U6115: Climate & WaterFriday, June 20 2003

“Eagles may soar, but weasels don't get sucked into jet

engines”

“Hard work pays off in the future.

Laziness pays off now”

•Systems and Cycles• Flux, Source/Sink, Residence time, Feedback mechanisms…

• Hydrological System• Specific reservoirs, Residence time, variability

• Water for the world• An introduction to management issues

Today: Water/Hydrology

Cycle ApproachSome Definitions

Transport and transformation processes within definite reservoirs: Carbon, Rock, Water Cycles

Reservoir: (box, compartment: M in mass units or moles) An amount of material defined by certain physical, chemical, or biological characteristics that can be considered homogeneous

– O2 in the atmosphere– Carbon in living organic matter in the Ocean– Water in the Ocean

Flux: (F) The amount of material transferred from one reservoir to another per unit time (M/s or M/s.L2)

– The rate of evaporation of water from the surface Ocean– The rate of deposition of inorganic carbon (carbonates on marine

sedimentsSource: (I or Q) A flux of material into a reservoirSink: (O or S) A flux of material out of a reservoir

More Definitions…Budget: A balance sheet of all sources and sinks of a reservoir.

If sources and sinks balance each other and do not change with time, the reservoir is in steady-state (M does not change with time). If steady-state prevails, then a flux that is unknown can be estimated by its difference from the other fluxes.

for a control volume this means: dM/dt = I'-O'Turnover time: The ratio of the content (M) of the reservoir to

the sum of its sinks (O) or sources (I). The time it will take to empty the reservoir if there aren’t any sources. It is also a measure of the average time an atom/molecule spends in the reservoir. Or:

0 = M/O (or M/I) Cycle: A system consisting of two or more connected

reservoir, where a large part of the material (energy) is transferred through the system in a cyclic fashion

Atmosphere (0.0155)

Oceans (1400)

Ice (43.4)

Lakes & Rivers (0.13)

Groundwater (15.3)

Evaporation (0.434)

Precipitation (0.398)

Evaporation (0.071)

Precipitation (0.107)

Runoff (0.036)

Transport (0.036)

All reservoir values are in 106 km3 while all fluxes are in 106 km3/yr

Adapted from Berner & Berner (The Global Water Cycle; Prentice Hall, 1987)

The Water (Hydrologic) The Water (Hydrologic) CycleCycle

A Mighty Exchange

The Water Cycle (in detail)The Water Cycle (in detail)The volume (M) of water at the surface of the Earth is enormous: 1.37 109 km3! (total reservoir) – The Oceans cover 71% of the Earth’s surface (29% for the continent masses above sea level)

Reservoir Volume (km3) % TotalBiosphere 0.6 103 0.00004

Rivers 1.7 103 0.0001Atmosphere 13 103 0.001Lakes 125 103 0.01Groundwater 9500 103 0.68Glacial and other land ice (?) 29000 103 2.05

Oceanic water and sea ice 1,370,000 103 97.25

Total 1,408,640 103 100

Adapted from Berner & Berner (Adapted from Berner & Berner (The Global Water CycleThe Global Water Cycle; Prentice Hall, 1987); Prentice Hall, 1987)

Of total yearly evaporation, 84% evaporates from the Oceans and 16% from surface of continents.

However, return to Earth via precipitation: 75% falls directly on the Oceans and 25% on the continents.

During the year, the atmosphere transports 9% of Oceans’ evaporation to the continents!

This water is returned via surface streams and as groundwater

Fluxes (F in 10Fluxes (F in 1033 km km33/yr)/yr)

Precipitation and Precipitation and evaporation are difficult evaporation are difficult to measure precisely to measure precisely over the oceans. They over the oceans. They are mostly estimated are mostly estimated from models and from models and satellite data.satellite data.

Groundwater reservoir Groundwater reservoir estimates bear a estimates bear a inherent error in the inherent error in the fact that they are fact that they are indirectly determined.indirectly determined.

Soil moisture and Soil moisture and evapotranspiration evapotranspiration rates depend on rates depend on indirect measurements indirect measurements and average soil quality and average soil quality and global/regional and global/regional respiration ratesrespiration rates

Errors!Errors!

The simplified residence time turnover timeThe time it would take to empty a reservoir if the sink (O)

remained constant while the sources were zero

0 = M/O (or M/I)

M = 0O

Residence time of water in the atmosphere

M = ?; S = ?; 0 = ?

M = 13 103 km3

S = 297(O) + 99(C) 103 km3/yr = 396 103 km3/yr

Residence Time(years – months – weeks)

0 = 0.033 yr = 12 days!

Replacement ~30 times/year

The simplified residence time turnover timeThe time it would take to empty a reservoir if the sink

(O) remained constant while the sources were zero

0 = M/O (or M/I)

M = 0O

Residence time of water in the atmosphere

M = ?; S = ?; 0 = ?M = 1,370,000 103 km3

S = 334 103 km3/yr (evaporation)

Residence Time(years – months – weeks)

0 = M/S = 4102 yrs!

