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<br />r-~~~i'" ~, .,~<~..,.
<br />I "~ ~
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<br />
<br />.~, "6:t..,.~-
<br />I--or.- 31
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<br />. ?~."'\..-
<br />.; ":....\--.~
<br />- .....
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<br />
<br />Figure 2. Replicafe photographs 01 lake Powell at the confluence with the Dirty Devil
<br />River (entenng from lelt). A. June 29. 2002 B. December 23. 2003. (Photographs by
<br />John C. Dohrenwend.)
<br />
<br />The Suulhl'm (h..:ill~'Il\ln Indl".\ lSOIj
<br />IS J..l~l'd Itl mUll'ale till' ..1;.Ilu.. of I'......SO
<br />(Wchh and Iktann1urt. 1l)<J.:!; Cayan
<br />ami nth.:r... ]1I<)t)1. As ih name implic...
<br />ENSO fefle,ls an IN,:illall11n ~ly,cl'n
<br />\WIl !liLlic slalc," uJ Ihe r...:can. The warm
<br />l,haw {ncgal1\l' SOlI. l'atkd Ihe EI Ninn.
<br />invohcs W;LTTI1mg of the eastern tropical
<br />r-,ll:ific ("lI;l'J,ll \1ft till' l"l)a,l 1,1 Peru.
<br />Thl' warnl ....alcr spreads mlT1hy,ard In
<br />the eastern ~1lr1h Padfic lkean olf the
<br />wesl coast Ilf till' L'niwJ Stall"s. -rh~' l:Il!u
<br />pha~e \r(l~lIlH' SOli, .:alkd Ll :'\llla.'i!>
<br />Ih,:\'p('ll.'\l1".T,',ultin,!! U1al"(I(,lin,!!Ilf
<br />Ih~ wal~'r nn .....:It.:m North Amen~a_ A
<br />n.:ulral cIlndiulln U11~'r-..'enel hlr lc\eral
<br />)'.:arlhcl....eenlhet....\'.:IlII!>latl."lFlg.,1.,\I_
<br />E..'\1S0 r.:lkd~ U11.:rannual \ari,lllon III
<br />dl male and hclp~ Itl e\phun I h.' occurrerK,'
<br />of thll.I(h (Wet>t> and Iklanl'llurt. 1~21
<br />:1.\ wdl a\ drought\ (Ca~an and lltheT\.
<br />19<-)Q). \V:lml'Wllll~'r llOnm lend 1(' lx'
<br />enhanl-ed dunng 1-:1 :'\iiin, l-aU\U1g alxwe-
<br />.l\l'fage runon and thl(xh~ luch a\ dunng
<br />19S2-llJxl .-\!lh.'ugh the Illl:idl'nl:e of
<br />di~sipallllg trorreal 9dum'l I,'nd\ 10 lx:'
<br />Ulcr,'al,-J durin!! EI Nine> n'ndllllln\. th~"
<br />\umm,'r mulll..on ma;. t1",. dlmlmlheJ'In
<br />Ulan;. ;.I'ar\- NIlt ;111 [I :'\iill' eWnlo;; k;IJ
<br />
<br />10 irKrealeJ ruIW1f; for ell.amplc. runolf
<br />during lhe 20CJ.\ EI Nino ....a\ lx:lllw
<br />awrage in Ihe Cnll'raJo Rner t>;I~tn, L;I
<br />Nina wndllionl. whil"h Jumin;\leJ the
<br />pl.'rioJ of IIJ%thrllugh 2002 (PUllclu.lted
<br />hy thl' EI Nino tlf JlNlll, l"aull'd lx:low-
<br />a\\.'rage no.... in lhl' Clllmado RiH'r.
<br />:\n dalloratc mde.\ calleJ the P';KIIil.:
<br />lk.:aJ<l1 ()~':lllall{ln ,PDt); Fig. :\Bl
<br />rclh'cls del'<ldal SST \anahillly and
<br />\t'a-Ie\'d pre~o;;Uf\' of Ih~' :'\orth P<ll"ilic
<br />Ocean north of 20'S (M.mlua and
<br />1I,lfe. 2(02). JIlJ I~ rdaled h' rndKe\ .'1
<br />ENSt' The rDp rdl,....\ J..,',ld<ll-ll'ak
<br />vdnablhl} and 10;; UlI'd 10 e\plarn long-
<br />lenn r""no\h \.1 arnl\e- or bclow-.I\er;tge
<br />prl'l:trllallnn In lhe regh'lt: Shill.'> in lhe
<br />rDO uccurr.'d In alll'ul IIJ_U, 11J04, and
<br />11J77 (McCabe and olht'T'S. .:.'!:()().l). Th.:
<br />f\'~'.:nt lhllt in the PDO in alll,ut 11)t~
<br />i.. thoughl III herald a ch,mgt' from ....CI
<br />In dJ) ..:nlldlll\ln~ III Ih,' Soulhwe~l.
