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6 4 w 2 ::l ...J ;; 0 X W C Z -2 -4 -6 In In In In In In In In In In In N cr> 0 N '" V In <0 "- <Xl cr> 0 <Xl cr> cr> cr> cr> cr> cr> cr> cr> cr> cr> 0 ~ ~ ~ ~ ~ ~ N Figure 3. Palmer Drought Severity Index for Utah, 1895-2002. inches on the Great Salt lake Desert to about 60 inches in the highest mountains (Butler and MarscH, 1972). Three types of moisture- producing weather systems generally account for most precipitation in Utah: Pacific frontal systems, dissipating tropical storms, and summer thunderstorms with moisture originating from the Gulf of Mexico. Pacific frontal storms generally produce winter mountain snowpack. and the subsequent spring snowmelt increases river flows and reservoir levels. During some winters, high. pressure ridges can dominate over the Western United States and push storm systems northward. These persistent high-pressure ridges result in decreased snowfall in Utah mountain ranges (U.S. Geological Survey, 199t). Mountain snowpacks have generally been below normal statewide since the wimer of 1998.99, and Utah has experienced significant reductions in spring runoff since 2000, Many Federal and State government agencies use the Palmer Drought Severiry Index (PDSI) to classify and assess long-term meteorological droughts (Hayes, 2002). The PDSI drought index responds to abnonnally wet or dry weather conditions and classifies the conditions on a scale from -6 to 6. On this scale, -4.0 or less signifies extreme drought conditions and 4.0 or more signifies extremely wet conditioIls_ Summarized data from the Utah State University Climate Center in Logan, Utah (Donald Jensen. written commun.. 2002), illustrates the variable nature of precipitation in Utah (fig. 3). On the basis of the PDSI classification scale, the droughts of 1988-93 and 1999-2002 are severe to extreme. but conditions are not as dry as those during 1896- t 905 (fig. 3). Table 1. Chronology of major and other memorable floods and droughts in Utah, 1884.2002 - . . . . Aood .. Drought - . Aood I. Drought . Flood . Drought . Flo(xJ . Flood . Flood . Flo(xJ . F-lood . Fhxxl . Drought . Flood . Flood . Flood . Flood . !-l,x>d Date Area affected July 4, 1884 Colorado River 1896.1907........ - - -Statewkle-- - Aug. 13, 1923 1930-36 Apr. 28-Junc II. 1952 1953-65 June 16, 1963 June fO-II, f965 Dec. 6-7, t966 Aug. 1-2.1968 Sept. 5-7, 1970 Aug. 27. 1972 1974-78 Apr. IO-June 25. 1983 Apr. 17-June 20. 1984 May 22, 1984 June 15. 1984 June 3, 1986 . Flood June 7, 1986 . Drought 1988-93 - -- - . F10txJ Jan. I. 1989 . FI()(xJ Feb..Mar. 1995 . Flood May 1997 . Drought 1 999-presem 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1910 1920 1930 1940 1950 1960 1970 1960 1990 2000 12,000 350 A~" 10,000 300 .- . 8,000 250 6,000 200 150 4,000 100 2,000 50 I- 0 0 W W U. 200 250 iii 175 Whiterocks River near Whiterocks. UT Smith'S Fork near Border. WY cr 150 1930-2002 IMlrage annual 200 1943-2O(l2avurllg611nnual 0 Slrellm!low139,500lIer&-1oo1 -0: 125 slreamllow 81,900 acre-leet 150 U. 100 0 15 100 A~" m M..... e 50 50 $tr&llmJlow Z 25 -0: m 0 0 :::> 0 10.000 350 J: 300 I- 8,000 ~ 250 s: 6.000 200 0 4,000 150 ..J U. 100 ::E 2.000 50 -0: w 0 0 cr I- 5.000 100 m 4,000 15 3,000 50 2,000 1.000 25 0 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1910 1920 1930 1940 1950 '960 1970 1980 1990 2000 Figure 4. Relation of annual streamflow to average annual streamflow for the periOd of record. - ---- Tributaries 10 Great Salt Lake between Ogden and Sail Lake City --- Statewide - Strawberry. upper Price, upper San Rafael. Ogden. Weber, Provo. and Jordan Rivers; Blacksmith and Spanish Fork; upper Muddy and Chalk Creeks Statewide Duchesne River Ashley Cn."