CHAPTER 5 - DEGRADATION OF IRRIGATED LAND

TABLE OF CONTENTS:
-.-.
(5-A) -
Global Overview
[1] Irrigation System Degradation; [2] Irrigation system Abandonment

(5-B) - Regional Degradation--Asia
[Alphabetical by Country or Region] [1] Bangladesh, [2] Central Asian Republics, [3] China, [4] India, [5] Iran, [6] Iraq, [7] Israel, [8] Jordan, [9] Middle East, [10] Pakistan, [11] Syria, [12] Turkey, [13] USSR (former)

(5-C) - Regional Degradation--Africa and Australia
[1] Africa (North), [2] Egypt, [3] Australia

(5-D) - Regional Degradation--N. and S. America
[Alphabetical by Country or State] [1] USA, [2] California, [3] Colorado, [4] New Mexico, [5] Texas, [6] Argentina, [7] Brazil, [8] Mexico, [9] Haiti, [10] Peru
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SECTION (5-A) - Global Overview
[1] Irrigation System Degradation, [2] Irrigation system Abandonment

[1] Irrigation System Degradation
A World Bank study of the performance of Bank-funded irrigation projects concluded that the Bank should not insist that its client countries construct drainage systems before they are needed, but that it should at least fund pilot schemes to identify the best solutions (to the salinization problem) before large-scale schemes get under way. (Wm. I. Jones, "The World Bank and Irrigation", World Bank, Washington DC, 1995) Comments: Drainage systems are what prevent salinization and waterlogging.~ After an irrigation system has been built and paid for and in operation for some years and salination problems appear, the World Bank would appear to have little leverage to force installation of drainage systems.

Although half of the world's irrigation capacity has been developed since 1950, water-logging and salinity are impairing the productivity of many systems (78B2).

As many as half of all existing irrigation systems in the world are influenced by secondary salinization, alkalization and waterlogging (88S1) (FAO and UNESCO data).

FAO estimates that salt build-up in soil has severely damaged 300,000 km2 of the world's 2.4 million km2 of irrigated land.~ Another 800,000 km2 are affected by a combination of salinization and waterlogging (98H1).

250,000 km2 of irrigated lands appear to suffer from salt buildup enough to lower crop yields.~ Salination is spread at up to 20,000 km2/year, offsetting a good portion of gains achieved by irrigation expansion (Ref.12 of 96P1).

Soil salination is spreading at up to 20,000 km2/year (globally), offsetting a significant portion of the increased productivity achieved by expanding irrigation (Dina L. Umali, "Irrigation-Induced Salinity", World Bank, Washington DC, 1993).

Yields on 50% of all irrigated land--1.2 million km2--have fallen in recent years (98H1). Comments: Ref.98H1 does not list its information sources.)

A 1995 study, drawing on the global data of the 1980s, estimated that 20% of the world's irrigated area suffers from salination (Ref.52 of 96G2).

20% of irrigated land is losing productivity because of spreading salination. (99P1) Comments: Because such a large fraction (60%??) of the world's irrigation systems is younger than 50 years, and because the growth of irrigation has slowed so dramatically, and because it takes some decades for salination (and waterlogging) to begin degrading productivity, the fraction of irrigated lands losing productivity is sure to climb dramatically in coming decades.

More than 50% of the world's irrigated soils are affected by secondary salination and/or alkalization (Ref.355, 356, p.207 of 88S1).

The area of irrigated land damaged by salt in 1995-97 is charted for 8 regions of the world on p.58 of Ref.00W1.

UNEP estimates irrigated area damaged by salination at 400,000 km2 (Ref.15 of 89P3).

Salinity seriously affects productivity on 200,000 km2 of the world's irrigated lands (Ref.14 of 85E1).

200,000-300,000 km2 of the world's irrigated area suffer serious salination (94P2).

600,000 to 800,000 km2 are moderately affected by salination (Ref.5 of 94P2).

Productivity on at least 1/3 of the world's irrigated land is being undermined by salinity problems (76E1).

A third of irrigated lands today have serious salination problems (79S1).

26% of the World's irrigated area suffers from some degree of waterlogging and salinity (91B3).

