Download Diversity of Irrigation by Hydrological Conditions, etc.

3
Diversity of Irrigation by Hydrological
Conditions, etc.
Irrigation undertaken with the use of agricultural water takes a variety of forms in
different parts of the world. This results from a combination of differences in
rainfall, sunshine, temperature, and other climatic conditions, differences in soil,
topography, and other geographical conditions, differences in the water
requirement of agricultural crops on farmland, and so on. These factors lead to a
very rich diversity of irrigation.
Meanwhile, there is a close correlation between annual precipitation and regions
that cultivate the world's big three grains (rice, wheat and maize).
If the regions are divided into arid and humid regions for comparison, it becomes
that they differ in the very purpose of irrigation.
1
Great diversity of precipitation supporting water cycles on
the planet, from deserts to humid regions
Global annual precipitation averages around 1,000 mm. However, it is characterized by a very
wide divergence from desert regions, where it is virtually zero, to other regions where it exceeds
4,000 mm.
Distribution of annual precipitation
Annual precipitation (mm)
0 - 400
400 - 1000
1000 - 2000
＞2000
Source: Climate Data sets, GNV174 - Annual precipitation (UNEP)
15
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, and
elsewhere.
Distribution of “water Balance”
(calculated by subtracting potential evapotranspiration from precipitation)
（mm）
400
（mm）
400
Lyon (France)
350
300
300
250
250
200
200
150
150
100
100
50
50
0
0
Moscow (Russia)
（mm）
350
400
Tokyo (Japan)
350
300
250
200
150
100
50
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
0
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
（mm）
400
350
San Francisco (USA)
300
250
200
150
100
50
0
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
（mm）
（mm）
400
350
Water Balance (mm/yr)
∼−1000
−1000∼−500
−500∼0
0∼＋500
＋500∼＋1000
＋1000∼＋1500
＋1500∼
Precipitation (mm)
Potential Evapotranspiration (mm)
400
Banghazi (Libya)
Colombo (Sri Lanka)
（mm）
400
350
350
300
300
300
250
250
250
200
200
200
150
150
150
100
100
100
50
50
0
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
0
Canberra (Australia)
50
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
0
.
.
.
r.
y
v.
Jan Ma Ma Jul. Sep No Jan
Note: Diagram compares annual precipitation with potential annual
evapotranspiration. The actual water balance for individual regions may
therefore be different, depending on precipitation patterns and the
situation 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)
Regions having annual precipitation of less than 500 mm are called "arid regions". In these
regions, 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 generally
used as grasslands for grazing livestock, as well as rain-fed cultivation of beans, wheat and other
crops that have a smaller water requirement.
In this pamphlet, regions with annual precipitation of less than 1,000 mm (including arid-subhumid
regions) shall be referred to as "arid regions", and those with annual precipitation above this as
"humid regions" for the purpose of our discussion.
16
3
2
Diversity of Irrigation by
Hydrological Conditions,
etc.
The Asia monsoon region: A warm, high-precipitation
climate with severe hydrological conditions
In East and Southeast Asia, there are regions that have annual precipitation of more than 1000
mm, under the influence of monsoons. These regions belong to temperate, subtropical or tropical
zones, 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 western
interior, the Yellow River basin, and surrounding areas), all of Southeast Asia (the Indochina
peninsula and the island nations), Nepal, Bhutan, Bangladesh, Sri Lanka, and areas east of the
Deccan Plateau plus southwestern coastal regions of India. In this pamphlet, these regions shall
be referred to collectively as the "Asia monsoon region".
The Asia monsoon region generally has extreme seasonal or short-term fluctuations in river flow
rate, under the influence of monsoons. It also has a relatively conspicuous tendency for flash
flooding, and it contains numerous fast-flowing rivers.
This is why, at first glance, the countries in this region appear to have large absolute quantities of
water resources. But in fact, they suffer from severe water shortages and water pollution, resulting
from an imbalance against increasing demand for water due to population growth and other
factors. Thus, these countries could be said to suffer from severe hydrological conditions,
demanding immense efforts to improve the utilization efficiency of water resources.
17
3
The world's agricultural production: Regional characteristics
in cultivation of the "big three grains" (rice, wheat and maize)
Rice, wheat and maize are the three grains with the highest individual production volumes in the
world. A survey of the cultivation of these "big three grains" in various regions of the world shows
that 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 crop
in South America, while wheat and maize account for the majority of grain cultivation in North and
Central America.