('k and ocher streams Oetween Manila and Vernal. and west of Manila Virgin and Santa Clara Rivers Cottonwood Wash and other nearby tributaries to San Juan River San Juan River and tributaries from McElmo Creek to Chinle Creek Vernon Creek Statewide Lower Duchesne and Jordan Rivers and tributaries (including Spanish Fork); upper Price. Bear. Sevier, and San Pitch Rivers; Chalk. Easl Canyon. Trout. and George Creeks; Great Salt Lake and tributaries belween Ogden and Salt Lake CilY White, upper Price. and Fremont Rivers: lower Bear and Sevier Rivers and tributaries: Beaver River; Red Butte Creek; Spanish Fork; Jordan River Sevier Lake Ut.ah Lake Great Salt Lake Provo River Stalewide - Quail Creek, lower Virgin River - -- Santa Clara River Soulh Fork Ogden River. Logan River. Blacksmith's Fork Statewide Streamflow Remarks Data from eight long-term streamflow- gaging stations maintained by the USGS Utah District were used to assess historic and current drought conditions. The stations (fig. I) were selected from a network of more than 150 stations in Utah and are considered index sites because they generally reflect streamflow conditions in their local area. Major darns have regulated flow on the Colorado, Green, and San Juan Rivers upstream from the index sites since the early I 960s. The Beaver, Virgin, and Weber Rivers arc lightly regulated by small headwater reservoirs or power genemting facilities. Smith's Fork and the Whitcrocks River have small diversions in upper watershed areas but are not regulated upstream from the gages. Despite these modifications to the drainages, these index sites are considered to generally reflect hydrologic conditions in their respective watersheds, including snowpack and the amount of water stored in reservoirs. Probably snowmelt combined with rainfall. Reg~;1. Locally intense thunderstorms. Deaths, 7; damage. $ 300,000. Regional. - Melling of snowpack having maximum-of-record water content for Apr. I. Disaster declared. Deaths. 2; damage, $8.4 million. Regional. Dam failure. Three days of inlense rainfall on rhick snowpack above altitude of 9,200 feet. Deaths, 7; damage. $814.000. Four days of light to intense rainfall of as much as 12 inches. Damage, $1.4 million. Locally inten5e thunderstorms tollowing II days of rainfall. Damage. .$34.000. Historic Streamflow Data Record-breaking rainfall. Deaths. 2; damage. $700.000. Locally intense Ihunderstorms, A chronology of significant flood5 and droughts in Utah from 1884 to 2002 and a summary of their eITects on infrastructure, population, and the environment is presented in table I. Prior to current drought conditions. Utah experienced drought on a regional scale most recently in the late I 980s to early 1990s. Other major droughts occurred during 1896. t 905. 1930-36, 1953-65, and 1974-78. The average length of these droughts is about 5 years and they recur about every 10 to 20 years. A hydrologic drought is defined as "a period of below average watcr content in streams, reservoirs, ground-water aquifers, lakes and soils" (Yevjevich and others, 1977). The relation of annual streamflow to average annllal streamflow for the period ofrccord for the eight index sites (tig. 4) shows the cyclical nature of wet and dry conditions in Utah. Regional. Rapid melting of snowpack having ma:\imum.of-record water content for June I. Result of large El Nino event. Disaslerdeclared by President. Damage, $621 million. Runoff from greater-than-average snowpack for Apr. I and spring precipitation. Result of large EI Nino event. Runoff in Sevier River from Nov. 1982 through June 1984 exceeded upstream reservoir c.lpacity~ about 1.5 million acre~feet of water conveyed to Sevier Lake. On May 22. 1984. lake reported to be as deep as 35 feet deep after being dry or nearly dry since about 1880. Runoff from greater-than-normal precipitation since Sept. 1982 increased lake level to 10 I-year record of 5.46 feet above compromise level on June 15. 