Water cycle Flashcards
What is the water/hydrological cycle?
The hydrological cycle refers to the continuous circulation of water through the earth’s land, ocean, and atmosphere.
How can the hydrological cycle be described as a closed system?
The total amount of water within the hydrological cycle is fixed and finite - energy is transferted in and out of the system while the total amount of water stays the same
.
What are flows driven by?
Solar energy, which powers changes of state
gravitational potential energy, whcih causes the movement of water
How much water is there on earth?
1.386 billion km cubed
What are the varying sizes (%) of the following stores?:
* oceans
* atmosphere
* cryosphere
* groundwater
* surface water
- Oceans - 96.9%
- Cryosphere - 1.9%
- Groundwater - 1.1%
- Atmospheric moisture - 0.001%
What are the annual fluxes between:
1. ocean - atmosphere
2. atmosphere - ocean
3. land - atmosphere
4. atmosphere - land
in km cubed:
1. 400,000
2. 370,000
3. 60,000
4. 90,000
What are the diffrent resident times for the cryopshere and the atmosphere.
cryosphere - 15000 years
Atmospheric water - 10 days
What is a drainage basin?
A drainage basin is an area of land that is drained by the a river and its tributaries. It is seperated from neighbouring drainag basins from a water shed.
What type of system is a drainage basin?
They are an open system - inputs are not governed by outputs, so can lose more than they recieve. They are subsections of the global hydrological cycel
What are the different inputs, flows and outputs that occure in a db? define them
Inputs
* Precipitation Patterns: The distribution and intensity of precipitation (rain, snow, hail) that falls on the Earth’s surface. It varies by location, season, and climate.
Flows
* Interception: The process by which precipitation is caught and held by vegetation (e.g., leaves, branches) before it reaches the ground.
* Infiltration: The movement of water from the surface into the soil or rock layers below.
* Direct Runoff: Water that flows over the ground surface directly into rivers and streams, typically from heavy rainfall that cannot be absorbed by the soil.
* Saturated Overland Flow: Water that flows over the surface after the soil has become saturated (i.e., when it cannot absorb more water), often during heavy or prolonged rainfall.
* Throughflow: The lateral movement of water within the soil, from higher to lower areas, before it reaches rivers or streams.
* Percolation: The downward movement of water through the soil and rock layers, typically into deeper groundwater reserves.
* Groundwater Flow: The movement of water through underground aquifers or soil layers, usually toward rivers, lakes, or the sea.
Outputs
* Evaporation: The process by which water changes from a liquid to a vapor, primarily from bodies of water (oceans, lakes) and wet soil, driven by heat from the sun.
* Transpiration: The process by which plants absorb water through their roots and release it as vapor through small openings in their leaves.
* Channel Flow: The movement of water within the bed of rivers and streams, typically towards the ocean.
Explain the physical factors which inflluence a drainage basins inputs, flows and outputs. Evaluate their importance.
- Climate - precipitation is highest at the tropics, where intense solar radiation fuels the convection of humid air, causing convectional precipitation. Eg Amazon db recieves 1.8-3m of water a year. Therefore, it directly influences the inputs in the system. This has the knock on effect of determining ground saturation which will effect the rate of infilitration excess overland flow. warmer climate produces vegitation with more foliage so interception will be higher. Storage times within a db are also directly influenced by climate - eg most precipitation in the yukon db falls as snow, so is temporally stored in the cryosphere.
- soils - The permeability of soils determines how much water can infiltrate versus how much will flow as runoff. Sandy soils allow more infiltration while clayey soils are less permeable resulting in greater runoff. Sacromento db in cali, which has loamy soils, water infiltrates well and groundwater recharge is significant. On the other hand, in the Mississippi Delta, where clayey soils dominate, surface water quickly becomes runoff due to poor infiltration.
- Vegetation intercepts rainfall, slowing down runoff and reducing the amount of water that reaches the soil. Plants also transpire water back into the atmosphere, affecting precipitation. While in a desert, little vegitation cover reduces evotranspiration. E.g, in the Amazon, interception can be up to 40%
- geology - if the bedrock of an area is permeable like sandstone, water can percolate and form an aquifer. if bedrock is impermeable, then water which has infiltrated the soil will flow latterally over the bedrock in the form of groundwater flows.
- Relief - relief will affect the relative importance of fllows and impact how quickly inputs will become outputs. Steeper gradients will reduce the time precipitation has to infiltrate, increase surface run off as gravity can work more effectively.
What human factors influence a drainage basin
human factors are permantly changing how the local hydrological cycle operates within a db.
