Hydrosphere I Flashcards
one sentence on what the hydrological cycle is
earths hydrological system is the largest circulation of matter within the earth atmosphere system. water ‘washes’ the surface of the earth and is ‘recycled’ (purified) by evaporation.
where can water be evaporated from
through saline lakes, soils, plants and direct from ocean
how does the water cycle help to dissipate heat
water vapour, h2o is a greenhouse gas that absorbs heat loss from earths surface - there are heat surpluses at the tropics - water cycle helps to dissipate it though ocean circulation and atmospheric circulation
what is one way of sustaining the food supply if rainfall is uncertain/unreliable
irrigation
where does ocean evaporation go
more ocean evaporation goes straight to clouds and back into the ocean but the rest is primarily river discharge but also direct groundwater discharge
tell me about the units of fluxes
if given in units km^3 then
1km^3 = 10^9 m^3
1m^3 = 100 litres
therefore to go from km^3 to litres just multiply by 10^12
what are fluxes
water moving from one store to another
what proportion of the global water supply is saline
97.5%
what proportion of global water is freshwater
2.5%
how is the supply of global freshwater split up into sources
- 9% is glaciers and permanent snow cover
- 9% is fresh groundwater
- 3% freshwater lakes and river storage
- 9% other; soil moisture, swamp water & permafrost
what is the only renewable source of freshwater and what proportion is it
0.3% of the 2.5% freshwater is renewable and this is freshwater lakes and river storage
what is freshwater
water with less than 1g of salt per litre, low salinity
what is ocean salinity
around 35g/l
how does precipitation vary
latitudinally with zones of atmospheric convergence
what are zones of convergence
zones of convergence are where you have air masses that converge and force one to rise over the other and in doing so the rising air is less able to hold moisture as it cools and forms condensate and then precipitate
what cells are zones of convergence associated with
hadley cells, polar cells and ferrel cells
what is the global distribution of precipitation affected by
ocean circulation affecting evaporation and convergence zones
what is high rainfall in rainforests driven by
orographic effects e.g. the Andes
define orographic precipitation
precipitation caused by the forced ascent of air over high ground. uplift of air leads to cooling, if the air is moist it may lead to condensation and eventually precipitation.
even where rain of convectional or cyclonic origins is falling, the orographic influence can still be seen in larger and sometimes longer precipitation events over the hills. The extra uplift will ensure that the precipitation processes in the clouds operate more effectively.
what does the global distribution in evaporation rate depend upon
temperature (water/air), windspeed and critically the supply of water: rate high over oceans due to unrestricted access to water.
how much of the tropics are covered by ocean
73% - where solar radiation exceeds losses to spaces and so drives global climate
what is the Clausius-Clapeyron relation
warmer air holds more water vapour, the relation represents the relationship as a function of temperature so as air temp increases, the ability of air to hold moisture increases and it increases exponentially not linearly.
why is the clausius-clapeyron relation important
so the warming of a climate has a bigger effect as moisture holding ability grows exponentially.
does the clausius-clapeyron relation have the same effect all over the world
no, warmer areas near the equator will have much more of an increased ability to hold water vapour if there’s an increase in temperature, compared to colder areas where there will be less of an effect. (think of the exponential graph and how it starts flat and then gradient starts climbing).
warmer tropical air masses can hold more water vapour - evaporation at higher latitudes and elevations is often constrained by the water holding capacity of cold air.
How does the clausius-clapeyron relation explain more extreme weather under global warming
the relation further explains the amplification of extremes. if warmer air is able to hold more moisture in a warmer world, it will require more evaporation and water vapour for clouds to meet their dew point so it takes more and so it will take longer to reach the saturation vapour pressure (dew point) and so it makes it harder to rain and from precipitate but when it does form there is a greater volume. so it will be less frequent but more intense. worse flooding.
what is the proper name for dew point
saturation vapour pressure
how is there climate injustice between different parts of the world and the clausius-clapeyron relation
1 degree c warming in the tropics (~24 degrees) increases the water holding capacity of the atmosphere amplifying extremes ~3 times as much as it does at mid-latitudes (~10 degrees)
what is ironic about the water vapour climate injustice
areas in equatorial regions are more at risk than at temperate latitudes (western europe and north america) but these areas are the ones mostly responsible for the global warming in the first place.
how does the intensification of the earths hydrological system represent a positive feedback
warming increases evaporation, releases freshwater from ice storage, raised water holding capacity in the atmosphere so ice storage evaporates so more h20/ water vapour in the atmosphere so then heat is absorbed (retained) and reradiates on earth to melt more ice storage and so on….
will there be rising freshwater resources under climate change?
projected changes in mean annual precipitation show increases over tropical oceans (zone of convergence) which are much larger than they are on land. The biggest declines in mean annual precipitation predictions are on land so more water overall will circulate but wont necessarily be accessible to us.
net balance shows that climate change will have land surfaces freshwater declining and only increasing in the oceans.
how do we work out river discharge
Q(river) = P - ET +/- change in S where Q(river) is discharge P is precipitation ET is evapotranspiration and change in S is change in storage
so river discharge is essentially the balance between evapotranspiration and precipitation
tell me about the relationship between P and ET and river discharge
rainfall can hit the ground and then there is evapotranspiration. if there is surplus rainfall then this forms discharge in the river. can form contributions to or from groundwater, lakes or reservoirs.