1984. Mainly a resull of large EI Nino event of 1983-84. Damage. $5.9 million. - High runoff from greater.than-normal precipitalion since Sepl.. 1982 increa<>ed lake level to 140-yenr reconl altitude of 4.211.85 feci on June 3, 1986. Partially a result of large EI Nino event of 1983-84. Damage. $268 million. 101111998 4/111999 1011/1999 41112000 101112000 4/112001 101112001 4/112002 101112002 100,000 Colorado River near Cisco. UT e z o o w m cr w 0- I- W W U. o iii :::> o ~ s: o ..J U. ::E -0: w cr I- m 10.000 1,000 100.000 Green River near Green River. UT 10,000 1,000 100.000 San Juan River near Bluff, UT 10,000 1.000 1011/1998 4/1/1999 1011/1999 4/112000 101112000 41112001 101112001 4/112002 101112002 EXPLANATION - Average daily mean streamflow - Dally mean streamllow Figure 5. Relation of daily mean streamflow for water years 1999-2002 to mean streamflow for period of record, Current Streamflow Data 2. In 1999, streamflow was near or below average for the Colorado River, Beaver River, and Virgin River. These streamflow-gaging stations are all located in southern Utah. By 2000, an of the index sites indicated below.average flow. This trend has continued through 2002 with the exception of the Whiterocks River, which had slightly higher-than-average flow in 200 I. The Whiterocks River nows down the southern slope of the Uinta Mountains in northeastern Utah (fig. I). This area accumulated average snowpack during the winter or2001 (Natural Resources Conservation Service, 2002); however, on average, the larger Green River basin accumulated a substantially lower.than. average snowpack for (he same period as The end.of-season snowpack, as measured by the Natural Resources Conservation Service SNOTEL system on April I, 2002. was below average statewide, The snowpack, and therefore the relative amount of water available for runoff, was about 78 percent of average in northern Utah drainages and ranged from 24 percent to 54 percent of average in the southern part of the State. In eastern and southeastern Utah, the end. of-season snowpack was the lowest since 1977 and 1999 (Natural Resources Conservation Service, 2002). The percentage of average flow for the eight index sites for 1999-2002 is show" in table Table 2. Annual streamflow data for eight long-term streamflow-gaging stations [kac-ft, thousands of acre-feet) Trial Lake dam failure. Slope-area meusuremenl. II, - -- II RegIOnal. Quail Creek Reservoir dike failed on Jan. I. 1989, releasing aboUI 25.000 acre-feel of waler 10 [he Virgin River near Hurricane. Damage. $12 million. Average 1999 I 2000 2001 2002 tolal ~ Rank of annual lowest !low lor Total Total Total Total lotal Station Name Penod 01 period 01 annual Percenl annual Percent annual Percent annual Percent annual record record Itow 01 !low 01 flow 01 flow 01 !low (kac-h) (kae.'I) average (kac-ft) average (kac-ft) average (kac-ft) average 2002 Colorado River near Cisco, UT 1914-2002 5,297 4,807 90 3,856 72 3,003 56 1.856 35 I - - Whiterocks River near Whiterocks. UT 1930-2002 82 116 140 62 75 87 106 33 40 2 Green River near Green River. UT 1906.2002 4,463 5,392 1211 3.206 71 2.464 55 1,591 36 2 San Juan River near Bluff. UT 1916.1928. 1930-21102 1,638 1.837 III 838 51 1161 70 538 33 I Virgin River near Virgin, UT 1910-2002 1,4-1 102 70 90 62 100 69 61 43 I Smiths Fork near Border, wy 1943-2002 139 179 127 107 76 72 51 74 53 4 Weber River near Oakley. UT 1905-2002 158 184 116 II~J 69 1110 63 93 59 8 Beaver River near Beaver. UT 1915-2002 38 37 97 25 65 29 77 16 -II 3 \\f~ ? \=::'OCj 0 IS GreateNhaa.noffi1al snowp<ld,: in lhe Bear and Weber River drainage basins caused minor 1100xJing. Minor damage occurred to cabins and campgrounds in the area. Regional.