Paddy rice has a large physiological water requirement, on the one hand, but is also most resistant
to inundation. Moreover, although it has a higher ratio of production for food, it also has an
extremely low ratio of use in international trade. Of the big three grain crops, therefore, it offers the
greatest potential for self-sufficiency. By contrast, maize has a lower ratio of use for food, and is
more important as a fodder grain.
Distribution of major cereal harvested areas
Russia
48
（6.5％）
Europe
133
（17.8％）
North and
Central America
96
（12.9％）
West Asia
52
（7.0％）
Africa
92
（13.0％）
Other
Rice
Maize
Wheat
South America
35
（4.7％）
Note: Upper - Cereal harvested area (million ha)
Lower - The ratio to world cereal harvested area
Source: Statistical Databases (FAO)
18
South Asia
128
（17.1％）
East Asia
98
（13.0％）
Southeast Asia
49
（6.6％）
Oceania
16
（2.2％）
3
Diversity of Irrigation by
Hydrological Conditions,
etc.
Comparison of the 3 major grains
Name
Rice Paddy
Wheat
Maize
Name
Rice Paddy
Wheat
Maize
Notes:
Harvested area Annual production Water required to
(2000) 1）
(2000) 1）
produce 1g of
dried plant body 2）
①
(mil. ha)
(g)
(mil. tons)
154
214
138
600
585
593
Consumption of ①
as food 1）
②
②／①
(mil. tons)
(%)
521
419
115
87
73
19
682
557
349
Ability to
withstand
immersion
○
×
×
Amount of ① exported 1）
③
(mil. tons)
36
138
85
③／①
(%)
6
24
14
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
19
4
Asia and the West each produce 40% of the world's wheat
The world's wheat production in 2000 was about 590 million tons. Of this total, 40.9% was
produced in Asia, 22% in Europe, and 15.9% in North and Central America. In terms of production
volume by country, the majority of the world's wheat is produced in regions with annual
precipitation of less than 1,000 mm, including the 10 countries with the largest production volumes.
Ratio of wheat production by region (2000)
11.3％
3.9％
3.5％
40.9％
15.9％
2.5％
22.0％
Asia
Africa
Europe
South America
Oceania
Former Soviet
Union countries
North and
Central America
Source: Statistical Databases (FAO)
Top 10 wheat production countries (2000)
Rank
1
2
3
4
5
6
7
8
9
10
Country
China
India
USA
France
Russian Federation
Canada
Australia
Germany
Pakistan
Turkey
Sub-total
Other
Total
Source: Statistical Databases (FAO)
20
Ratio to
world production
(%)
17
13
11
7
6
5
4
4
4
4
75
25
100
Production
Harvested area
(mil. tons)
(mil. ha)
100
76
61
37
35
27
22
22
21
21
422
152
585
27
27
22
5
20
11
12
3
8
9
144
70
214
3
Diversity of Irrigation by
Hydrological Conditions,
etc.
Ratio of wheat harvested area to cereal harvested area (%)
Relationship between precipitation and wheat planting ratio
100
Mainly Middle Eastern countries
Uzbekistan
Australia
75 Saudi Arabia
Arabia
Turkey
Iran
Iran
Greece
50
Syria
Syria
Egypt
BelgiumLuxembourg
BelgiumLuxembourg
England
France
Chile
Bulgaria
Bulgaria
Ukraine
Ukraine
Canada
Italy
Russian Federation
Denmark
Denmark
Germany
Spain
USA
India (northern)
Sweden
Sweden
China (central and western)
Hungary
Hungary
Mainly European countries
0
0
Argentine
Rumania
Poland
Poland
25
Pakistan
500
Ethiopia
1,000
1,500
2,000
Annual precipitation (mm)
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
21
5
Asia, with annual precipitation of more than 1,500 mm,
produces 90% of the world's rice
The world's rice production in 2000 was about 600 million tons (unhulled), of which 91.1% was
produced in Asia. The top 10 rice-producing countries all have annual precipitation in excess of
1,500 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 exceeds
50% generally have annual precipitation of more than 1,500 mm.
