3 diversity of irrigation by hydrological conditions, etc....15 1 diversity of irrigation by...
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Diversity of Irrigation by Hydrological
Conditions, etc.
Global annual precipitation averages around 1,000 mm. However, it is characterized by a verywide divergence from desert regions, where it is virtually zero, to other regions where it exceeds4,000 mm.
Irrigation undertaken with the use of agricultural water takes a variety of forms indifferent parts of the world. This results from a combination of differences inrainfall, sunshine, temperature, and other climatic conditions, differences in soil,topography, and other geographical conditions, differences in the waterrequirement of agricultural crops on farmland, and so on. These factors lead to avery rich diversity of irrigation.Meanwhile, there is a close correlation between annual precipitation and regionsthat cultivate the world's big three grains (rice, wheat and maize).If the regions are divided into arid and humid regions for comparison, it becomesthat they differ in the very purpose of irrigation.
Great diversity of precipitation supporting water cycles onthe planet, from deserts to humid regions
Annual precipitation (mm)
0 - 400
400 - 1000
1000 - 2000
>2000
Distribution of annual precipitation
Source: Climate Data sets, GNV174 - Annual precipitation (UNEP)
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Distribution of “water Balance”(calculated by subtracting potential evapotranspiration from precipitation)
400
350
300
250
200
150
100
50
0
(mm)
400
350
300
250
200
150
100
50
0
(mm)
400
350
300
250
200
150
100
50
0
(mm)
400
350
300
250
200
150
100
50
0
(mm)
400
350
300
250
200
150
100
50
0
(mm)
400
350
300
250
200
150
100
50
0
(mm)
400
350
300
250
200
150
100
50
0
(mm)
Precipitation (mm)Potential Evapotranspiration (mm)
Water Balance (mm/yr)
~-1000
-1000~-500
-500~0
0~+500
+500~+1000
+1000~+1500
+1500~
Lyon (France)
Banghazi (Libya)
San Francisco (USA)
Moscow (Russia)
Colombo (Sri Lanka)
Tokyo (Japan)
Canberra (Australia)
Jan.Mar. May Jul. Sep.
Nov. Jan.Jan.
Mar. May Jul. Sep.Nov. Jan.
Jan.Mar. May Jul. Sep.
Nov. Jan.
Jan.Mar. May Jul. Sep.
Nov. Jan.
Jan.Mar. May Jul. Sep.
Nov. Jan.
Jan.Mar. May Jul. Sep.
Nov. Jan.
Jan.Mar. May Jul. Sep.
Nov. Jan.
Note: Diagram compares annual precipitation with potential annual evapotranspiration. The actual water balance for individual regions maytherefore be different, depending on precipitation patterns and thesituation of water use.
Sources: 1) Climate Data Sets, GNV183 - Tateishi Monthly Potential and Actual Evapotranspiration and Water Balance (UNEP)
2) Fukui, E., et al. "Japan and World Climate Charts", 1985 (Tokyodo Shuppan) (original chart by J.R. Mather)
The "water balance" is calculated by subtracting potential evapotranspiration from precipitation.This balance is negative in most parts of Africa (except Central Africa), the Middle East,Central Asia, central and western North America, western South America, Australia, andelsewhere.
Regions having annual precipitation of less than 500 mm are called "arid regions". In theseregions, soil is often desertified, and agricultural products are difficult to cultivate without irrigation.By contrastingly, arid-subhumid regions with annual precipitation of 500 - 1,000 mm are generallyused as grasslands for grazing livestock, as well as rain-fed cultivation of beans, wheat and othercrops that have a smaller water requirement. In this pamphlet, regions with annual precipitation of less than 1,000 mm (including arid-subhumidregions) shall be referred to as "arid regions", and those with annual precipitation above this as"humid regions" for the purpose of our discussion.
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In East and Southeast Asia, there are regions that have annual precipitation of more than 1000mm, under the influence of monsoons. These regions belong to temperate, subtropical or tropicalzones, and include zones in which orogenic movement is lively due to plate tectonics (shift zones).They are generally assumed to include Japan, the Korean peninsula, China (except the westerninterior, the Yellow River basin, and surrounding areas), all of Southeast Asia (the Indochinapeninsula and the island nations), Nepal, Bhutan, Bangladesh, Sri Lanka, and areas east of theDeccan Plateau plus southwestern coastal regions of India. In this pamphlet, these regions shallbe referred to collectively as the "Asia monsoon region".The Asia monsoon region generally has extreme seasonal or short-term fluctuations in river flowrate, under the influence of monsoons. It also has a relatively conspicuous tendency for flashflooding, and it contains numerous fast-flowing rivers.This is why, at first glance, the countries in this region appear to have large absolute quantities ofwater resources. But in fact, they suffer from severe water shortages and water pollution, resultingfrom an imbalance against increasing demand for water due to population growth and otherfactors. Thus, these countries could be said to suffer from severe hydrological conditions,demanding immense efforts to improve the utilization efficiency of water resources.
