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)