Ratio of rice production by region (2000)
1.8％
3.4％
0.2％
0.4％
0.2％
2.9％
91.1％
Asia
Africa
Europe
South America
Oceania
Former Soviet
Union countries
North and
Central America
Source: Statistical Databases (FAO)
Top 10 rice production countries (2000)
Rank
Country
Ratio to
world production
(%)
Production
(unhulled)
(mil. tons)
Harvested area
1
2
3
4
5
6
7
8
9
10
China
India
Indonesia
Bangladesh
Vietnam
Thailand
Myanmar
Philippines
Japan
Brazil
Sub-total
Other
Total
32
22
9
6
5
4
4
2
2
2
87
13
100
190
129
52
38
33
26
21
12
12
11
524
76
600
30
45
12
11
8
10
6
4
2
4
132
22
154
Source: Statistical Databases (FAO)
22
(mil. ha)
3
Diversity of Irrigation by
Hydrological Conditions,
etc.
Malaysia
Malaysia
100
Laos
Guyana
Guyana
Sri Lanka
Sri
Vietnam
Korea
Korea
Liberia
Liberia
Ratio of rice harvested area to cereal harvested area (%)
Myanmar
Japan
Madagascar
Sierra Leone
Sierra
Bangladesh
Thailand
75
Indonesia
Mainly Asian countries
Cuba
Philippines
Mainly South American
and African countries
Ecuador
50
India (eastern)
Colombia
Urugua
Ur
uguayy
Uruguay
Per
eruu
Peru
Venezuela
Venezuela
25
Egypt
Bolivia
Mozambique
0
Ivor
Iv
Ivory
oryy Coast
Pakistan
Pakistan
Tanzania
Tanzania
Mali
0
Guiana
1,000
China (southern)
Brazil
Nigeria
Nigeria
2,000
3,000
4,000
Annual precipitation (mm)
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, 1994
3) Land & Water Resources Bureau, Ministry of Land, Infrastructure and Transport, 2002
23
3
Diversity of Irrigation by
Hydrological Conditions,
etc.
6
Irrigation has a single purpose in arid regions but a
multiple one in humid regions
In arid regions, where precipitation is small, the absolute volume of moisture needed for the growth
of crops tends to be in short supply. Therefore, supplying the moisture needed for crop growth is
the single main purpose of irrigation in these regions.
The same may also be true in high-precipitation humid regions when prolonged dry weather
causes unforeseen abnormal droughts. Normally, however, the purpose of irrigation in humid
regions 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 agricultural
water in excess of the moisture supply volume of crops in the rainy season, and at other times
when 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 the
proliferation of weeds, making use of the nutrients present in irrigation water, preventing soil
erosion, preventing replant failure, and removing salinity. It also makes it possible, for example, to
avoid typhoon damage immediately before the harvest by irrigating during the dry season, thereby
advancing the planting phase. Irrigation, therefore, also broadens the range of options for crops
and planting times.
Main purpose of irrigation by region
Region
Humid
regions
Arid regions
Including
arid-subhumid
regions
Annual precipitation
＞1,000mm
500∼1,000mm
250∼500mm
＜250mm
Main purpose of
irrigation
(Reference)
Main purpose of drainage
・Supplement the non-uniform temporal ・Remove excess rainfall
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 ・Prevent salinization
the crop production season
・An essential condition for cultivation ・An essential condition for the prevention
of salinization
Source: Prepared with reference to Hitoshi Fukuda, 1974
24
Inundation during the rainy season
(Bangladesh)
Irrigation zone in northern Israel
Source: Ie-no-hikari Association, 1995
Source: Ie-no-hikari Association, 1995
4
Irrigation in Arid Regions
In arid regions, wisdom on securing water for agricultural production and daily life
has been passed down since ancient times. These traditional forms of irrigation
are characterized as being sustainable, even though relatively small in scale.
Meanwhile, in Israel, central and western USA, Australia and other arid
regions,modern large-scale irrigation systems have been developed. Here, largescale, low-cost farming has evolved making use of the climatic conditions of arid
regions, 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 salinity
in soil, the loss of groundwater resources, the impact on ecosystems, and other
negative aspects. A famous case of this is the example of the Aral Sea. Such
cases can cause situations that threaten human habitation itself. The occurrence
of these side-effects could also be seen as another example in which the
characteristics of rain-starved arid regions are conspicuously manifest.
