
21The Fifth Revolution
longer droughts have been observed over wide areas since the 1970s, par-
ticularly in the tropics and subtropics. The frequency of heavy precipitation
events has increased over most land areas, consistent with warming and
increases in atmospheric water vapor. Figure 1.13 shows conditions in the
United States. Note that the region around Texas and Oklahoma is currently
experiencing extreme to severe drought, while during June and July 2007,
the region suffered severe ooding. In China, there are similarities. At least
18 million people have been affected by the worst drought in 50years. The
southwestern region of Chong