A 1977 UN report indicated that 210,000 km2 of irrigated land (10% of the total) were waterlogged, and productivity has dropped 20% (78B3) (81B2) (Ref.23 of 78B2).~ 200,000 km2 were affected mainly by salination, and productivity has been reduced by a similar amount (Ref.14 of 78B3) (81B2).~ These data imply an overall reduction in productivity in the World's irrigated lands of 4% (cumulative) (78B2, 78B3).~ (50% of global irrigation capacity has been developed since 1950 (81B2)).

Waterlogging and salination are reducing yields to varying degrees in virtually all of the 30 or so countries with over 5000 km2 of land under irrigation (76E1).

150,000 km2 in developing countries are experiencing serious reductions in crop yields because of salt buildup in irrigated soil (Ref.9 of 92P1).~ 250,000 km2 (over 10% of the world's irrigated area) are suffering from salt buildup sufficient to reduce yields (Ref.10 of 92P1).

Soil salinization is spreading at a rate of up to 20,000 km2/year, offsetting a significant portion of the increased productivity achieved by expanding irrigation. (Dina L. Umali, "Irrigation-Induced Salinity", World Bank, Washington DC, 1993) Comments: These statements are also in the Soil Degradation Review.

10% of the world's irrigated area appears to be suffering from salination serious enough to reduce yields.~ Another 30% may be moderately affected (Ref.20, Ch.8 of 94B1).~ Additional amounts suffer from waterlogging (Ref.9, Ch.11 of 94B1).

20% of the world's irrigated area suffers from salination (97G1).

60% of the world's irrigated area needs upgrading to remain in good working order (90P1).

Large irrigated regions with serious salinity problems include (85D1):

Irrigated Land Damaged by Salinization (89P1, Table 2) (90P1)
(Areas (Col.2) are in km2.)
Region~ |Area~ ~ | % of irrigated land
India ~ |200,000 | (36%)
China ~ | 70,000 | (15%
US~ ~ ~ | 52,000 | (27%
Pakistan| 32,000 | (20%
USSR~ ~ | 25,000 | (12%
Total ~ |379,000 | (24%
World ~ |602,000 | (24% (by extrapolation)

Irrigated Land Damaged by Salinization in the late 1980s
Region~ ~ ~ |Area(km2| % of irrigated land
India ~ ~ ~ | 70,000 | 17%
China ~ ~ ~ | 67,000 | 15%
Pakistan~ ~ | 42,000 | 26%
US~ ~ ~ ~ ~ | 42,000 | 23%
Uzbekistan~ | 24,000 | 60%
Iran~ ~ ~ ~ | 17,000 | 30%
Turkmenistan| 10,000 | 80%
Egypt ~ ~ ~ | ~9,000 | 33%
Subtotal~ ~ |281,000 | 21%
World Est.~ |477,000 | 21%
Source: F. Ghassemi, A.J.Jakeman, H.A.Nix, "Salinization of Land and Water Resources", University of New South Wales Press, Sydney, 1995

[2] Irrigation System Abandonment
The major problems of water resource development and operation are not technical, but relate to the socio-political situation (74F1).~ (The author (a hydrologist) is reasonable certain that most, if not all, the water projects he designed will meet the same fate as the ancient Middle-Eastern irrigation projects people now find buried in the sands.)

Recent research puts the current loss of world farmland due to salination at 15,000 km2/year (Ref.60 of 94K1).

20-30,000 km2/year of irrigated lands may be coming out of production due to salination.~ (Average irrigated-area expansion in recent years has been about 20,000 km2/year) (Ref.12 of 96P1).

David Seckler, Director General of Int'l. Irrigation Mgmt. Inst., believes that losses in irrigated areas may now exceed gains (97B2).

A Soviet soil scientist estimates that 60-80% of the world's irrigated lands are becoming saline and hence infertile.~ By his calculation, 200-250,000 km2 have been laid to waste over the centuries by mismanaged irrigation systems, and 2000-3000 km2/year out of a total world-wide irrigated area of nearly 2 million km2 pass from cultivation due to waterlogging and salinity (76E1) (1978 Aspen Institute study in Ref.82S1).

Salination severe enough to remove land from production claims 15,000 to 25,000 km2/year. (Ref.52 of 96G2)

Soviet agronomist Victor Kovda estimates a global rate of irrigation system abandonment of 10,000-15,000 km2/year (Ref.12 of 90B1).