The Asia monsoon region: A warm, high-precipitationclimate with severe hydrological conditions
Diversity of Irrigation byHydrological Conditions,etc.3
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3
North and Central America
96 (12.9%)
South America35
(4.7%)
Europe133
(17.8%)
Russia48
(6.5%)
West Asia52
(7.0%) East Asia98
(13.0%)
Southeast Asia49
(6.6%) South Asia128
(17.1%) Oceania16
(2.2%)
Africa92
(13.0%)
OtherRice
Wheat
Maize
Distribution of major cereal harvested areas
Note: Upper - Cereal harvested area (million ha) Lower - The ratio to world cereal harvested area
Source: Statistical Databases (FAO)
Rice, wheat and maize are the three grains with the highest individual production volumes in theworld. A survey of the cultivation of these "big three grains" in various regions of the world showsthat the cultivation of rice (paddy rice) predominates in East Asia, Southeast Asia and South Asia.Southeast Asia, in particular, accounts for the majority of production. The cultivation of wheat,meanwhile, predominates in Europe, Russia, West Asia, and Australia. Maize is the dominant cropin South America, while wheat and maize account for the majority of grain cultivation in North andCentral America.Paddy rice has a large physiological water requirement, on the one hand, but is also most resistantto inundation. Moreover, although it has a higher ratio of production for food, it also has anextremely low ratio of use in international trade. Of the big three grain crops, therefore, it offers thegreatest potential for self-sufficiency. By contrast, maize has a lower ratio of use for food, and ismore important as a fodder grain.
The world's agricultural production: Regional characteristicsin cultivation of the "big three grains" (rice, wheat and maize)
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154 214 138
Name
Rice PaddyWheatMaize
Harvested area(2000) 1)
(mil. ha)
600 585 593
Annual production(2000) 1)
① (mil. tons)
682 557 349
Water required to produce 1g of
dried plant body2)
(g)
○ × ×
Ability to withstand immersion
521 419 115
Name
Rice PaddyWheatMaize
Consumption of ① as food 1)
②
(mil. tons)
87 73 19
②/① (%)
③/① (%)
36 138 85
Amount of ① exported 1)
③
(mil. tons)
6 24 14
Comparison of the 3 major grains
Notes: 1) Rice production is based on unhulled rice.2) The amount of water required to produce 1g of dried prant body has a degree of latitude depending on the reference.
Source: 1) Statistical Databases (FAO)2) Black, C. C., T. M. Chen and R. H. Brown, Biochemical basis for plant competition. Weed Soc.17,10-20, 1969
Diversity of Irrigation byHydrological Conditions,etc.3
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Ratio of wheat production by region (2000)
4
11.3%
3.9%
3.5%
15.9%
22.0% 2.5%
40.9%
North and Central America
Asia
South America
Africa
Oceania
Europe
Former Soviet Union countries
Source: Statistical Databases (FAO)
Top 10 wheat production countries (2000)
12345678910
ChinaIndiaUSAFranceRussian FederationCanadaAustraliaGermanyPakistanTurkey Sub-totalOther Total
CountryRank
17 13 11 7 6 5 4 4 4 4 75 25 100
Ratio to world production
(%)
100 76 61 37 35 27 22 22 21 21 422 152 585
Production
(mil. tons)
27 27 22 5 20 11 12 3 8 9
144 70 214
Harvested area
(mil. ha)
Source: Statistical Databases (FAO)
The world's wheat production in 2000 was about 590 million tons. Of this total, 40.9% wasproduced in Asia, 22% in Europe, and 15.9% in North and Central America. In terms of productionvolume by country, the majority of the world's wheat is produced in regions with annualprecipitation of less than 1,000 mm, including the 10 countries with the largest production volumes.
