✅C&W 3.1.1.2 - The Water Cycle Flashcards
What is precipitation?
Transfer of water form the atmosphere to the ground. It can take the form of rain, snow ,hail, dew etc
What is interception? How does it vary with density?
Water intercepted and stored in the leaves of plants
Denser - more interception
58% in rain forest, 22% in deciduous forest
What is throughflow?
Water flowing through soil towards the river channel
What is infiltration? What affects it
Transfer of water from the ground surface into soil where it may then percolate into underlying rocks
Gravity, soil porosity, capillary action
What is percolation?
Water soaking into rocks
What is groundwater flow?
Transfer of water very slowly though rocks
River flows: downstream vs Upstream
Slowest at the side with friction
Downstream: laminar flow, fast and smooth
Upstream (nearer source): eddies, like small whirlpool, due to friction with angular bed
Causes of deposition
Lower gradient, less discharge, shallow, increased load, lower velocity (friction), flocculation
What if flocculation
Process where small particles suspended in water lump& form larger pieces
Due to when salt water meets fresh water
Coagulation of particles makes them sink, can cause mudflats
Changes to local water cycle: Deforestation
less interception, more runoff, flooding
less soil, fewer plants, less transpiration, less rain in LT
Changes to local water cycle: Storm events
saturation, more runoff
Changes to local water cycle: seasonal changes
Spring: more vegetation, interception,
Summer: less rain, harder ground, more runoff when rains
Autumn: less vegetation, less interception, more runoff
Winter: hard ground, runoff
Changes to local water cycle: agriculture
pastoral farming: animals trample ground, more runoff
Arable: more vegetation, more interception, less runoff + ploughing means looser soil and more interception
Irrigation: ground water depletion
Changes to local water cycle: urbanisation
impermeable ground, runoff, lower lag time, higher flood risk, flash floods
Although drains help
What is surface tension?
How the molecules on the surface of water behave and how tightly they are held together by hydrogen bonds
What is atmospheric water?
Water found in the atmosphere- mainly water vapour
0.04% of all water
Short residency time, dynamic equilibrium
As temps rise, more water vapour stored (hot air stores more water): for every 1C temp rise, atmospheric water store rises 7% - more intense rainfall
What is cryospheric water?
The water locked up on the Earth’s surface as ice
5 stores of cryospheric water
permafrost- ground which stays at/below 0°C for at least 2 years. Locks up CO2
alpine glaciers
sea ice
ice sheets- glacial land over 50,000 km^2. E.g, Antarctica
ice caps
as cryosphere decreases, oceanic increases
Positive feedback with albedo effect
albedo, ice reflects sunlight, so less ice means less reflection, means more heat absorption, more melting
What is the hydrosphere?
A discontinuous layer of water at or near the Earth’s surface waters, groundwater held in soils and rock and atmospheric water vapour
What is oceanic water?
Acidity?
The water contained in the Earth’s oceans and seas
Salty, but has decreased in pH due to fresh water (ice caps) melting into it. 8.25 pH to 8.14 pH over 250 years
Damaging ecosystem
What is terrestrial water?
This consists of groundwater, soil moisture, lakes, wetlands and rivers
stores of terrestrial water
Surface water- free flowing like rivers- largest river is the Amazon, discharge 209,000m^3/s- 0.0002% of all water
Ground water- 20% of fresh water, but decreasing due to extraction from agriculture
Soil water
Biological water- very little, not long residency time
Which is the largest store of water?
Oceanic water, 97% of all water
Where is most of the freshwater on Earth stored?
In the Antarctic and Greenland ice sheets
Parts of a river
Source: start of river, supply
River channel: space between bed& banks (main river)
Confluence: where tributary meet river channel
Tributary: smaller side river
What is a drainage basin
The area of land drained by a river and all it’s tributaries. AKA catchment area
They are all next to each other in one cascading system of open systems
What are inputs into the drainage basin?
Precipitation
Energy from the sun
What are stores in the drainage basin?
Lakes Soil/Ground water Interception/vegetation River flow Surface flows
What are transfers in the drainage basin?
Ground water flow
Percolation
Transpiration
Precipitation
What are the outputs from the drainage basin?
River discharge
Evapo-transpiration from vegetation, water
Water vapour
What is the fastest movement of water through the drainage basin?
Along the surface where there are relatively few obstacles in the way of the water
How fast is water movement though soil?
Somewhat slow, but varies more as clay soils retain water, slowing it down, but aerated soils and woodland channels allow it to move faster
What is the slowest form of movement in the drainage basin?
Groundwater flow, as it can be held for millennia
How much of the water on Earth is available for use by humans?
3% is fresh water
20% of this is groundwater, 79% is ice caps
What is soil storage?
The amount of water stored in the soil
What is vegetation storage?
The water stored in plants as they take it up from the soil
What is transpiration?
Water lost from plants through stomata, released back to the atmosphere
What is infiltration capacity?
The point where the soil becomes saturated
How does soil type affect infiltration capacity?
Depends on pore sizes:
40-60% in clay soil
25% in sand
Fewer pores- less space to store water
What is water balance/budget?
The balance between inputs and outputs within the drainage basin
What is the river’s regime?
As discharge levels rise and fall, often showing an annual pattern
What is the formula for water balance?
Precipitation (P) = discharge (Q) + evapotranspiration (E) +/- changes in storage (S)
Most varies by season. In summer -20mm, in Winter +90mm
What is stemflow?
The portion of precipitation intercepted by the canopy that reaches the ground by flowing down stems, stalks or trees.
What are the factors impacting the soil moisture budget?
Precipitation
Potential evaporation
What is potential evaporation?
The amount of evapotranspiration that could occur if there was sufficient water available in the system
What is the formula for river discharge?