According to the UN-FAO and UNESCO, irrigated lands are abandoned at a rate of 100,000 km2/year, mainly due to secondary salination and alkalization (88S1).~ Comments: This figure is way out of line--10,000 km2/year is more likely.

Aerial views of abandoned irrigation lands in the world's dry regions reveals vast expanses of glistening white salt-encrustation--useless land (Ref.21 of 89P1).

Ref.87P2 references a study (not named) claiming that as much irrigated land is being taken out of production due to salination and waterlogging as is being bought into production by new irrigation schemes.

20,000 km2/year of irrigated land are lost to salination (Ref.29 of 94P1).

Waterlogging and salination are sterilizing 10,000-15,000 km2/year (85P1).

Salination is spreading at a rate of 10,000-15,000 km2/year, which is about half the rate at which new land is being bought under irrigation (Ref.10 of 92P1).

Salination may be spreading by as much as 10-15,000 km2/year (Ref.7 of 94P2).

Ref.18 of 79S1 estimates that 34 million km2 of arid lands have been converted to desert by Man's destruction of vegetation and altering the water budget unfavorably.~ Ref.79S1 estimates 9 million km2.

Rejuvenating salt-covered fields costs $100,000-200,000/km2, and the effort often fails.~ But salination can be prevented with just a simple set of underground pipes to draw excess water off the field (95W1).

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-.-.-. WEB-SITE NAVIGATION AID--WHERE DO YOU WANT TO GO?
(5A) Top of this Section--Global Overview
(5TC) Top of this Chapter--Degradation of Irrigated Lands
(8) Top of this Review's Appendices (units, conversions, definitions)
(9) Top of this Review's Reference List
(SE) Topsoil Loss--Causes, Effects, Implications
(DF) Forest Land Degradation: A Global Perspective
(OG) Grazing Land Degradation: A Global Perspective
(IR) Irrigated Land Degradation: A Global Perspective (Current Choice)
(FI) Fishery Degradation: A Global Perspective
(T) Title Page of this entire web site (IMPORTANT--visit early!)
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SECTION (5-B) - Regional Degradation--Asia
(Alphabetical by Country or Region) [1] Bangladesh, [2] Central Asian Republics, [3] China, [4] India, [5] Iran, [6] Iraq, [7] Israel, [8] Jordan, [9] Middle East, [10] Pakistan, [11] Syria, [12] Turkey, [13] USSR (former)

[1] Bangladesh
Bangladesh irrigation systems do not suffer from salination because the heavy monsoon rains wash away any accumulated salt (81G1).

[2] Central Asian Republics (Also see USSR (fmr.))
In the Central Asian republics, salination has caused cotton yields to fall from 280 tons/km2 to 230, even with increased fertilizer (97G1).

In the Central Asian republics, salination reduced cotton yields from 280 to 230 t/km2 between the late 1970s and late 1980s, despite increasing use of fertilizer during this period (Ref.52 of 96G2).

The share of irrigated land that is moderately to heavily salted is 35% in Tajikistan and 80% in Turkmenistan (all in the Aral Sea Basin) and 60% for the entire basin (Ref.25, Ch.8 of 94B1)(91B2).~ Land productivity in the Area Sea basin (in terms of cotton yields) has fallen 15% since its peak year in 1979 (Ref.26, Ch.8 of 94B1).

21% of Kazakhstan's irrigated area is salinized (93M3).~ 13% of Kazakhstan's irrigated area is waterlogged (93M3).~ (Irrigated cropland: 18,560 km2)

In Uzbekistan, 15,000 km2 of land have been abandoned during the past 30 years (500 km2/year) due to high salinity (81F1).~ (To grow 1.0 kg. of cotton requires 660 gal. of water in this region.)

Khakimov estimates yield loss due to salinity at 30% in Uzbekistan, 40% in Turkmenistan, 30-33% in Kazakhstan, 18% in Tadjikistan, and 20% in Kirghizia (89K1).

Mainguet quotes Khakimov in her book as saying that the percent of moderate-to-severe salinization of irrigated areas in Central Asia are: Uzbekistan-60%, Turkmenistan-80%, Tadjikistan-35%, Kirghizia-40%, Kazakhstan-60-70% (89K1).

Turkmenistan expanded its irrigated area by 31% during 1990-94.~ Newly irrigated lands were not equipped with drainage, so the salt problem may worsen. (99P1)

[3] China
Salinity has cut yields on nearly 25% of China's irrigated land (98H1).

