~ CHAPTER 2 ~
PARAMETERS USEFUL FOR PERSPECTIVE AND CALCULATION
Edition 9 of March 2010 (
NOTE: PART (2-D-i) AND BEYOND ARE IN ANOTHER FILE.
(2-A) ~ Sizes of Small Things ~
(2-B) ~ Areas and Volumes of Large Things ~
~ (2-B-a) ~ Partitioning The Planet's Surface Area ~
~ (2-B-b) ~ Water Impoundments ~
~ (2-B-c) ~ Areas and Volumes of Fresh Water Bodies ~
(2-C) ~ Precipitation and Runoff ~
(2-D) ~ Land-Use Data and Estimates of Potential Cropland ~
~ (2-D-a) ~ Original Vegetation Distribution (Global and Continents)
~
~ (2-D-b) ~ Forested Land ~
~ (2-D-c) ~ Crop Lands (active and fallowed) ~ [Dc1]~Inventory, [Dc2]~Growth Rate, [Dc3]~Grain-land, [Dc4]~Fallowed Cropland,
~ (2-D-d) ~ Grazing Lands ~
~ (2-D-e) ~ Biologically Unproductive Lands (Global) ~
~ (2-D-f) ~ Land-Use Distribution (Global) ~
~ (2-D-g) ~ Definition of Cropland, Grassland, Forest ~
~ (2-D-h) ~ Land-Use Data (Tables) (by nation and Region) ~
~ (2-D-i) ~ Potential Croplands ~ [Di1]~Global, [Di2]~Regional Data, ~
(2-E) ~ National Land-Use Information ~
~ (2-E-a) ~ Asia
~ [Ea1]~General, [Ea2]~Central Asia, [Ea3]~Asian Sub-Continent, [Ea4]~Far East, [Ea5]~Southeast Asia, [Ea6]~Middle East, ~
~ (2-E-b) ~ Africa
~ [Eb1]~General, [Eb2]~North Africa, [Eb3]~Eastern Africa, [Eb4]~Central Africa, [Eb5]~West Africa, [Eb6]~Southern Africa, ~
~ (2-E-c) ~ North America ~ [Ec1]~Canada. [Ec2]~US Land Basics, [Ec3]~US Fallow Land, [Ec4]~US Floodplains, [Ec5]~US Cropland Inventory, [Ec6]~US Land-Use Inventory, [Ec7]~Changes in US Cropland Area, [Ec8]~Potential for Conversion to Cropland, [Ec9]~Conversion of US grasslands to cropland, [Ec10]~US Croplands Maps, Tables and Charts, [Ec11]~Removals from the US Cropland Inventory, [Ec12]~US Forest Land Inventory Changes, ~
~ (2-E-d) ~ South America and Central America ~ [Ed1]~Amazon Basin, [Ed2]~Brazil, [Ed3]~Andean Mountain Region, [Ed4]~Central America, [Ed6]~Southeast South America, ~
~ (2-E-e) ~ Europe and Australia ~ [Ee1]~Australia, [Ee2]~Europe, ~
(2-F) ~ Climatic Data ~
NOTE: The notation (su1) means that the data is used in the document analyzing the sustainability of the productivity of the world's food, fiber and water supply systems. (See elsewhere in this website.)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - se2
SECTION (2-A) ~ Sizes of Small Things ~
Sizes ((87W2), p. 5):
zooplankton ~ ~ ~ | lx10-5 to lx10-1
m.
silt~ ~ ~ ~ ~ ~ ~ | 2x10-6 to 4x10-5 m.
phytoplankton ~ ~ | 10-6 to 10-1 m.
clay~ ~ ~ ~ ~ ~ ~ | 2x10-7 to 2x10-6 m.
Brownian motion ~ | 10-6 m.
dissolved matter~ | Under 4x10-7 m.
bacteria~ ~ ~ ~ ~ | 3x10-7 to 3x10-6 m.
viruses ~ ~ ~ ~ ~ | 10-8 to 10-7 m.
colloids~ ~ ~ ~ ~ | 1x10-9 to 2x10-7 m.
humic acids # ~ ~ | 2x10-9 to 4x10-8 m.
particulate matter| over 4x10-7 m.
fulvic acids #- ~ | 1x10-9 to 3x10-8 m.
* The most commonly cited molecular weights of these organic acids are in the range of 20-50,000 (Steelink, 1963, in (70O1)).
# A soil component
SECTION (2-B) ~ Areas and Volumes of Large Things ~ [a]~
Partitioning of the World's Surface Area, [b]~Areas and Volumes of Water Impoundments, [c]~Areas and Volumes of Fresh Water Bodies,PART (2-B-a) ~ Partitioning the World's Surface Area ~
Of the total tropical land area of 40 million km2, 8.6% is arable, 1.0% is in permanent crops and 25.1% is in pastures. The total cultivated land is about 4.18 million km2. Most of this land is under subsistence farming practices (99B1). Comments: 8.6% of 40 million km2 is 3.4 million km2 of arable land - a number smaller than the total cultivated land area. Something is wrong here.
Components of the Earth's Surface: (areas in millions of km2) (la)
Earth's Surface Area ~ ~ |510.0|(68H1)
Ocean Surface Area ~ ~ ~ |361.0|((92Q1), p.76)
Continent Area ~ ~ ~ ~ ~ |148.9|(82M1)
Glaciated Area ~ ~ ~ ~ ~ | 15.8|(82M1)
Ice-Free Area~ ~ ~ ~ ~ ~ |133.1|(=148.9-15.8)
Ice-Free Area~ ~ ~ ~ ~ ~ |130.0|(78B3)
Ice-Free Area~ ~ ~ ~ ~ ~ |133.6|(91W1)
Inland Drainage Basins **| 33.2|(82M1)
** "endoreic" runoff
Hence, land drained by rivers to oceans = 133.1-33.2 = 99.9 million km2 (exoreic runoff) (82M1). Ref.(68H1) (See below) gives exoreic runoff area of 99.8 million km2.