2) Continental Distribution

• quantitative description applying  the principle of conservation of mass

• for any given control volume at steady state:

dV/dt = 0 = p + rsi + rgi - rso - rgo - et = 0 (all averaged)

• For continents as control volume this can be written as

dV/dt = p - rso - et = 0 (all averaged)

on average this means: p =  rso + et

Continental Mass Balance

the water budget for all land areas of the world is:p=800mm, rs = 310mm, and et = 490mmthe global runoff ration (rs/p) is ~39% there are lots of local and regional variations.

2) Continental Distribution

System Approach…Feedback: All closed and open systems respond to inputs

and have outputs. A feedback is a specific output that serves as an input to the system.

Negative Feedback (stabilizing): The system’s response is in the opposite direction as that of the output. CLOUDS!

System Approach…Positive Feedback (destabilizing): The system’s

response is in the same direction as that of the output.

"Bacteria in a bottle"

0.0E+00

2.0E+17

4.0E+17

6.0E+17

8.0E+17

1.0E+18

1.2E+18

1.4E+18

0 10 20 30 40 50 60

Time (minutes)

Nu

mbe

r o

f ba

cte

ria

59 min

Bottle half full

System Approach…Positive Feedback (destabilizing):

CLOUDS!

Modified from http://water.usgs.gov/watuse/wuto.html

Source, use &disposition of water in the US, (1990)

Surface waters

BRF

Watershed, catchment, drainage basin

“A catchment (watershed, drainage basin) is an area of land in which water flowing across the land surface drains into a particular stream or river and ultimately flows through a single point or outlet on that stream or river”

Measurement techniques

=> precipitation => evapotranspiration

Measurement techniques

dischargeBRF

flow depth (stage)

Colorado Riverhydrograph

Questions:

• When does discharge peak and why?

• The hydrographs were taken at different locations of the river, what is the difference in the hydrographs and why is there one?

• Hydrographs are variable between years

• Discharge often peaks in late winter or spring, snowmelt

• Reservoirs smooth out extremes

Colorado Riverhydrograph

Canada del Oro hydrograph

http://water.usgs.gov

extended periods with no discharge at all!

Groundwater

Hornberger et al., 1998

Groundwater flow is controlled by– differences in water table

(hydraulic head)

– hydraulic conductivity (relation between specific discharge – Vol/t – and hydraulic gradient)

– Hydraulic conductivity depends on both the nature of the fluid (viscosity) and the porosity of the material

Measurement techniques

Hydraulic head, conductivity

Physical flow model

““Access to safe water is a fundamental human need and, Access to safe water is a fundamental human need and, therefore, a basic human right.therefore, a basic human right.

Contaminated water jeopardizes both the physical and Contaminated water jeopardizes both the physical and social health of all people. It is an affront to human dignity” social health of all people. It is an affront to human dignity”

Kofi AnnanKofi Annan – UN Secretary-General on World Water Day – UN Secretary-General on World Water Day

Water: Counting every drop…

“Making prediction is very difficult, especially about the future” – Casey Stengel

Water scenarios: Projected and actual global withdrawals.From Gleick (2000): The World’s Water, 2000-2001

“North America’s abundant water resources represent 14% of the global renewable fresh water”

0

400

800

1200

1600

2000

Pe

r C

ap

ita

(m

3 /yr)

Canad

a

Mex

ico

United

Sta

tes

North

Am

erica

Wor

ld

Annual Freshwater Withdrawals

CanadaMexicoUnited StatesNorth AmericaWorld

Water: Our U.S. Budget

Main loss (66%)

Humans (~2%)

Stream Flow (32%)

“North America’s abundant water resources represent 14% of the global renewable fresh water”

in many areas of the US more water is withdrawn than is renewed* global warming* floods, hurricanes* groundwater and surface water contamination

3 Major Basins providing water to Corpus

Colorado

Nueces

Lavaca

South Texas Coastal Bend:A Case Study

“Making predictions…”

Aquiferrecharge

proposed

Pass through needsfor estuaries

Mary Rhodes pipeline

The case for water quality!“If I die, I will die, but I will not fetch water from another man’s house” –

Bangladeshi villager

The case for water quality!“If I die, I will die, but I will not fetch water from another man’s house” –

Bangladeshi villager

• Arsenic is conservative (high during drought intensive periods!)

• Desalination expensive and exacerbate hypersalinity of lagoons

• Groundwater Bangladesh anyone?

The case for water quality!“If I die, I will die, but I will not fetch water from another man’s house” –

Bangladeshi villager

Concluding Thought

•And after you’ve “heard” this story of great misfortunes, you will no doubt dine well, blaming the author for your own insensitivity, accusing him of wild exaggeration and flights of fancy. But rest assured: this tragedy is not a fiction. All is true”

•Honoré de Balzac