* Deforestation - around 20% of the amazon has been lost, close to the 25% tipping point where evapotranspiration falls to such an extent that the climate dries, impactiing local inputs and outputs. A fall in vegitation will reduce interception in the catchment area, meaning precipitation can fall directly onto the soil, meaning the iinfiltration capacity is likely to be exceeded causing infilitration excess overland flow. This creates flashy hydrographs
* urbanisation - rapid urbanisation in jakarta has lead to frequent flooding near the Ciliwung DB. Urbanisation reduces permeable surfaces, meaning infiltration is vastly reduced, increasing surface run off and reducing groundwater flows
* resevoirs - resevoirs delay flows of water through drainage basins and increase the outputs (evaporation). Globally, 7% more water in resevoirs is lost by evaporation than is used by humans.
What is a water budget graph?
Shows annual changes in precipitation and potential evapotranspiration, and how this affects soil moisture.
What are the different stages of a water budget graph
A. Precipitation is greater than evaporation,
therefore the soil’s moisture increases
creating a soil moisture surplus.
B. As temperature increases, the rate of
evaporation will increase. The soil uses the
moisture gained during its surplus, through
soil moisture utilisation.
C. The point of maximum evaporation. This is the point of highest risk of drought.
D. Despite evaporation decreasing, there isn’t enough precipitation to provide for vegetation use of water loss, therefore there is a soil
moisture deficit.
E. As precipitation exceeds evaporation rates, the soil will regain moisture and reduce its deficit, through soil moisture recharge.
What is the formula of the wataer budget
Precipitation = Discharge + Evaporation ± changes in stores
What is a River Regime
A regime is the annual variation in discharge of a river at a particular location, measured in cumecs
Explain why river regimes may vary between basins (the two types of regime)
A simple river regime portrays a river which experiences seasonally high discharge followed by a period of low discharge. This is usually associated with rivers in colder climates, such as the Arve in Chamanoix, where water stored locally in the cryosphere melts in the summer and enters the river
A complex river regime usually show larger rivers, which span across mulitple geographic regions, casuing there to be a less apperant trend in discharge across seasons. For example, the nile goes through 11 countries, meaning discharge will be effected by different climatic events experienced in the different countries
What is a storm hydrograph? What two forms can they take?
Storm hydrographs represent the relationship between peak discharge and peak precipitation within a short period of time. They can be flashy, with a short lag time and a steep rising limb, or subdued, with the opposite.
What are two physcial and two human factors which will influence the shape of a storm hydrograph
physcial:
* Climate - a climate which experiences periods of intense rainfail, such as in the Ganges, precipitation exceeds the infiltration capacity of the soil, so large amounts of water will flow directly off the soil, leading to a low lag time and a steepening of the rising limb
* relief - steep catchment areas will increase the effectiveness of gravity, meaning water flows more rapidly from hills and reduces the time it has to infiltrate.
Human
* Land use - areas which have been deforested (Amazon has lost 20%) will have a reduced vegitation cover, so interception is reduced, so lag time will be reduced
* urbanisation - concrete is an immpermeable surface, so water can not infilitrate and will flow in the form of direct run surface run off, steepening the rising limb and decreasing lag time
What is a drought? (UN)
an extended period of deficient precipitation relatuve to the statistical multiyear average for that region
What are the causes of a meterological drought?
- Blocking anti cyclone - high pressure is dry weather , while low pressure causes precipitation and the formation of clouds. Sometimes, a front of very high pressure can sit over an area for many weeks, preventing low pressure systems from moving to it. This can cause a drought
- the postition of the itcz - the iitcz is where the nortern and southern trade winds meet, which bring together humid air masses which get heated by the sun, causing precipitation. It moves throughout the year, due to the tiliting of the earth relative to the sun, meaning areas will experience periods of wet and dry weather
- ENZO cycles
What happens in a La Nina event?
Trade winds across the pacific intensify, meaning the warm mass of air in the Pacific move further East (closer to SE asia), causing more extreme upwelling of cold water on the coast of south America. This creates flooding events in SE Asia, and more extreme droughts in Chile
What happens in el nino?
Trade winds over the western pacific weaken, causig the warm mass of water in the ocean to shift further eastwards towards south America. This reduces upwelling, and causes increased percipitation in south america as there is more ocean evsaporation, and more drought conditions in SE Asia, this waas a major cause of the Austrailian bbig dry
What are two examples of human activity making drought worse?
- The sahel - a region just south of the sahara, and thus is at risk of desertification. Human activity, especially the over grazing of livestock, has removed vegitation cover, meaning they can no longer transpire, and means soil is left bare. It erodes and then dries up, making it more difficult for the water to infiltrate and thus increases water lost to evaporation. in the 1968-73 drought, 100,000 people died
- The big dry, Australia - in 2006, a 1-1000 year drought occured.
