“Water, water everywhere nor any drop to drink…”

Talk by Ron OxburghHong Kong 11January 2002

Material derived from many sources but particularly from Postel et al., Science,1996

2

Water Cycle annual fluxes

RAIN 110 RAIN 390

Land Ocean

Evaporation

Runoff

70 430

40

3

Water

• only 2.5% of the Earth’s water is fresh• 2/3 of fresh water (1.73%) exists as ice• remainder 0.77% = 10,665 km3 (rivers, lakes,

swamps & atmosphere)• all human extraction is from runoff• much is inaccessible• uncertainty in estimates

The Present

Inaccessible Water% Global Runoff % global popln.

Amazon 15 0.4Zaire/Congo 3.5 1.3Tundra rivers 5 0.2

21% of Global Runoff is not useable

6

1990 Global water use and consumption

Use Consumption km3 pa km3 pa %

Agriculture 2880 1870 65Industry 975 90 9Municipaities 300 50 17Reservoir losses 275 275 100TOTALS 4430 2285

Stream flow needs 2350 2350 100

Total as % of Runoff 62% 43%

Different Water Withdrawals

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 2 4 6 8 10 12

distance km

rela

tive

prop

ortio

n of

flow

Series1

Series2

Min. flow

The past

9

Global water withdrawals over time, per cap. & total

01234

1940 1950 1960 1970 1980year

per cap, thou. m3/yr

Total thou. km3/yrUS

10

Population, water withdrawals & irrigation

0

1000

2000

3000

4000

5000

600019

00

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

YEAR

mill

ion

& k

m3/

yr

0

50

100

150

200

250

300

mill

ion

ha

populnWat. withdrawsIrrigated areas

11

Irrigation

• driven by food needs• much of Earth’s surface too steep, too cold

or too dry for cultivation• irrigation allows cultivation in some dry

areas & enhances yield in others• BUT irrigation water is CONSUMED• at present is 80% of consumption• significant energy for pumping

12

Growth in Irrigated land

0.00

50.00

100.00

150.00

200.00

250.00

300.00

1950 1960 1970 1980Year

mil.

ha

OceaniaS.AmericaN.AmericaEuropeAsiaAfrica

Increase in irrigated land area

13

World land use 1700 - 2000

Forest

Pasture

Crops

010002000300040005000600070008000

1600 1700 1800 1900 2000year

mill

ion

ha

14

Rice yields in Japan 600 - 2000

Japanese rice production over time Mather & Chapman p82

t/ha600 0.6800 1

1000 1.61200 1.71400 1.81600 21800 2.51900 2.72000 6

0

1

2

3

4

5

6

7

600 800 1000 1200 1400 1600 1800 2000 2200time

tonn

es /h

a

Irrigated Area Vs World Population 1950 – 2000

0.00

50.00

100.00

150.00

200.00

250.00

300.00

0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0 7000.0

World Population, millions

Irrig

ated

are

as, m

illion

ha

The Future

17

World Population(middle estimate)

EuropeN. America

Latin Amer./Carib.CHINA

INDIA

Rest of Asia

Africa

Oceania

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

1950 1975 2000 2025 2050

peop

le -

mill

ions

Population Growth and Water Needs

0

2000

4000

6000

8000

10000

12000

14000

km3

fres

h w

ater

6000 6500 7000 7500 8000 8500 9000World Population, millions

DeficitAvailableBorrowUSEFlow needsInaccessible

19

What next?

• Water not where needed - population growth in ‘wrong’ places

• Climate change• Novel resources ?

– desalination - expensive in energy– Ice– Pipe-lines -water expensive to transport

20

Santa Barbara story

• 1970s drought• Water only $0.47/m3 - severe W shortage!• Desalination plant and pipe line built• 1996: Water now expensive - $1.55/m3 • demand drops to 61% of pre-drought level• desal. plant unnecessary (now only as back-

up)

Conclusions

• not enough water overall – there will be problems

• so solutions have to be more or less local• New technology• Litigation• War?