1
Groundwater used since ancient times due to
lack of precipitation
A traditional form of irrigation in arid regions is the "khanat", which uses groundwater. This method
of extracting groundwater have been passed down in arid regions since prehistoric times. Though
going under different names in different countries, they involve driving vertical shafts into the
ground, digging horizontal underground tunnels that stretch laterally from hundreds of meters to
tens of kilometers, from which groundwater is gathered.
Plane and cross-sectional views of a qanat
(example on the Arabian Peninsula)
Open channel
zone
Transfer
zone
Tunnel
zone
Mother well
Drinking water
Village
Seasonally
arable area
Primary
arable area
Vertical shaft
Mother well
Village
Ground surface
e in salt
Increas tration
n
e
c
con
iclude
Groundwater level
Aquifer
Aqu
Spring water
Impermeable layer
Source: Toshisuke Maruyama, Ryota Nakamura et al., 1998 (Asakura Shoten)
25
2
Effective use of rainwater and other precious water
sources
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 land
of 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.
Conceptualization of irrigation using floodwater (example in Pakistan)
Bank
Irrigated area
Earth dam
Irrigated area
Bank
Simple water diversion
Water harvesting system from the main water channel
Source: Toshisuke Maruyama, Ryota Nakamura et al., 1998 (Asakura Shoten)
Conceptualization of water harvesting (example in Tunisia)
W
ate
rh
ar
ve
sti
ng
ar
ea
ab
Ar
Closs sectional view
rea
a
le
EL
（m）
Water harvesting area
Arable area
22
16
0
100（m）
Source: Toshisuke Maruyama, Mashahiko Tomita et al., 1996 (Asakura Shoten)
26
4
Desert zones irrigated with water from highlands as far as
200 km away
In Israel, water is lifted from the Sea of Galilee in the north of the country, where there is relatively
abundant rainfall in the winter. From here, 300 million cubic meters of water a year are conveyed
to Tel Aviv in the center and to the southern Negev desert (where rainwater is virtually nil) through
water channels that traverse the country for about 200 km. However, since even then it is still not
possible to maintain a supply commensurate with the demand for water, the reuse of processed
sewage and other initiatives are now being promoted.
Kinneret Negev National Canal (Israel)
Har-Kenaan
35
Map of Israel
180
Golan Heights
160
30
Lebanon
di
Me
Syria
140
ean
a
Se
Jordan River
100
15
80
60
10
West Bank of
the Jordan
40
5
Precipitation (mm)
mb
0
No
ve
pte
mb
Ju
Se
Sedom
er
er
ly
y
Ma
nu
Ja
rch
0
Dead Sea
20
Ma
Jerusalem
Gaza
20
ary
Tel Aviv
120
Precipitation (mm)
Sea of
Galilee
Haifa
Temperature (℃)
ran
ter
25
Temperature (℃)
Eilat
Negev Desert
35
180
160
30
Jordan
140
Eilat
Canal
Reservoir
Pump
station
120
20
100
15
80
Precipitation (mm)
Egypt
Temperature (℃)
25
60
10
40
5
20
Precipitation (mm)
em
be
r
r
0
No
v
Se
pte
mb
e
Ju
ly
y
Ma
h
Ma
rc
ua
ry
0
Ja
n
3
Irrigation in Arid Regions
Temperature (℃)
Source: 1) Ie-no-hikari Association, 1995
2) Israel Central Bureau of Statistics website
27
4
Wasteland revived by irrigation
Annual average precipitation in California, USA, is 580 mm. Near the northern Sierra Nevada
mountains it exceeds 2,000 mm, while the central and southern parts are mostly arid regions with
less than 250 mm. The northern rainwater and snowmelt water are stored in a group of huge
dams, before being carried through the 710 km California Water Canal (flow rate 370 m3 per
second) and others to irrigate more than 3 million ha of arable land. Making maximum use of this
plentiful water and a warm climate, California's production of agricultural produce is now the
highest in the entire USA, in monetary terms. However, the salinity contained in low concentrations
in 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.
