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Slide 29 Yadu N. Pokhrel, Oki Lab. IIS Irrigation Pumping and Groundwater Depletion 4
Global Groundwater Withdrawal
Results agree fairly well for many countries Even the reported values
may have significant uncertainties as they are reconstructed based on population distribution
Global total ~630 km3
Large withdrawals in North India, Western US, Middle East, Spain More than 90% is used for
irrigation
Reported: Wada et al., 2010 (IGRAC)
http://hydro.iis.u-tokyo.ac.jp/ 30
Groundwater withdrawal
Unit: km3/yr This study WRI (2007)
India 129.3 169.1
USA 78.8 68.4
Pakistan 47.3 54.0
Mexico 12.3 16.0
Bangladesh 6.6 9.4
Saudi Arabia 6.0 13.0
Unit: mm/yr
This study
USDA (2002)
Area km2
Maize 369 331 36.02
Wheat 408 247 6.33
Cotton 434 255 5.55
Groundwater withdrawal in major countries
Ground water withdrawal in the Ogallala aquifer
(Hanasaki et. al,
J. Hydrol. , 2010)
Slide 31 Yadu N. Pokhrel, Oki Lab. IIS Representing Human Impacts in MATSIRO 2
Simulated River Discharge (Highly Regulated Basins)
Seasonal variation improves significantly in many regulated basins.
R.I. Reservoir capacity/annual flow volume * 100
Slide 32 Yadu N. Pokhrel, Oki Lab. IIS Representing Human Impacts in MATSIRO 2
Global Irrigation Water Requirements
Simulated net irrigation water requirement: grid averaged values.
Slide 33 Yadu N. Pokhrel, Oki Lab. IIS Representing Human Impacts in MATSIRO 2
Validation of Irrigation Water Use
Observed data: FAO AQUASTAT (country statistics), 1998~2002 Water use efficiency: Doll & Siebert (2002)
Year 2000 Year 1987
The model estimates of irrigation water withdrawals agree well with the observations. Error bars: uncertainty due to precipitation data.
Slide 34 Yadu N. Pokhrel, Oki Lab. IIS Human Regulation of Terrestrial Water Cycle in the Past 3
Human Impacts: River Discharge and TWS
Storages (Global)
Aral Sea Inflow
510 km3 in 50 years
http://hydro.iis.u-tokyo.ac.jp/ 35
•7 out of top 10 importing countries are seriously poor in water resources.
•7 out of top 10 exporting countries are rich in water resources.
•Denmark (10) and India (18) are water stressed but exporting RW in net.
Virtual Water Balance in Countries (m3/c/y) in 2000
Blue: Exporting Red: Importing
Exporting Importing (Oki, et. al, 2004)
Major crops
and meat
http://hydro.iis.u-tokyo.ac.jp/ 36
World Water Resources Considering Virtual Water Trade
Seriously Stressed (~1) Stressed (1~2) Slightly Stressed (2~5)
103 m3/capita/year Moderate (5~10) Rich (10~)
Potentially Available Water Resources per Capita in 2000
Country
base
+VW
GSWP2 ensemble runoff, SRES A1/B1 population
http://hydro.iis.u-tokyo.ac.jp/ 37
Conventional Water Resources Assessment
Potentially Available Water Resources per Capita in 2000
Seriously Stressed (~1) Stressed (1~2) Slightly Stressed (2~5)
103 m3/capita/year Moderate (5~10) Rich (10~)
GSWP2 ensemble runoff, SRES A1/B1 population
Country
base
http://hydro.iis.u-tokyo.ac.jp/ 38
4 34 11
0%
20%
40%
60%
80%
100%
~ 1, 000 USD 1, 000~ 5, 000
USD
5, 000~ 20, 000
USD
20, 000USD~
GDP per capi t a ( US$/y/c)
Sl i ght l y
St r essed
Ser i ous
2
12
0
2
3
6
2
0 0
31
0%
20%
40%
60%
80%
100%
~ 1 , 000 USD 1 , 000-5 , 000
USD
5 , 000-20 , 000
USD
20 , 000 USD~
GDP per cap i t a ( US$/y/c)
Sl i g ht l y
St r es s ed
Ser i ous
Water Resources Assesment Considering VW trade
22 Countries were classified into “seriously stressed” in 2000 by
conventional water resources assessment.
+Virtual Water Import
Rich Countries are
saved by VW import Poor Countries
remain
Water Poor
Seriously Stressed
Stressed
Slightly Stressed
Burundi: 31m3/c/y
Rwanda:53m3/c/y
VW Balance
Egypt:141m3/c/y
Oman: 512m3/c/y
Bahrain:313m3/c/y
UAE:4,490m3/c/y
(Oki, et. al, 2004)
http://hydro.iis.u-tokyo.ac.jp/ 39
Rws= (W-S)/Q and Awc= Q/C(m3/y/c) have similar global
distribution Is (W-S)/C globally uniform?
http://hydro.iis.u-tokyo.ac.jp/ 40
4.9
38.9
8.9
1.4
2.2
1.3
2.5
Other:3.3
Total : 64.0km3/y
Virtual Water Import to Japan
Vi r t ua l Wat er I mpor t t o Japan
t hr ough each pr oduct s
( km3/y)
14, 5
12, 1
9, 42, 4
2
14
3, 6
2, 5
2, 2
1, 3
Mai ze
Soybean
Wheat
Ri ce
Bar l ey
Beef
Por k
Chi cken
Mi l k
I ndus t r i a lPr oduct s
(for JFY in 2000)
0.3 0.3
Domestic Withdrawals in Japan: 89 km3/y Domestic Blue Water in Japan: 400 km3/y Domestic Green Water in Japan: 30 km3/y
Blue+Green water
Blue water only
(Oki, et. al, 2002, IHE-UNESCO)
Slide 41 Yadu N. Pokhrel, Oki Lab. IIS Irrigation Pumping and Groundwater Depletion 4
Groundwater Representation
Koirala (2010) • Based on Yeh and Eltahir (2005a,b)
• Soil Column has explicit saturated and unsaturated soil zones. – Interacting through exchange
of moisture flux (GW recharge)
• GW Recharge is estimated based on Richards’ equation:
• Lateral flow between grid cells is not considered
• Water Balance of GW reservoir: • Baseflow initiates when WTD is
shallower than threshold value:
gw
y gw gw
dS I Q
t
0 00
0
0
gw gw gw
gw gw
Q K d d if d d
Q if d d
Sy: Specific yield, Igw- recharge, Qgw is baseflow, dgw- water table depth (WTD), d0- threshold WTD, K-outflow constant.
1gwd
I kdz
6 more layers of 1m and one of 90 m thickness
Slide 42 Yadu N. Pokhrel, Oki Lab. IIS Irrigation Pumping and Groundwater Depletion 4
Groundwater Withdrawal (US Aquifers)
Groundwater contributes ~75% of all water uses in areas overlying the HPL.
Simulated withdrawals compare well with USGS observations. Groundwater is mainly used for irrigation.
High Plains Aquifer (HPL)