Hydrosphere I

Question 1

one sentence on what the hydrological cycle is

Answer 1

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.

Question 2

where can water be evaporated from

Answer 2

through saline lakes, soils, plants and direct from ocean

Question 3

how does the water cycle help to dissipate heat

Answer 3

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

Question 4

what is one way of sustaining the food supply if rainfall is uncertain/unreliable

Answer 4

irrigation

Question 5

where does ocean evaporation go

Answer 5

more ocean evaporation goes straight to clouds and back into the ocean but the rest is primarily river discharge but also direct groundwater discharge

Question 6

tell me about the units of fluxes

Answer 6

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

Question 7

what are fluxes

Answer 7

water moving from one store to another

Question 8

what proportion of the global water supply is saline

Answer 8

97.5%

Question 9

what proportion of global water is freshwater

Answer 9

2.5%

Question 10

how is the supply of global freshwater split up into sources

Answer 10

68. 9% is glaciers and permanent snow cover
69. 9% is fresh groundwater
70. 3% freshwater lakes and river storage
71. 9% other; soil moisture, swamp water & permafrost

Question 11

what is the only renewable source of freshwater and what proportion is it

Answer 11

0.3% of the 2.5% freshwater is renewable and this is freshwater lakes and river storage

Question 12

what is freshwater

Answer 12

water with less than 1g of salt per litre, low salinity

Question 13

what is ocean salinity

Answer 13

around 35g/l

Question 14

how does precipitation vary

Answer 14

latitudinally with zones of atmospheric convergence

Question 15

what are zones of convergence

Answer 15

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

Question 16

what cells are zones of convergence associated with

Answer 16

hadley cells, polar cells and ferrel cells

Question 17

what is the global distribution of precipitation affected by

Answer 17

ocean circulation affecting evaporation and convergence zones

Question 18

what is high rainfall in rainforests driven by

Answer 18

orographic effects e.g. the Andes

Question 19

define orographic precipitation

Answer 19

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.

Question 20

what does the global distribution in evaporation rate depend upon

Answer 20

temperature (water/air), windspeed and critically the supply of water: rate high over oceans due to unrestricted access to water.

Question 21

how much of the tropics are covered by ocean

Answer 21

73% - where solar radiation exceeds losses to spaces and so drives global climate

Question 22

what is the Clausius-Clapeyron relation

Answer 22

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.

Question 23

why is the clausius-clapeyron relation important

Answer 23

so the warming of a climate has a bigger effect as moisture holding ability grows exponentially.

Question 24

does the clausius-clapeyron relation have the same effect all over the world

Answer 24

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.

Question 25

How does the clausius-clapeyron relation explain more extreme weather under global warming

Answer 25

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.

Question 26

what is the proper name for dew point

Answer 26

saturation vapour pressure

Question 27

how is there climate injustice between different parts of the world and the clausius-clapeyron relation

Answer 27

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)

Question 28

what is ironic about the water vapour climate injustice

Answer 28

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.

Question 29

how does the intensification of the earths hydrological system represent a positive feedback

Answer 29

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....

Question 30

will there be rising freshwater resources under climate change?

Answer 30

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.

Question 31

how do we work out river discharge

Answer 31

``` 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

Question 32

tell me about the relationship between P and ET and river discharge

Answer 32

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.

Question 33

what is the river basin

Answer 33

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)

Question 34

what are the basin scale processes at the land surface:

Answer 34

``` 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 ```

Question 35

define precipitation

Answer 35

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.

Question 36

define evapotranspiration

Answer 36

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.

Question 37

define interception

Answer 37

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.

Question 38

define infiltration

Answer 38

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,

Question 39

define run-off

Answer 39

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.

Question 40

define interflow

Answer 40

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.

Question 41

define recharge

Answer 41

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.

Question 42

what is potential evapotranspiration

Answer 42

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.

Question 43

what is actual evapotranspiration

Answer 43

refers to the ability of the atmosphere to remove water depending upon the water supply

Question 44

what is the relationship between AET and PET when there is adequate water supply

Answer 44

AET = PET

Question 45

when will AET < PET

Answer 45

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

Question 46

when will AET > PET

Answer 46

this could occur in rainforests when there is more vegetation to evaporate water.

Question 47

how do we define climate zone

Answer 47

the ratio of P/PET (precipitation (moisture supply) : potential evapotranspiration)

Question 48

What is the P/PET ratio like for highly arid/ dry zones

Answer 48

very low

Question 49

what is the P/PET ratio like for humid zones

Answer 49

very high

Question 50

what P/PET ratios constitute which climate zones

Answer 50

``` < 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 ```

Question 51

what is runoff generation versus infiltration

Answer 51

capacity of the soil to accept received precipitation partitions the precipitation so that it either infiltrates pr runs overland.

Question 52

what is the Horton Hypothesis in 4 words

Answer 52

infiltration-excess overland flow

Question 53

explain the Horton Hypothesis

Answer 53

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

Question 54

when do we know if there will be no overland flow with the Horton hypothesis

Answer 54

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

Question 55

define soil infiltration capacity

Answer 55

the maximum rate at which precipitation can be absorbed by a given soil when in a given condition - it is a dynamic property

Question 56

why could the infiltration rate change

Answer 56

rate decreases as soil surface is compacted by raindrops, swelling of clays. and find sediment clogs soil pores.

Question 57

when the infiltration rate stabilises what does it become

Answer 57

the infiltration capacity

Question 58

what is the Hewlett hypothesis

Answer 58

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.

Question 59

so is the Horton Hewlett hypothesis right?

Answer 59

reality is runoff can be formed by both hypothesis.

Question 60

what does river discharge derive from

Answer 60

runoff (Horton and Hewlett processes) and baseflow provided by groundwater

Question 61

What will climate change amplify

Answer 61

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.

Question 62

what is the global distribution of evaporation and precipitation rates explained by

Answer 62

convergence zones and orographic effects

Question 63

what is the key control on precipitation and evaporation

Answer 63

the Clausius-Clapeyron relation

Question 64

define stormflow

Answer 64

The runoff of land surface water from rainfall. (same as runoff)