Asia and the West each produce 40% of the world's wheat
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Relationship between precipitation and wheat planting ratio
Annual precipitation (mm)
Ratio
of w
heat
har
vest
ed a
rea
to c
erea
l har
vest
ed a
rea
(%)
0
25
50
75
100
0 500 1,000 1,500 2,000
UzbekistanUzbekistan
Saudi ArSaudi Arabiaabia
IrIranan
GreeceGreece
SyrSyriaia
EgyptEgypt
SwSwedeneden
PPolandoland
SpainSpain
HungarHungaryyEthiopiaEthiopia
ArgentineArgentine
BelgiumLuxBelgiumLuxembourgembourgEnglandEngland
ItalyItaly
RumaniaRumania
DenmarDenmarkk
UkrUkraineaineBulgarBulgariaia
ChileChile
Uzbekistan
Saudi Arabia
Iran
Greece
Syria
Egypt
Sweden
Poland
Spain
HungaryEthiopia
Argentine
BelgiumLuxembourgEngland
Italy
Rumania
Denmark
UkraineBulgaria
Chile
Mainly Middle Eastern countries
Australia
Pakistan
Russian Federation
Canada
Turkey
Germany USA
France
India (northern)
China (central and western)
Mainly European countries
Notes: 1) Annual precipitation in China and India is the figure for main cities in provinces that cultivate wheat (China: Beijing, India: New Delhi). In other countries, it is the figure for the national capital or cities near the capital.
2) Countries with wheat cultivation of less than 100,000ha or a wheat cultivation ratio of less than 10% are not included. The diagram was drawn up to show the top 30 wheat producing countries.
3) The top 10 wheat producing countries are boxed.
Source: 1) Statistical Databases (FAO)2) Japan Meteorological Agency, 1994
Diversity of Irrigation byHydrological Conditions,etc.3
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5
2.9%
0.4% 1.8% 3.4% 0.2%
0.2%
91.1%
North and Central America
Asia
South America
Africa
Oceania
Europe
Former Soviet Union countries
Ratio of rice production by region (2000)
Source: Statistical Databases (FAO)
Top 10 rice production countries (2000)
12345678910
ChinaIndiaIndonesiaBangladeshVietnamThailandMyanmarPhilippinesJapanBrazil Sub-totalOther Total
CountryRank
32 22 9 6 5 4 4 2 2 2 87 13 100
Ratio to world production
(%)
190 129 52 38 33 26 21 12 12 11 524 76 600
Production(unhulled)(mil. tons)
30 45 12 11 8 10 6 4 2 4
132 22 154
Harvested area
(mil. ha)
Source: Statistical Databases (FAO)
The world's rice production in 2000 was about 600 million tons (unhulled), of which 91.1% wasproduced in Asia. The top 10 rice-producing countries all have annual precipitation in excess of1,500 mm. About 87% of the world's rice is produced in these 10 countries, of which 9 are in Asia.Similarly, countries whose proportion of rice cultivation to the total grain cultivation area exceeds50% generally have annual precipitation of more than 1,500 mm.
Asia, with annual precipitation of more than 1,500 mm,produces 90% of the world's rice
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Annual precipitation (mm)
Ratio
of r
ice
harv
este
d ar
ea to
cer
eal h
arve
sted
are
a (%
)
0
25
50
75
100
0 1,000 2,000 3,000 4,000
China (southern)
Brazil
Vietnam
India (eastern)
Philippines
Myanmar
Bangladesh
Indonesia
Thailand
Japan
Mainly Asian countries
Mainly South Americanand African countries
IvIvorory Coasty CoastUrUruguauguayy
ColombiaColombia
PPereruu
GuianaGuiana
EgyptEgypt
CubaCuba
MadagascarMadagascar
KKoreaoreaLaosLaos
MalaMalaysiaysiaGuyGuyanaana
SrSri Lankai LankaLiberLiberiaia
SierrSierra Leonea Leone
BoliviaBolivia
MozambiqueMozambiqueNigerNigeriaia
MaliMali
TTanzaniaanzania
PPakistanakistanVVenezuelaenezuela
EcuadorEcuador
Ivory CoastUruguay
Colombia
Peru
Guiana
Egypt
Cuba
Madagascar
KoreaLaos
MalaysiaGuyana
Sri LankaLiberia
Sierra Leone
Bolivia
MozambiqueNigeria
Mali
Tanzania
PakistanVenezuela
Ecuador
Notes: 1) Annual rainfall is the value for the major cities in the region (China: Hong Kong, India: Calcutta) where rice is growth primarily in the case of China and India2). It is the national average in the case of Japan3).In other countries, it is the value in the capital or in a city near the capital2).
