Environmental Science 12th Edition by William Cunningham,Mary Ann Cunningham

Exercise 9

One definition of water stress is when annual water supplies drop below 1,700 m 3 per person. Water scarcity is defined as annual water supplies below 1,000 m 3 per person. More than 2.8 billion people in 48 countries will face either water stress or scarcity conditions by 2025. Of these countries, 40 are expected to be in West Asia or Africa. By 2050, far more people could be facing water shortages, depending both on population projections and scenarios for water supplies based on global warming and consumption patterns. The graph shows an estimate for water stress and scarcity in 1995 together with three possible scenarios (high, medium, and low population projections) for 2050. You'll remember from chapter 7 that according to the 2004 UN population revision, the low projection for 2050 is about 7.6 billion, the medium projection is 8.9 billion, and the high projection is 10.6 billion.

How does the percentage of the population in these two categories vary in the three estimates