have been developed around the world. Consequently, for example, the Ogallala Aquifer in the United States, one of the world's largest groundwater layers, has a total area of some 450,000 square kilometers, about 1.2 times Japan's land area. Since the start of irrigation agriculture, according to a survey of over 3,600 water wells, the water level has declined by an average of about 4.3 meters, with the ratio of wells whose water level dropped 3.0 meters or more standing at about 26%, that of wells with the water-level decline of 7.6 meters or more at about 18% and that with the water-level decline of 15.2 meters or more at about 11%. Wells where the water level rose 3.0 meters or more accounted for a mere 2% (Figure 4-1-2).

The annual amount of water consumed globally has increased about 2.9 times from about 1,400 cubic kilometers in 1950 to about 4,000 cubic kilometers in 2000. This amount is equivalent to 144 times the quantity of water of some 27.5 cubic kilometers held at Lake Biwa. The annual amount of water consumed is likely to come to about 5,200 cubic kilometers by 2025, a further increase of about 1.3 times from the 2000 level (Table 4-1-1).

Water resources on the earth as a whole are sufficient

Table4-1-1 Changes in Global Water Demand

1950	1980	1995	2000	2025
Population	2542	4410	5735	6181	7877
Agriculture	1080	2112	2504	2605 (66%)	3189 (60.1%)
Industry	86.7	219	344	384 (9.7%)	607 (11.6%)
Cities	204	713	752	776 (19.5%)	1170 (22.3%)
Total	1382	3715	3788	3973 (100%)	5235 (100%)

to satisfy human demand for water, but the geographically uneven distribution of water resources presents a major problem (Figure-Int.-2-9). The Human Development Report 2006 of the U.N. Development Program (UNDP) points out that one out of every five people living in developing countries (about 1.1 billion) is not able to satisfy the international standard of securing “at least 20 liters of safe water from a safe water source within one kilometer from his/her home,” and may lose life by consuming unsanitary water near his/her home and becoming ill.

## 2 Impact of Global Warming

According to the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), the progress in global warming will expose several hundred million people to increased water stress going forward, and the increased frequency of droughts and flooding is projected to adversely impact regional crop production, particularly production of subsistence crops in low-altitude regions. The rise in the global average temperature due to climate change is feared to bring about various impacts on water resources.

According to a global warming simulation conducted by a joint research team of the National Institute for Environmental Studies, the University of Tokyo's Center for Climate System Research (now, the Atmosphere and Ocean Research Center) and the Japan Agency for Marine-Earth Science and Technology, the global average temperature in 2071-2100 is projected to rise by 4.0 degrees C from the 1971-2000 level under a scenario that assumes the economy-focused future world will see a further progress in globalization. Precipitation, meanwhile, is projected to increase in low- and high-altitude areas and some tropical areas but decline in

Figure4-1-3 Projected Changes in Precipitation in the World in 2100

Source : National Institute for Environmental Studies, University of Tokyo, Japan Agency for Marine-Earth Science and Technology