In China, 20% of irrigated land suffers from salination. (99P1) (00W2).

Waterlogging and salinity have reduced productivity on 15% of China's irrigated land (p.71 of 95B3).

China: About 20% of cropland suffers from salination in northwest (Baotou and Tarim basin) and along the coast (89H1).

Yields on at least 20% of the irrigated area of some major regions are reduced by salinity, and hundreds of thousands of km2 throughout the country are barren because of salt--some of it natural, and some of it left by farmers in the past (76E1).

During the 1950s and 1960s, salt-affected soil occurred in over 40,000 km2 of the North China Plain (85X1).

Over 9300 km2 of irrigated farmland have come out of production since 1980 (1160 km2/year) (Ref.14 of 89P1) (90P1).~ Comments: 46% of China's 970,000 of croplands are irrigated (90W1).

Waterlogging and salination are reducing productivity on 15% of China's irrigated land (94B2).

China has 70,000 km2 of saline and alkaline agricultural land (90P1).

[4] India
In Haryana (important breadbasket for India) 4000 km2 now have a water table up to within 3 meters of the surface--dangerously high.~ The high water table threatens to spread to 20,000 km2 (99P1).

In India, 20% of irrigated land suffers from salination (99P1) (00W2).

Nonexistent or inadequate drainage seriously limits irrigated agriculture in India.~ 85,000 km2 are damaged by salinity (70T1).

Over 60,000 km2 have been severely damaged by waterlogging and salinity out of a total irrigated area of 400,000 km2 (76E1).

In India and Pakistan, an estimated 120,000 km2 have been degraded (85P1).

In Rajasthan in N.W. India, 24 km2 of irrigated land has been lost to salination, and another 40.3 km2 are threatened (Ref.27 of 78B2).

Extent of degraded land in India, circa 1980 (88B1): 70,000 km2 are saline or alkaline, as compared to 130,000 km2 that are wind-eroded, 740,000 km2 that are water-eroded, and 350,000 km2 that are degraded forest land (out of India's total land base of 3,290,000 km2).~ 60,000 to 70,000 km2 of India's irrigated lands are affected by water-logging, salinity and alkalinity (Ref.45,54 of 81G1).

Salinity reduces crop yields on 200,000 km2, and 70,000 km2 have been abandoned as salty wasteland (90P1).

Over 20,000 km2 of India's salinized land have been abandoned (96G2).

[5] Iran
Officials say that the majority of irrigated lands are saline, and crop yields are depressed by the toxicity of salt (Ref.13 of 76E1).

More than 50% of irrigated soils in Iraq and Iran is affected by secondary salination (Ref.388 of 88S1).

Salination affects 160,000 km2 of Iran's agricultural land, and has forced over 80,000 km2 out of production (96G2).

[6] Iraq
Barley, more salt-resistant than wheat, is the predominant cereal in southern Iraq, even though farmers would prefer to plant wheat.~ This pattern holds true also for ancient- and Islamic Mesopotamia (74G1).

Mesopotamia agricultural systems had the capacity to feed 17 million people when Babylon flourished.~ In the many centuries since that time, the lower valleys of the Tigris and Euphrates Rivers have not sustained more than 3 million people (70W1).

20-30% of Iraq's potentially irrigable land is unusable (76E1), i.e. has been converted to desert by salination of irrigation projects (79S1).

Viewed from the air, vast areas of southern Iraq glisten with salt like new-fallen snow (85S1) (76E1).

[7] Israel
Israel faces serious nitrate-pollution and salinity in the coastal aquifer.~ Continued water shortages and rising fuel prices may make the Negev's agricultural system uneconomical (78E1).

[8] Jordan
In 1970, less than 10 years after Jordan initiated irrigation agriculture in the Jordan River Valley, salt and sogginess were affecting 12% of the project area, and the extent of the damage was increasing every year (76E1).

[9] Middle East
Over 10,000 km2 of irrigated land in the Arab states region suffer from salination. (96M2)

Grain yields declined in most Middle East countries in the first half of the 1960s due to (70T1):

[10] Pakistan
In 1947, 400 km2/year of Pakistan's irrigated land were going out of production due to waterlogging and salt buildup.~ Underlying water tables were rising steadily.~ Aerial photos (1952-58) showed nearly 50,000 km2 of land were highly salty (99P1).