2) Countries with less than 100,000 ha in rice cultivation or countries with less than 10% are not indicated in the diagram above.
3) The name of the ten top ranking rice producing countries are displayed in boxes.
Source: 1) Statistical Databases (FAO)2) Japan Meteorological Agency, 19943) Land & Water Resources Bureau, Ministry of Land, Infrastructure and Transport, 2002
Diversity of Irrigation byHydrological Conditions,etc.3
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Main purpose of irrigation by region
6
>1,000mm
500~1,000mm
250~500mm
<250mm
Humidregions
Arid regionsIncluding arid-subhumid regions
Annual precipitationRegion Main purpose ofirrigation
(Reference) Main purpose of drainage
・Supplement the non-uniform temporal and spatial distribution of rainfall・Prevent frost damage・Hinder the growth of weeds・Insurance for short-term drought・Increase crop revenues that require a
water supply that is more uniform than rainfall・Produce high value crops that would be
impossible if they depended on rainfall・Supplement rainfall shortages during
the crop production season・An essential condition for cultivation
・Remove excess rainfall
・Prevent salinization
・An essential condition for the prevention of salinization
Inundation during the rainy season(Bangladesh)
Irrigation zone in northern Israel
Source: Ie-no-hikari Association, 1995
In arid regions, where precipitation is small, the absolute volume of moisture needed for the growthof crops tends to be in short supply. Therefore, supplying the moisture needed for crop growth isthe single main purpose of irrigation in these regions. The same may also be true in high-precipitation humid regions when prolonged dry weathercauses unforeseen abnormal droughts. Normally, however, the purpose of irrigation in humidregions is not only to supply the moisture needed for crops to grow. Paddy field irrigation,particularly predominant in the Asia monsoon region of all humid regions, supplies agriculturalwater in excess of the moisture supply volume of crops in the rainy season, and at other timeswhen potential water resources are abundant. By so doing, it achieves a multiplicity of purposes,including simplifying the work of plowing the land (turning the soil in paddy fields), reducing theproliferation of weeds, making use of the nutrients present in irrigation water, preventing soilerosion, preventing replant failure, and removing salinity. It also makes it possible, for example, toavoid typhoon damage immediately before the harvest by irrigating during the dry season, therebyadvancing the planting phase. Irrigation, therefore, also broadens the range of options for cropsand planting times.
Irrigation has a single purpose in arid regions but amultiple one in humid regions
Source: Prepared with reference to Hitoshi Fukuda, 1974
Diversity of Irrigation byHydrological Conditions,etc.3
Source: Ie-no-hikari Association, 1995
25
1
Primary arable areaSeasonally
arable area
Ground surfaceVillage
Vertical shaft
Spring water
Increase in salt
concentration
Aquiclude
Village
Open channel zone
Transferzone
Mother wellTunnelzone
Impermeable layer
Drinking water
Groundwater level
Aquifer
Mother wellMother well
4
Source: Toshisuke Maruyama, Ryota Nakamura et al., 1998 (Asakura Shoten)
Irrigation in Arid Regions
A traditional form of irrigation in arid regions is the "khanat", which uses groundwater. This methodof extracting groundwater have been passed down in arid regions since prehistoric times. Thoughgoing under different names in different countries, they involve driving vertical shafts into theground, digging horizontal underground tunnels that stretch laterally from hundreds of meters totens of kilometers, from which groundwater is gathered.
In arid regions, wisdom on securing water for agricultural production and daily lifehas been passed down since ancient times. These traditional forms of irrigationare characterized as being sustainable, even though relatively small in scale.Meanwhile, in Israel, central and western USA, Australia and other aridregions,modern large-scale irrigation systems have been developed. Here, large-scale, low-cost farming has evolved making use of the climatic conditions of aridregions, i.e. warmth and plenty of sunshine, as well as expansive land conditions. The side effects of this, however, are concerns over the accumulation of salinityin soil, the loss of groundwater resources, the impact on ecosystems, and othernegative aspects. A famous case of this is the example of the Aral Sea. Suchcases can cause situations that threaten human habitation itself. The occurrenceof these side-effects could also be seen as another example in which thecharacteristics of rain-starved arid regions are conspicuously manifest.
