Contact: Dr. Taikan Oki, at Research Institute for Humanity and Nature, oki@chikyu.ac.jp

World Water Resources andGlobal Climate Change
Dr.Taikan Oki (Hydrological Cycle Research Program)T

he 21st century iscalled the "centuryof water." That is
becausethere

areregions where water
scarcity

results

Change in Annual River Discharge
Under Global Warming Condition
Double CO2 - current［106m3 /year/ 0.5゜grid］

inpoverty, poor sanitary

210゜ 240゜ 270゜ 300゜ 330゜0゜30゜60゜2060 - 199090゜ 120゜ 150゜ 180゜

conditions, and disease, and anticipated60゜population growth will
increase the demand

30゜for potable water inurban areas and irrigation water for crop

0゜-30゜production. Economic
growth will induce an-60゜increase in the consumption of cereal

-5000

-1000

-500

-100

-10

10100

500

1000

5000

crops and also increase
the water demand.

Figure 1 Estimated change in annual river discharge based on the runoff simulation under global warming conditions in2060 using an atmospheric general circulation model of CCSR, Uni. of Tokyo and NIES. A global river channel

An accurate future

network and a river routing model was used.

projection for the supply and demand of water is essen-

for Climate SystemResearch,in the region is estimated to be lesstial for the adoption of suitable

University of Tokyo and the National

than it would be without climate

alternatives to cope with such con-Institute for Environmental Studies.

change. Conversely, water stresscerns. Water demand in the future isThe runoff from the model is used towill increase due to climate change

estimated by considering thecalculate the river discharge using a

in the west of the Black Sea andincrease of unit demand of water

global river channel network and aaround the Florida Peninsula inthat

population

river routing model (Saruhashi,North America.

growth and economic development.

2001). Primary factors affecting theIn this result of global warming

On the other hand, nowadays, water

future water crisis are believed to be

simulation, global mean precipita-

supply in the future is commonly

the societal ones such as population

tion and runoff increase , and theestimated using general circulation

growth, with the effects of climaticwater stress in the future is esti-models that consider climatechange as secondary factors.

mated to be alleviated on a globalchange such as global warming.

However, a slight increase in precipi-scale. However, there is anotherFigure 1 illustrates the change intation and runoff is estimated for theresearch result that suggests

annual river discharge estimatednorthern part of China, close to thefuture water stress will become

from the results of the general

Yellow river basin, as shown inmore serious due to global warm-

circulation model of the Center

Figure 1, and the future water stressing. Eliminating the uncertainty inaccompanies

4also at Institute of Industrial Science, Univ. of Tokyo, Japan, taikan@iis.u-tokyo.ac.jp

the prediction of detailed geo-

Japan using irrigation. Considering

Referencesgraphical distribution and quantity

the water required to cultivate

Saruhashi, T. (2001): Global Waterof increase and decrease in pre-feed cereals, livestock for meat

Resources Assessment Using

cipitation and runoff is muchneeds several times more water

Totalanticipated.

resources by weight. Based on thePathways, Master's thesis,

On the other hand, upstream

estimates of unit water consump-

Graduate School of Engineering,water withdrawal, deterioration

tion, the total annual import of vir-of water quality, and the shortage

tual water to Japan is illustrated inOki, T., Y. Agata, S. Kanae,of social infrastructure limit theFigure 2. The total annual import

T. Saruhashi, D. Yang, andavailability of water resourcesof virtual water to Japan accounts

K. Musiake (2001): Global(Oki, 2001), and such social factors

for approximately 100 billion m

3

Assessment of Current Water

should be considered in an assess-and it is comparable with total

Resources using the Total

ment of world water resources.

national water use of 90 billion mRunoff Integrating Pathways.

RunoffIntegrating

University of Tokyo.

3

Even though future projections ofper year. It is not surprising sinceHydrol. Sci. J., 46, 983-996.

the water supply in some areas ofthe self-sufficiency ratio for food in

Miyake, M. (2002): International

the world seem very serious, inJapan is 40% by calorie base.

Trade of Virtual Water to andJapan, no population growth isHowever, Figure 2 shows thatfrom Japan, Graduate thesis,

predicted, agricultural production

Japanese should consider theFaculty

is decreasing, and industrial water

world water problem as an issueUniversity of Tokyo.

use is not increasing, so there is noclose to home and Japan should

concern about a future water crisis

encourage research on the current

on the whole. However, Japanand future situation of global water

should still care about the antici-resources.

ofEngineering,pated water crisis in theworld. One of the major
reasons is that Japan

Total Import of Virtual Water to Japan

imports many agricultural and industrial
products from abroad,and these products

Other：72

1054
Share of virtual water
Import to Japan

consume local water
resources in the country of origin. In a sense,
importing goods and155596

Pork 4.3%

18.6%
Wheat

using them is just like
importing and consum-

256

ing "virtual water."
Miyake (2002) esti-27

Corn

Beef
45.3%

12.4%
Soy
16.0%

mated that 8m 3 ofwater is used to produce 1kg of polished

Total：103.5 bil.m3/yDomestic Withdrawals in Japan：89.0 bil.m3/yrice and 4m3 of water isused to produce 1kg offlour if produced inFigure 2 Import of virtual water to Japan. The figures illustrate how much water would be required if these goods
were produced in Japan.

5Frontier Newsletter

No.19
Jul. 2002