P l ti G th & U f S ilP l ti G th & U f S ilPopulation Growth & Use of Soil Population Growth & Use of Soil & Water& WaterNREM 461

Dr Greg BrulandDr. Greg Bruland

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I. Population Growth & Use of Soil & Water

A. Hunter-gatherer (HG) lifestyle supported global pop. of ~ (Tillman et al. 2002)

B. Shift to AG lifestyle ↑ global pop. to 800 million

C. Industrial Revolution ~

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D. Rev. Thomas Malthus, English demographer & political economist (1766-1834)political economist (1766 1834)

1. In 1798 wrote:

Po = initial populationr = growth rate

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gt = time

P(t) = Poert

on es( ) o

Pop

ulat

ioR

esou

rc

P(t) = mt + b

Time Limiting factors in nature, i.e. food production stayproduction, stay constant or grow linearly

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Was Malthus’ prediction correct?

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a. Global cereal production doubled from 1960-00 (Tilman et al 02)00 (Tilman et al. 02)

( )

2 Since 1950 proportion of AG land ↑ only slightly

(Tillman 2002)

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2. Since 1950, proportion of AG land ↑ only slightly,even though population doubled (Trewavas 02)

So if we haven’t been farming more land, how have yields i d?

a.

increased?

i.

ii.

iii. iv.

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8(Tillman et al. 2002)

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Temperature & precipitation effects onTemperature & precipitation effects on the sustainability of productive agriculture

(Stewart 1990)1990)

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F Do bling of global food demand e pected in ne t 50 rsF. Doubling of global food demand expected in next 50 yrs (Tilman et al. 2002)

1 Prediction: Modern AG has capacity to meet food1. Prediction: Modern AG has capacity to meet food needs of 8-10 billion people, & ↓ proportion of pop.who go hungry (Tilman et al. 2002)

2. 2000-2002, FAO estimated 850 million people undernourished, 96% in developing countries (2006), p g ( )

a.

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G. Cause for concern

1. To feed 1 person a diverse diet

a Requires 1 hectare (ha) of arable landa. Requires 1 hectare (ha) of arable land (Troeh et al. 04)

b. Most countries now have > people than ha of cropland

c.

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1 1 1 billion people currently lack access to fresh

H. Water Resources & Population Pressure (MEA 06)

1. 1.1 billion people currently lack access to fresh drinking water

2. 2.6 billion people currently lack access to basic sanitation

a. Consequences:

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Percent of the population with access to safe water, 2000

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Water availability/crowding per capita by country, 2000

20(Gleik 2003)

4. Location of rapid growtha. 1750-1950: rapid growth in Europe, N. p g p ,

Americab. 1950-Present: rapid growth in Africa,

Middle East AsiaMiddle East, Asiac. 90% of new pop. will arrive in

developing countries55.

(Chiras et al. 2002)

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6. Global freshwater use doubled from 1960-2000, at ,a rate of 17% decade-1

aa.

(Gleik 2003)

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Review global population stats:Review global population stats:

1 0 to 1 billion 1800:1. 0 to 1 billion, 1800:

2 1 billion to 2 1930:2. 1 billion to 2, 1930:

3 2 billion to 4 1975:3. 2 billion to 4, 1975:

4 4 billion to 6 1999:4. 4 billion to 6, 1999:

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J. How to calculate doubling time of a population, (assuming growth rate constant)

1. Rule of thumb: divide the “magic number” 70 by the l % th tannual % growth rate

2. If annual global growth rate = 1.3%, what’s the doub time of earth’s pop?doub. time of earth s pop?

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Comparison of Developed & Developing Nations in 2000

Developed Developing

Avg Birth Rate 11/1000 25/1000Avg. Birth Rate 11/1000 25/1000

Avg. Death Rate 10/1000 9/1000

Avg. Pop. Growth Rate <0.1-0.25% 1.5-1.7%

Doubling Time 800 years 40 yearsDoubling Time 800 years 40 years

Avg. Pop. Density 23 people km-2 59 people km-2

Avg. Pop. Density 2050 23 people km-2 93 people km-2

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(Chiras et al. 2002, Cohen 2003)

2. Current trends continue world pop. predicted to stabilize at 10 5 billion in 2110stabilize at 10.5 billion in 2110a. if birth rate ↓: 2040 atb. if birth rate ↑: 2130 at

i. 4-6 billion person difference has major implications for S&W use (Kormondy &

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Brown 1998)

3. Urban vs. rural populationa. 1800: 2% of people lived in citiesb. 2000: 47% of people lived in cities c. 1900: no cities w/ > 10 milliond. 2000: 19 cites w/ > 10 million

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4. 5-25% of global freshwater use exceeds long-term accessible supplypp ya. withdrawls exceed rate of renewal, esp. w/ GW

5 Discharges from several of world’s largest rivers5. Discharges from several of world s largest rivers (i.e. Nile, Yellow, Colorado, Amu Darya, Syr Darya) are severely ↓ or absent due to demands from i i ti & b l ti tirrigation & urban population centers

(Gleik 2003)

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Land Damage by Irrigation in the 1980s

Country Million ha of land damaged

% of irr. land damaged

Land Damage by Irrigation in the 1980s

gIndia 20 36

China 7 15

USA 5 2 27USA 5.2 27

Pakistan 3.2 20

World 60.2 24

(UNEP)

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K. Major challenge for AG in 21st century = reconcile ↑world food production w/ greater protection of the environmentenvironment

1. (Trewavas 02)

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“Unless the poorest places of“Unless the poorest places of the world can feed themselves and feel secure, there is no security for thethere is no security for the rest of us.”

(J. Sachs, WCSS 2006)( , )

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