Download The hydrologic cycle

The hydrologic cycle
Jean-Marc Mayotte
[email protected]
Earth is neat
• 70% of Earth is covered by water
– Probably arrived during the very early stages of
Earth as it was being bombarded by comets and
asteroids
• Earth is unique in that almost all of its water is
allowed to remain in its liquid form
– Life is supported by liquid water
• The movement of water around the globe is
what sustains life
Where is the water (globally)?
Freshwater
3%
Saltwater
97%
Total: 1444 10⁶ km³
Atmosphere
Biosphere
Surface Water 0.0353%
0.0046%
0.2886%
Groundwater
35%
Ice
65%
Berner and Berner, Global Environment: Water, Air and Geochemical Cycles, Second Edition, Princeton University Press, 2012, table 1.1
What does that look like?
All the water in the world (1.4087 billion cubic kilometers of it) including sea
water, ice, lakes, rivers, ground water, clouds, etc. Right: All the air in the
atmosphere (5140 trillion tonnes of it) gathered into a ball at sea-level density.
Shown on the same scale as the Earth.
Oceans
97% is seawater
Total: 1400 x 10⁶ km³
Ice
Total: 28,39 10⁶ km³
1,97 % of global water
65% of freshwater
Ice Shelves (floating): 2,47%
Ice caps and glaciers: 0,32%
Ice Sheets:
97,22%
Antarctica accounts for 90% of all ice
Groundwater
Total: 15,95 10⁶ km³
1,06% of global water
35% of freshwater
Atmosphere
Total: 0,0155 10⁶ km³
0,0011% of global water (but it is very
important)
Terrestrial:
0,0045 10⁶ km³
Oceanic:
0,0110 10⁶ km³
Surface freshwater
Total: 0,1267 10⁶ km³
0,0088% of global water
0,2886% of freshwater
Fluxes of water
Transpiration
E
Precipitation P
Evaporation
Ground surface
Run-off R
P = E + R + ΔS
Precipitation
Evapotranspiration
Runoff
Δ (Change in) Storage
Global Water cycle
precipitation
Salt lakes
104 (0.008%) (10-1000y)
Atmosphere
13 (0.0009%) (9d)
111 000/y
40 000/y
Freshwater lakes
125 (0.009%) (1-100y)
Rivers
1.2 (0.00009%) (12-20d)
40 000/y
425 000/y
Evaporation
Evapotranspiration
Evaporation
29 000 (2.08%) (16 000y)
71 000/y
precipitation
Polar ice, glaciers
385 000/y
Soil moisture
67 (0.005%) (280d)
Groundwater (active)
4000 (0.29%) (300y)
Reservoir
Pool size [10³km³], pool size [%], turnover time
Schlesinger, 1993; Murray, 1992
Ocean
1.37x10⁴ (97.61%) (37000y)
How does water move between
reservoirs?
•
•
•
•
Evaporation
Precipitation
Runoff
Groundwater flow
Two most important mechanisms.
Driven by the sun’s energy
Evaporation
• Water changes phases (liquid to gas)
– Requires energy (from the sun)
• Difference in vapour pressure provides
gradient (move from high to low pressure)
– Depends on the surface’s temperature and the
relative humidity of the air
• Wind can have a profound effect by constantly moving
moist air and replacing with dry air thus increasing the
difference in vapor pressure
Potential evaporation (PET)
• The ammount of evaporation that would occur if there
were no limits on water supply (demand-side
calculation)
– Actual evaporation is the net of the atmospheric ”demand”
for water and the ability of a water surface to supply the
water
• Many methods available to estimate PET but they are
empirically derived and can result in a lot of error
– Thorthwaite Eqn.
– Penman Eqn.
– Penman-Monteith Eqn.
Global Evaporation
Annual mean evaporation in Sweden
Difficult to measure. Can be
estimated as a residual term
in the water balance:
E = P – R – DS Precipitation
Evapotranspiration
Runoff
Δ (Change in) Storage
Transpiration
The loss of water
vapor from plants
Clouds forming over the
amazon as a result of
transpiration
Precipitation
• Result of saturation and condensation of
atmospheric water
• Saturation can occur either through cooling or by
addition of more water
• Three types of precipitation:
– Liquid (drizzle, rain)
– Freezing (sleet)
– Frozen (snow, graupel, hail)
• Liquid freshwater deposits are a result of
precipitation
Frontal
Causes of precipitation
Two bodies of air meet (warm and
wet meets cold and dry)
Convective
Strong updrafts fueled by intense
evaporation force large bodies of
warm, moist air high into the
atmosphere where it rapidly cools
and condenses
Orographic
Air is forced up by the landscape,
cools and precipitates
Global precipitation
Annual mean precipitation in Sweden
Notice: more precipitation at the
higher elevations
Snowfall
Note: More snow at the higher
elevations as well
Note: Snowfall increases from
south to north
Precipitation - Evaporation
S. Scandinavia
Available surface
water is
determined by the
difference in
evaporation and
precipitation rates
Precipitation
(mm/year)
Pot. evapotranspiration
(mm/year)
2m
Start
After one year
After two years
S.Europe
E. Africa
1000
1000
1000
500
1000
1500
Atmospheric circulation
(General model)
Atmospheric circulation
Runoff
Occurs when the ground is saturated and water pools on the
surface.
Pooling
Unsaturated soil
Water-saturated soil
Interception
P
• Interception
I = P – crown drip –
trunk flow – penetrating
precipitation
Interception (I)
Trunk flow
Penetrating
precipitation
Crown drip
Groundwater
Unsaturated soil
Porosity
Water-saturated soil
Total volume
Pore volume
porosity 
Porosity = 0.30
Water content = 0.05
pore volume
total volume
Water content
Watercontent 
water volu me
total volume
Porosity = 0.30
Water content = 0.30
Groundwater Discharge
Recharge area
Recharge area
Location of
landfill?
Regional groundwater
flow
Three near lying wells sample
groundwater that originally comes from
widely separated locations
Groundwater in Sweden
Surface water discharge
Reservoirs, lakes, rivers...
Usable freshwater
Transpiration
Precipitation P
E
Evaporation
Surface run-off
Soil surface
Infiltration
Percolation
Storage DS
Run-off R
(Rising/lowering of groundwater level)
Groundwater
Groundwater
discharge
Practical Applications