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<br />Historical Perspectives on Colorado Drought <br /> <br /> <br />. <br /> <br />Each of the definitions provided above has important contextual implications for the <br />state of Colorado. Taken as a collective whole, this account ufthe meaning of <br />drought will serve as the cornerstone that completes the foundation of our <br />understanding of Colorado's drought history. <br /> <br />Maasuling droughrs savBrity: nut avaryona agl'8ssl <br /> <br />In the past 100 years or so, researchers. scientists. and government agencies have <br />established a complex net\vork of instrumentation that is utilized for monitoring <br />climatic variables. The key variables in terms of assessing drought arc precipitation. <br />snowpack. and streamflow. McKee e/ oJ. (2000) enlighten us to their significance. <br />stating, "these climate observation networks provide important data to analyze <br />current and historic droughts and rclate water availability to thc obscrved impacts." <br />Furthennore, years of experience have revealed that the types and levels of drought <br />impacts display a direct relation to the following drought characteristics: <br /> <br />in comparison with historic <br /> <br />or "dryness" and the duration of the <br /> <br />the drought <br /> <br />impacted by <br /> <br />IS <br /> <br />. <br /> <br />Drought indices <br /> <br />Due to the impossibility of analyzing the voluminous climatic data collected every <br />day in real time, simpler tools are needed to characterize droughts in a manner that <br />can be readily and effectively applied by water supply managers for immediate <br />decision-making and future planning purposes. This necessity has led to the <br />development of a number of drought indices. The NOMe (2003) describes drought <br />indices in a general sense as follows: "Drought indices assimilate thousands of bits <br />of data on rainfall. snowpack. streamflow. and other water supply indicators into a <br />comprehensible big picture. A drought index value is typically a single number, far <br />morc useful than raw data for decision making." <br /> <br />Severity <br /> <br />A number of computational drought indices, including the Palmer [)rough <br />Index (1'DSl) and the Standardized Precipitation Index (S1'I), have come to <br />prevalence in the scientific community as means for assessing the severity of a <br />drought. Both ofthcse indices are employed by the state of Colorado for drought <br />monitoring and planning purposes. Other common drought indices include the <br />Palmer Crop i\loisture Index (C~II) and the Palmer llydrological Drought Index <br />(PIIDI). <br /> <br />The Palmer Drought Indices <br /> <br />Developed by Palmer (1965). the PDSI \vas the first quantitative tool available for <br />assessing the severity of drought. Although the specific details of these indices arc <br />quite complex. the NCMC (2003) provides us with simple explanations of each: <br /> <br />- <br /> <br />Page 13 <br /> <br />HDA Engineering, Inc. <br />Printed on 30% post-<:onsumer recycled content paper <br /> <br /> <br />the water deficits arc <br /> <br />Magnitude-how large <br />averages <br />Duration -how long the drought lasts <br />Severity-combination of the magnitude <br />drought <br />Aerial extent-what area <br /> <br />. <br /> <br />. <br />. <br />