Regions of semi-arid climates occupy nearly 1/3 of the earth's land area (ice-free land area?) and are home to about one billion people and are responsible for nearly 20% of the world's food production (
06B1) (la). Comments: Is that food production in units of tonnage or dollar-value?It has been estimated that, today, 83% of the world's free-ice lands are impacted, directly or indirectly, by humans (
Sanderson E. W., Jaiteh M, Levy M. A., Redford K. H., Wannebo A. V., Woolmer G., "The Human Footprint and the Last of the Wild". Bioscience 52 (2002) pp. 891-904.) Comments: The area of ice-free land in the world is about 131 million km2. Some 83% of 131 is 109 million km2. But only about 90 million km2 are reasonably biologically productive (See elsewhere in this review.). (su1)Sediment Deliveries to Oceans by Continent
(68H1) (la)(Other sediment data is found in Section (4-G-e))
* ice-free land areas
** Areas are from Livingston, 1963 (68H1)
Some Useful Data on Land Masses (68H1) (la)
(Areas in millions of square miles and in (millions of km2))
This leaves 39.2 (148.9-13.0-2.2+0.34-34.2 = 99.8 million km2) of ice-free land contributing runoff and water-borne sediments to oceans (68H1).
Land above 3000 meters elevation (about 10000 ft.) is about 5% of the world's terrestrial surface (97G2) (la). Comments: 148.9 * 0.05 = 7.45 million km2 above 3000 meters. Tree-lines are rarely above 3000 meters, so this land is almost certainly rocks, tundra, low shrub, etc. with little if any potential for serving as cropland, grazing land or forest land.
Land above 1000 meters elevation is about 27% of the world's terrestrial surface. ((97G2), p.17) (la)
PART (2-B-b) ~Areas and Volumes of Water Impoundments ~
Total volume of water on Earth is 1.41 million km3 (Ref. 30 and 31 of Ref. (90W1), p. 166). If spread over the entire surface of the Earth, it would be 3.0 km. deep ((90W1), p.166). If spread over the 71% of the Earth occupied by ocean, its depth would be 3.0/ 0.71= 4.2 km.
Total volume of water stored in man-made reservoirs: 5000 km3, or 11% of the annual runoff from land to oceans (87W1).
A more recent estimate gives 6000 km3, (13% of annual runoff of 47,000 km3/ year) ((90W1), p. 170). Over 30,000 storage basins have been built around the world Some 75% of these were built in past 35 years ((90W1), p. 170).
Dam-based storage basins cover 400,000 km2 ((90W1), p.170). (la)
In the US, over 40,000 km2 have been covered by artificially impounded water (56G2) (unpublished USGS and US SCS estimates). Comments: Obsolete data. US impounded water area is 40,000/ 400,000 = 10% of world's total, even though US land area is only 7% of global land area.
PART (2-B-c) ~ Areas and Volumes of Fresh Water Bodies ~
The volume of fresh water in the world's rivers and streams at any one time is 1999 km3 (76 in Europe; 533 in Asia, 184 in Africa, 236 in North America, 946 in South America, and 24 in Australia) ((90W1), p.166). Comments: Something is wrong here. The total volume of man-made reservoirs, alone, is 6000 km3 (See Section (2-B-b) above), and all this must be fresh water. So probably the 1999 km3 figure above does not include dam impoundments. How about lakes?
Lakes, rivers and streams occupy 1.7% as much area as (ice-free?) land does (77B2). (1.7% of 130 million km2 = 2.2 million km2.) (la)
Lake Inventory by Continent (Analysis of Encyclopedia Britannica data) (Areas are in km2) (la)
These data cover lake-sizes down to about 600 km2. If one plots total area of lakes larger than Size X vs. X, and extrapolates down to X = 0, one obtains a total (global) area of lakes and inland seas of 1.40 million km2. Data for this extrapolation are given below:
Minimum Area (km2)
If total area of inland seas (Caspian+ Aral+ Dead = 412,000 km2) is deducted, one obtains a total global lake area of about 1.0 million km2. If the total area of lakes+ rivers+ streams is 2.2 million km2 (See estimates above.), then this implies a total area of world's rivers and streams of 1.2 million km2. (la)
Lake Baikal (north of Mongolia), (largest body of fresh water in the world) contains 80% of former Soviet Union's supply of fresh water (90F1).
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Top of this Section-Areas and Volumes of Large ThingsSECTION (2-C) ~ Precipitation and Runoff ~
See Chapter 11, Section (11-F) for a compilation of databases containing data on water withdrawals by nation and region.
Humans use 60% of freshwater run-off (Postel S. L., Daily G. C., Ehrlich P. R. "Human appropriation of renewable freshwater", Science 271 (1996) pp. 785-788). Comments: The question now arises - How much is consumed? The bulk of human use is for irrigation that typically consumes about 60% due to transpiration, salt buildup etc.
A world map of annual precipitation is contained in A. N. Strahler, The Earth Sciences, Harper and Row, New York (1963) p. 681 (68H1). Average rainfall (precipitation) on land is 100,000 km3/ year (=26-27"/ year) (=67.3 cm/ year) (Putnam, 1964) (68H1).
World-wide runoff is 0.82 ft3/ sec/ mi2 = 33 million ft3/ sec. = 11.1"/ year (=28.2 cm/ year) = 29,500 km3/ year (Durum, 1960 and 1968) (68H1).