what is the river basin
natural drainage of water defined by surface topography, wherein precipitation is returned to the ocean directly or via a lake or another river or the atmosphere via a lake or wetland. (closes basin: dead sea, lake chad)
what are the basin scale processes at the land surface:
precipitation (main input) evapotranspiration (combine evap and transpo as too difficult to know how much is of each when separated accurately. interception runoff infiltration interflow recharge
define precipitation
the deposition of water from the atmosphere in solid or liquid form. it covers a wide range of particle sizes and shapes such as rain, snow, hail, dew. in most parts of the world rain is the only significant contribution to annual precipitation totals and the terms are frequently used synonymously. in polar regions and at high altitudes snow will be the dominant type of precipitation. the process whereby water vapour is converted into precipitation are explained in cloud microphysics.
define evapotranspiration
the diffusion of water vapour into the atmosphere from a vegetated surface. it is influenced by climate, soil hydrology and plant characteristics and this term has been criticised for combining these elements when they can respond in different ways to energy and moisture variations. however, it is convenient to consider a homogeneous vegetated surface for many hydrological applications and this concept is widely used. Plant stomata remain open for the processes of photosynthesis and respiration, which are essential to growth. this exposes the moist interiors of the stomata and encourages the diffusion of water vapour, that is, transpiration.
define interception
the process by which precipitation is trapped on vegetation and other surfaces before reaching the ground. interception loss is the component of intercepted precipitation which is subsequently evaporated, although this is also frequently described as interception. the character of the intercepting surfaces has a major impact on the amount of precipitation that is intercepted and then lost through evaporation.
define infiltration
the process by which water percolates into the soil surface. two main zones can be observed in the soil when infiltration is proceeding at its maximum rate,
define run-off
water that drains from an area of the land is referred to as the run-off. this process may be considered at various scales, spanning continental run-off, the run-off from a river basin, or catchment area or from a small area of land such as a roof or field. Run-off follows both above-ground and sub0surface pathways and may then be referred to explicitly as surface run-off, sub-subsurface run-off or groundwater run-off.
define interflow
a component of streamflow which responds to rainfall more slowly than surface run-off and more rapidly than baseflow. some literature uses the term interflow interchangeably with subsurface soil flow or throughflow.
define recharge
the process by which precipitation is absorbed through the soil or regolith, transmitted, and ultimately added to the saturated or phreatic zone within the underlying soil or bed-rock, thereby replenishing groundwater reserves. The term can also be used to describe mechanisms by which the soil moisture is replenished after is has been depleted due to percolation loss to underlying horizons or by evapotranspiration.
what is potential evapotranspiration
refers to the ability of the atmosphere to remove water. the flux of PET refers to where there is no limit to the supply of water.
what is actual evapotranspiration
refers to the ability of the atmosphere to remove water depending upon the water supply
what is the relationship between AET and PET when there is adequate water supply
AET = PET
when will AET < PET
when there is declining water availability. AET is measure on land so in systems where you run out of water (eg not the ocean) then AET is less eg. Sahara desert has a high PET but low AET due to lack of water
when will AET > PET
this could occur in rainforests when there is more vegetation to evaporate water.
how do we define climate zone
the ratio of P/PET (precipitation (moisture supply) : potential evapotranspiration)
What is the P/PET ratio like for highly arid/ dry zones
very low
what is the P/PET ratio like for humid zones
very high
what P/PET ratios constitute which climate zones
< 0.03 highly arid 0.03 to 0.20 air 0.20 to 0.50 semi arid 0.5 to 0.65 sub humid > 0.65 humid
what is runoff generation versus infiltration
capacity of the soil to accept received precipitation partitions the precipitation so that it either infiltrates pr runs overland.
what is the Horton Hypothesis in 4 words
infiltration-excess overland flow
explain the Horton Hypothesis
whether water infiltrates or surface run-off. there is some capacity of soil to receive and infiltrate precipitation so if land surface is unable accept the INTENSITY of rainfall then infiltration excess causes overland flow
when do we know if there will be no overland flow with the Horton hypothesis
no overland flow will occur if rainfall intensity is less than or equal to the infiltration capacity of the soil.
eg. 1.5cm/hr rainfall and 1.5cm/hr infiltration rate will mean no overland flow
2. 5cm/hr rainfall and a 2cm/hr infiltration rate will cause a 0.5cm/hr overland flow rate
define soil infiltration capacity
the maximum rate at which precipitation can be absorbed by a given soil when in a given condition - it is a dynamic property
why could the infiltration rate change
rate decreases as soil surface is compacted by raindrops, swelling of clays. and find sediment clogs soil pores.
when the infiltration rate stabilises what does it become
the infiltration capacity
what is the Hewlett hypothesis
theory about overland flow production. Over much of a basin, precipitation infiltrates the soil (saturation - overland flow)
infiltrating water causes water table to rise and saturate the ground surface adjacent to the river channel. Ground becomes fully saturated so infiltrating water causes water table to rise so not because of intensity, overland flow will occur is soils are fully saturated.
so is the Horton Hewlett hypothesis right?
reality is runoff can be formed by both hypothesis.
what does river discharge derive from
runoff (Horton and Hewlett processes) and baseflow provided by groundwater
What will climate change amplify
the amplification of precipitation extremes under climate change increases runoff and so risk of flooding. IPCC AR6 chapter 8: changing water cycle.
more intense flooding in low income areas, inequality.
intensification of earths hydrological system as the planet warms leads to more frequent and intense flood events and longer and more frequent droughts.
what is the global distribution of evaporation and precipitation rates explained by
convergence zones and orographic effects
what is the key control on precipitation and evaporation
the Clausius-Clapeyron relation
define stormflow
The runoff of land surface water from rainfall. (same as runoff)
