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<br />;Water in the Balance; <br /> <br />northern half of Colorado. The only examples of four <br />or more consecutive years with less than 80% of the <br />long term average falling each year were found over <br />southwestern Colorado near t.l1e turn of the last <br />century (1899-1902), in southeastern Colorado during <br />the dustbowl years (1933-1937), and over isolated <br />areas of eastern Colorado 1952-1956. <br /> <br />Based on SPI analyses, four droughts with a duration <br />of at least four years (48 months) have occurred <br />during the past century (see graph below). <br /> <br />The significance and impacts of drought tend to <br />increase with increasing duration (1930s, 1950s). <br /> <br />Brief but extreme droughts can also have severe <br />impacts. For example, extremely dry weather in eastern <br />Colorado in April, May and June can ruin most of the <br />winter wheat crop, even if the rest of the year is quite <br />wet. Likewise, a very dry December, January and <br />February can have very adverse financial impacts on <br />Colorado's winter recreation industry, even if late <br />season snows make up most of the precipitation <br />deficit. <br /> <br />Drought episodes have lasted as long as 10 years <br />(1930s). However, these long-duration droughts are <br />interspersed with periods of wet weather. For example, <br />some of Colorado's wettest months on record (April <br />1900, May 1935, September 1938) were embedded in <br />long-duration drought episodes. <br /> <br />5) Spatial patterns of drought. <br /> <br />There appears to be no such thing as a <<typical" <br />drought pattern. <br /> <br />Each of the largest and most severe droughts have <br />had their own unique formation and spatial patterns. <br /> <br />Each region of the state has its own drought history <br />which may be similar or totally different from other <br />regions of the state. Northern Colorado is sometimes <br />wet when southern Colorado is dry and vice versa. <br />The same is true for east versus west. <br /> <br />It is rare for the entire state to exhibit similar precipita- <br />tion patterns for more than a few months in a row. <br /> <br />6) Drought severity - how dry can it get? <br /> <br />Many areas of Colorado have gone without any <br />measurable precipitation for up to 60 consecutive <br />days. For a six-month winter season, 25-40% of the <br />average accumulated precipitation represents an <br />extremely dry winter (October-March)_ For an entire <br />year, 50-60% of average represents an extreme drought <br />year. Two to four months in a row with less precipita- <br />tion than average is common. Five or more consecu- <br />tive months with below average precipitation is very <br />rare. Some weather stations have never had 6 or more <br />consecutive dry months. <br /> <br />Multiyear droughts of up to three consecutive years <br /> <br />with less than 60% of average precipitation have <br /> <br />occurred once or twice in the past 110 years at some <br />locations in southeast and southwest Colorado. In <br />Colorado's northern mountains, few sites have <br />experienced two years in a row with less than 80% of <br />average precipitation. <br /> <br />Another way of looking at drought is by determining <br />"accumulated deficits". For example, if your average <br />annual precipitation is 16 inches, but you only <br />received 12 inches, your accumulated deficit would be <br />4 inches for that year (see chart on the next page). <br />When you accumulate deficits and surpluses year <br />after year, you find that Colorado's worst droughts <br />reach an equivalent deficit of about two full years of <br />average precipitation. In Colorado's northern <br /> <br />Fraction or Colorado in Drought Based on 48-month SPI <br /> <br /> .. <br /> " <br /> .. <br /> .., <br />, <br />! .. <br /> .., <br /> .., <br /> ., <br /> ! ! ! ! ! ! <br /> <br /> <br />! ! ! ! ! ! - - - ! ! ! ! ! ! ! <br />v.., <br />i6 <br />