-- CHAPTER 6 -

ARID LANDS AND OTHER BIOLOGICALLY NON-PRODUCTIVE LANDS

TABLE OF CONTENTS
(6-A) -Arid Lands
(6-B) -Hyper-Arid Lands and Deserts - [A] Global Data, [B] Africa, [C] Latin America, [D] Asia, [E] North America, [F] Oceania
(6-C) - Biologically Non-Productive Lands

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(6-A) - ARID LANDS 

Maps of Africa, Asia, Australia, North America, and South America showing the location of extremely arid, arid, and semi-arid regions are found in Ref. (og70D1). These maps can be measured planimetrically to produce the results shown in the table below. (All areas are in units of millions of km2, and include only ice-free land.) Precipitation rates on semi-arid land, arid land, and hyper-arid land can be converted to run-offs using a correlation in the review of Irrigated Land Degradation.
~ ~ ~ ~ ~ |~ ~ ~ ~ ~ Areas
Region~ ~ | Total| Semi~| Arid| Hyper
~ ~ ~ ~ ~ | Land | Arid | ~ ~ |-Arid
Australia | ~7.62| 2.52 | 3.66| 0.00
Africa~ ~ | 29.64| 6.37 | 7.23| 4.50
Cent.Amer.| ~2.79| 0.61 | 0.64| 0.03
S. America| 17.54| 1.74 | 1.20| 0.21
US.(48) ~ | ~7.68| 1.87 | 0.83| 0.04
Canada~ ~ | ~9.22| 0.40 | 0.00| 0.00
Eurasia ~ | 53.79| 8.58 | 8.62| 1.08
Oceania*# | ~0.27| 0??? | 0?? | 0???
Alaska~ ~ | ~1.53| 0??? | 0?? | 0???
Totals ***|130.07|22.09 |22.18| 5.86
(Total of semi-arid + arid + hyper-arid = 50.13)
*# excluding Australia *** Columns may not add due to round off.
Comments: Arid lands receive 10-25 cm. (4-10") of rainfall annually (og85D1). Semi-arid land receives 25-50 cm. (10-20") of rainfall annually (og85D1).

Arid lands (10-25 cm./ year rainfall (se85D2)) cover 12% of the earth's land surface (Ref. 63 of (se90S3)).
Semi-arid (25-50 cm. rainfall/ year (se85D2)) grasslands and woodlands occupy an even larger area.
So total extent of dryland ecosystems is about 1/3 of the earth's land surface (Ref. 103 of (se90S3)).
Comments: "Arid" (above) probably includes hyper-arid (precipitation under 10 cm/ year).

Analysis in the Irrigated land Degradation review:
22.09 million km2 are semi-arid land (25-50 cm. / year of precipitation (se85D2)),
22.18 million km2 are arid land (10-25 cm./ year of precipitation (se85D2))
5.86 million km2 are hyper-arid land. (less than 10 cm./year of precipitation] (se85D2)
50.13 million km2 = Total (hyper-arid +arid +semi-arid) of the above three figures.
Comments: Since it is doubtful that any hyper-arid land is grazed, it appears that 85% of the world's rangeland is semi-arid or arid. Hence (15/85)*43.3 = 7.6 million km2 of rangeland is humid or semi-humid - probably called managed pasture or permanent pasture (land too hilly for crops).

85% of Mexico's land area is either arid or semi-arid (ir97R1). (la)

Australia's arid zone: 5.7 million km2 -- 74% of Australia's land (og70P2). (la)

Around 1900, alfa-grass steppe covered 80,500 km2 in North Africa (20% of arid zone land) (p. 238 of (og70L1)).

Arid land in India and Pakistan: 1.7 million km2 (se86G3) (og86G1) (se86G2). (la) Comments: In most places where rainfall is under 25 cm./ year (classed as arid land), land use is restricted to grazing or irrigated croplands. (la)

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(6-B) - HYPER-ARID LANDS AND DESERTS
 [A] Global Data, [B] Africa, [C] Latin America, [D] Asia, [E] North America, [F] Oceania

[A] - Global Data

5.86 million km2 are hyper-arid land. (less than 10 cm./ year of precipitation] (se85D2) (See Section (5-A)) Comments: This land is essentially vegetation-free.

