Laserfiche WebLink
<br />Historical Perspectives on Colorado Drought <br /> <br /> <br />measures short-term drought on a weekly <br />5 impacts on agriculture during the <br /> <br />The Palmer Crop Mois/ure Index <br />scale and is used to quantify drought <br /> <br />growmg season. <br /> <br />The Palmer Drought SeverilY bllle.t attempts 10 measure the duration and <br />intensity oflhe long-term drought-inducing circulation patterns. Long-tcrm <br />drought is cumulative, so the intensity of drought during the current month is <br />dependent on the current weather patterns plus the cumulative patterns of <br />previous months. Since ,,,.cather patterns can change almost literally <br />overnight from a long-term drought pattern 10 a long-term wet pattern, the <br />PDSI can respond fairly rapidly. <br /> <br />The hydrological impacts of drought (c.g., reservoir levels, groundwater <br />levels, etc.) take longer to develop and it takes longer to recover from them. <br />The Palmer lIytlrologica1 Drought 1ude.l, another long.tenn drought index <br />was developed to quantify these hydrological effects. The I)IIDI responds <br />more slowly to changing conditions than the POSt <br /> <br /> <br />--....-...- <br />--...-- .-- <br />'-'-- <br /> <br />Advantages of the PDSt. as outlined by <br />Alley (1984). include the following: <br /> <br />..~~_lt__, <br />...-...-- <br />......,.,--, <br />."....._~ <br /> <br />ncipieut wet spcl <br />~ear normal <br />Incipienl dr~. suel <br />:\.liId drough <br /> <br />0.5 to 0.99 <br />0.-.9 to -0'-'9 <br />-0.5 10 -0.99 <br />-1.0 to -1.99 <br /> <br />It provides decision makers with a <br />measurement of the abnonnality of <br /> <br />recent weather for a region <br />It provides an opportunity to place <br />current conditions in historical <br /> <br />perspective. <br />It provides spatial and temporal <br />representations of historical <br />droughts. <br /> <br />An additional means for monitoring drought, thc Surface Watcr Supply Index <br />(SWSI). is designed to complement the Palmer indices in the state ofC'olorado. <br />where mountain snowpack is a key element of water supply. This index is calculated <br />by river basin, based on snowpack. streamflO\l,', precipitation. and reservoir storage <br />(NDMC 2003). <br /> <br />Page 14 <br /> <br />The Standardized Precipitation Index (SPI) <br /> <br />A more recent drought-monitoring tool, the SPI emerged from research conducted by <br />McKee e/ a1. (1993). As before, we turn to the NCDC (2003) for a straightforward <br />examination of this index <br /> <br />HOR Engineering. Inc. <br />Printed on 30% post-consumer <br /> <br />2. <br /> <br />3 <br /> <br />recycled content paper <br /> <br />