3.Water Balance in the Asian Continent

Asian Continent and its surrounding land, which accounts for 27.4% (4.345 billion hectares) of land area on the earth (148.89 billion hectares), has approximately 60% of the world's population (5.716 billion in 1995). Human activities that have been con- tinuing since prehistoric times are inevitably becoming more vigorous and are accompa- nied by rapid increase in water demand for use in municipalities, industry and agriculture.

Meanwhile, a very and region with estimated average annual preciptitation of 742mm spreads extensively in the interior of the Asian Continent. This is the third smallest pre- cipitation in the world after Australia and Africa and corresponds to only 930m³ of an- nual rainfall per capita. According to the data obtained from the International Hydro- ligical Decade(IHD), water balance in the Asian Continent is as shown in Figure 3.

As shown in the diagram, 32.2 × 103km³ of water is fed to the continent each year in the form of precipitation, of which 18.1 × 103km³ is lost in the atmosphere through evapotaranspiration. Of all the water that flows into rivers(144 × 103km³), 94% (13.5 × 103km³) flows into the ocean every eyear from estuaries and the remaining 6% (0.57 × 103km³) turns into groundwater. Therefore, average runoff ratio of the Asian Conti- nent will be as follows:

　

　

　

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