<br />The rt'..:enlly dewlnp..'d Illdl'\ 01
<br />tlw ..\11<11111<: :\lultid~~'adal lh...lllallon
<br />h\:\10; Enlicld and lllhl'rs, 20tHl rclk..:1S
<br />CllndlllOll\ In Ih~' AllallllC O,'l'an Ihat
<br />llla\ ail...,'1 dlmal~' III Nonh '-\lJll'nl'a
<br />tFig:, 3l'\, Although Ihe ,\Iblltlc (>':~'an
<br />
<br />.
<br />
<br />IS downslr...am fwm lhe mllisnJfe~
<br />dcli\'ery o;;ouree\ to th.: Southwt'st.lwarm
<br />r.:ondltluns "indi...aled hy Pllsiti,'\' AMO
<br />arc imhcati\'c nf drought. for dample Ihe
<br />Dw,t Bowl ollhe earl)' 19.'Os tSchubcn
<br />and ll(heN. 200..l) and at olher tImes
<br />during the lasl century (McCallc and
<br />othen;, 2(X~). During positive AMO
<br />,:~,"Jitions. almo..pheric Oow is shilled
<br />to dl'hvcr k~.'> moisture 10 the continenlal
<br />Untted Slales. Flucluations in lhe AMO.
<br />.:,'mhilll'd wilh th~' "DO. may hdp In
<br />ellplatllMlIllcllflhelllllg-temll1ucluati{ln..
<br />in rUlwff in lhl' Colorado Rivt'r tMsin,
<br />willie the Sol Ill<l\i l"plaln \Jnatwn
<br />within lit..: ,honer-ierm dllllall~ \Iat.:.
<br />
<br />Drought and Indices of Global
<br />Climate
<br />
<br />Drought iscau..cJ hyp>.'rli..lcnl dclicits
<br />In prccipilation o'er a region. As \w:h. the
<br />sewril)' of droughts 1\ a lunctinnofspatial
<br />extcnt. dumllon, and lht' magmlude uf the
<br />prcclpilalion deli":l!. Thl\ cOlllhmallllO
<br />of \'anahks makes dn.u~ht prediction
<br />an "Jdr~mdy lhfticuh pro('ll.hit;on, The
<br />r",.:uN uJ 2()'" ...entuT)' drought ulually
<br />is JI'pKled Ullllg Ihe Palmer Dmughl
<br />SC\Cnl)' InJe\ 11'1>Sll. ....hlch lake~ 1111\1
<br />al.:{:{)unI hOlh preopilalion ;Inti f'\'tcrllial
<br />C\djl('lran\pHall"n, U~inF a ..lale,w!,lc
<br />PUSI mdc", (Fig. _'0; Nalinnal Ocl'anic
<br />anJ Almo..pheri..: AJmJllistralion.
<br />20U.H. the 111(l~1 \I'\'erl' Jrouj;hts in
<br />Ulah ('I(~'U1TCJ helween alloUl UNo and
<br />19t~. JUTlng Ihe early 19~O\. Ilclween
<br />19':X and 190J (the mid-cenlury
<br />drought). bt'l...."'I.n 1972 and 11J7b, from
<br />IYX5 lhrough 1991. and after 11,)1.)6.
<br />Re"c;\n-hl'f'; use a ClImhinalioll of Ihe
<br />SOl. POO. Jlld AMO indll'<'~ IU <'lIrlain
<br />Ih.. "......tlrTt'n~'c Jl1d lpalial t'\lenl of
<br />drought" If\kCallc and olh<:r\, ;!()()-l).
<br />P.:rli\l...nl ('II.l~ill\C SOl cnndillon~ (I.a
<br />NIna) arc indlcali\t' thai a t1wught of
<br />al Iea\l ~h(ln,tenn duratioll is glling
<br />10 ('I(cur in lht' SllUth....t'st. In nllllra",t,
<br />pl.'r"i'tent nl'gallw SOl condltiun..,
<br />Whl...h wdlcatc Ihe occurrencc of EI
<br />~!jj{l. indlcale a poten!ial ranl,'e from
<br />Jrought to c\IT~'mdy WCI Cllflditrnn\.
<br />Howewr. n~'llh,'r I.a Nina nur EI Ninl)
<br />..:undltl\ln~ fX'rM~t for nhlre lh;ln 2-.:
<br />yearl Ilcfof\' \wll...hing \tatt'\. Long"
<br />teon dn,ught\. ~uch ,I~ the mid-n.ntury
<br />e\enl. arc' as\lIc:I<lled ....ilh r.:rSl'\lt'nl
<br />negall'c I'DO and fl<Nlivc AMO indkcl_
<br />
<br />Flow in the Colorado River
<br />
<br />Row in the Colnr.tdn Ri\er has \aned
<br />\lgniti..:antly during th~' 20'" cemul').
<br />l..l."e'~ hrry tFig, II. Il Ihe leparalil'n
<br />point of 110.... Ixt....t'cn the uppl.'r-ha.,in
<br />~lale\ 01 Wy.}ming, Cnlllrado. Utah. and
<br />
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