The Water (or Hydrologic) Cycle


Fluxes (B&B Fig. 1) of evaporation/precipitation (0.505*10^6 km^3/yr) necessarily balance globally but not locally - evap>ppt over oceans and vice versa

(*10^6 km^3/yr)

continents

oceans

precipitation

0.107

0.398

evaporation

0.071

0.434

continental runoff

0.036

Sources of terrestrial water: meteoritic influx (early accretion of carbonaceous chondrites), outgassing of the planetary interior (subduction recycling), ongoing cometary influx

Distribution of surface water varied widely with time depending on climate change - during glacial periods much more water occurred as ice caps and glaciers on the continents than at present, whereas during warmer periods practically all the continents were ice-free; during the last Pleistocene glacial maximum (18000 yrs BP), sea level was lower by 130 m and the continent water reservoir was about double that at present (~90*10^6 km^3)

Source: Berner EK & Berner RA (1996) Global Environment: Water, Air, and Geochemical Cycles. Prentice Hall


World Water Supply

Location

Surface
Area
(10^
6 km^2)

Water
Volume
(10^
6 km^3)

% Total
Water

Residence
Time

Oceans

361

1230

97.2

103 yr

Atmosphere

510

0.0127

0.001

9 da

Rivers & Streams

-

0.0012

0.0001

14 da

Groundwater

130

4

0.31

~103 yr

Lakes

0.855

0.123

0.009

decades

Ice caps & Glaciers

28.2

28.6

2.15

104 yr
Source: U.S. Geological Survey


Distribution of Colorado River Water

Area

Legal
Entitlements
(km^
3/yr)

Actual
Distribution#
(km^
3/yr)

Lower basin

California

5.461

5.461

Arizona

4.674

2.522

Nevada

0.369

0.369

subtotal

10.455

8.303

Upper basin

Colorado

4.774

2.959

Utah

2.122

1.316

Wyoming

1.292

0.801

New Mexico

1.038

0.643

subtotal

9.225

5.720

Mexico

1.845

1.845

Total

21.525

17.835
# Includes losses to evaporation of 0.740 km^3/yr in the upper basin and 1.110 km^3/yr in the lower basin, and 1.110 km^3/yr inflow to lower basin from local streams.

Source: W.L. Graf (1985) The Colorado River, Resource Publications in Geography, Association of American Geographers, Washington, D.C.


Additional References: