CHAPTER 4 ~ GLOBAL SOIL EROSION ~
Edition 9 of March 2010 (
Updated October 2010)

NOTE: Chapter 4 Sections (4-G) and beyond are in another file.

~ TABLE OF CONTENTS ~

(4-A) ~ Specific Cropland Soil Erosion Data ~ [A1]~General, [A2]~Table of Specific Erosion Data by Continent, [A3]~Table of Specific Erosion Data for Various Land-Uses, [A4]~Canada, [A5]~China, [A6]~US, ~
(4-B) ~
Gross Soil-Loss and Soil-Organic-Matter Loss Data ~ [B1]~Gross Erosion Data, [B2]~Africa, [B3]~Anthropogenic Effects, [B4]~Canada, [B5]~US, [B6]~Far East, ~
(4-C) ~
Shifting Agriculture ~ [C1]~Table of Cycle Times, [C2]~Carrying Capacity under Shifting Cultivation, [C3]~Tropical Cropland Lifetimes, ~
(4-D) ~
Wind Erosion Data ~ [D1]~Africa, [D2]~Australia, [D3]~Asian Sub-Continent, [D4]~Central Asia, [D5]~US, [D6]~Far East, [D7]~Middle-East, [D8]~Generally,
(4-E) ~
Cropland Loss to Urbanization, Chemical Contamination and Erosion ~
(4-F) ~
Cropland Loss to Salinization and Water-Logging ~ [F1]~Global, [F2]~North America, [F3]~Latin America, [F4]~Middle East, ~
(4-G) ~
Sediment Delivery ~
~ (4-G-a) ~
Sediment Chemistry ~
~ (4-G-b) ~
The Upper End of Sediment Delivery ~ [Gb1]~Fraction of Erosion not entering a Waterway, [Gb2]~The Dependence of Sediment Delivery Ratio on Sediment Load, [Gb3]~Extremes in the Time-Variation of Sediment Delivery, [Gb4]~Dependence of Sediment Delivery on Drainage Basin Size, [Gb5]~Dependence of Sediment Load on Runoff, [Gb6]~Ceylon, [Gb7]~China, [Gb8]~Nepal, [Gb9]~US, ~
~ (4-G-c) ~
Sediment Trapping in Reservoirs ~ [Gc1]~General, [Gc2]~Rates (%/ year) of Depletion of Reservoir Capacity due to Siltation (table), [Gc3]~Capacities of Major Reservoirs (table), [Gc4]~Reservoir areas of hydroelectric dams (table), [Gc5]~North Africa, [Gc6]~Southeast Asia, [Gc7]~Canada, [Gc8]~China, [Gc9]~Latin America, [Gc10]~Asian Sub-Continent, [Gc11]~US, [Gc14]~Sub-Saharan Africa, ~
~ (4-G-d) ~
Bed Load Contributions to Sediment Delivery ~
~ (4-G-e) ~
Sediment Transport to Oceans ~ [Ge1]~General, [Ge2]~Suspended Sediment Yields of Selected Rivers (table), [Ge3]~Data for Major Rivers of the World (table), [Ge4]~Major Sediment-Yielding Rivers of the World (table), [Ge5]~Average Sediment Discharge to Oceans (table), [Ge6]~Suspended Sediment Discharge from Continents (table), [Ge7]~Sediment Yields of Rivers to Oceans (table), [Ge8]~Estimates of Suspended Sediment Reaching the Oceans (table), [Ge9]~Yellow River, [Ge10]~Peruvian Rivers, [Ge11]~Great Lakes, [Ge12]~Southeastern US, [Ge13]~Sediment Deposited at River Mouths, ~
~ (4-G-f) ~
Dissolved-Solids Transport to Oceans ~
(4-H) ~
Grazing Land Erosion ~
(4-I) ~
Deforestation-caused Erosion ~ [I1]~General, [I2]~Italy, [I3]~California, [I4]~Southeast Asia, [I5]~Madagascar, [I6]~Nepal, [I7]~USSR, ~

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - se4

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.)

Comments:

Evaluating the magnitude of topsoil loss involves, first, breaking the loss up into its basic components, and then evaluating each component. The global rate of topsoil loss is taken, in this document, to be the sum of 8 components:

* total sediments minus non-topsoil sediments.

Each component is evaluated either in this document or in a companion document on irrigation-system degradation. Erosion sediments deposited in lakes can be largely neglected. Because various land-uses differ so strongly in their productivity, it is also important to attempts to quantitatively identify the sources of topsoil loss, apportioning the losses among:

A high degree of accuracy should not be expected of topsoil loss evaluations, since the phenomenology is complex. Despite massive amounts of research on sediment delivery and various other aspects of the issue, and the importance of the issue, rough estimates appear to be the best that can be accomplished. The low status of knowledge in the field of sediment delivery provides perhaps the main source of uncertainty in this study (90M1), (89N1), (83W2). But any carefully structured study may set up a reference point for future, more refined analyses, and this, alone, may justify the effort.

SECTION (4-A) ~ Specific Cropland Soil Erosion Data ~ [A1]~General, [A2]~Table of Specific Erosion Data by Continent, [A3]~Table of Specific Erosion Data for Various Land-Uses, [A4]~Canada, [A5]~China, [A6]~US, ~

Comments: Much work has been done studying soil loss under a wide variety of conditions. These measurements, unfortunately, do not translate readily to estimates of global rates of soil loss because erosion-measurement sites tend not to be selected at random. For example, erosion rates are rarely measured on flat alluvial plains where erosion rates are negligible; erosion rates tend to be measured most in developed nations where erosion rates tend to be much less that in "developing" nations, and few measurements exist of soil erosion on grazing land despite the nearly universal practice of over-grazing, and the very large sediment loads carried by rivers draining grazing lands (82W1), (81S1).

Part [A1] ~ Cropland Soil Erosion Data ~ General ~

Soil erosion on cropland ranges from about 13 tons per hectare per year (tonnes/ ha/ year) in the US to 40 tonnes/ ha/ year in China (Pimentel, D., and Wen, D. (2004). China and the World: Population, Food and Resource Scarcity. In Tso, T. C., and He, K. (editors), Dare to Dream: Vision of 2050 Agriculture in China. China Agricultural University Press, Beijing, pp. 103-116.)

Worldwide, topsoil erosion averages 30 to 40 tonnes/ ha/ year, or 30- to 40-times faster than the replacement rate of topsoil (Pimentel, D. (2006). "Soil Erosion: A Food and Environmental Threat." Environment, Development and Sustainability 8: pp.119-137.

Between 1945 and 1990, an estimated 20 million km2 of agricultural land (almost 18% of the earth's vegetated land) has been degraded as a result of human activity. Of these, an estimated 12 million km2 (almost 11% of the earth's vegetated land) has been moderately or strongly degraded (90O2).

A global assessment commissioned by the UNEP found that almost 11% of the earth's vegetated land has been moderately or strongly degraded, implying that productivity has been significantly reduced (90O2). The extent of degradation is estimated to be particularly high in Africa, where about 3.2 million km2 are moderately or strongly degraded. (99P1)

Today, about 1.9 billion hectares (19 million km2) of land worldwide are affected by land degradation (United Nations (1997): Dryland degradation keeping hundreds of millions in poverty. Press Release. Secretariat of the United Nations Convention to Combat Desertification, Geneva, Switzerland.)

This year (1998), as in previous years, about 21 million hectares (210,000 km2) of cropland will become so degraded that crop production becomes uneconomic, and about 6 million hectares (60,000 km2) of land will be irreversibly lost for production. (von Baratta, M. (Editor) (1998): Der Fischer Weltalmanach. Fischer Taschenbuchverlag, Frankfurt am Main, Germany.)

The livelihoods of more than 900 million people in some 100 of the world's 180 countries are now directly and adversely affected by land degradation (United Nations (1994): Earth Summit - Convention on Desertification. Proceedings of the United Nations Conference on Environment and Development (UNCED), Rio De Janeiro, Brazil, pp. 3-14 (June 1992) Department of Public Information, United Nations, New York, USA.)

Estimates of degraded land by region as a percentage of cultivated land are: Australia 16%, Europe 25%, North America 26%, Asia 38%, South America 45%, Africa 65% and Central America 74% (Overall 38% of today's global cultivated land base (99B1)). About 15% of the global total of cultivated land base has been taken out of production (presumably as a result of degradation, not urbanization, etc.) (99B1).

Global average soil erosion rates from croplands are estimated at 5 tonnes/ ha/ year for water erosion and 3 tonnes/ ha/ year for wind erosion. Assuming 1.3 Gt./ year erosion by water and 0.3 Gt./ year erosion by wind and a delivery ratio of 10% (96W3), total sediment displaced to other lands from croplands is estimated at 16 Gt./ year (99B1).

Of the estimated 13-20 million km2 of degraded soil worldwide, as much as 75% may be in the tropics (99B1).

An assessment by International Soil and Reference Information Centre (ISRIC) found that, of the 115 million km2 of vegetated land on Earth, 17% was degraded, largely through erosion, and 16% could no longer support crops. The main causes, according to the survey, were deforestation and farming practices such as overgrazing (04K1). Comments: Other analysts contend that the global area of reasonably biologically productive land is on the order of 90 million km2 -not 115 million, and about 4.75 million of that is now urbanized.

Stanley Wood, senior scientist at the International Food Policy Research Institute (IFPRI) says, "As a global problem, soil loss is not likely to be a major constraint to food security" (04K1). Comments: Does this statement consider soil loss to urbanization of agricultural lands? Are river bottom sediments a part of this analysis?

A map of the world that plots severity of soil losses (tonnes/ ha/ year) is in (85D2) for arid regions.

Soil erosion rates are highest in Asia, Africa and South America (3000-4000 tonnes/ km2/ year), and lowest in the US and Europe (1700 tonnes/ km2/ year) (Ref. 16 of (95P1)).

In a February, 1995 issue of Science, David Pimentel and associates cite a book by Norman Myers (Gaia: An Atlas of Planetary Management, Anchor and Doubleday, Garden City NY (1993)) in stating that the global rate of soil erosion is 75 Gt./ year (97C1).

Reports of losses exceeding 10,000 tonnes/ km2/ year are common for individual plots, especially on sloping terrain, in many developing countries (Ref. 46 of (96G2)).

Topsoil losses in developing countries average 3000 tonnes/ km2/ year (97P3). Comments: Is this for croplands? Is this for grazing lands? If forested areas were included, this figure would be impossible to believe.

About 80% of the world's agricultural land suffers from moderate- to severe erosion, and 10% suffers slight-to-moderate erosion (Ref. 9 of (95P1)).

Soil loss rates on almost all "sloping" soils under cultivation far exceed soil formation rates (Ref. 24 of (83S1)).

Before the early 1990s, no reliable estimates of the amount of soil erosion around the world were available, let along estimates of productivity consequences (97C1). Comments: P. Crosson seems unaware of the Fournier study (60F1).

Part [A2] ~ Specific Erosion Data by Continent ~

Some Specific Cropland Soil-Erosion Data from Around the World
Location- - - - - - - - - - - -|Erosion Rate|
- - - - - - - - - - - - - - - -|(t/km2/year)|References
Africa
Niger (Majjia Valley) ~ ~ ~ ~ ~ ~ | ~ ~ 2000| (88P1),p.93
Rwanda (average)~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 1000| (88L2)
Rwanda (maximum)~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ -28600| (88L2)
North of Equator (cropped land) ~ |1000-4000|88L1,Ref.30,52
Madagascar~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |2500-4000|88L1,Ref.13
Zimbabwe (degraded rangeland) ~ ~ | ~ ~<9000| (90C1)
Zimbabwe (communal lands) ~ ~ ~ ~ | ~ ~ 5000| (92T1)
Zimbabwe (average) -(30% runoff)~ | ~ ~ 4940| (92T1)
Zimbabwe (cont. corn)(35% runoff) | ~ ~ 7410| (92T1)
Zimbabwe (cont.maise)(20% runoff) | ~ ~ 3370| (92T1)
ASIA:
China (Loess Plateau)(Yellow R.)~ | ~ ~ 6500| 89P2,Ref.12
China's cultivated loess (" -" )~ | ~ ~10000| 86P1,Ref.6
China Yellow R. watershed average | ~ ~ 2700| 81R1
India (Deccan black soil region) |4000-10000| 86P1,Ref.5
India (See Ref.(92S1) for a map of Indian soil erosion.)
Java (Tjatjaban catchment)~ ~ ~ ~ | ~ ~ 6625| 67D1
(reservoir trap data, so total erosion is much larger)
Philippines (as high as)~ ~ ~ ~ ~ | ~ 40,000| 95P1,Ref.1
Russia (Baltic Seashore region) ~ | ~ ~ 5900| 84B2,p.60
Russia (Rostov region)~ ~ ~ ~ ~ ~ | ~ ~ 4600| 84B2,p.60
Russia (Transcaucus region) ~ ~ ~ | ~ ~ 3200| 84B2,p.60

(In above 3 Russia cases erosion is due largely to bare fallow periods.)

NORTH AMERICA: ~ ~ ~ ~ ~ ~ ~ ~ ~ |t/km2/year| Reference
W. Kiowa County, CO (Cl.IV land) | ~ ~ 4490 | 81S1, p.78
Colorado ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 2470 | 84D1
Florida Everglades croplands ~ ~ | ~ ~33700-| 76F1
Illinois (average) ~ ~ ~ ~ ~ ~ ~ | ~ ~ 1500 | 84S1, 80U2
Illinois (worst 40%) ~ ~ ~ ~ ~ ~ | ~ ~ 2470 | 84S1
Iowa (1949)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 4740 | 83B1
Iowa (1974)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 3860 | 83B1
Iowa (1977)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 2220 | 80U2
Iowa (unprotected, sloping)~ ~ ~ | ~ ~ 2930 | 77B1,Ref.11
Iowa ("current") ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 3000 | 95P1,Ref.13
Minn. (Olmstead Co.)(average)~ ~ | ~ ~ 2470 | 88U3
Minn. (Olmstead Co.)(top 2.4%) ~ | ~ ~ 8890 | 88U3
Missouri ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 2450 | 80U2
New Mexico ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |2690-4040 | 81S1
Palouse (conventional tillage) ~ | ~ ~ 5600 | 82O1,Ref.2
(parts of Washington, Oregon, Idaho)
Palouse (minimum tillage)~ ~ ~ ~ | ~ ~ 1100 | 82O1,Ref.2
Palouse (15-25% slope, 1977) ~ |11200-22400 | 80U2
Southern Mississippi Valley~ ~ ~ | ~ ~ 4490 | 80U2
Tennessee (soybean fields) ~ ~ ~ | ~ ~ 4490 | 85R1
Texas (Gaines County)~ ~ ~ ~ ~ ~ | ~ ~ 8980 | 81S1,p.89
- - (Mainly wind erosion on dryland cotton monoculture)
Wisconsin (5 watersheds, SW Wis.)| ~ ~ 1520 | 77B1
US ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 2700 | 78B1
US ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 1350 | 76P2
US (5 billion tons/ year)~ ~ ~ ~ | ~ ~ 2690 | 76P2
US ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 3140 | 76P2
US (1982) (90W1,p.116, Ref.106)~ | ~ ~ 1630 |

Central America - - - - - - - - - - - |t/ km2/year| Refs.
Costa Rica (slash/ burn cult.)~ ~ ~ ~ | ~ ~ 72600-|(90W1)
Haiti - - - - - - - - - - - - - - - - |t/ km2/year| Refs.
typic silty clay, 35% slope, maize~ ~ |40200-48300|(90P2)
silty clay loam, 70% slope,maize,beans| ~ ~ ~26000|(90P2)
typic loam, 55% slope, maize, beans ~ |16800-44200|(90P2)
typic soudy clay,35% slope,maize,beans| 7400-18400|(90P2)
sandy clay rhodudent,60% slope, maise | ~ ~ ~37000|(90P2)
sandy clay loam,75% slope, sorghum~ ~ | ~ ~ ~27600|(90P2)
sandy clay ustropent,55% slope,sorghum| ~ ~ ~38400|(90P2)
Jamaica (as high as)~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ ~40000|(95P1)

South America - - - - - - - - - |t/km2/year| Reference
Ecuador (Santa Catalina near Quito)
- Typical volcanic soils, 14% slope| 7400 |(91N1)
- (a slope less than on most croplands in the highlands)
Peru (Atakualpa) (1978-1980)
Treatment I ( runoff= 37 cm/ year)~| 4940 |(90A3)
" -II (water runoff= 27 cm/ year)~ | 4390 |(90A3)
" III (water runoff= 31 cm/ year)~ | 5210 |(90A3)
" -IV (water runoff= ~9 cm/ year)~ | ~800 |(90A3)

(I = bare soil fallow)
(II = corn-cowpea-potato-peanut-cassava, rows follow max. slope, no fertilizer)
(III= corn-cowpea-potato-peanut, rows follow max. slope, with fertilizer)
(IV = same crops as II; rows follow max. slope, mulch+ min. tillage, w/fertilizer)
Peru (Amaru site, 1976-77 season)
Treatment I (runoff= 22 cm/year)~ | 14800 | (90A3)
~ " -II (water runoff= 20 cm/year)| 11900 | (90A3)
~ " III (water runoff= ~7 cm/year)| ~ 130 | (90A3)
~ " -IV (water runoff= 14 cm/year)| ~4600 | (90A3)
~ " -V (water runoff = 23 cm/year)| ~7200 | (90A3)

(I = bare soil)
(II = fallow + burning, corn-cowpea-potato, no organic input or tillage, rows follow maximum slope)
(III= pasture)
(IV = potato-corn-potato-corn, rows follow maximum slope, mulch tillage)
(V = fallow-pineapple, rows follow maximum slope, no organic input or tillage)
Peru (Santa Ana Site, 1975-1979) (Runoff in mm/ year [tonnes/ km2/ year]~)
Treatment|Runoff~ ~ |Reference
I~ ~ ~ ~ |186 [ 410]| (90A3)
II ~ ~ ~ |307 [1180]| (90A3)
III~ ~ ~ |184 [ 570]| (90A3)
IV ~ ~ ~ |295 [1070]| (90A3)
V~ ~ ~ ~ |125 [ 320]| (90A3)

(I = continuous fallow)
(II = potato-corn-potato-corn, rows follow maximum slope, no organic input or tillage)
(III= potato-corn-potato-corn, contoured rows, no organic input or tillage)
(IV = potato-corn-potato-corn, rows follow maximum slope, green manure incorporated before each crop)
(V = wheat-corn-potato-oats, rows follow maximum slope, mulch (no incorporation and maximum tillage).

Part [A3] ~ Specific Erosion Data for Various Land Uses
Land Use: ~ ~ ~ ~ ~ ~ ~ ~ ~ |t/km2/year| References
Corn-wheat-clover ~ ~ ~ ~ ~ ~ ~ | ~ 610|(81B3)(84B3)(84B2)
Corn-wheat-meadow ~ ~ ~ ~ ~ ~ ~ | ~2000| (957S1
~(8% slope, 4.9" runoff)
Corn-wheat-meadow ~ ~ ~ ~ ~ ~ ~ | ~ 380| (57S1
~(3% slope, 8.4" runoff)
Corn-Oats ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~1400| (57S1
~(3% slope, 11.7" runoff)
Corn-corn-oats-wheat-sw. clover | ~ 900| (57S1
~(3% slope, 8.8" runoff)
Corn-oats-sweet clover~ ~ ~ ~ ~ | ~ 700| (57S1
~(3% slope, 8.4" runoff)
Corn-wheat-sweet clover ~ ~ ~ ~ | ~ 450| (57S1
~(3% slope, 7.9" runoff)
Continuous alfalfa~ ~ ~ ~ ~ ~ ~ | ~ ~22| (71R1, p.89
Continuous corn ~ ~ ~ ~ ~ ~ ~ ~ | ~1707| (81B1, p.82
Continuous corn ~ ~ ~ ~ ~ ~ ~ ~ | ~4910| (76E1, p.129
Continuous corn ~ ~ ~ ~ ~ ~ ~ ~ | ~4420| (81B3, 84B3
Continuous corn (US)**~ ~ ~ ~ ~ | ~5380| (76P2
Corn, continuous, 0.5-3% slope~ | ~4600| (90G3
~(lost 36.7cm in 100 years)
Continuous corn ~ ~ ~ ~ ~ ~ ~ ~ | 11500| (57S1
~(8% slope; 8.2" runoff)
Continuous corn (WI) (16% slope)| 19980| (76P2
Continuous wheat~ ~ ~ ~ ~ ~ ~ ~ | ~2270| (84B3, p.11
Continuous wheat (US)*# ~ ~ ~ ~ | ~1730| (76P2
Continuous wheat (Aust.)~ ~ |6000-20000| (87H2, Ref.9
Continuous corn across contour~ | ~4940| (71R1, p.89
Continuous corn along contour ~ | ~ 770| (71R1, p.89
corn-corn-soy bean-soy bean ~ ~ | ~3940| (88S2
Continuous corn ~ ~ ~ ~ ~ ~ ~ ~ | ~3500| (88S2
corn-corn-barley-barley ~ ~ ~ ~ | ~2910| (88S2
corn-corn-alfalfa-alfalfa ~ ~ ~ | ~2240| (88S2
(Above 4 cases on 7% slope, 90m. slope length, Guelph loam)
Continuous cotton ~ ~ ~ ~ ~ ~ ~ | ~4940| (53L1
Continuous cotton ~ ~ ~ ~ ~ ~ ~ | ~4470| (81B1, p.82
Continuous cotton (USA)*# ~ ~ ~ | ~4440| (76P2
Continuous sorghum~ ~ ~ ~ ~ ~ ~ | ~2829| (81B1, p.82
Continuous soybeans ~ ~ ~ ~ ~ ~ | ~1841| (81B2, p.82
Cassava ( 1% slope) ~ ~ ~ ~ ~ ~ | ~ 300| (84B2,84B3,p.10
Cassava ( 5% slope) ~ ~ ~ ~ ~ ~ | ~8700| (84B3,84B3,p.10
Cassava (15% slope) ~ ~ ~ ~ ~ ~ | 22100| (84B2,84B3,p.10
Wheat/fallow~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~1460| (81B1,p.82
Tobacco (N. Carolina)~ ~ ~ ~ |3300-4000| (86W1, Ref.6
Fallow (w/o cropping), 8% slope | 14400| (53L1
5 cm. gross rainfall/ year and:
- -No soil cover or tree cover~ | ~ 120| (87B1
- -No soil-cover, but tree cover| ~ ~80| (87B1
- -litter-cover and tree cover~ | ~ ~ 4| (87B1
Bare, cultivated, no crops~ ~ ~ | ~9206| (80C2, p.17
Continuous bluegrass~ ~ ~ ~ ~ ~ | ~ ~67| (80C2, p.17
Grass ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~60| (76P2
Forested land ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~ 3| (76E1, p.129
Forested land ~ ~ ~ ~ ~ ~ ~ ~ ~ |0.4-2.| (76P2
Forest (undisturbed)~ ~ ~ ~ ~ ~ | 0.4-5|(95P1,Refs.18,19)
Grassy pasture~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ 400| (76E1, p.129
Gullied land~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 40900| (76E1, p.129
Furrow-irrigated row crops~ ~ ~ | ~ 450| (77K1

~(in Colorado's Grand Valley).

*# Erosion rates in developing countries are considered to be roughly twice the corresponding US rates (76P2).

Soil Losses from Various Crops (76P2) (tons/ acre/ year (Col. 3) and tonnes/ km2/ year (Col. 4))
Crop - Location~ ~ ~ ~ ~ ~ |Slope |Loss |Loss~ | Year
Corn (continuous) - MO ~ ~ | ~-3.7|-19.7| 4424 | 1935
Corn (continuous) - WI ~ ~ | ~-16.|-89~ |19985 | 1937
Corn MS~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | - - -|-21.8| 4895 | 1965
Corn IA~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | -9. -|-28.3| 6355 | 1967
Corn (plow-disk-harrow) IN | - - -|-20.9| 4693 | 1967
Corn (plow-disk-harrow) OH | - - -|-12.2| 2739 | 1967
Corn (conventional) OH ~ ~ | - - -|-2.8 | ~629 | 1967
Corn (conventional) SD ~ ~ | -5.8 |-2.7 | ~606 | 1972
Corn (cont. chem.) MO~ ~ ~ | -3. -|-21~ |-4715 | 1973
Corn (contour) IA~ ~ ~ ~ ~ | -2-13|-21.4|-4805 | 1974
Corn (contour) IA~ ~ ~ ~ ~ | - - -|-24~ |-5389 | 1974
Corn (contour) MO~ ~ ~ ~ ~ | - - -|-24~ |-5389 | 1974
Cotton ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | -2-10|-19.1|-4289 | 1939
Cotton GA~ ~ ~ ~ ~ ~ ~ ~ ~ | - - -|-20.4|-4581 | 1965
Wheat MO ~ ~ ~ ~ ~ ~ ~ ~ ~ | -3.7 |-10.1|-2268 | 1935
Wheat NB ~ ~ ~ ~ ~ ~ ~ ~ ~ | -4. -|-6.3 |-1415 | 1960
Wheat Pacific NW~ ~ ~ ~ ~ | -5-10|-1123|-2245 | 1960
Wheat-Pea rotation Pacific NW|- - |-5.6 |-1257 | 1961
Wheat after fallow WA~ ~ ~ | -6.9 |-9.9 |1549-2223| 1968
Bermuda Grass TX ~ ~ ~ ~ ~ | -4. -|-0.03| ~7 ~ | 1939
Native Grasses KS~ ~ ~ ~ ~ | -5. -|-0.03| ~7 ~ | 1939
Forest NC~ ~ ~ ~ ~ ~ ~ ~ ~ | -10 -|-0.002| .45 | 1939
Forest NH~ ~ ~ ~ ~ ~ ~ ~ ~ | -20 -|-0.01|-2.2~ | 1974

Part [A4] ~ Cropland soil Erosion Data ~ Canada ~

Soil loss rates in Pearl River Canada have been recorded as high as 1600 tonnes/ km2/ year from summer fallow. Loss rates as high as 3000 tonnes/ km2/ year have occurred in Fraser Valley Canada under row crops (Ref. 20 of (86D1)).

Part [A5] ~ Cropland soil Erosion Data ~ China ~

The sediment load of China's Yellow River is equivalent to a soil loss of 2700 tonnes/ km2/ year over the River's entire watershed (81R1). Comments: Much of that erosion comes from the loess soils in the headwaters that are of very low productivity.

China's Yangtze River carries 1/4 as much sediment as the Yellow River, even though it has a much larger drainage area and discharge (81R1). Comments: This is probably the result of the loess soils in the headwaters of the Yellow River.

Part [A6] ~ Cropland soil Erosion Data ~ US ~

A table of erosion rates from various categories of land in North Carolina is in (79B3).

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SECTION (4-B) ~ Gross Soil Loss Data and Soil-Organic Matter Loss Data ~ [B1]~Gross Erosion Data, [B2]~Africa, [B3]~Anthropogenic Effects, [B4]~Canada, [B5]~US, [B6]~Far East, ~.

Physical degradation includes mainly soil compaction and waterlogging of irrigated areas. It affects less than 5% of degraded areas worldwide (96M3).

Globally 83% of land degradation is in the form of erosion: 70% is mere loss of topsoil and 13% is more severe terrain deformation (96M3). Comments: "terrain deformation" probably refers to gully erosion.

Part [B1] ~ Gross Erosion Data ~

More than 40% of agricultural land (globally) has degraded soils (03U_ - Reference lost). Comments: "Degraded" needs a definition.

About 33% of the harvested area in developing countries in 2030 is projected to be irrigated land (Table 4.8), vs. 29% in 1997/99. This is generally flat or well-terraced land with little erosion. However, parts may be at risk from salinization, particularly in more arid zones (01N2). In addition, 25% of harvested rain-fed land is estimated to have slopes of less than 5%, which are generally not prone to heavy water erosion. Soil losses of such rain-fed lands of slope less than 5% are around 10 tonnes/ ha/ year (NET?) This should be reduced where economically feasible, but such rates could be tolerated for several hundred years before they have appreciable impacts on crop production. In all, around half of the world's cropland will not be markedly prone to soil erosion, although it may be subject to other forms of land degradation including salinization, nutrient mining, soil acidification and compaction (03N1). (Comments: This material is also in the Irrigated Lands Degradation file.)

Regional patterns of land degradation (96M3)
C.2 - % of wasteland
C.3 - % lightly or moderately degraded
C.4 - % strongly or extremely degraded
Region~ ~ ~ ~ ~ |C.2 |C.3 |C.4
Africa~ ~ ~ ~ ~ | 25 | 12 | 4
N./Cent. America| ~6 | ~6 | 1
South America ~ | ~1 | 11 | 1
Asia~ ~ ~ ~ ~ ~ | 11 | 15 | 3
Australasia ~ ~ | 11 | 11 | 0
Europe~ ~ ~ ~ ~ | ~0 | 22 | 1

Over 100,000 km2 of cropland (global) are degraded and lost annually due to wind and water erosion. (David and Marcia Pimentel, Population Press (4/4/00)). Comments: This figure includes salinization and urbanization - at least according to some sources - see below.

Soil erosion and other forms of land degradation now rob the world of 50-70,000 km2/ year of farming land (98H1).

Worldwide, soil erosion has caused abandonment of 4.3 million km2 of arable land during the last 4 decades (90U1), (90U2). (The 4.3 million km2 estimated to have been abandoned during a 4 decade period is further confirmed by the World Resources Institute's estimation that cropland is lost by erosion at 100,000 km2/ year.)

Globally, At least 100,000 km2/ year of cropland are lost to degradation (92P2). The breakdown is 50-70,000 km2/ year to soil erosion, 20-40,000 km2/ year to urbanization, and 20-30,000 km2/ year to salinization and waterlogging for a total of 90-140,000 km2/ year (94K3).

Soil degradation affects 15% of the Earth's cropland area (91L3).

Some Gross Cropland Soil-Erosion Data
(Rates are in millions of tonnes / year):
Location - - - - - - - - - - - -| Rate | Reference
AFRICA
South African Province of Natal | ~200 | 84B2, 81B4
Ethiopian Highlands ~ ~ ~ ~ ~ ~ | 1000 | 85T1, 89B2, 84B2
ASIA
Armenia ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ 12 | 71R1, p.86
China ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 3300 | 84B2, p.60
China ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 4300 | 84B3, p.21
China ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 5000 | 85X1
China (delivery ratio= 0.25 ) ~ | 5023 | 85B3, p.228
India (1975)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 5000 | 89B2
India ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 6000 | 84B2, p.59
India (delivery ratio= 0.25)~ ~ | 5850 | 85B3, p.228
India - - - - - - - - - - (See Ref.92S1 for map of rates.)
Soviet Union ~ ~ ~ ~ ~ ~ ~ ~ ~ |*#2300 | 84B2, p.60
~(620 million acres of croplands suggests gross erosion rate of 5120)
Soviet Union ~ ~ ~ ~ ~ ~ ~ ~ ~ |*#2500 | 84B3, p.19
~(620 million acres of croplands suggests gross erosion rate of 5320)
Soviet Union~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 1500 |(91F1)
Soviet Union (deliv. ratio=0.25)| 5091 |(85B3)

North America:~ ~ ~ ~ ~ ~ |t/ km2/year| References
Columbia River Drainage ~ ~ | ~ ~110 |(82O1
Colorado~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~206 |(84D1
Iowa~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~182 |(78B2, p.23
Iowa - - - - - - - - 50%/past 150 years (95P1) Ref.27,28
USA ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ 4500 | 85R1
USA -(1930s)~ ~ ~ ~ ~ ~ ~ ~ | ~ 2700 |(76P2, Ref.25
USA -(1970s) (water)~ ~ ~ ~ | ~ 3600 |(76P2, Ref.23,45
USA -(1970s) (wind only)~ ~ | ~ ~900 |(76P2
USA -(1982) (water+ wind) ~ | ~ 2800 |(88B3
USA -(delivery ratio= 0.25) | ~ 3460 |(85B3
Palouse (N.W. US) 40%/ past 100 years (95P1) Ref.13?
SOUTH AMERICA:
Colombia~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ ~426 |(48B1), 78B2
EUROPE:
Czechoslovakia (former) ~ ~ | ~ ~ ~5 | (91F1)
AUSTRALIA:
(nationwide - govt. est.)~ | 90/1.1 | (90S2)
GLOBAL:
(Delivery ratio## = 0.25) ~ | 37,360 |(85B3), p.228
Wind and water erosion~ ~ ~ | 75,000 | (Ref.2 of (95P1)

The last two figures above are apparently in millions of tonnes/ year.
(2/3 of removals coming from croplands and grazing lands land)
## Delivery ratio = sediment entering the oceans/sediments eroded. A reasonable global-value would be about 0.1, and considering sediments trapped behind dams, a better ratio would be around 0.05.
*# These are "excess" rates. To get gross rates, add 5 tons/ acre x cropland area.

Part [B2] ~ Soil Loss and Soil Organic Matter Loss ~ Africa ~

In the southern and southwestern parts of Tunisia, the movement of sand dunes poses a major threat to farmland (Khatteli, H. and D. Gabriels (1998): A study on the dynamics of sand dunes in Tunisia: Mobile Barkhans move in the direction of the Sahara. Arid Soil Research, 12, pp. 47-54.)

Some 85% of Africa north of the equator is undergoing accelerated erosion (88L1) (UN FAO estimate).

In Zimbabwe (1974) 40% of the land is affected by severe erosion (88L1). 15% of Zimbabwe's agricultural land is very severely eroded; 13% is severely eroded; 19% is moderately eroded (Ref. 11 of (92T1)). Comments: Much of the "communal" farmlands are on steep slopes.

Part [B3] ~ Soil Loss and Soil Organic Matter Loss ~ Anthropogenic Effects ~

Human activity has increased the global rate of soil erosion three-fold since pre-historic times, based on the evidence of the sediment load of the world's rivers compared to the history of earlier sediment loads (90W1), p. 257 of (77E1) Comments: This analysis neglects a transient effect that developed along with modern agriculture ~ the sediments that collect on the bottoms of rivers and reservoirs. (Anthropogenic erosion is 30-100 times the natural rate.)

Part [B4] ~ Soil Loss and Soil Organic Matter Loss ~ Canada ~

Summer fallow (keeping cropland vegetation-free for a growing season) is a prime cause of soil degradation in the Canadian prairie. In 1981, farmers summer-fallowed 95,000 km2, or 30% of cultivated land in 3 Prairie Provinces (87M1).

Part [B5] ~ Soil Loss and Soil Organic Matter Loss ~ US ~

In the US, soil erosion is contended to be as serious a problem in the 1980s as it was when the SCS was established in 1935 (Ref. 80 of (89S2)). Comments: This statement is highly controversial.

In the winter of 1995-96 the wheat-growing areas of Kansas lost topsoil at 15000-20000 tonnes/ km2 (97P3).

Part [B6] ~ Soil Loss and Soil Organic Matter Loss ~ Far East ~

Much of China's land is degraded. Erosion affects about 3.67 million km2 of China's land (96G2). Salinization has lowered crop yields on 70,000 km2 in China. Untreated sewage has damaged 25,000 km2. Nearly 70,000 km2 of China's lands are polluted with industrial waste. Agricultural soils in the sub-tropical and tropical regions of China include about 410,000 km2 of cultivated land and 480,000 km2 of wasteland (99B1).

SECTION (4-C) ~ Shifting Agriculture ~ [C1]~Table of Cycle Times, [C2]~Carrying Capacity under Shifting Cultivation, [C3]~Tropical Cropland Lifetimes, ~

Part [C1] ~ Shifting Agriculture ~ Cycle Times ~

Some Cycle Times for Shifting Cultivators: (times in years)
Location - - - - - -| Time~ ~ | References
Africa (overall)~ ~ | 5-10~ ~ |(90B2)
Venezuela (parts of)|"short*#"|(78B2), p.29
Nigeria (parts of)~ | ~ ~5~ ~ |(78B2), 84B3
Madagascar~ ~ ~ ~ ~ | ~ ~0##~ |(56G1)
Thailand (northern) | ~2-4~ ~ |(84B3)

*# So short, fertility is declining
## Forests are gone.

In general, probably only about 50% of the tropical forestland cleared expands the area yielding agricultural benefits; the other half replaces abandoned land (Ref. 29 of (95D3)).

Pasture soils, after tropical-forest clearing, degrade slower than under slash-and-burn cropland agriculture (5-10 years vs. 2-3 years) (Hecht, 1982, Serrao and Homma 1982 in (86B1)).

India (states of Assam, Manipur, Meghalaya, Nagaland, Sikkim, Tripura, and Union Territories of Arunachal Pradesh and Mizoram): About 27,000 km2 are used for shifting cultivation, so vast areas of the region are denuded (85P2).

Average fallow period in India = 4.3-5.9 years (91J1). Forest area affected = 94,700 km2 (4.2 million families) (FAO, 1981 Landsat data) (Area burned annually is much less.). This area is broken down among 11 Indian states in (91J1). Comments: A lot more data on shifting agriculture is given in a companion document "Forest Land Degradation - A Global Perspective".

Malaysia (Sarawak): Shifting cultivation in some areas has fallow periods as short as 3 years (91H4). Comments: Fallow periods of around 20 years are normally required for restoring soil nutrients.

Part [C2] ~ Shifting Agriculture ~ Carrying Capacity under Shifting Cultivation ~

A tribe in former Northern Rhodesia practicing shifting cultivation supports 2.6 people/ km2 sustainably, compared to 400 people/ km2 in Zaire, 360 people / km2 in India, and 250 people/ km2 in Brazil. Comments: The later 3 numbers are not necessarily sustainable. (p. 339 of (56G1)).

Ruanda-Urundi practices something a little better than shifting cultivation on its 21,000 km2 and supports 135 people/ km2 (393 people/ cultivated-km2) (56G1).

Shifting cultivation can be stable (1-3 years of cultivation followed by 10-30 years of fallow) only for population densities of under 8 people/ km2 (Ref. 14 of (82B1)).

Part [C3] ~ Shifting Agriculture ~ Tropical Cropland Lifetimes ~

After removal of forest cover in western Nigeria, maize yields drop from 500 to 150 tonnes/ km2/ year after 2 years, and to 50 tonnes/ km2/ year after 4 years (Refs. 24, 37 of (88L1)).

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SECTION (4-D) ~ Wind Erosion Data (Also see Section (3-H-g).) ~ [D1]~
Africa, [D2]~Oceania, [D3]~Asian Sub-Continent, [D4]~Central Asia, [D5]~US, [D6]~Far East, [D7]~Mid-East, ~

Part [D1] ~ Wind Erosion Data ~ Africa ~

Dust storms from the Sahara Desert have increased by a factor of 10 during the past 50 years. A major cause is the use of four-wheel drive vehicles. A professor of geography at Oxford University blames this for destroying a crust of lichen and stones that has protected vast areas of the Sahara for centuries. Four-wheel drive use, with overgrazing and deforestation, were the major causes of the world's growing dust storm problem, the scale of which was much bigger than previously realized. 2-3 billion tonnes of dust are carried on the wind each year. Storms transport Sahara dust into the atmosphere and deposit it as far away as Greenland and the US. Britain was seeing increasing dust levels in spring that came direct from the Sahara. From an aircraft over the Alps it is possible to see the red dust on the mountains. Although storms are mainly particles of quartz, they also contain salt, pesticide, herbicide and diseases such as foot-and-mouth disease. The largest dust source is the Bod?l? Depression in Chad, between Lake Chad (that is 5% of its size in the 1960s) and the Sahara Desert. That depression releases 1.27 billion tonnes of dust a year, 10 times more than when measurements began in 1947. Taking the whole Sahara, and the Sahel, dust volumes increased 4-6 times since the 1960s. In the Caribbean, scientists linked the death of coral reefs to smothering by the same dust that also found its way to Greenland, The dark-colored dust absorbs the sun's heat, causing the ice on which the dust sits to melt. The airborne dust reflected sunlight back into space but blanketed the earth, holding the heat in. When it drops into the sea, it fertilizes the plankton that absorbs carbon dioxide and cool the ocean surface, creating fewer clouds and less rain. Where the source was the dried-up bed of a lake or sea, salt deposited from the storms could ruin agricultural land. Worldwide, dust in the atmosphere is predicted to be 2-3 billion tonnes in 2004. Florida receives more than 50% of the African dust, causing increased respiratory problems. Mauritania had two dust storms per year in the 1960s. Now Mauritania has 80 dust storms/ year. The worst dust storm to reach Great Britain was in 1903 when an estimated 10 million tonnes landed from the Sahara Desert (04U1). (also in Grazing Lands Degradation Review)

Oxford-based expert Norman Myers says Morocco, Tunisia and Libya are each losing over 1000 km2 of productive land a year to desertification (Stephen Leahy, "Environment: Millions Flee Floods, Desertification", I.P.S., Brooklin, Canada (10/12/05)). (su1)

About 25% of Africa's land is now subject to water erosion, and about 22% to wind erosion. Over 45% of Africa is affected by desertification 55% of which is at high, or very high, risk ("Roundup: Africa Facing Critical Choices on Environment", Xinhua General News Service (5/24/02)).

Wind erosion is responsible for 38% of soil losses in Africa (ENN Direct (10/15/99)).

About 0.1-0.4 Gt./ year of wind-borne North African soil gets carried out over the Atlantic Ocean (p.15 of (84B3)) (p. 58 of (84B2)). Ref.16 of (84B2) reports similar wind-induced soil losses from Asia into the Pacific. 25-37 million tons/ year of wind-blown soil cross the Atlantic (Ref. 53 of (88L1)).

Part [D2] ~ Wind Erosion Data ~ Australia ~

A dust storm in Southeast Australia blew 30 million tons of topsoil to sea in June, 1994. The storm was 500 miles wide and 125 miles long at its peak (94U1).

Soil losses due to wind erosion may be several times greater than losses due to water erosion in western Australia (83C3).

Part [D3] ~ Wind Erosion Data ~ Asian Sub-Continent ~

Extent of land degradation, circa 1980: 130,000 km2 of wind-degraded land as compared to 740,000 km2 of water-eroded land and 70,000 km2 of saline- and alkaline land out of a total land area of 3,290,000 km2 (88B4).

Part [D4] ~ Wind Erosion Data ~ Central Asia ~

About 5000 km2/ year of Russian croplands are abandoned because they are so severely wind-eroded that they are no longer worth farming (p. 18 of (84B3)).

Wind erosion removes 15,000 km2/ year of cropland from production in the Soviet Union, and a much larger area is damaged to some degree each year (89S3).

Since the mid-19th century, over 25,000 km2 of field shelterbelts have been established in the Soviet Union to protect 198,000 km2 of agricultural land (89S3).

Part [D5] ~ Wind Erosion Data ~ US ~

Wind accounts for 1 billion tons/ year of soil erosion (as compared to 4 billion tons/ year of water-induced erosion) (76P2). Comments: It seems safe to assume all this wind erosion is topsoil erosion, not subsoil erosion. These data are obsolete. No-till agriculture and the Conservation Reserve Program have reduced US soil erosion significantly.

Wind Erosion on Great Plains Croplands in 1977 (tonnes/ km2/ year) (80U2)
CO 2000 |KS 651 |MT 853 |NB ~393 |NM 2582
ND ~404 |OK 674 |SD 674 |TX 3346 |WY ~539

In Dawson County TX (Amarillo soil) in Southern High Plains, average annual wind erosion from continuous dryland cotton is 2-6 times greater than for cotton-wheat or cotton-sorghum-wheat rotations. Used 48 year run (89L2).

Part [D6] ~ Wind Erosion Data ~ Far East ~

China's Gobi Desert is expanding by more than 10,000 km2/ year, threatening many villages (Stephen Leahy, "Environment: Millions Flee Floods, Desertification", I.P.S., Brooklin, Canada (10/12/05). (su1)

Some 24,000 Chinese villages have either been abandoned or have had their farm economies seriously impaired by invading deserts. In the arid northern half of China where most of the wheat is grown, tens of thousands of wells go dry each year. These trends, combined with weak grain prices that lower planting incentives, shrank the harvest from its peak of 123 million tons in 1997 to 86 million tons in 2003 (04B1).

Accelerating wind erosion of soil in China, and the resulting land abandonment, are forcing people to migrate eastward, not unlike the US westward migration from the southern Great Plains to California during the Dust Bowl years (Lester R. Brown, "Dust Bowl Threatening China's Future", Earth Policy Institute (5/23/01) www.earth-policy.org.).

Part [D7] ~ Wind Erosion Data ~ Mid-East ~

Wind-erosion measurements by ICARDA in Syria revealed soil losses of up to 6000 tons per km2 (equivalent to a loss of approximately 3 mm of soil depth) during the windy season from July to September in areas that had been opened for rain-fed cereal cultivation without erosion-protection measures (ICARDA (1991): Annual Report. International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria.)

In the Sistan basin of Afghanistan and Iran, more than 100 villages have been abandoned because of windblown dust (03E1).

Soil erosion via wind erosion is the main form of land degradation in 12 of the 15-nation Arab State Region, while in the rest of the world water erosion is the major problem (96M3). (Water erosion is dominant in Morocco, Lebanon and Turkey.)

Part [D8] ~ Wind Erosion Data ~ Generally ~

Soil degradation by region in susceptible drylands, 1990s data, Columns 2-6 are in units of millions of ha.

 

~ ~

Water
erosion

Wind
erosion

Chemical
deterioration

Physical
deterioration

Total

North America

38.4

37.8

2.2

1.0

78.4

South America

34.7

26.9

17.0

0.4

79.0

Europe

48.1

38.6

4.1

8.6

99.4

Africa

119.1

159.9

26.5

13.9

319.4

Asia

157.5

153.2

50.2

9.6

370.5

Australasia

69.6

16.0

0.6

1.2

87.4

Total

467.4

432.4

100.7

34.7

1035.2

Source: United Nations Environment Program (UNEP)

Soil degradation by degree in susceptible drylands, 1990s data. Columns 2-6 are in units of millions of ha.

~ ~

Water
erosion

Wind
erosion

Chemical
deterioration

Physical
deterioration

Total

Light

175.1

197.2

44.3

10.8

427.3

Moderate

208.5

215.4

31.4

15.0

470.3

Strong

79.0

18.0

24.2

8.9

130.1

Extreme

4.8

1.8

0.8

0.0

7.5

Total

467.4

432.4

100.7

34.7

1035.2

Source: United Nations Environment Program (UNEP)

Drylands are more susceptible to wind erosion than any other form of degradation because soils tend to be dry, poorly structured and sparsely covered by vegetation (Mainguet, M. and G. G. Da Silva (1998): Desertification and drylands development: What can be done? Land Degradation & Development, 9, pp. 375-382.) According to earlier studies, wind erosion only reaches threatening proportions when people disturb the balance of the ecosystem (Middleton, N and D. Thomas (Editors) (1997): World Atlas of Desertification. Arnold - Hodder Headline Group, London, UK (Mainguet and Da Silva, 1998).)

Over considerable parts of Central and Western Asia and North Africa, large areas of the traditional semi-nomadic rangelands, the steppe, are being opened for barley cultivation. The consequent removal of the vegetation cover has exposed the soil surface, leading to the loss of the fine fertile fraction of the shallow soils through wind erosion. This has led to a tremendous decline of soil productivity. (Mainguet, M. and G. G. Da Silva (1998): Desertification and drylands development: What can be done? Land Degradation & Development, 9, pp. 375-382. (Sivakumar et al. (1998). (Sivakumar, M.K.V., M. A. Zöbisch, S. Koala and T. Maukonen (Editors), (1998): Wind Erosion in Africa and West Asia: Problems and Control Strategies. International Center for Agricultural Research in the Dry Areas, Aleppo, Syria.

SECTION (4-E) ~ Cropland Loss to Urbanization and Erosion ~

Chemical degradation (e.g. salinization, loss of soil nutrients/ and pollution), which accounts for 12% of soil degradation at the global level, has a much higher impact in Egypt, Iraq, Syria and Algeria (96M3).

Some Cropland Loss Rates (in km2/ year (%/ year)) to Urbanization and Erosion
Region - - - - - - - - - - - - - - - |Loss Rate|References
California (urbanization)~ ~ ~ ~ ~ ~ ~ | ~ 178 | 86U1
China (Pollution etc.)Wall St.J.6/12/96|10,000 |
China + Japan + S. Korea + Taiwan~ ~ ~ |50,000 |90B2,Ref.25
Egypt (urbanization) ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ 260 | 76E1
Pakistan (Punjab area)(erosion)~ ~ ~ ~ | 20-30 | 81B4,78B2
Poland (Class I farmland to urbanized) | (5.4) | 85T1
Poland (Class II farmland to urbanized)| (0.5) | 85T1
Russia (wind erosion)~ ~ ~ ~ ~ ~ ~ ~ ~ | 5,000 | 84B3
Russia (wind erosion)~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ 500 | 84B2,p.59
Soviet Union (to gullies)~ ~ ~ ~ ~ ~ ~ | 1,000 | 90B2
Soviet Union (abandoned since 1977)~ ~ |10,000 | 89B2
Texas (prime farmland to non-ag. use)~ | ~ 486 |(86U1
US (urbanization)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |11,740 |(79?1
~(1417 Class 1+ 6073 Class 2+ 4251 Class 3)
US (Urbanization)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 1,506 |(79B1
US (urbanization)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 4,453 |(79B1
US (urbanization)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |12,146 |(79B1
US (urbanization)~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 2,870 |(79B1
US (to non-ag. uses) ~ ~ ~ ~ ~ ~ ~ ~ ~ |11,640 |(84U2
US (to non-ag. uses) ~ ~ ~ ~ ~ ~ ~ ~ ~ | 3,644 |(81B1
US (to non-ag. uses) ~ ~ ~ ~ ~ ~ ~ ~ ~ | 2,400 |(76E1
US (Cl. 1,2 to non-ag. uses) ~ ~ ~ ~ ~ | 5,668 |(75U1
US (Cl. 1,2 to non-ag. uses) ~ ~ ~ ~ ~ | 3,100 |(85B2, p.25
US (to non-ag. uses) ~ ~ ~ ~ ~ ~ ~ ~ ~ |12,550 |(78C1)
US (to non-ag. uses) ~ ~ ~ ~ ~ ~ ~ ~ ~ |10,000 |(78B1),p.48
~(offset by 5000 km2/ year of irrigation- and drainage projects)
Pennsylvania (prime farmland to non-ag | ~ 405 |(78J1)
Pennsylvania (1954-74) ~ ~ ~ ~ ~ ~ ~ ~ | 1,012 |(78K1)
Global -nearly 1/3 of arable land lost by erosion in past 40 years (95P1).
Global (arable land) ~ ~ ~ ~ ~ ~ ~ ~ ~ |100,000|(95P1)
Global (arable land) ~ ~ ~ ~ ~ ~ ~ ~ ~ |120,000|(95P1),Ref.1
destroyed/ abandoned due to non-sustainable practices
Global (cult. Land to non-ag. Land~ ~ |(0.5-1.)|(78B3),p.110
Global (wind and water erosion, ~ ~ ~ | 50,000 |(78B3),p.110
~ salinization, sodication, desertification)
~ Global (as above) (Dumont, 1973) ~ ~ |190,000|(78B3),p.110
Global (as above) (Kovda , 1973) ~ ~ ~ |500,000|(78B3),p.110
Global *#* ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | 60,000|(91B2),Ref.11

*#* cropland + grazing land + forest land

Some Cumulative Cropland losses to Urbanization, Erosion, Etc.
Region - - - - - - - - - - - |Loss(km2 or %)|References
Mexico (erosion) ~ ~ ~ ~ ~ ~ ~ ~ |1500-2000 |48B1, p.50
Poland (chemical contamination)~ | ~ ~(25%) |88B1,p.7
USA (since 1967- to non-ag. uses)| ~235,000 |86U1
USA (1945-1975 - to non-ag. uses)| ~180,000 |80P2,Ref.34
USA (N.E. and S.E.) (1939-1978)~ | ~ ~(33%) |83B1
USA (since start of agriculture) | ~ ~(33%) |76P2
FL (to lose all of prime ag. land by 2000)~ |86U1
VA (to lose 24% of prime ag. land by 2000)~ |81B3
CA (to lose 16% of prime ag. land by 2000)~ |81B3
Global*#*~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~ 89,000 |92U2

*#* Cropland + rangeland + forest land
Comments: See Chapter 6 for more data on urbanization.

Global
Globally, 100,000 km2 of croplands are lost to erosion, other forms of degradation (e.g. salinization), or conversion to urban developments annually (95L2) (95P1).

Since WWII, as many as 89,000 km2 of the world's lands have been so ruined by over-grazing, deforestation, and unstable agricultural practices that they will be impossible to reclaim. Another 12 million km2 are considered seriously degraded. They could be restored, but only at great cost (92U2).

Some 67% of all seriously eroded land is in Asia and Africa (92U2).

In Central America, 25% of vegetated land is moderately to severely degraded (4.4% for North America) (from a WRI study, funded by UNEP) (92U2).

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SECTION (4-F) ~ Cropland Loss to Salinization and Water-logging ~ [F1]~Global, [F2]~North America, [F3]~Latin America, [F4]~Middle East, ~

Part [F1] ~ Cropland Loss to Salinization and Water-logging ~ Global ~

Globally, more than 770,000 km2 of land is salt-affected by secondary salinization: 20% of irrigated land, and about 2% of dryland agricultural land (FAO, AGL, 2000 data) (05S1). (This data is also in Irrigated Lands Degradation Review.) Comments: The area of irrigated cropland is about 23% of the area of dryland agricultural cropland.

Irrigated land loss to salinization and waterlogging: 20-30,000 km2/ year (94K3). (More data in Irrigated Land Degradation Review document.)

Part [F2] ~ Cropland Loss to Salinization and Water-logging ~ North America ~

Soil salinity in Canada's Prairie Provinces affects 22,000 km2. In addition, 1000 km2 of Canada's irrigated land suffer the effects of salinization. These areas are expanding at a rate of 10%/ year. Crop yields have been reduced by 10-75% (50% on average) (84S2).

Part [F3] ~ Cropland Loss to Salinization and Water-logging ~ Latin America ~

Expansion in the 20th century of irrigation in northwest Mexico has been plagued by serious salinity problems. In Yaque Valley, 400 km2 were damaged by salt, and 150 km2 had to be retired from production by the mid-1960s. In the Colorado Delta, 80% of arable land was affected by salinity, and 14% was too saline for cultivation by 1965 (p. 127 of (76E1)).

Part [F4] ~ Cropland Loss to Salinization and Water-logging ~ Middle East ~

In Euphrates Valley of eastern Syria, above the Euphrates entry into Iraq, 25-50% of the total agricultural area has been rendered unfit for cultivation by soil salinity and saturation. Average cotton yields in the valley's remaining farmland dropped from 250 tonnes/ km2/ year in the early 1950s to about 150 by 1966. Over 50% of the combined irrigatable land of the Euphrates and Khabour Valleys (2200 km2) had been harmed or destroyed by salinity as of 1970. Nearly all damage has occurred in the past 25 years since the introduction of perennial cotton production (p. 125 of (76F1)). Comments: A compilation of data on irrigated land degradation is not included here, but is contained in a different document - See Navigation Aid below.

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