorter time scales such as annual temperature fluctuations means more snow falls in winter than summer
What are hydrographs
Hydrographs are graphs of river discharge over time. They show how the volume of water flowing at a certain point in a river changes over a period of time. Flood hydrographs show river discharge around the time of a storm event and cover a relatively short time period.
A basin with a rapid runoff and not much storage capacity gives the hydrographs a short lag time and high peak discharge. This is called a flashy hydrograph. A long lag time and low peak discharge is a subdued hydrograph.
Peak discharge on a hydrograph
The highest point lm the graph when the river discharge is at its greatest
Lag time on a hydrograph
This is the delay between peak rainfall and peak discharge. This delay happens because it takes time for the rainwater to flow into the river. A shorter lag time can increase peak discharge because more water reaches the river during a shorter amount of time.
Rising limb on hydrograph
This is the part of the graph up to peak discharge. The river discharge increases as rainwater flows into the river.
Falling limb in a hydrograph
This is the part of the graph after peak discharge.Discharge is decreasing because less water is flowing into the river. A shallow falling limb shows water is flowing in from stores long after it has stopped raining.
Factors that affect runoff and hydrograph shape
Size of drainage basin - larger catch more water so have higher peak discharge. Smaller average shorter lag time as less distance for water to travel
Shape of basin - circular basins more likely to be flashy as lots of water will meet the same measurements at the same time
Ground steepness - water flows more quickly downhill shortening lag time. Runoff is also higher as less time to infiltrate
Rock and soil type - impermeable rocks dormant store water or let it infiltrate increasing runoff so peak discharge increases as more water reaches the river in a shorter period
Water cycle varies due to physical factors - STORMS AND PRECIPITATION
Intense storms generate more precipitation and greater peak discharge than light rain showers. The larger input of water causes flows to increase in size. Some flows such as infiltration may not be able to occur rapidly enough for the size of the input so increasing run-off.
Water cycle varies due to physical factors - SEASONAL CHANGES AND VEGETATION
The size of inputs flows and stores in the water cycle varies with the seasons. During the winter temperatures may drop below 0° causing water to freeze. This can reduce the size of flows in drainage basins while the store of frozen water grows. When temperature increase again flows through drainage basins can be much larger as the ice melts.
Many plants show seasonal variation. Vegetation intercepts precipitation and slows its movement to the river channel interception is highest when there’s lots of vegetation and deciduous trees and their leaves. the more vegetation there is in a drainage basin. The more water is lost through transpiration and evaporation before it reaches the river channel reducing run-off and peak discharge.