Groundwater used since ancient times due to lack of precipitation
Plane and cross-sectional views of a qanat(example on the Arabian Peninsula)
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Conceptualization of irrigation using floodwater (example in Pakistan)
2
Simple water diversion Water harvesting system from the main water channel
Bank
Bank
Irrigated area
Irrigated area
Earth dam
Source: Toshisuke Maruyama, Ryota Nakamura et al., 1998 (Asakura Shoten)
Conceptualization of water harvesting (example in Tunisia)
160
22
EL (m)
Water harvesting area
Closs sectional view
100(m)
Arable area
Arable areaWater harvesting area
Source: Toshisuke Maruyama, Mashahiko Tomita et al., 1996 (Asakura Shoten)
In arid regions, dams are sometimes built on dried-up rivers in which water does not normally flow.From these, water is extracted in flood seasons and used for irrigation. Elsewhere, the "water harvesting method" is sometimes used. Here, rainwater is collected on landof a certain size, and crops are sown in hollows and low-lying areas on a smaller part of that land.This is classified as rain-fed agriculture, but it could also be characterized as self-contained,sustainable small-scale irrigation.
Effective use of rainwater and other precious watersources
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Golan Heights
Syria
Lebanon
Haifa
West Bank of the Jordan
Tel Aviv
Sedom
Gaza
Negev Desert
Jordan
CanalReservoirPump station
Egypt
Eilat
Jerusalem
Dead Sea
Sea of Galilee
Map of Israel
Mediterranean Sea
0
5
10
15
20
25
30
35
Tem
pera
ture
( ℃)
Prec
ipita
tion
(mm
)
0
20
40
60
80
100
120
140
160
180Har-Kenaan
Precipitation (mm) Temperature (℃)
Precipitation (mm) Temperature (℃)
0
5
10
15
20
25
30
35
Tem
pera
ture
( ℃)
Prec
ipita
tion
(mm
)
0
20
40
60
80
100
120
140
160
180Eilat
Jordan River
Janu
ary
March
May July
Septe
mber
Novem
ber
Janu
ary
March
May July
Septe
mber
Novem
ber
Kinneret Negev National Canal (Israel)
Source: 1) Ie-no-hikari Association, 19952) Israel Central Bureau of Statistics website
3
In Israel, water is lifted from the Sea of Galilee in the north of the country, where there is relativelyabundant rainfall in the winter. From here, 300 million cubic meters of water a year are conveyedto Tel Aviv in the center and to the southern Negev desert (where rainwater is virtually nil) throughwater channels that traverse the country for about 200 km. However, since even then it is still notpossible to maintain a supply commensurate with the demand for water, the reuse of processedsewage and other initiatives are now being promoted.
Desert zones irrigated with water from highlands as far as200 km away
Irrigation in Arid Regions4
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4
San Francisco
San Francisco
Los Angeles
More than 2000mm
1500―2000
1000―1500
500―1000
250― 500
125― 250
Less than 125mm
0
5
10
15
20
25
30
0
20
40
60
80
100
120
Tem
pera
ture
( ℃)
Prec
ipita
tion
(mm
)
Janu
aryFe
bruary
March
April
MayJu
ne July
Augu
stSe
ptembe
rOcto
ber
Novem
ber
Decem
ber
Precipitation (mm) Temperature (℃)
125125125
125125125250250250
250250250
500500500
500500500
500500500
500500500
500500500
500500500
500500500
100010001000
100010001000150015001500
150015001500
150015001500200020002000
1500
1500
1500
Source: 1) Tatsuro Katsuyama, 1993 (Chikyusha)2) Japan Meteorological Agency, 1994
Annual precipitation in California
Annual average precipitation in California, USA, is 580 mm. Near the northern Sierra Nevadamountains it exceeds 2,000 mm, while the central and southern parts are mostly arid regions withless than 250 mm. The northern rainwater and snowmelt water are stored in a group of hugedams, before being carried through the 710 km California Water Canal (flow rate 370 m3 persecond) and others to irrigate more than 3 million ha of arable land. Making maximum use of thisplentiful water and a warm climate, California's production of agricultural produce is now thehighest in the entire USA, in monetary terms. However, the salinity contained in low concentrationsin irrigation water has gradually accumulated in irrigated arable land. Due to this and other factors,about 900,000 ha of irrigated arable land is already affected by salinity accumulation.
