FIGURE 1.1 Change in world urban and rural population from 1950 to 2030 (projected). Inset shows change in world urban and rural population for the United States from 1790 to 1990. SOURCE: Grimm, N. B., S.H.Faeth, N.E.Golubiewski, C.L.Redman, J.Wu, X.Bai, and J.M. Briggs. 2008. Global Change and the Ecology of Cities. Science 319(756):756-760. Reprinted with permission from AAAS.



elevated concentration levels for gaseous pollutants and aerosols, and street canyon winds.

In addition, the high density of population results in enhanced vulnerability to not only traditional hazardous weather phenomena such as severe thunderstorms and blizzards, but also to heat and cold waves, air pollution, and the rapid spread of airborne disease through a concentrated, susceptible population. Indeed, many of the major weather disasters in the last three decades have been in urban settings. Ranging from tornadoes, major ice and snow events, to floods (often triggered by spring melting of winter snow), to land falling hurricanes, to runaway wild fires, these “Billion

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