Water - Its Properties and Role in the Environment

Outline:

• Role in early history and science

• Unique chemistry

• Hydrologic cycle - redistribution, climate effects

• Ocean circulation - basic wind & thermohaline

Chemically unique

Exists in all three phases at atmospheric temperatures & pressures

(high melting and boiling points compared to molecules of similar

size It is the only substance that does this!

• High heat capacity (4.2 J/g/K). It stores a lot of heat energy which

makes it a good medium for spreading the planet’s heat

• High heat of fusion (solid to liquid ~ 335 J/g/K) and vaporization

(liquid to gas ~ 2400 J/g/K) so more effectively transfers heat when

changing phase in atmosphere/ocean

Chemically and Physically unique

•Water is physically

unique because it is less

dense as a solid (ice) than

as a liquid.

•The maximum density of

liquid water occurs at 4ºC

Physically Unique

• High surface tension so it forms drops & helps make good cell

membranes

• Dissolve other compounds very easily and so can transport

chemicals (e.g., NaCl, nutrients)

• Mediates or facilitates most chemical reactions in living systems

(e.g., takes water to photosynthesize) - neutral pH

Chemically and

Biologically

Unique

Covalent and Ionic Bonds

Hydrogen Bonds - 10 x stronger than normal

intermolecular (van der Waals)

forces.

100%326,000,000Total water

volume

0.0001%300Rivers

0.001%3,100Atmosphere

0.005%16,000Soil moisture

0.008%25,000Inland seas

0.009%30,000Fresh-water lakes

0.61%2,000,000Ground water

2.14%7,000,000Icecaps, Glaciers

97.24%317,000,000Oceans

Percent of

total

water

Water volume, in

cubic milesWater source

Distribution of water

Hydrologic Cycle (in 103 km3)

Quantitative Hydrological Cycle

several hoursBiological water

8 daysAtmospheric moisture

16 daysChannel network

1 yearsSoil moisture

5 yearsBogs

17 yearsLakes

10000 yearsGround ice of the permafrost zone

1600 yearsMountain glaciers

9700 yearsPolar ice

1400 yearsGround water

2500 yearsWorld Ocean

Period of renewalWater of Hydrosphere

http://www.unesco.org/science/waterday2000/Cycle.htm

Period of Renewal

Aquifers

Freshwater Resources

1407000Flux

(cubic miles / year)

1400 yrs16 daysResidence Time

200000300Volume

(cubic miles)

GroundwaterRivers

Atmospheric circulation

Equatorial Hadley Cells

http://psb.usu.edu/psbdept/faculty/lh/bmet2000/Image56.gif

To see the animated version go to

http://geography.uoregon.edu/envchange/clim_animations/gifs/prate_web.gif

Precipitation

Rain shadow

Global warmingGlobal warming(temperature increase)(temperature increase)

Effects of global warming on water cycleEffects of global warming on water cycle

Speeds up globalSpeeds up globalwater cyclewater cycle

More extreme weather eventsMore extreme weather events

•• DroughtsDroughts

•• StormsStorms

•• FloodsFloods

Projected Changes in Annual Precipitation for the 2050sProjected Changes in Annual Precipitation for the 2050s

Source: The Met Office. Hadley Center for Climate Prediction and Research

The projected change is compared to the present day with a ~1% increase per year in equivalent COThe projected change is compared to the present day with a ~1% increase per year in equivalent CO22

GreenGreen •• = increasing, Brown= increasing, Brown •• = decreasing= decreasing

Global Precipitation TrendsGlobal Precipitation Trends

(% per decade) (% per decade) 1900 - 19941900 - 1994

Source: Watson 2001

U.S. Precipitation Trends: 1901 to 1998U.S. Precipitation Trends: 1901 to 1998

Source: National Climatic Data Center/NESDIS/NOAA

GreenGreen •• = increasing, Brown= increasing, Brown •• = decreasing= decreasing

All stations/trends displayed regardless of statistical significanceAll stations/trends displayed regardless of statistical significance

Extreme Precipitation Events in the U.S.Extreme Precipitation Events in the U.S.

Source: Karl, et.al. 1996.