Salinity has cut yields on 21% of Pakistan's irrigated land (98H1).

About 25% of the 121,000 km2 of irrigated land in the Indus River Basin are encountering serious drainage- and salinity problems (74F1).
Waterlogging and salinity have reduced yields of major crops by 30% (92P1).

Because of the limited water in much of the country, and the lack of adequate drainage systems, salinity has become a major constraint (70T1).

Pakistan's Mona Reclamation Area began irrigation in 1901.~ Close to 90% of the soils were waterlogged by the early 1960s.~ The problem is now being corrected by foreign-aid-supported reclamation (81B2).

In some districts in Pakistan, virtually all irrigated land is plagued with waterlogging and salinity (Ref.28 of 78B2) (76E1).

By 1960, waterlogging and salinity were severely affecting more than 20,000 km2 of the Indus Plain.~ As many as 400 km2/year of new areas were being affected (76E1).

Of 138,000 km2 of irrigated land, 21,000 are salinized after a few years of irrigation (Ref.387 of 88S1).

25,000-35,000 km2 in Pakistan have severe salinity problems, and another 25,000-45,000 km2 are moderately affected by salinity.~ Provinces of Sind and Punjab are areas most damaged (Ref.62 of 81G1).~ Yields on tens of thousands of km2 of Pakistan's irrigated cropland have been substantially reduced.~ Water tables are within 3 m. of the surface in more than 50% of the irrigated area, and within 1.5 m. in some regions (Ref.62 of 81G1).

Pakistan has 32,000 km2 of saline and alkaline agricultural land (90P1).

Over 16% of Pakistan's agricultural land suffers from salination (96G2).

[11] Syria
The FAO reports of salinity in the Euphrates Valley (Ref.20 of 88S1):

[12] Turkey
More than 25% of alluvial soils are affected by salinity (88S1).

[13] USSR (fmr.) (Also see Central Asia Republics)
25,000 km2 are salinized, most of them in irrigated deserts of central Asia (Ref.10 of 92P1) (90P1).

Egorov et al found that in the USSR cotton belt, weakly- and medium-saline soils increased from 49.6% to 85% during 1945-61 (71R1).

12% of irrigated farmland (25,000 km2) is contaminated with salt or salt compounds due to poor drainage systems (89P1) (91F1).~ Between 1975-85, salinized land area nearly doubled (89P1) (Ref.31 of 91F1).~ Irrigation ceased on 29,000 km2 during 1971-85 (2,100 km2/year) (Ref.14 of 89P1).~ This was 25% of the new area bought under irrigation in that period (Ref.11 of 90P1).

Winds pick up 90-140 million tons/year of salt from the dry Aral Sea bed and deposit it as far away as Byelorussia (91B2).

Winds pick up dried salt from the Aral Sea basin and deposit 43 million tons/year of it on 150,000 km2 of cropland and pasture (Ref.16 of 89P3).

Nearly all of Karakalpakia's agricultural land is either salinized or waterlogged.~ (Karakalpahia is the republic around the southern portion of the Aral Sea (Pop.: 1.2 million)).~ The process began around 1958, therefore no more than 37 years were required to salinize (95H1).

In 1994, 28% of the Aral Sea Basin had salt buildup severe enough to lower crop yields by 20-50%, compared to 23% 4 years earlier (99P1).

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-.-.-. WEB-SITE NAVIGATION AID--WHERE DO YOU WANT TO GO?
(5B) Top of this Section--Regional Degradation--Asia
(5TC) Top of this Chapter--Degradation of Irrigated Lands
(8) Top of this Review's Appendices (units, conversions, definitions)
(9) Top of this Review's Reference List
(SE) Topsoil Loss--Causes, Effects, Implications
(DF) Forest Land Degradation: A Global Perspective
(OG) Grazing Land Degradation: A Global Perspective
(IR) Irrigated Land Degradation: A Global Perspective (Current Choice)
(FI) Fishery Degradation: A Global Perspective
(T) Title Page of this entire web site (IMPORTANT--visit early!)
!- --------------------------------------------------------------------------ir5

SECTION (5-C) - Regional Degradation--Africa and Australia
[1] Africa (North), [2] Egypt, [3] Australia

[1] Africa (North)
Irrigated agriculture is rather non-productive in the 2000 km2 of irrigated croplands of the arid- and desert zones.~ Lack of drainage causes excessive salt deposits or hydromorphology (waterlogging?) or both (70L1).

