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28 ROGER A. PIELKE. JR. NINE FALLACIES OF FLOODS 429 Deaths 18 160 140 15 ~ 120 $ 12 100 ~ 80 @ 9 60 ~ ~ 6 40 0 20 3 o ~ g ~\~ ~ * ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - - - - - - - - - ~ - - - - - - - - - - - Figure 2. Flood deaths in the United Stales; 1903-1994; eat:h point represents average annual deaths of previous 25 years. 2.7, DATA ON FLOOD DAMAGES IS A PROXY FOR FLOOD RISK As in the case of trends in people at risk to floods. analysts have sought to use trends in flood damages as a prox.y for trends in property at risk to floods. However. it is at least as difficult to form definitive conclusions about vulnerabihty from the damage data as it is from the casualty data. Flood damages occur every yea~ in various places around (he United Slates. Such damages, per se, are not sufficl~nt evidence of a policy problem. As the Task Force on Federal Flood Con.trol Pol.lcy noted in 1966 (p. 13), 'it may well be that the advantages of flood pi am location outweigh the intermittent costs of damages from floods. Further. there are some kinds of activity which can only be conducted near a watercourse'. Flood damages (or losses) have been defined as the 'destruction or impainnent, partial or complete, of the value of goods or services, or of health, resulting from the action of flood waters and the silt and debris they carry. Easy to define, flood losses are difficult to set down in dollar figures' (Hoyt and Langbein, 1955, p. 77). Because of rhe methodological difficulties in assessing flood damages, as well as the limited data available, 'taking all in all, it is evident that any evaluation of flood damage is only a rough approximation' (Hoyt and Langbein. 1955, p, 79), Nevertheless, the historical record of flood damages provides some insight as to trends in flood impacts on society. Figure 3 shows annual flood damages for the period 1903-19~4 3: t3buJ~ted by the National Weather Service (d. F. Richards, personal communIcation). FIgure 4 shows the same data from the standpoint of a 25~year moving average. The data 1910 1920 1930 1940 1950 1960 1970 1980 1990 2= Hydrological Year Figure 3. U.S. flood damages, 1903-1997, with 5-year running mean. show that flood damages have been increasing steadily at this time scale (using constant dollars). A pattern of climate underlies the trends in flood casualties and losses. For many years hydrological analyses assumed that climate of floods - the distribution of flood events around some central tendency - remained constant (FIFMTF, 1992). In recent years, SCientists and policy makers have come to realize that we live in a climate that i!; changing in ways that are difficult to assess and predict (e.g.. Karl et aI., 1996). In other words, both the distribution of events and the central tendency may be changing in unpredictable ways. A consequence is that climate fluctuations such as those associated with El Nino events might be responsible for some of the variance in flood-related deaths and damages. This means that determination of vulnerability to floods must consider explicitly both physical and societal factors. 2.8. KNOWLEDGE LEADS TO ACTION Those who study public response to narural disasters are well~yersed in the per~ sistence of this fallacy which really means: knowledge by itself is generally not sufficient for policy actiOn. As Sims and Baumann (1983, p. 167) note in the context of public response to natural disaster, 'it doesn't necessarily follow that because information is given it is received or because education is provided there is learning'. Knowledge does not always lead to action, but only 'under highly specified conditions, and if properly executed, with certain target public. informa.