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.24 ROGER A. PIELKE, JR. J.5. floodplains containing 9.6 million households with $390 billion in property F[FMTF. [992. p, 3-2). (Table [ summarizes these data on floodprone regions; lee also Thompson and White, 1985). The wide disagreement among these data mggests a growing recognition of regions subject to flooding, but caution is advised in drawing definitive conclusions until more reliable data is available. ac ~ ~ <( :E ~ ;;;; ~ ~ 0 Ji . . Vi 0 ~ ~ '" ~ '2 r::: 0> ~ 0 '" oS ,S U ~ '" " " ~ = ;i' g '" ~ ,~ '" . Q OJ [ :g ..J '" ;! [ ;;; ~ g '" ~ tl ~ . 1! '" <( ~ u '6 ~ ::! " '" u > OJ ~ 0 ~ u 0 ~ r::: ~ :l: , "" '" 2i ~ , '" Vi 0> ~ 0 c u u ;< :;; u . '\i 5 ;>- < Popu.lation at Risk A consequence of the lack of data on the areal extent of floodplains in the United States is that a difficulty exists in assessing trends in and current levels of popula- tion at risk to Roods. Trends in population at risk to flood events are an important factor in any determination as to whether societal vulnerability to floods in de~ creasing. increasing. or remaining relatively constant. One can easily hypothesize that increasing population and urbanization in the United States has led to a com~ mens urate increase in population at risk. Yet. one can also hypothesize that the various societal responses to floods may have more than compensated for popula- tion growth and in fact fewer people are today at risk to flood events. Currently. data is lacking to reliably assess trends in population at risk to floods events. and therefore it not possible to systematically assess whether sociCl<.:d vulnerability to floods has increased or decreased over recent decades. Property at Risk Accurate determination of property at risk to flooding faces many of the same obstacles facing accurate determination of people at risk to noading. Tuble I sum- marizes the findings of the various studies (ef, Goddard. 1973. Table 5), The Table shows that there is relalively linle systematic data collected on property at risk to flooding. Again. the lack of data limits what can be said about trends in vulner- ability to flooding. It is likely that the Federal Insurance Administration. which operates the National Flood Insurance Program. has in its records data on property at risk to floods for the communities which it has worked with since the early 1970s. However. this data has seen only limited use, e.g., in determination of repetitive losses and substantial damages over 50%. and has yet to be systematically assessed from the standpoint of trends in societal vulnerability to floods. Differences in the estimates of people and property at risk to floods are at- tributable to actual demographic changes, but also to differences in floodplain definitions. and simply that the data has not been collected and systematically analyzed. The data that does exist allows for only gross generalizations and thus limits what can be authoritatively concluded about trends in societal vulnerabil- ity to floods (cf. Changnon et aI., 1983). An understanding of trends in societal vulnerability is one factor (along with trends in climate. policies, etc.) that would comprise an evaluation of the effectiveness of U.S. flood mitigation policies. NINE FALLACIES OF FLOODS "' I M ~ 8 ~ "' ::'! M ~ 0 ~ ~. '" a ~ " " '" , '" ;0 M g ;;: " .. , " '. ii 0. u , 0 8 '- '~ ~ ~ ~ '. ..., c ..., ~ -0 ~ 0. 'e " 'e ~ t 8 . 'E ~ 8. ,g- -e ,g- , -ll 0 e c 0> '" "- 425 -=- -"""":')i! c >. \0 (J 0 l) U ....:. ~ 0 G: ~ ~;! ]g~E<; "5;o-€ Q..c: u ~~::.5E~ tJ :q ~ <.~;t ~ .:; ~ :J '':;; --: E g ~ ....:. 5 \0 Co ",::e N V)",?.Q.g >.~ r:~~:ff:; ~ - Cl c oo(.l.. -u -0.'::; ti_!;;; '" UJ c ff E" ]6~f~fi: z g ~ 0. G .f 6EUJ.5'E-O .~ ~ '. ... >L. ~ c: <<i~..E -o.~ ~E~~~~ C l) - > ' o - ......- "" u.= ~;Oj d Bl " .' t E ." ~ ~ :l ~ ~ 03 3~~:ie~ -0 ~ e .....:.:.2 E ~ u .Cboo S J:!. ~s~:;cfr ~OQ.l'::'EV) _ ~ 0 g c.g o':vi_.Q"B ~ B:J . ~.<: E$~~O~ ~. r- '0 c.g ..5~~ Q:;.2 ~ <o ~ ~ ~:J " .15.....-0... -g r; III f'& U III .:; ?: ~ 0 ~ eo.f --:..: ~ 1t.~ ~ r-- t>>l V) =tV) ~tfi tl .,s-a ....- ... -"""":'...... ... --o~L?c.~ ~ ~..!:! Cl ::.? '3u!::!e~:r: .~ >. -2 ~ E ~ ~.~".u <t: -<~:E 0. t 'Ovi~:3~~ _-:~i:i:4l'O ~ -' UJ~.c c E-g~7;:: !; ....." - ~ v Q.-:<C~t::~ U ,-?: ... 2. 3 o Cl '0 ~ U V) . ,U 35' 1i? ~ . e.~ ~...' 0 ~ E ....- <IJ_ <.; ~ E ~ .~ ~ l.>.- E. ~ . ~ ~ Bl.~;g ~ c55~~2i:o; " ~ :0 ~ M ..