[2] Egypt
Half of all irrigated land is salinized enough to show reduced yields (90P1).

Over the past 22 years, Egypt has reclaimed 3,600 km2 south of the Nile Delta, but 65 km2 have relapsed into barren wastes, and the remainder can be operated only through massive subsidies (77A1).

Egypt's Aswan Dam made possible the cultivation of over 3,600 km2 of former desert, but 810 km2 of this are once again barren (due to salinity?), and the rest are cultivated at a loss (77U1).

Before Aswan Dam, annual flooding washed salt away.~ After Aswan Dam, irrigation replaced annual flooding, so Nile Delta salt levels are rising rapidly.~ Before dams, seasonal floods were effective in carrying salts to the rivers.~ Today the salt is being stored within river basins, and salt levels in irrigated soils are rising (87P1).

Ref.76E1 describes salination problems of Egyptian irrigation systems outside the Nile flood-plain.~ Waterlogging and salinity are becoming major problems.~ The Aswan Dam has contributed to the salination problem (76E1).

Waterlogging and salinity have reduced yields of major crops by 30% (92P1).~ Cultivated land in the Nile Delta (100% irrigated) grows increasingly saline, since annual flooding no longer flushes out evaporitic salt (Ref.40 of 93S1).

Nearly 50% of Egypt's Delta is affected by salinity, alkalinity, and waterlogging.~ Rising water tables in Egypt's Western Desert is causing salination (89E1).~ 75% of Egypt's Delta topsoil is non-saline, 15% moderately-to-highly saline; 10% is very highly saline (89E1).

[3] Australia
In Southwestern Australia, 4400 km2, once used as cropland or pasture, are now salt-affected--a +500% increase in salinized area since 1955.~ Virtually all secondary soil salinity is found in the rain-fed wheat belt of Western Australia where 130,000 km2 of indigenous woodlands have been cleared in the 20th Century (90C1).

800 km2 in the valley of the River Murray and in northern Victoria are affected by secondary salinity and alkalinity (Ref.389 of 88S1).

Over 45,000 km2 of Australia's drylands--10% of all croplands and more than 8% of irrigated area--are affected by salination.~ Area affected by dryland salting doubled in size during 1975-89 (96G2).


SECTION (5-D) - Regional Degradation--N. and S. America

(Alphabetical by Country or State) [1] USA, [2] California, [3] Colorado, [4] New Mexico, [5] Texas, [6] Argentina, [7] Brazil, [8] Mexico, [9] Haiti, [10] Peru

[1] USA
In the US, 20% of irrigated land suffers from salination (99P1) (00W2).

21% of irrigated US cropland is fed by drawing down water tables (USDA data) (91B3).

About 25% of US irrigated land suffers from some degree of salination or waterlogging (78D1) (82S1).

Salt accumulation is lowering crop yields on 25-30% (50,000 km2) of US irrigated land (92P1).

Bower and Foreman estimated that 25% of irrigated soils in the US were salty or alkaline to the point where productivity was lowered (71R1).

Dry cropland areas in the western US where production has ceased or is significantly reduced due to increased salinity: 600-800 km2.~ This area is growing at 10%/year (80C1).

20-25% of all US irrigated land (40,000 km2) suffers from salt-caused yield reductions (Ref.2 of 85E1).

Maps showing US irrigation problem areas (salinity and/or waterlogging) in 17 western states are shown in Ref.82S1 and in Ref.85E1.

25-35% of irrigated western US croplands have excessive salinity (83B1).~ Salt buildup lowers crop yields on 25-30% of irrigated lands (90P1).

[2] California
25% of California's irrigated land is moderately- to heavily salted (91B2).

Of California's 34,800 km2 of irrigated land, 18,200 km2 are affected by salinity or sodicity (85G1).~ Croplands damaged by salinity are expected to increase from 18,200 to 21,000 km2 by 2000 (Ref.8 of 85G1).

The amount of water-storage capacity lost through aquifer compaction in California's Central Valley is over 40% of the combined storage capacity of all human-made reservoirs in California (00S1).

