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418 ROGER A. PIELKE. JR. NINE FALLACIES OF FLOODS 419 perature variability. and a more active hydrological cycle, including the possibility of more floods (see IPee, 1996a,b, on the science and impacts associated with ~Iimate change). One result of scientific and political concern about the possibility of global warming is a frequent association by the media and the public of almost every extreme weather event with global warming. For instance, the cover of Newsweek from 22 January 1996 carried the following title: 'THE HOT ZONE: Blizzards. Floods. and Hurricanes: Blame Global Warming'. This article, and others like il. carry the implication thaI global warming is responsible for recent climatic extremes. In fUl.:t. it is essenlially impossible lo attribute ally particular weather event to global warming. At the regional level scientists have documented various increasing and decreasing trends in the frequency or magnitude of extreme events, but are not able to associate those changes to global warming. Globally it is diffi. cult for scientists to discern recent trends in extreme events. As the IPCC (1996a, p, 173) notes: Overall, there is no evidence that extreme weather events, or climate vari- ability, has increased, in a global sense, through the 20th century, although data and analyses are poor and not comprehensive. On regional scales there is clear evidence of changes in some extremes and climate variability indicators. Some of these changes have been toward greater variability; some h~ve been toward lower variability. Does the lack of a linkage between extreme weather events and global warming mean that the public and policy makers need not concern themselves with climate change? On the contrary; there are many reasons for the public and policymakers to have an increasing concern about the impacts of extreme events. And this concern is largely independent of the global warming hypothesis, for the following reasons. Current knowledge is limited as to the potential impacts of a changing climate on the number and intensity of hydrologic flood events (lPCC, 1996a; OTA, 1993; Dracup and Kendall, 1990). It is certain that for particular regions and communities the climate will change in some way or another. There will likely be some regions thaI experience more flood events and others thaI experience less. It will almost certainly be more straightforward to document these changes than to attribute them to specific: causes such as human-caused global warming. For example, several regions in the Upper Mississippi River Basin have seen trends (at 80% and 90% confidence for different regions) of increasing precipitation since 1965 (Bhowmik et aI., 1994). Meanwhile, the Colorado river basin has seen a decrease in streamflow over the latter two thirds of the twentieth century (Frederick and Kneese, 1990). Such 'winners and losers' have been documented in regions and nations around the world (e,g.. Rao. 1995; Karl et aI., 1995), In the United States (about 6% of the Earth's land surface), recent decades have seen an increasing trend (at vario~s levels of confidence) in precipitation in certain regions and also streamflow (Kunkel et aI., 1997; Karl et aI., 1996; Lins and Michaels, 1994). But it is not clear that more precipitation (or changed frequencies of precipitation events) in the United States are the cause of the documented increase in losses in recent decades; other factors (such as human occupancy of flood plains, land use change, channel engineering, nonstructural mitigation policies, etc.) must also be taken into account to arrive at a final detennination of the relation of climate and impacts. There are at least three implications of the uncertain climate future for societal responses to floods. First, there is a continued need to document how climate has changed in the past. So much atternion is focused on developing better predictions of the future that we often neglect the wealth of data about the past. Second, there is a need to systematically evaluate successes and failures in responding to past climatic extremes. While we do not know exactly what the fUlUre will bring, we do in many cases know that our responses to past events has been less than optimal. Thus, at a minimum we should take care to ensure that we are at least prepared to deal with the variability and extremes that have already occurred and been docu- mented (Glantz, 1988). Finally, the uncertainty in the climate future underscores the need to better understand the societal dimensions of the climate threat and to take those adaptive measures that make sense based on our imperfect knowledge of the certain past and uncertain future. A first step in that effort is to better understand societal exposure to variability and extreme events. No matter what the climate future holds, flood impacts on society may continue to get worse. A study conducted by the U.S. Congressional Office of Technology Assessment concluded that 'despite recent efforts, vulnerability to flood damages is likely to continue to grow' (OTA, 1993, p. 253). The study based this conclusion on the following factors, which have very little to do with climate: I. Populations in and adjacent to flood-prone areas, especially in coastal areas, continue to increase, putting more property and greater numbers of people at risk, 2. flood-moderating wetlands continue to be destroyed, 3. little has been done to control or contain increased runoff from upstream development (e.g., runoff caused by paving over land), 4. many undeveloped areas have not yet been mapped (mapping has been con- centrated in alre'ady-developed areas), and people are moving into-such areas without adequate information concerning risk, 5. many dams and levees are beginning to deteriorate with age, leaving property owners with a false sense of security about how well they are protected, 6. some policies (e.g., provision of subsidies for building roads and bridges) tend to encourage development in flood plains. At a minimum, when people blame climate change for damaging flood events, they direct attention away from the fact that decision makers already have the means at their disposal to significantly address the documented U.S. flood problem.