The water (precipitation) input to the 99.9 million km2 of lands draining into oceans = 37,400 km3/ year (Baumgartner and Reichel, 1975, in (82M1)). Comments: Clearly, most precipitation evaporates from the land rather than running off. Percent transpiration loss = (67.3-28.2)/ 67.3= 58% = 58,000 km2/ year, giving a total runoff of (100,000-58,000) = 42,000 km2/ year (some of which is endoreic). Thus the 37,400 km3/ year figure represents only runoff, not total precipitation.
The total volume of precipitation received at the Earth's surface is equivalent to 577,000 km3/ year. (=113 cm/ year =44.5 inches/ year). Continents (29% of the Earth's surface) account for 20% (115,400 km3/ year) of precipitation, and 12.5% (72,125 km3/ year) of transpiration loss (87W1). The difference (115,400-72,125) results in an annual runoff of 47,000 km3/ year to oceans (87W1). Comments: Mistake in subtraction?? (115,400-72,125 = 43,275, not 47,000). Compare to Baumgartner-Reichel's figure, above, of 37,400 km3/ year.
Mean precipitation over land = 86.4 cm/ year (87W1).
Annual runoff in contact with soil and rock on the land surface = 47,000 km3/ year (87W1).
A map of global river runoff (in mm.) is on p. 168 of Ref. (90W1).
A map of global ground-water flow to rivers is on p. 169 of Ref. (90W1).
As much as 6% of global river runoff evaporates through human manipulation - mainly irrigation, but also from reservoirs (Ref. 3 of (94D2)). In the Colorado River, 32% of flow is evaporated from reservoirs (Ref. 23 of (94D2)), and 64% is consumed by irrigation (94D2). (Note: This is also in the irrigated land file.)
River Runoff and Groundwater Discharge Data by Region (km3/ year) ((90W1), p. 167)
(Col. 2 = Total River Runoff = Col. 3 + Col. 4)
(Col. 3 = Ground-water Discharge to Rivers)
(Col. 4 = Surface Runoff)
(Col. 5 = Water withdrawn for Irrigation ((90W1), p. 172))
(Col. 6 = Water withdrawn for Domestic and Municipal Consumption ((90W1), p.173)
(Col. 7 = Water withdrawn for Use in Industry ((90W1), p.173)
(Notes: Ref. (90W1) also gives data on consumptive use and recycled water pertinent to Columns 5, 6 and 7. Col. 5, 6 and 7 pertain to the 1980s)
Some Basic Data on Major Rivers
((70P1), p. 17)Relation between Runoff and Precipitation (58L1)
Fig.1 of Ref. (58L1) plots this on a log-log plot. (Precipitation is in units of inches per year) (Runoff (line 2) is in inches per year.) (Runoff (line 3) is in cm/ year.)
Precipitation| 7.8 |10.0 |15.0 |20. |30. | 40. |50. |60.
Australia: A rainfall map is on p. 306 of Ref. (70P2).
Mexico: A map of runoff (mm/ year) is in Ref. (76W2), p. 142.
United States:
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Top of this Section-Precipitation and RunoffSECTION (2-D) ~ Land-Use Data and Estimates of Potential Croplands [Da]~Original Vegetation Distribution, [Db]~Forested Land, [Dc]~Croplands, [Dd]~Grazing Lands, [De]~Biologically Unproductive Lands, [Df]~Land-Use Distribution, [Dg]~Definition of Cropland, Grassland, Forest, [Dh]~Land-Use Data (Tables), [Di]~Potential Cropland,
See Chapter 11 Section (11-F) for a compilation of databases on the areas and population densities of nations and regions of the world.
Part [Da] ~ Original Vegetation Distribution (Global and Regional) ~
World's vegetation, prior to historically widespread human disturbance (35J1) (la)
Land Category - - - - - - | % of land area
Tropical forests~ ~ ~ ~ ~ | 13
Boreal forests~ ~ ~ ~ ~ ~ | ~9
Mid-latitude mixed forests| ~7
Mediterranean scrub forest| ~1
Grasslands~ ~ ~ ~ ~ ~ ~ ~ | 19
dry land~ ~ ~ ~ ~ ~ ~ ~ ~ | 17
Mountains ~ ~ ~ ~ ~ ~ ~ ~ | 18
Polar ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 16
Total ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |100%
(Total is 30% forest+ 19% grassland+ 51% unproductive (last 3 categories))
Part [Db] ~ Land Use data ~ Forested Lands ~
See Chapter 11 Section (F) for a list of large databases pertinent to the topic of forested lands,
As much as 70-80% of on-going deforestation, both tropical and temperate, is associated with the spread of agriculture (94K3).
About 25% of earth's land surface (including ice-covered land) is forested (51S1) (FAO data). Comments: 25% of 148.9 = 37.2 million km2
FAO's 1986 tabulation (90B1) of global land-use gives 27.1% forest (including open forests and savannas). (See below) (la)
Ref. (78B3), p. 109, gives 40 million km2 as the world's forested area. Comments: This must include both open and closed forests. (la)
Ref. (90W1), p. 268, gives 40.74 million km2 as the world's forested area in 1985-87 (la). Soils underlying 95% of the remaining tropical forests are infertile and degrade easily through erosion, laterization and other processes once the vegetative cover is removed (Ref. 30 of (90W1), p.107). Thus they become unproductive a few years after trees are removed and require a fallow period to recover fertility.
Forest Land Categories of Major Global Regions (million km2)
(63U1) (la)
Region- - - -| Forest ~ | Forests~ | Land
- - - - - - -| Land** ~ | Total~ ~ | Area
North America| 7.50(40%)| 7.10(38%)| 18.75
Cent. America| 0.76(28%)| 0.71(26%)| ~2.72
South America| 8.90(51%)| 8.30(47%)| 17.60
Africa ~ ~ ~ | 7.10(24%)| 7.00(24%)| 29.70
Europe ~ ~ ~ | 1.44(31%)| 1.38(29%)| ~4.71
USSR ~ ~ ~ ~ | 9.10(42%)| 7.38(34%)| 21.44
rest of Asia | 5.50(20%)| 5.00(19%)| 27.00
Pacific *#*~ | 0.96(11%)| 0.92(11%)| ~8.42
World~ ~ ~ ~ |41.26(29%)|37.79(26%)|130.34*
* The reason for the difference between this number and the Earth's actual ice-free land area (133 million km2 (82M1)) (See Section (2-B-a)) is unknown (Greenland's ice-free area = 0.342 million km2
(91W1)).