1620 km2 of irrigated farmlands in San Joaquin Valley are affected by high, brackish water tables (81S3, 81S1, 83B1) resulting in a 10% reduction in productivity since 1970.~ (Ave. rainfall= 14" in the north, and 5" in the south.) By 2080, 4,500 km2 of San Joaquin farmlands will become unproductive unless sub-surface drainage systems are installed (81S1).

Trends in salinity in irrigated lands in San Joaquin Valley indicate that in two decades, 3,000 km2 will be affected (82S1).~ San Joaquin Valley crop yields have declined 10% ($31.2 million) since 1970 because of high saline water tables.~ Losses are expected to increase to $321 million/year if action is not taken (Ref.19 of 85E1).

Not far below the surface of California's San Joaquin Valley and Imperial Valley (like the Tigris-Euphrates Valley) is a tight layer of material that blocks water passage.~ Hence saltwater builds up.~ When it meets the roots of plants, salt is drawn up to the surface, destroying the irrigation system (81S1).

Imperial Valley (S. Cal.) experienced about 90% of the agricultural damage from salinity in the US portion of the Colorado River Basin.~ Imperial Valley is under pressure to give some of its water to nearby cities (87P1).~ The Imperial Dam on the Lower Colorado River sends about 95% of the water flowing into it to California and to Wellton-Mohawk (AZ) for irrigation.~ When Wellton Mohawk opened in 1961, the average salinity of the water delivered by the Colorado to Mexico doubled to 1,500 ppm., causing Mexican crop failures and protests (87P1).

A recent study in the Grand Valley (which puts 0.5 million tons of salt into the Colorado River yearly) found that 85% of the water reaching rivers was irrigation water, carrying salt from marine shales that lie under local farms (87P1).

Some irrigation problems (water-table rises, salt-buildup) and solutions (improved drainage) in Southern California's Imperial Valley are described in Ref.56T1.

[3] Colorado
In Crowley County, salt crusts are visible on a number of irrigated fields.~ Urban areas (Colorado Springs, Pueblo) are buying water rights, so irrigation systems are being abandoned (Ref.331 of 81S1).

Arkansas River salinity increases from a trace to 2200 mg/l. over 120 miles (85E1).~ (This is usually due to seepage and return-flow from irrigated land.)

[4] New Mexico
In the Pecos River, salinity increases from 760 to 2020 mg/l. over 30 miles (85E1).

[5] Texas
Rio Grande River salinity increases from 870 to 4000 mg/l. over 75 miles (Ref.5 of 85E1).~ (This is usually due to seepage and return flow from irrigated land.)

[6] Argentina
A U.N. survey found that 20,000 km2 of irrigated land have declined in productivity due to salination and alkalination (78B2).

20-30% of agricultural lands in the Patagonia region have been damaged by salt accumulation (76E1).

50% of the 400 km2 irrigated in the 19th century are salinized (88S1).

[7] Brazil
In N.E. Brazil, at least 50% of irrigated land is affected by water-logging and salinity.~ Yields on some irrigated fields are lower than before irrigation (76E1).

Brazil, Sertao (nearly 3/4 of area of the Northeast Brazil): Irrigation leads rapidly to salination of soils.~ Water supplies have average salinity of 500 mg/l+ (85L1).

[8] Mexico
Salination reduces crop output by one million tons of grain/year (90P1).

[9] Haiti
FAO researchers identified salinity as the reason why N.W. Haitian farmers have had to change from peanuts and beans to cotton to cactus and thorn brush (76E1).

[10] Peru
The lack of complete studies for irrigation projects has caused increased drainage and salinity problems on the coast.~ This is the main problem facing irrigation agriculture on the coast, and affects 2500 km2.~ In all irrigation projects on the coast, drainage- and salinity problems have developed within a few years after the beginning of irrigation.~ Documentation supporting this is presented for the Santa Rosa- and several other irrigation projects (70C2).

A UN survey found that, of 8000 km2 of irrigated land in the coastal desert, 3000 km2 are affected by poor drainage and salination (Ref.27 of 78B2).

Over 2000 km2 along Peru's coast (almost a third of the cultivated area) suffers from salinity and rising water tables (76E1).

Nearly all of Peru's irrigated alluvial soils show salinity/ alkalinity (Ref.64 of 88S1).

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