The Water Cycle- C+W Flashcards
3.1.1.1- Talk about the water cycle system in a local scale.
DRAINAGE BASIN- an area of land where all flowing surface water converges to a single point, such as a river mouth. Inputs and outputs aren’t balanced therefore an open system.
What is the INPUT into a drainage basin?
Precipitation
What are the three types of rainfall?
- Relief: when warm air is forced upwards by a mountain causing it to condense above the mountain and precipitate behind it.
- Frontal: Warm air rises over cool air when they collide as warm air is less dense therefore lighter, causing it to condense
- Convectional: When the sun heats the surface of the earth causing liquid to evaporate and rise, which cools and condenses.
What are the OUTPUTS out of a drainage basin?
Evapotranspiration- mix of evaporation (the sun heating surface water causing it to rise) and transpiration (the release of water when plants respire)
Runoff- All the water that flows out of a drainage basin.
Talk about the FLOWS which occur in a drainage basin.
Infliltration- when water reaches the ground, it soaks into the soil. This can be increased through grass crips and tree roots creating passages for water to flow.
Percolation- movement of water through rocks
Throughflow- movement of water through the soil into streams and rivers.
Surface run-off- movement of water above land
Groundwater Flow- water moves through the ground
Streamflow- movement of water through channels
Stemflow- Movement of water down the side of bark of stems of vegetation.
Talk about STORES in a drainage basin system.
Soil Storage- the amount of water stored in the soil
Groundwater- Water stored in the pore spaces of rocks
Channel Storage- Water stored in rivers
Intercpetion Store- Amount of water intercepted by vegetation and plants
Surface Storage- Water stored on the ground in places like lakes and ponds.
What are some examples of positive and negative feedback in the water cycle?
Positive- rising global temperatures cause polar ice to melt, reduces albedo effect, increased absorption of heat, more ice melts…#
Negative- Increased temperature leads to more evaporation, more water vapor leads to more cloud formation, clouds reflect solar radiation, offsets temperature increase
3.1.1.2- Talk about the global distribution and size of the stores of water.
Hydrosphere- any liquid water, containing 97% of the global water supply. This is mainly from the ocean which is undrinkable.
Lithosphere- water stored in the ground, contains 1.7%
Cryosphere- any frozen water, 1.7%
Atmosphere- water vapour contains only 0.001%.
Talk about the distribution of freshwater globally.
Out of global water, only 2.5% is fresh. Of this, 69% is frozen and 30% is underground. Therefore, accessible freshwater only accounts for 1% of global stores.
Talk about the factors which drive the change in magnitude of water stores?
Evaporation- energy from solar radiation hits the surface and causes liquid water to change to water vapour increasing the atmospheric water rate. This can be increased through global warming and leads to more cloud formation.
Condensation- as air cools, its able to hold less water vapour. once its significantly cooled, ot becomes so saturated (dew point temperature) . The excess water in the air condesnes onto a surface.
Global atmospheric circulation- determins cloud formation and rainfall containing different zones of rising and falling air leading to convectional rainfall.
Cryospheric Processes- over the last quaternary period, there have been many glacial periods and inter-glacial periods affecting the amount of accumulated ice.
95% of frozen water is locked in ice-sheets, as snow falls on ice sheets and becomes compressed and enters long term stores, however almost all of the worlds glaciers are shrinking causing sea levels to rise.
What is the water balance?
The balance between inputs and outputs within a drainage basin annually. It can be shown on a graph.
Jan- may- Precipitation is greater than potential evaporation so water is in surplus leading to overland flow and flooding.
June- Sept- Warms up so potential evapotranspiration exceeds precipitation so the water store is used by plants and the soil (utilisation). This means river levels fall and plants potentially wilt- deficit
Oct-dec- Precipitation once again exceeds evapotranspiration and the soil water store will recharge.
Talk about Flood Hydrographs.
Flood hydrographs are used to represent rainfall for the drainage basin compared to discharge during storms.
Discharge- The volume of water passing through a cross-sectional point of the river at any one point in time, measured in cubic meters per second (cumecs), area x velocity
Rising Limb- The line on the graph representing discharge increasing
-Falling Limb- discharge decreasing.
Lag-Time- Time between peak rainfall and peak discharge
Baseflow- level of groundwater flow
Stormflow- overland flow and throughflow
Talk about the natural changes in the water cycle.
Storm Events- large amounts of rainfall saturates soil so infiltration cant occur increasing surface runoff.
Seasonal Changes- Spring + summer- More vegetation so more interception, ad less rainfall so hard, impermeable ground therefore more surface runoff, Autumn and Winter- less vegetation, and more rainfall. Frozen ground may be impermeable. Snow takes time to melt so increases lag-time
Talk about the human impacts on the water cycle?
Deforestation- less interception by trees so surface runoff increases. The soil is no longer held together by roots so soil water decreases and transpiration decreases
Agriculture- Pastoral Farming- relating to livestock, trample the ground reducing infiltration. Arable Farming- ploughing increases infiltration as looser soil which decreases surface runoff however digging ditches increases surface runoff. Irrigation- moving water by human intervention, can lead to groundwater depletion
Urbanization- impermeable surfaces reduce infiltration and increases surface runoff reducing lag-time and increasing flood risk.
Water Abstraction- reduces volume of water surface stores. Increases in drier seasons. lowers water table
What are flashy hydrographs and what are they caused by?
Short lagtime and high peak discharge, most likely occur through a storm event therfore have higher floodrisk
- High rainfall intensity- soil more likely to reach field capacity, increasing surface runoff, decreasing lagtime
- Impermeable geology- decreases percolation, greater amount of throughflow
- high drainage density- many tributaries increases speed of drainage and decreasing lag time
- small basin- rainfall reaches the central river quickly decreasing lag time
- circular basin- as above
- low temperature- less evapotranspiration so greater peak discharge.
- precipitation type- snow takes time to melt increasing lagtime
- vegetation cover- forested areas means there is more interception decreasing floodrisk.
- Urbanization- more impermeable surfaces so runoff increases.
- Pastoral Farming- ground is trampled so less interception and more surface runoff
- deforestation- less interception by trees, so water reaches the ground quickly.
