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Historical Perspectives on Colorado Drought . l Stream Aow Based on Tree Rtng Evidence, Boulder Creek Near Ck-odell PToj.et.dflow'or2002 (.dJust.dtob.const$t~WIIh truring dlQ).32.ooo AF L_st.,..... b...d 01'1 trH ring fYkMnc. .29.600 A; . . ""'" FIow.1J.700AF 1.0.... 110,'" Tree ring analysis of streamflow suggests that the 2002 drought is the severest to impact northeastern Colorado In almost 300 years! 140.... 120,000 100,00' 80,0" 10,1'0 40,000 20,000 . 11'0 2000 1115 Figure 3 Streamflow on Boulder Creek based on tree ring analysis near Ordel Colorado that shows the comparative impact of droughts since 1700. Creek Press More than half the state has been in moderate drought during the droughts of the 1890's. 1930's and the current drought of 1999-2003. However. short-term droughts (3.momh duration) have previously covered as much as 80% of the slate, and longer- duration droughts (2-4 years) have encompassed as much as 70% of the state. The data in Table 2., edited from a table in r-.1cKee et al. (2000), "shows the periods during which at least 60% of Colorado was dr)\ as determined by the Standardiled Precipitation Index (Sill) values for 2-4-month periods:' Notc that the dates are not identical to those discussed above, as they were determined using a different methodology, namely the SPI instead of water year precipitation totals. Ilowever, it is clear that the 1999.2002 drought ranks as one of the most severe to affect the state during the instrumented period ofn..'Cord The questiun remains how this drought compares to historical droughts of the past 300 to 500 years. Paleo-climalology may prO\:ide that insight. ears cars cars cars cars Page 6 paper HDR Engineering. Inc. Printed 00 30% posl-coosumer recycled content ~ . ~ ~ " c .; ~ ;; > . . ~ " .. . :> .. . " " c 115. 1125 t'OO tin tl5. tl25 tlOO t175 1750 t725 Hydrosphere qualified the regional significance ufthe study, saying, "Boulder is fairly representative of most of the northern Front Range and most of the tributaries into the Colorado.Big Thompson (system] as well" (Associated 2002). 2 o 6 4' ~ 2 3 905 -l9-l1 \-\957 999-2002 -- 963- 965 -- 975 978 -\ 893- 93 95