Principal Deserts of the World (la) (Norris McWhirter, ed., Guinness Illustrated Encyclopedia of Facts, Bantam Books, 1981)
Desert ~ ~ |1000|1000 |Territory
Name ~ ~ ~ | mi2| km2 |
Sahara ~ ~ |3250| 8420| Algeria, Chad, Libya, Mali, Mauritania,
--- ~ ~ ~ ~ ~ ~ ~ ~ ~ |-Niger, Sudan, Tunisia, Egypt, Morocco
Australian | 600| 1550| Australia
Arabian~ ~ | 500| 1300| Saudi Arabia, Yemen,
Gobi ~ ~ ~ | 400| 1040| Mongolia, China (Inner Mongolia)
Kalahari ~ | 200| ~520| Botswana
Takla Makan| 125| ~324| Sinkiang, China
Sonoran~ ~ | 120| ~311| Arizona, California, New Mexico
Namibian ~ | 120| ~311| S.W. Africa (Namibia)
Kara Kum ~ | 105| ~272| Turkmenistan, USSR
Thar ~ ~ ~ | 100| ~259| N. W. India, W. Pakistan
Somali ~ ~ | 100| ~259| Somalia
Atacama~ ~ | ~70| ~181| Northern Chili
Kyzyl Kum~ | ~70| ~181| Uzbekistan-Kazakhstan
Dasht-i-Lut| ~20| ~ 52| Eastern Iran
Mojave ~ ~ | ~14| ~ 35| Southern California
Desierto de|
Sechura~ ~ | ~10| ~ 26| N.W. Peru
Totals ~ ~ |5804|15041| (Global)

Comments: Hyper-arid lands cover about 6 million km2 while arid lands cover about 22 million km2, so the above 15-million km2 figure must also include some arid lands.

World area of desert land: 46 million km2 (Ref. 63 of (se90S2)).
Comments: 46/ 148.9 = 31% of continental area; 46/130 = 35.4% of ice-free land area. This figure probably includes semi-arid, arid and hyper-arid lands. Semi-arid lands are often grazed. Arid lands are sometimes grazed though productivities are extremely low, and livestock grazing is not economically viable.

Ravenstein's 1891 Estimates of Desert Land (See Joel E. Cohen, How Many People Can the Earth Support?, W. W. Norton and Company, New York (1995 )) (Areas are in units of 1000 km2.) (la)
Region~ ~ ~ |Desert| Total| Polar
Europe~ ~ ~ | ~ ~0 | ~9208| ?
Asia~ ~ ~ ~ | 3108 | 38099| ?
Africa~ ~ ~ | 5765 | 29821| ?
Australasia | 1590 | ~8516| ?
N. America~ | ~246 | 16695| ?
S. America~ | ~117 | 17708| ?
Totals~ ~ ~ |10826 |120047| 12662

Comments: A table of major deserts of the world (above) give about 15 million km2 of desert, but hyper-arid regions cover only about 5.9 million km2 (se85D2).
Comments: Total land area above should be about 132,000 for the world's ice-free land, and (Total+ polar) should be about 148,000 for all land, including ice-covered. Perhaps mountains above tree line have been neglected. Also, deserts seem to be under-estimated.
Comments: Other estimates of global ice-covered land give 148,000 - 132,000 = 16,000 km2

Moisture Zones in Africa (Areas are in millions of km2) (se93H1) (M. Hulme, R. Marsh, P.D. Jones, Climate Research, 2 (1992) pp. 1-22) (la)
Moisture~ ~ ~ | ~ Precip.| Area~ | Area
Zone~ ~ ~ ~ ~ |(cm/ year)|1931-60|1961-90
Hyper-Arid~ ~ | 0-10 ~ ~ | 4.51~ | 5.02
Arid~ ~ ~ ~ ~ |10-25 ~ ~ | 6.77~ | 6.80
Semi-Arid ~ ~ |25-50 ~ ~ | 6.21~ | 6.07
Dry, sub-humid| ?~ ~ ~ ~ | 2.64~ | 2.50
Humid ~ ~ ~ ~ | ?~ ~ ~ ~ | 9.72~ | 9.47
Totals~ ~ ~ ~ | -- ~ ~ ~ |29.85~ |29.86
Comments: Since 5.86 million km2 of the Earth's lands are hyper-arid land. (less than 10 cm./year of precipitation] (se85D2) (See Section (5-A)) The above table suggests that a large fraction of the Earth's hyper-arid land is found in Africa (the Sahara Desert?).

