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River Basin Population tree-ring studies going back to year 481 in at least
<br /> Average one basin. Several researchers have used tree-ring
<br /> Annual Doubling
<br /> Percent Time, data to reconstruct various climatic parameters such
<br /> Basin 1990 1998 Change years
<br /> South Platte 2210,700 2,714,000 2.8% 25 as precipitation, the Palmer Drought Severity Index,
<br /> Arkansas 662,500 807,600 2.7% 26
<br /> Rio Grande 36,600 45,500 3.0% 23 and stream flow in the case of the Colorado River.
<br /> Colorado Mainstem 164,700 214,200 3.8% 19 The Palmer Index is based on soil moisture and is
<br /> Dolores&San Juan 72,800 94,600 3.7% 19
<br /> Gunnison 58,700 75,900 3.7% 19 used by the Department of Agriculture to determine
<br /> Yampa&White 31,900 38,100 2.4% 29
<br /> North Platte 1,900 2,100 1.3% 53 when to provide federal drought assistance.
<br /> Fact Sheet Totals 3,239,800 3,992,000 2.9% 24
<br /> CWCB River Basins
<br /> Reservoir storage has been a critical element of
<br /> 6
<br /> western drought management strategy. It has 1ampa.White \ 3 1
<br /> been estimated that approximately 80% of the 5 South Platte
<br /> surface water supply in Colorado is naturally colurldo Nlainstem
<br /> available during the four-month snowmelt runoff
<br /> period in April, May,June, and July. ^
<br /> 2
<br /> Arkansas
<br /> Dolores River at Dolores, CO 3
<br /> 7 Rio Grande
<br /> asoo orwaxmm rear,9az) San M%uey-Dolores
<br /> n uan
<br /> ii Average Dally Flow(1898.1987) --I
<br /> uo,nnm Year 119]])
<br /> �Excea00E 1%of rime
<br /> 3,000
<br /> 2,600 South Platte River Basin
<br /> Sufficient precipitation records are available from
<br /> I:: 1 1891 in the lower South Platte River Basin and
<br /> ,.990 from 1880 in the upper basin. Recent droughts in
<br /> the lower South Platte River Basin occurred in
<br /> , 1891-1892, 1895-1898 (extreme), 1911-1912, 1931-
<br /> "°" 'Dec 1-Jan -Feb, 1-Mar '- 1-May '�rn '�� '"� 1$e° 1941, 1953-1957, and 1974-1979. Recent droughts
<br /> in the upper South Platte River Basin occurred in
<br /> 1880-1881, 1893-1895 (extreme), 1903, 1912-1913,
<br /> Reservoir storage grew tremendously after droughts 1931-1937, 1940-1941, 1954-1956, 1963-1965, and
<br /> in the 1930's and 1950's. By about 1970, active 1977-1979.
<br /> reservoir storage per capita in Colorado peaked at
<br /> about 1.5 acre-feet per person and has been steadily Tree-ring Record for Northeastern Colorado
<br /> declining ever since. By about 1990, total statewide -� (Point 58), 1700-1978
<br /> active reservoir storage capacity exceeded 4 million 4.0
<br /> acre-feet, but the population is growing faster than o 30
<br /> new surface water supplies and reservoirs are being a 2.0
<br /> c 1.0
<br /> developed. 1 ,1 � 1mlN11
<br /> o.o
<br /> Each of Colorado's eight major river basins has a-2.0
<br /> I IIIIV�I IJI�II LUJI I t.�I,WL1 m
<br /> a unique history of drought. The following is a o 3.0 1
<br /> brief summary of historic droughts for each river
<br /> basin. The information comes from precipitation a .5.0
<br /> records, available from 1880 in some basins, and ...,„,,....0
<br /> 6.0
<br /> 3
<br />
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