** Includes "unstocked" forest land.
*#* Includes Australia.
Part [Dc] ~ Land Use Data ~ Crop Lands (Active and Fallowed) ~ [Dc1]~
Inventory, [Dc2]~Growth Rate, [Dc3]~Grain-land, [Dc4]~Fallowed Cropland, ~Sub-Part [Dc1]~ Croplands ~ Inventory ~
Temperate croplands cover 6.9 million km2 (93S2).
See Chapter 11, Section (F) for a list of large databases of interest to the issue of land-use data including agricultural land data and irrigated cropland data.
As transport systems and urbanization expands, 100,000-350,000 km2 (about 1%/ year) of cropland a year are being lost. The average per-capita cropland, worldwide, has diminished to 0.25 hectare, or about half the amount needed to provide diverse food supplies similar to those in the US and Europe. In 80 countries, water demands exceed supplies - 300 cities in China suffer from inadequate water supplies (
David Pimentel, "Last Orders Please ... Room is Running Out at the Global Dinner Table" 7/2/02). Comments: Most other estimates of cropland lost to abandonment, salinization, and urbanization give a figure of 100,000 km2/ year, so Pimentel's estimate of 7/2/02 may be too high.A global map of areas converted to agriculture and urban or built-up areas is on p. 25 of (
00W1).Some 14.06 million km2 of cultivated land in the world (2 million are irrigated) (Ref. (78B3), p. 109). Comments:
Irrigated area around the yea 2000 was about 2.7 million km2.
Some 14.737 million km2 of cropland (Section (2- D-h)) (90W1).
Ref. (81B2), p. 97-99, gives a table of arable areas in 13 regions of the globe during 1951-75 (USDA data).
Global totals (in million km2) are: 12.75 in 1951-1955, 13.83 in 1961-1965, and 14.77 in 1971-1975. (ha/ capita dropped from 0.48 to 0.39 over this 25 years) (81B2).
Some 15 million km3 are used to produce crops (11% of world's ice-free land) (1986 UN FAO tabulation).
About 45% of the world's agricultural (cropland + pasture -not range) land is "steep" (slopes in excess of 8%) (
00W1). (la) Comments: This is not very useful, since "steep" pasture is of minor concern, while "steep" cropland is of significant concern.Cropland Inventories ((
00W1) Table AF.2) (la)Sub-Part [Dc2]~ Croplands ~ Growth Rate ~
Amount of land planted to crops increased until 1981. Since then, the area of newly reclaimed cropland has been offset by that lost to degradation and/or converted to non-farm use (90B1). Comments: Some more recent data dispute this (
00W1).Post-WWII cropland area-growth slowed to under 0.5%/ year (85O1).
As much as 50% of the growth in food output during 1900-1950 resulted from expanded cropped acreage (85O1).
Per-capita arable area shrank from 0.5 ha. to less than 0.33 ha. during 1950-1985 (85O1).
In the 1970s, the world's cropland area had a net gain of nearly 0.7%/ year (94K3). In 1990, net cropland gain was 0.35%/ year, largely due to deforestation (94K3).
Total (global) cropland area expanded 16,000 km2/ year (0.1+%/ year) during 1979-1994. (FAO, 1995 Production Yearbook, (Rome, 1996) Comments: S. Postel, in her 1999 book "Pillar of Sand" contends that since cropland losses are often not fully counted in official statistics, net cropland expansion could well be close to zero. She also contends that possibilities for opening up new cropland are mostly in areas where long-term crop production potentials are relatively low.
FAO statistics indicate that the total area in agriculture (croplands + grazing [pasture?]~lands) expanded slowly between 1966-1996 -from 45.5 to 49.2 million km2 (0.27%/ year - 123,000 km2/ year) (
00F1).The US and western Europe have been removing land from agriculture over the past 30 years, and Oceania has been removing land for the past 20 years. These 3 regions have removed 490,000 km2 from agricultural production [during the past 30 years?]~(
00F1). Comments: Falling food prices may have contributed to cropland abandonment.Sub-Part [Dc3]~ Croplands ~ Grainland ~
In the mid-1990s, 1.0 million km2 were used to grow the world's rice crop. About 800,000 km2 (of this) are wetlands (99B1).
Global grain land area growth: +0.7%/ year during 1950-1981, and -0.5%/ year during 1981-1992 (93B1). Comments: Part of this could be a result of expansion of soybean area.
Global grain-harvested area is plotted vs. time (1950-1988) in Ref. (88B4). Typical values: 6 million km2 (1950); 6.5 (1960); 6.9 (1970); 7.2 (1980), 6.9 in 1988. (la)
Area planted to rice worldwide has not increased since 1980 (94R1). Comments: Part of this may be due to soybean-growing area expansion.
Sub-Part [Dc4]~ Croplands ~ Fallowed cropland ~
Summer fallowing is a practice used in dryland agriculture to retain moisture content of the soil. It also reduces the soil organic matter (SOM) content of the soil because exposed soil without a vegetation cover can release carbon to the atmosphere (99B1).
Fallowed Cropland (in millions of km2) (la)
Canadian farmland left fallow (uncultivated) is expected to decline 3% in 1992 to 78,400 km2 - lowest in 52 years (92U1).
Until recently, as many as 240,000 km2 in the US have lain fallow as a result of payment-in-kind programs, annual set-aside requirements, and mandatory conservation (94L1).
The fallow system in the West African Sahel region was used to preserve soil fertility. That system has almost disappeared. Farmers in some regions now cultivate their land year-around, and with low levels of fertilization, causing the soils to quickly lose their productivity (
07N1).PART [Dd] ~ Grazing Lands ~
Brazil has over 2 million km2 of savanna. These are used extensively as pasturelands made up of introduced grasses, which sequester carbon deep in the soil (99B1).
The UNEP (UN Environment Program) has called for a moratorium on the expansion of large mechanized farms in Sudan's central semi-arid regions, warning that it was a "future flashpoint" for conflicts between farmers and pastoralists (
08U2). Comments: Conflicts between farmers and pastoralists are becoming increasingly common throughout Africa as farmers are forced onto semi-arid lands due to a shortage of undeveloped arable land.Globally, 38 of the 131 million km2 of ice-free land area have been converted to agriculture and urban- or built-up areas. Agricultural conversions to croplands and to "managed" pastures affect 33 million km2 ((
00W1), p. 24). Urban or built-up areas occupy 4.75 million km2 ((00W1), p. 24). Comments: Apparently "managed pastures" does not include rangeland, since total grazing land includes about 32 million km2. The above numbers come from satellite data and the PAGE analysis ((00W1), p. 52). The FAO (00F1) estimates 37% (48.5 million km2) in agriculture based on national production statistics. The main difference apparently comes from the fact that the FAO counts all permanent pasture - including rangeland. (la)Grazing lands comprise 31 million km2 of the Earth's land area (76H2). (Obsolete data)
Some 20% of the earth's land surface (including ice-covered lands?) is in "grasslands" (grasses, legumes, herbs and shrubs) (51S1) (FAO data). (Obsolete data)
FAO's 1986 tabulation (90B1) of global land use gives 21.8% pasture and rangeland. (See below) Comments: 21.8% of 133.1 million km2 (ice-free land) = 29 million km2.
Ref. (90W1) gives 32.155 million km2 of permanent pasture, but correcting errors in its table of national data gives 28.656 million km2. (See Section (2 -D-h).) A further analysis (See Review of Grazing Land Degradation) gives 32.7 million km2.
Savannas cover 10 million km2 of tropical Africa (92C1) (la). Comments: These are believed to have once been forestland.
Dregne and Chou examined degradation-induced percentage losses of land productivity in the world's dry regions (Ref.17 of (97C1)). Using FAO data they found that 51 million km2 of land fell into the "dry" category (39% of the earth's ice-free land). 85% of this land was used at rangeland (43.3 million km2), 9% as rain-fed croplands (4.6 million km2), and 3% as irrigated croplands (97C1). Comments: In the Irrigation Degradation review, an analysis finds 22.09 million km2 of semiarid land, 22.18 million km2 of arid land, and 5.86 million km2 of hyper-arid land. Total (hyper-arid +arid +semi-arid) = 50.13 million km2. Since hyper-arid land is not grazed, it appears that 85% of rangeland is semi-arid or arid, so (15/85)*43.3 = 7.6 million km2 of rangeland is humid or semi-humid. (la)
Arid lands (10-25 cm./ year rainfall (85D2)) cover 12% of the earth's land surface (Ref. 63 of (90S3)). Semi-arid (25-50 cm. rainfall/ year (85D2)) grasslands and woodlands occupy an even larger area, so the total extent of dryland ecosystems is about 1/3 of the earth's land surface (Ref. 103 of (90S3)). Comments: "Arid" (above) probably includes hyper-arid (precipitation under 10 cm/ year). (la)
A map showing all of the world's savannas is found in Ref. (83B3).
Cultivation is expanding into rangelands with 30-50 cm. of rainfall/ year. As a result, good grazing lands are becoming poor cropland (Ref. 10 of (85D2)).
The total area of land used for agriculture rose from 45.5 to 49.3 million km2 in 1996. (IFPRI data) (
00L1) Comments: These numbers apparently refer to cropland plus grazing land. Virtually all of this increase would have to occur on grazing lands, since croplands expand by only a few tens of thousands of km2/ year (if at all). A 10% increase in grazing lands in one year seems doubtful.Ravenstein's 1891 Estimates of Land Categories and the Population each can Support (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)
Comments:
A table of major deserts of the world (elsewhere in this document) give about 15 million km2 of desert, but hyper-arid regions cover only about 6 million km2.(la)Part [De] ~ Land Use Data ~ Biologically Unproductive Lands (Global) ~
Desertification occurs in drylands, which span a third of the earth 's land surface in over 110 countries. Each year 120,000 km2 are lost to deserts (globally). (UNEP data) (
00E1).Degradation of drylands caused by over-cultivation, overgrazing, deforestation and inefficient irrigation affects an estimated 20% of the world's drylands. (UNEP data) (
00E1).See Chapter 11 Section (11-F) for a compilation of databases that have data of interest to the topic of biologically unproductive lands.
Ice-Covered Lands:
Greenland's ice-covered land area = 2.2-0.34 million km2 = 1.9 million km2 (encyclopedia data). (la)
Size of Antarctica = 13 million km2. (la)
Total (global) ice-covered area = 15.8 million km2 (See Section (2-B-a).) (la)
About 40-45% of the earth's land surface (including ice-covered land) is barren desert, polar areas, or high mountain areas (51S1) (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 areas now cover roughly 4.5 million km2, so the remainder would be about 85 million km2. The total area of (grazing lands + forested lands + croplands) could easily account for this area.
In 1986, FAO tabulation of global land-use (90B1) (See below) gives 41.5% deserts, wastelands, urban areas, and ice-covered areas - areas supporting little biological activity. (la) Comments:
Some 87.35 million km2 of land worldwide are being used for permanent and annual crops and permanent pasture or being maintained as forest and woodland (Ref. 16 of (97C1)) (UNFAO data, 1990). Comments: This number is something on the order of the amount of the world's reasonably biologically productive land. Adding urban lands and wetlands would give 93.35 million km2 for the amount of reasonably biologically productive land in the world. The 87.35 million km2 figure suggests a non-productive area of (131-87.35 = 43.65 million km2. (la)
Vegetated Surface area of the Earth: 117 million km2 (95D3). Comments: Apparently this definition includes lands too cold to grow even one crop, since most discussions of reasonably biologically productive land consider only about 85-90 million km2 of the Earth's 131 million km2 of ice-free land to fall into this category, and this includes about 4.75 million km2 (
00W1) of developed (urban) land. (la)Of the 130 million km2 of ice-free land in the world, 26 million are not arable because the temperature is below freezing over 9 months of the year. In an added 19 million, there are fewer than three months of the year when available moisture from rain, snow, or water stored in the soil exceeds potential transpiration from plants and soil, and there are no practical sources of irrigation water. Climate alone, therefore limits potentially arable land to 85 million km2 (76R1). Comments: Also subtract urban lands (See Chapt.6) and excessively steep lands. Other estimates of reasonably biologically productive land give about 90 million km2 (See elsewhere in this document.) (la)
Desert Land Data: (la)
World area of desert land: 46 million km2 (Ref. 63 of (90S2)). 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 and arid lands are often grazed.
Size of Sahara Desert: 8,633,000 km2 (1980); 9,982,000 km2
(1984) (91T1).
Chili's Atacama Desert is described in Ref. (70C2).
Peruvian Desert is described in Ref. (70C2).
China's deserts are widely distributed throughout the northern districts and cover 13% of China's land area (86W3).
The 30,000 km2 Tengry Desert (northwest China) is China's 4th largest desert (now merging with the 50,000 km2 Bardanjilin Desert) (
Principal Deserts of the World (la)
(Norris McWhirter, editor, Guinness Illustrated Encyclopedia of Facts, Bantam Books, 1981)
Go to
Top of this Section-Land-Use data and Estimates of Potential CroplandPart [Df] ~ Land-Use Distribution (Global) ~
Resources used and/or available per capita per year in the US, China, and the world to supply the basic needs of humans, (FAO. (2006). FAO, Agricultural Statistics Global Outlook. FAO Statistics Division. Food and Agricultural Organization, United Nations, Rome. Retrieved September 2009 from FAO
http:// faostat.fao.org/portals/_faostat/documents/pdf/world.pdf); (Goklany, I. M. (2001). Modern Agriculture. Property and Environment Research Center Reports 19(1): pp.12-14. Retrieved September 2009 from PERC http://www.perc.org/search.php)
Resources |
U.S. |
China |
World |
Cropland (ha) |
0.59 |
0.10 |
0.22 |
Pasture (ha) |
0.79 |
0.30 |
0.52 |
Forest (ha) |
1.01 |
0.15 |
0.61 |
Total |
3.06 |
0.71 |
2.00 |
Water (liters×106) |
1.70 |
0.45 |
0.60 |
Fossil fuel |
9,500 |
700 |
2,100 |
Total Global land area: 130.49 million km2 (UNEP data) (
00E1).More than 47% of the earth's (ice-free land) surface (i.e., 6.1 billion hectares) (61 million km2) is dryland. These lands are the habitat and source of living for about 20% of the world's population (
00E1).Table 3.2 (p.118) Global Land Use - Areas unchanged (km2) and Conversions (1987-2006) (km2/ year) (
07A1) (la)
From |
To |
To Woodland/ |
To |
To |
Losses |
Gains |
Net |
Forest |
39,699 |
30 |
98 |
2 |
-130 |
+57 |
-73 |
Woodland/ |
14 |
34,355 |
10 |
2 |
-26 |
50 |
24 |
Farmland |
43 |
20 |
15,138 |
16 |
-79 |
108 |
29 |
Urban Areas |
n.s. |
n.s. |
n.s. |
380 |
0 |
20 |
20 |
Totals |
- |
- |
- |
- |
-235 |
235 |
0 |
Table 3.5 (p.130) Categorization of the world's land by water availability (in %): (
07A1) (la)
Hyper-arid |
7% |
<200 mm rainfall/ year |
~ ~ |
Arid |
12% |
<200 mm rainfall/ year |
~ ~ |
Semi-Arid |
18% |
200-800 mm rainfall/ year |
drought 1 year in 2 |
Dry Sub-humid |
10% |
800-1500 mm. rainfall/ year |
~ ~ |
Moist Sub-humid |
20% |
1500-2000 mm rainfall/ year |
floods, waterlogging |
Humid |
33% |
>2000 mm rainfall/ year |
floods, waterlogging |
Total: |
100% |
~ ~ |
~ ~ |
Presumable only ice-free lands are considered here, so the total land area would be about 130 million km2
Table 4.8 ~ Arable land in use, cropping intensities and harvested land (
03B3) (la) ~The FAO's 1986 tabulation of global land-use gives (90B1): (la)
Comments: This final figure neglects ice-covered areas such as Antarctica (13 million km2) and 2.2 million-0.34 million = 1.9 million km2 of Greenland. The usually accepted figure for total land area (including ice covered land) is 148.9 million km2. If these percentages are converted to a total-land-area basis, the 1986 FAO data changes to:
Comments: About 2% of the Earth's landmass is wetland (swamps, marshlands, bogs, etc.) (See Section (3-C)). The table in Section (3-C) gives 4-6 million km2 of swamps, marshes, bogs, peatlands, lakes and streams. Where does this fit into the above breakdown?
Some 87.35 million km2 of land worldwide are being used for permanent and annual crops and permanent pasture or being maintained as forest and woodland (Ref.16 of (97C1)) (UNFAO data of1990). Comments: This number is something on the order of the amount of the world's reasonably biologically productive land. Adding urban lands and wetlands would give 93.35 million km2 for the amount of reasonably biologically productive land in the world. (la)
World's Protected Areas (Environment, 32(1) (1990) p. 37) (la)
(Areas are in units of 1000 km2)
Part [Dg] ~ Definition of Cropland, Grassland, Forest ~
Dregne and Chou (Ref. 18 of (97C1)) estimate the value of production of irrigated cropland at $62,500/ km2/ year ($9,500/ km2/ year for rain-fed cropland and $1,750/ km2/ year for rangelands). (la)
In most places where rainfall is under 25 cm./ year, land use is virtually restricted to grazing. (la)
Above 35 cm./ year, continuous dryland farming is possible (70P3). (la)
About 20"/ year (51 cm./ year) of precipitation is considered to be the minimum for dryland farming in Colorado ((81S1), p. 77). (la)
Forests generally occur only where precipitation exceeds 60 cm/ year (24"/ year) (Ref. 64 of (df91M1)). (la)
About 20-25% slope (9-11o) is generally considered the maximum that can be cropped in the US ((74C1), p. 70). (la)
Chinese government policy prohibits cultivation on slopes over 28% (82B2). (la)
In Java, slopes over 50% are being cultivated on a continuous basis (90H2).
Go to
Top of this Section-Land-Use data and Estimates of Potential CroplandPart [Dh] ~ Land-Use Data (Tables) ~
Drawing from the works of hundreds of researchers, the "Global Change" study (Chapter 3 of Refs. (
04S1) and (05C1)) concluded that perhaps 50% of the world's ice-free land surface has been transformed by human action; the land under cropping has doubled during the past century at the expense of forests, which declined by 20% over the same period. Comments: In recent decades, cropland expansion has also been at the expense of semi-arid grazing lands, and grazing land expansion has been at the expense of tropical forestland, particularly in Latin America. Both of these expansions require significant fallow periods to maintain productivity, and semi-arid croplands involve significant risk of wind erosion and prolonged droughts -recall the US "Dust Bowl" in Oklahoma and surrounding states and Kazakhstan's "Great Lands" debacle.See Chapter 11, Section (F) for a list of large databases of interest to the subject of this chapter. Among them are:
AQUASTAT (Database) http://www.fao.org/ag/agl/aglw/aquastat/dbase/index2.jsp
This FAO online database (global scope) provides information on water and agriculture (with some data on population and land degradation) by countries organized by categories such as land use, water use, land under irrigation, sources of irrigation, techniques, drainage, crops and intensification, and more. (2/11/05) A massive amount of easy-to-use, tabular, global and national data is given on this website. Below is a list of the tables and their column headings found on this website. (Reviewer visited this website on 2/15/05.)
TABLE 1 ~ Land-Use Data
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Area of the Country (ha)
Col.4 ~ Area of arable & permanent crops (ha)
Col.5 ~ Arable Area (ha)
Col.6 ~ Permanent crops (ha)
TABLE 2 ~ Water Resources Data
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Average Precipitation (1961-1990) (mm/ year)
Col.4 ~ Average Precipitation (1961-1990) (km3/ year)
Col.5 ~ Total renewable water Resources (km3/ year)
Col.6 ~ Groundwater produced internally (km3/ year)
Col.7 ~ Surface water produced internally (km3/ year)
Col.8 ~ Overlap in Surface- & Groundwater (km3/ year)
TABLE 3 ~ Land Under Irrigation
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Irrigation Potential (ha)
Col.4 ~ Year of Irrigation Data
Col.5 ~ Full/ Partial Control of Irrigation (ha)
Col.6 ~ Spate Irrigation (ha)
Col.7 ~ Equipped Wetlands (ha)
Col.8 ~ Total Irrigation (ha)
Col.9 ~ Other Cultivated Wetlands (ha)
Col.10 ~ Deep Water/ Flood Recession Cropping Area (ha)
Col.11 ~ Water-Managed Area (ha) (sum of previous 4 columns)
TABLE 4 ~ Source of Irrigation Water
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Full/Partial Control of irrigation area irrigated with surface waters (%)
Col.4 ~ Full/Partial Control of Irrigation area irrigated with ground water (%)
Col.5 ~ Full/ Partial Control of Irrigation area irrigated with non-conventional sources (%)
TABLE 5 ~ Irrigated Crops and Intensification
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Part of equipped area actually irrigated (%)
Col.4 ~ Irrigated Crops (ha)
Col.5 ~ Portion of grain production irrigated (%)
TABLE 6 ~ Population (2000)
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Total Population
Col.4 ~ Rural Population
Col.5 ~ Urban Population
TABLE 7 ~ Water Use (FAO Estimates for the Year 2000)
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Agricultural Water Use (km3/ year)
Col.4 ~ Agricultural Water Use (%)
Col.5 ~ Domestic Water Use (km3/ year)
Col.6 ~ Domestic Water Use (%)
Col.7 ~ Industrial Water Use (km3/ year)
Col.8 ~ Industrial Water Use (%)
Col.9 ~ Total Water Use (km3/ year)
TABLE 8 ~ Irrigation Techniques
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Surface Irrigation (ha)
Col.4 ~ Sprinkler Irrigation (ha)
Col.5 ~ Micro-irrigation (ha)
TABLE 9 ~ Environment ~ Drainage
Col.1 ~ Continent
Col.2 ~ Country
Col.3 ~ Area Salinized by irrigation (ha)
Col.4 ~ Total Drained Area (ha)
Key information from "
Population Growth Leading to Land Hunger", Earth Policy Institute 1/23/03 (www.earth-policy.org/Updates/Update21.htm )Analysis of Land-Use by Nation and Region
Some forest areas (1980) data are from "World Development Report 1991", Oxford U. Press (1991) (Ref.(91W1)) Table 33 (Laos, India, China, Myanmar, Malaysia).