River discharge = cross sectional area x velocity
What is water surplus?
When precipitation exceeds evapotranspiration
How does drainage basin shape affect the shape of a storm hydrograph?
Basins with a more circular shape have flashier hydrographs because each point is roughly equidistant from the channel
How do slope angles affect the shape of a storm hydrograph?
Drainage basins with steep sides have flashier hydrographs because water flows more quickly down steep slopes
How does drainage density affect the shape of a storm hydrograph?
Basins with a lot of surface stream tributaries have flashier hydrographs because all the water arrives at the same time
How does antecedent (prior) rainfall affect the shape of a storm hydrograph?
If the basin in already saturated, overland flow increases, so water moves quickly and peak discharge is higher, so flashier hydrographs
How does rock type affect the shape of a storm hydrograph?
If a rock is impermeable, overland flow will be higher, so lag time is reduced and the hydrograph is flashy
How does vegetation cover affect the shape of a storm hydrograph?
More vegetation leads to a subdued hydrograph because they intercepts and holds rainfall, slowing its path to the river channel
How does amount and intensity of precipitation affect the shape of a storm hydrograph?
Heavy storms with a lot of water entering at once produce flashy hydrographs. Slower lag time is precipitation is slow
How does drainage basin size affect the shape of a storm hydrograph?
Larger basins catch more precipitation and so have higher peak discharge. Smaller basins have shorter lag time, as water doesn’t travel as far
How does deforestation affect the shape of a storm hydrograph?
Reduces interception and lack of roots reduces infiltration rates, leading to rapid overland flow and flashy hydrographs
How does afforestation affect the shape of a storm hydrograph?
Opposite effect of deforestation, also decreases soil erosion, so less sedimentation of the channel, therefore increasing its capacity and reducing flooding
How does agriculture affect the shape of a storm hydrograph?
Ploughing allows infiltration, subdued hydrographs. Terraces stop water movement downhill, subdued hydrographs. Grass crops increase infiltration, subdued hydrograph
How does growth of urban areas affect the shape of a storm hydrograph?
Flashy hydrographs: impermeable surfaces, floodplains, water moved directly into river, loss of green spaces and vegetation
How does soft engineering flood management affect the shape of a storm hydrograph?
Some schemes attempt t reduce flashiness of hydrographs. Afforestation increases interception and infiltration, subdues discharge
How does water abstraction affect the shape of a storm hydrograph?
Reduces the base flow and so more water must reach the channel before it reaches bankfull capacity and floods
What is the base flow?
The normal day to day discharge of the river
What is the impact of deforestation on the water cycle?
New vegetation generally has fewer leaves and shallower roots, so uses less water
So less water evaporates from the land surface to be returned to the atmosphere
More water runs off the land and stream flow is increased
Amount of rainfall may decrease or river discharge will increase
What is the impact of agricultural soil drainage on the water cycle?
Heavy machinery can work the land without compaction, leading to more overland flow
The insertion of drains increases rate f through low in the soil
Can increase likelihood of flooding as discharge becomes more flashy and peak discharge increases
Soils can be eroded and soil water decreases
What is the impact of water abstraction on the water cycle?
Sinking water tables can make rivers less reliable, as their flows are maintained in the dry season by springs, that dry up when the water table falls
Ground water levels fall and saline intrusion can occur, contaminating water supplies
Precipitation and rainfall don’t replace water used
What is El Nino and La Nina?
A climate cycle of warm and cold temperatures measured using sea surface temperatures of the tropical Pacific. Alternates between El Nino and La Nina every 2-7 years
El Nino: Warmer in pacific (wet S American, dry SE Asian)
La Nina: Cooler in pacific (dry S American, wet SE Asian)
What is El Nino caused by?
Strong extensive interaction between the ocean and atmosphere
How can El Nino affect the water cycle?
Can cause droughts and global declines in evapotranspiration despite rising temperatures. Reduced precipitation leads to lower soil/ground water levels
How can tropical storms affect the water cycle?
Increased rainfall and storm surges over the land can lead to greater river discharge and saturated ground
How can drought affect the water cycle?
Causes reduction in water stores in rivers and lakes
Vegetation dies back or is destroyed by fires, affecting transpiration, interception and infiltration
Groundwater flow becomes more important as a long term transfer, soils dry out
Global Atmospheric Circulation Model
Descending cooler dry air, rising moist hot air
Between Hadely and Ferrel cells, unstable weather occurs and moved by the jet-streams. Causes changleable weather in UK
ITCZ between cells of rising air, low pressure zones where heavy rainfall and storms can occur
How human activity impacts the water cycle: land use, deforestation, examples NY
70- 90% of deforested land is used for agriculture
Less evapotranspiration, so less air humidity, so less rain in LT
Higher temperatures over time as more water in Earth and less in trees, warming planet- makes irregular rainfall
World lost 3% of forests from 1990-2005
2nd biggest human cause of CC
Forests are a cheap option for water treatment, in NYC trees were planted over 1 million acres to avoid $8bn water filtration plant
In Malawi, what effect did deforestation have on rainfall
In Malawi, a 14% decrease in forests led to 9% less precipitation- fewer crops
In Texas, what effect could deforestation have on a global level
Texas could get 25% less rainfall due to Amazon’s deforestation
How human activity impacts the water cycle: water abstraction
Draining aquifers, faster than they can replenish
70% of fresh water withdrawals are for agriculture
What is adiabatic cooling
when air volume increases, getting air closer to saturation. Can happen when air rises and expands in upper atmosphere. Causes rainfall.
Rainfall type: relief
Air rises, so greater volume, closer to saturation, rains
Rainfall type: frontal rainfall
masses of air meet, less dense is pushed up, causes rain
Rainfall type: conventional effect
warm surfaces cause air to expand and rise, then rain