In the tropics, deserts occupy 16% of the land ((se75S1), Ref. 16) (la).
Comments: "Desert" probably means arid and hyper-arid lands.
In the tropics, "semi-desert" occupies 11% of the land ((se75S1), Ref. 16) (la)
Comments: "Semi-desert" probably means semi-arid lands.

[B] - Africa

The Namib Desert in Africa stretching along Namibia's 1490-km. Atlantic coastline averages 97 km. in width (Area = 144,000 km2). It is one of the world's most barren regions (se95K1). (la)
Comments: The1981 table below gives an area for the Namib Desert twice as large.

Size of Sahara Desert: 8,633,000 km2 (1980 ); 9,982,000 km2 (1984) (se91T1).

Drylands, including hyper-arid deserts, cover 19.59 million km2 or 65% of the African continent. This area is one-third of the world's drylands. One-third of Africa's drylands is hyper-arid deserts (6.72 million km2). The remaining two-thirds, or 12.87 million km2, comprise the arid- and semi-arid lands of Africa (ir97D1). (la)

[C] - Latin America

Chile's Atacama Desert is described in Ref. (se70C2).
The Peruvian Desert is described in Ref. (se70C2).

[D] - Asia

During 1994-99, China's desertified land grew by 52,500 km2. Deserts now cover more than 25% of China (Frank Langfitt, "Deserts slowly swallowing up China", Pittsburgh Post Gazette, 4/28/02). (la)

The 30,000 km2 Tengry Desert (northwest China) is China's 4th largest desert (It is now merging with the 50,000 km2 Bardanjilin Desert) (se03E1).

The 50,000 km2 Bardanjilin Desert (Northwest China) is China's 3rd largest desert (se03E1).

China's Gobi Desert expanded by over 20,000 miles2 (51,800 km2) in the last half of the 1990s and now affects 40% of China's land (se03U1). Comments: This does not mean 40% of China is desert.

16% of China's land is desert (6/29/99 Xinhua). (la) Comments: Data above give 25% desert in China and data below give 28% desert. Comments: China's land area = 9.597 million km2. So 16% is 1.54 million km2. The 1981 data in the table below gives 1.04 million km2 for the area of the Gobi Desert. Could the difference be interpreted as expansion of the Gobi Desert in the 20 years since 1981?

China's deserts are widely distributed throughout the northern districts. They cover 13% of China's land area (og86W1) (se86W3). (la)

A 2001 survey by China's State Forestry Administration says 28% of China's land mass has been overtaken by desert, with 18% being decimated by effects of overgrazing and deforestation (China Daily reports, 1/31/02).

[E] - North America

Deserts (under 10" of precipitation/ year) cover 25% of 11 western US states (p. 60 of (og91J1)). (la)

[F] - Oceania

Total Australian land stock is 7.7 million km2 (og01F1).

The majority of Australia is hot desert (og01F1).

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(6-C) - BIOLOGICALLY NON-PRODUCTIVE LANDS

Africa's land area = 29.7 million km2 (se87L1). In early 1980s, 13.09 million km2 were shrubs, desert, urban and miscellaneous uses (se87L1). (la)

1986 FAO tabulation of global land-use (se90B1) (See below) gives 41.5% deserts, wastelands, urban areas, and ice-covered areas -- areas supporting little biological activity. (la)
Comments: 41.5% of 148.9 million km2 of continental area = 61.8 million km2 of little biological productivity.
Comments: 58.5% of 148.9 million km2 of continental area = 87.1 million km2 of biologically productive land.

40-45% of the earth's land surface (including ice-covered land) is barren desert, polar areas, or high mountain areas (se51S1) (FAO data). (la)
Comments: 0.4* 148.6 million km2 = 59 million km2. This suggests an area of reasonably biologically productive land of 148.6 - 59 = 90 million km2. Urban or built-up areas worldwide total 4.745 million km2 [(se00W1), p. 24], so the remainder would be about 85 million km2. The total area of (grazing lands + forested lands + croplands) could easily account for this area.

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