(Land Areas are in units of 1000 km2 of ice-free land)
Data for Myanmar (Burma), Mongolia, Malaysia, Lao P.D.R., North Korea, South Korea, Kampuchea, Japan, India, Cyprus, China Iran, Iraq, Israel, Jordan, Kuwait, Lebanon are inconsistent in Table 17.1 of Ref. (90W1). Corrections were obtained from 1994 Environmental Almanac (World Resources Institute (WRI), Houghton Mifflin Co. (1994) (94W2)).
Forest ~ Belize, S. Korea, Bangladesh, Kampuchea, Indonesia, Cyprus.
Pasture ~ Belize, Myanmar, Malaysis, Kampuchea, Bhutan, Laos P.D.R., Cyprus.
Total areas ~ Belize, Barbados, Laos P.D.R., Kampuchea.
Cropland ~ Laos.
Satellite data (Pittsburgh Press, 11/8/96) gives China's cropland area = 1.25 million km2 instead of 0.97 million km2 reported in Ref. (90W1).
NOTE: Check the databases in Chapter 11 for more recent data. The data below is obsolete and is of historical interest only.
Central - - - |Land |Crop|Irrig|Graz.|Forest|Population
America - - - |Area |Land| Land| Land| Land |(millions)
Year~ ~ ~ ~ ~ | 1987|1987|'85-7| 85-7|'85-87| 1990
Cent. America*| 2622| 377| ~ 69| ~934| ~ 667| 146
N./ CENTRAL - |Land |Crop|Irrig|Graz.|Forest|Population
America - - - |Area |Land| Land| Land| Land |(millions)
South - - - -| Land|Crop|Irrig|Graz.|Forest|Population
AMERICA - - -| Area|Land| Land| Land| Land |(millions)
South - - - - -| Land|Crop|Irrig|Graz.|Forest|Population
Asia- - - - - -| Area|Land| Land| Land| Land |(millions)
NORTH ASIA AND| Land|Crop|Irrig|Graz.|Forest|Population
EUROPE - - - -| Area|Land| Land| Land| Land |(millions)
EUROPE *~ ~ ~ | 4727| 1401| 166| ~839| 1571| 497
EUROPE *# ~ ~ | 4730| 1401| ~ 0| ~840| 1572| 498
OCEANIA / - - -| Land|Crop|Irrig|Graz.|Forest|Population
AUSTRALIA - - -| Area|Land| Land| Land| Land |(millions)
OCEANA, AUST.* | 8386| ~483| ~22| 4512| 1552| ~25
OCEANA, AUST.*#| 7887| ~496| ~ 0| 4515| 1563| ~27
TOTALS *~ ~ ~ |129152|15000|2409|32656|40434|5273
TOTALS *# ~ ~ |130225|14731| ~ 0|32155|40744|5292
TOTALS *##~ ~ |130765|14731|2210|32155|40744|5292
ICE-COVERED ~ | 15800|
* Line 1 for each region: total of individual nation data.
*# Line 2 for each region: regional total from Table 17.1 of (90W1).
*## Line 3 of final totals: final totals from Table 17.1 of (90W1).
Land areas that suffer physical and chemical constraints that prevent use as croplands (90W1) (la)
(Also See Section (3-K) for more data on this topic.)
(All areas in Column 3 are in units of 1000 km2.)
Columns 2/3 Total land area (2) and Area of no inherent soil constraints.
Col.4/5 Area constraint: steep slopes (4) and shallow soils ( 5).
Col.6/7 Poor drainage (6)- - - - - - - - - - - -and Tillage problems ( 7).
Col.8/9 Low nutrient retention (8) - - - - - -and Aluminum Toxicity ( 9).
Col.10/11 Phosphorous Fixation hazard (10) and low K reserves - (11)
Col.12/13 Excess Soluble salts (12) - - - and Excess of sodium- (13).
Region
Col.2| ~ ~3| ~ ~4| ~ 5| ~ 6| ~ 7| ~ 8| ~ 9| ~10| ~11| 12| 13
Africa
30113| 4427| 2609|3978|1982|1118|3966|5083|2051|6149|513|444
Central America
2740 | 5859| ~688| 441| 154| 187| ~69| 242| 151| 273| ~4| 19
South America
18983| 2076| 3290|1926|2128| 270|1172|8428|5997|9136|243|251
Southeast Asia
8976 | ~331| 2614| 907|1086| 758| 300|2413|1905|2575|173| 12
Southwestern Asia
6780 | ~456| 1614|1739| ~60| ~64| 370| ~41| ~21| ~41|490| ~0
Totals
67592|13149|10815|8991|5410|2397|5877|16207|10125|18174|-|-
The total land area of these 5 regions is further categorized by Ref. (90W1) by climate in Table 18.6 (p. 287) that is repeated below. (Areas in 1000 km2); (la)
Comments:
"Semi-arid" lands rainfall: 25-50 cm./ year (85D2). "Arid" lands rainfall: 10-25 cm./ year. Comments: North America, Europe, Central Asia, Australia and Oceania are omitted.Arable land areas ("No inherent soil constraints") of these 5 regions are further categorized (90W1) by climate as repeated below. (Areas in 1000 km2); (la)
Land Use and Population in Developing Countries
(Ref. 2 of (82D1)) (la)(of cultivated land)
Land Use and Population (Developing vs. Developed Countries) (la)Land Areas Converted to Regular Cropping
Go to
Top of this Section-Land-Use data and Estimates of Potential Cropland