Annual precipitation in California
25
100
20
80
15
60
00
10
40
5
20
0
0
0
50
00
20 00
15
1000
1500
0
00 50
10
Ja
nu
Fe ary
bru
ar
Ma y
rch
Ap
ril
Ma
y
Ju
ne
Ju
A ly
Se ugu
pte st
m
Oc ber
t
No obe
ve r
De mbe
ce r
mb
er
150
15
Precipitation (mm)
San Francisco
500
0
50
1000―1500
25 125
0
500
500―1000
250― 500
Los Angeles
Less than 125mm
Source: 1) Tatsuro Katsuyama, 1993 (Chikyusha)
2) Japan Meteorological Agency, 1994
500
125― 250
28
5
500
12
1500―2000
0
25
More than 2000mm
Temperature (℃)
Precipitation (mm)
120
0
Temperature (℃)
San Francisco
30
4
Irrigation in Arid Regions
Major water use facilities in California
Oregon
Major agricultural area
Clair Engle Dam
Rice production area
Shasta Dam
（1945
（1945）
1945）
）
Canal
Dam
Sacramento River
（ ）
ountains
evada M
Sierra N
Corning Canal
（1960）
year of completion
Oroville dam
（1968）
Tehama Colusa canal
（1961）
San Joaquin River
tral p
Cen
Sacramento plains
Nevada
lains
Sacramento
San Francisco
Friant-Kern Canal
Delta Mendota Canal
（1944
（1944）
1944）
）
terr
Mon
（1951）
Hoover Dam
Fresno
Las Vegas
ey p
San Luis Dam
lain
s
（1967）
Colorado River
California Canal
（1967）
Pacific Ocean
Los Angeles
Source: 1) Tatsuro Katsuyama, Turning Point for, 1993
(Chikyusha)
2) California State Water Resources Bureau
Arizona
Imperial plains
San Diego
Mexico
All American Canal
（1938）
Farmland subject to reduced productivity due
to salinity accumulation
Source: U. S. Soil Conservation Service, 1983
29
5
Paddy field irrigation in arid regions
The Murray River basin in southeastern Australia is an arid region with annual precipitation of
about 400 mm. Here, a paddy field zone of about 120,000 ha has been developed, using an
irrigation system that channels water from a group of massive dams some distance away. Using
superior 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 paddy
fields over such a wide area, however, water-logging and salt damage (accumulation of soil
salinity 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 large
amounts of salinity cannot be released into rivers downstream. Therefore, the water is channeled
into a massive evaporation reservoir constructed from 2,100 ha of purchased farmland, where it is
disposed of through evaporation.
Paddy field zone and annual precipitation in Australia
800mm
500m
m
800mm
500mm
80
Paddy field
0m
500mm
m
Sydney
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
Summary of paddy field zone
MIA
regio
n (1
Region
Paddy field
MV
56,000 ha
total
er
24,000 ha
3
10.0 million m /day
120,000 ha
Dam
Weir
Urban area
Irrigated area
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
30
a)
Riv
CIA
00 h
4.90 million m3/day
Murrumbidgee River
CIA region
MV region
y
rra
40,000 ha
Mu
MIA
90,0
Dam
100km
1.0 billion m3
Dam
Dam
1.6 million
billion mm33
3.0 billion m3
4
Irrigation in Arid Regions
Evaporation pond and drainage facilities
Ｎ
0
5km
evaporation pond
well and pipeline
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
Vast evaporation pond
Source: Toshio Tabuchi, 1999 (Yamazaki Agriculture Research Institute)
31
4
Irrigation in Arid Regions
6
Formation of a granary zone by tapping groundwater
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 the
Ogallala Aquifer, which stretches from northern Texas to Oklahoma, Kansas, Colorado, and
Nebraska.
The irrigated arable land that uses this aquifer accounts for about a fifth of all irrigated arable land
in the USA. But since 22.2 billion cubic meters of groundwater - or three times the volume of
groundwater accumulated from rainwater (6-8 billion cubic meters annually) - are brought up every
year, falling groundwater levels are becoming a problem. Meanwhile, due to rising costs for water
pumping accompanying this, many of the farmers who depend on this aquifer are abandoning
irrigation agriculture.
Distribution of annual precipitation in the U.S.
and the location of the Ogallala aquifer
Ogallala aquifer
：Ogallala aquifer
West
East
Nebraska
Colorado
Annual precipitataion (inches)
0∼10
40∼60
10∼20
60∼100
20∼30
＞100
↑
30∼40
Annual precipitaion 20-inch (510mm) line
Kansas
Oklahoma
Source: Hattori, 1992 (Fumin Kyokai)
Texas
(panhandle)
Scene of central-pivot irrigation
Source: Chiba Prefectural Information Education Center (provided by Kiyoshi
Ando)
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