In the 1960s and 1970s, pessimism was dominant in future prospects for birth rates in developing countries. During those years, only a few small nations with advanced economic status were at the turning point of the fertility transition, so it was widely held that fertility transition could not occur without modernization. However, from the 1980s through the 1990s, fertility began to decline in many populous countries, including China, even though they lacked economic progress, and this tendency is "not an exception but the norm" in the developing countries(6). The fertility started to decline even in the so-called extremely poor countries of South Asia or sub-Saharan Africa, and this demonstrates that well-managed family-planning programs, as well as social development programs (such as the elimination of poverty, expansion of primary health care, extension of basic education, improvement of women's status, etc.) can be promoting factors in reducing the birth rate.
2. Water Supply and Water Shortage
(1) Supply of Water
The total amount of water on the Earth is about 1.4 billion cubic kilometers (km3), which consists of 96.5% of salty sea water, and only 2.53% (approx. 35 million km3) of fresh water. Moreover, 69.6% of the fresh water on the Earth is locked in glaciers, etc., leaving only 30.1% (10.5 million km3) underground and 0.34% (119,000 km3) in rivers, lakes and marshes, etc(7).
Approximately 113,000 km3 of water is supplied to the land area as rainfall by the water circulation system. Of this amount, 63.7% or 720,000 km3 goes back to the atmosphere through evaporation and transpiration, and only 36.3% or 41,000 km3 is left in rivers, lakes and marshes, or under ground. The total replaceable water resources per annum which can be used by human beings is 41,000 km3.
