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<br />Historical Perspectives on Colorado Drought <br /> <br /> <br />,.,..dplt...l_ <br />~,...'l~. <br /> <br />[ <br /> <br />1;r_.lt6ocUon.Colar_ <br />~'''''''~H''P..t[l <br />. <br />. <br /> <br /> <br />,- <br />- <br />61__. <br />....... <br />U~,..._. <br />p~mI' <br />:; J::~S\ <br />........0 <br /> <br /> <br />, <br />. <br />j <br />! <br /> <br />______l <br />.u-..-.- <br /> <br />~ <br /> <br />~ <br /> <br />Gr_........,tl"".Col...._ ,.,..dpU.tl.... <br />1__H"P..tl.~,....,,,,"...s. <br /> <br />~ <br />~ <br /> <br />,- <br />61-90_. <br /> <br />1..1.,...._. <br />c:l;;!"If~~:f"S; <br />..li,.."** <br />........[] <br /> <br />___I <br />~1_H"''''- <br /> <br />.. <br /> <br />.. <br /> <br />.. <br /> <br />.. <br /> <br />- <br /> <br />.. <br /> <br />.. <br /> <br />.. <br /> <br />~ <br /> <br />EI Ninos tend to create wet <br />years statewide. <br /> <br />La Nina's tend to create <br />multi-year dry periods that <br />can accelerate into <br />ertended droughts. <br /> <br />Precipitation variability across Colorado's major river basins <br /> <br />Due to the variability in climale and topography that definc Colorado's landscapes, <br />is important to have an understanding of drought at a watershed level. "For many <br />water management and planning applications," reports ;..tcKee el al. (2000). <br />"Colorado is divided into seven water divisions". F..ach oflhcse basins originates in <br />high mountain environments and descends through mountain valleys and e'..entually <br />drops to much lower clevations. Thus. we can roughly divide each basin into an <br /> <br />Page 21 <br /> <br />HDR Engineering. Inc. <br />Prinled on 30% post.consumer recycled conlent paper <br /> <br /> <br />- <br /> <br />- <br /> <br />-. <br /> <br />- <br /> <br />- <br /> <br />.. <br /> <br /> <br />, <br />. <br />j <br />! <br /> <br />mpacts on monthly Grand Junction precipitation <br /> <br />Note that in Grand Junction and Denver, El Nino years tend to produce more <br />precipitation than in La Nina years. In Grand Junction the impact is more noticeable <br />as a reduction oflatc summer and fall precipitation during La Nina years ,....ith lesser <br />winter and spring impacts noticeable. In Denver both winter and summer <br />precipitation is higher during EI Nino periods. The heaviest EI Nino precipitation in <br />Denver is evident from late February inlo early June. The recent Saint Patrick's Day <br />snowstorm of t\.tarch 17.20 is an excellent example of an EI Nino-assisted major <br />precipitation event. From these four figures is quite evident that the El Nino and La <br />Nina patterns int1uence seasonal precipitation patterns differently cast and west of the <br />Continental Divide. Thesc differences are also notable in the statc's river basins. <br /> <br />EI Nino and La Nina <br /> <br />Figure 18 <br />