Wasteland revived by irrigation
29
Oregon
Sacramento River
Hoover Dam
San Joaquin River
Sacramento plains
(1960)
(1961)
San Luis Dam
(1967)
California Canal
(1967)
Delta Mendota Canal
(1951)
All American Canal
(1938)
Oroville dam
(1968)
Las Vegas
San Francisco
Mexico
Sacramento
( )
Major agricultural area
Rice production areaCanal
Dam
year of completion
Clair Engle DamClair Engle Dam
Colorado RiverColorado River
Shasta DamShasta Dam
((19451945))
Corning CanalCorning Canal
Tehama Colusa canalTehama Colusa canal
Friant-Kern CanalFriant-Kern Canal
((19441944))
Central plains
Central plains
FresnoFresno
Los AngelesLos Angeles
San DiegoSan Diego
Imperial plainsImperial plains
Monterrey plains
Monterrey plains
Sierra Nevada M
ountains
Sierra Nevada M
ountains
Clair Engle Dam
Colorado River
Shasta Dam
(1945)
Corning Canal
Tehama Colusa canal
Friant-Kern Canal
(1944)
Central plains
Fresno
Los Angeles
San Diego
Imperial plains
Monterrey plains
Sierra Nevada M
ountains
Pacific Ocean
Nevada
Arizona
Major water use facilities in California
Farmland subject to reduced productivity dueto salinity accumulation
Source: U. S. Soil Conservation Service, 1983
Source: 1) Tatsuro Katsuyama, Turning Point for, 1993(Chikyusha)
2) California State Water Resources Bureau
Irrigation in Arid Regions4
30
Paddy field zone and annual precipitation in Australia
5
800mm
800mm
500mm
500mm
800mm 500mmSydney
Paddy fieldPaddy field
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
Region Paddy field
MIA
CIA
MV
total
40,000 ha
24,000 ha
56,000 ha
120,000 ha
Murray River
Murrumbidgee River
DamWeir Urban areaIrrigated area
100km
10.0 million m3/day
4.90 million m3/day
Dam
Dam
Dam
1.6 1.6 million mmillion m331.6 billion m3
3.0 billion m3
1.0 billion m3
CIA regionMV region
MIA region (190,000 ha)
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
Summary of paddy field zone
The Murray River basin in southeastern Australia is an arid region with annual precipitation ofabout 400 mm. Here, a paddy field zone of about 120,000 ha has been developed, using anirrigation system that channels water from a group of massive dams some distance away. Usingsuperior cultivation technology and favorable sunshine conditions, a high single yield of 8 tons/ha(unhulled) has been achieved. Due to progressive underground percolation of water from paddyfields over such a wide area, however, water-logging and salt damage (accumulation of soilsalinity near the ground surface) have occurred in nearby upland fields and perennial croplands.To address this, shallow groundwater is being forcibly drained, but effluents containing largeamounts of salinity cannot be released into rivers downstream. Therefore, the water is channeledinto a massive evaporation reservoir constructed from 2,100 ha of purchased farmland, where it isdisposed of through evaporation.
Paddy field irrigation in arid regions
31
evaporation pond
well and pipeline
N 0 5km
Evaporation pond and drainage facilities
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
Vast evaporation pond
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
Irrigation in Arid Regions4
32
Scene of central-pivot irrigation
6
Source: Chiba Prefectural Information Education Center (provided by KiyoshiAndo)
Distribution of annual precipitation in the U.S. and the location of the Ogallala aquifer
30~40
0~10 40~6010~20 60~10020~30 >100
Annual precipitataion (inches)
Annual precipitaion 20-inch (510mm) line↑
West East
:Ogallala aquifer
Source: Hattori, 1992 (Fumin Kyokai)
ColoradoKansas
Oklahoma
Nebraska
Texas (panhandle)
In the central USA, meanwhile, large-scale agriculture has been developed using a system called"center pivot irrigation". This taps groundwater from a vast groundwater source known as theOgallala Aquifer, which stretches from northern Texas to Oklahoma, Kansas, Colorado, andNebraska.The irrigated arable land that uses this aquifer accounts for about a fifth of all irrigated arable landin the USA. But since 22.2 billion cubic meters of groundwater - or three times the volume ofgroundwater accumulated from rainwater (6-8 billion cubic meters annually) - are brought up everyyear, falling groundwater levels are becoming a problem. Meanwhile, due to rising costs for waterpumping accompanying this, many of the farmers who depend on this aquifer are abandoningirrigation agriculture.
Formation of a granary zone by tapping groundwater
Ogallala aquifer
Irrigation in Arid Regions4