Impacts of Climate Change and Land Use  on the Southwestern United States

Southwestern States Flood and Drought Summaries


This page is excerpted from Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, D.W., Compilers, National Water Summary 1988-89-- Hydrologic Events and Floods and Droughts: U.S. Geological Survey Water-Supply Paper 2375, 591 p.

Major floods and droughts are those that were areally extensive and had significant recurrence intervals - greater than 25 years for floods and greater than 10 years for droughts. The most significant floods and droughts in Nevada are listed chronologically in Table 1.

Table 1. Chronology of major and other memorable floods and droughts in Nevada, 1907-88

Flood or DroughtDateArea AffectedRecurrence Interval (in years)Remarks
FloodMar. 1907Sierra Nevada drainagesUnknownMay rank with 1950 and 1955 floods in Carson Valley and along Truckee River.
FloodFeb. 1910Upper Humboldt River basin>100Information limited. Similar to hydrologic conditions during Feb. 1962 flood.
Drought1928-37Most of State, especially Humboldt River and Sierra Nevada drainages.>25In parts of Humboldt River basin, extended from 1923 to 1941
FloodNov.- Dec. 1950Sierra Nevada drainages50Not as severe as Dec. 1955 flood in Carson River drainage.
Drought1953-55Most of StateAbout 10Dec. 1955 flood ended drought in Sierra Nevada.
FloodDec. 1955Sierra Nevada drainages40 to 100Most severe flood from upper Carson River drainage downstream to Carson City.
Drought1959-62Most of State10 to 20Lasted 3 - 4 years depending on location.
FloodFeb. 1962Humboldt River drainage>50 in upper Humboldt River basinRapid thawing and light rain on snowpack. Damage, $1.5 million.
FloodFeb. 1963Sierra Nevada drainages50Severe in Carson and Truckee River drainages.
FloodDec. 1964Sierra Nevada drainages20
FloodSept. 14, 1974Eldorado Canyon>100Lives lost, 9.
FloodJuly 1975Las Vegas ValleyUnknownLives lost, 2; damage, $4 - 5 million.
Drought1976-77Statewide, except for southAbout 10Most severe along Sierra Nevada drainages.
FloodAug. 1981Moapa Valley and vicinityUnknownSevere damage to agriculture and highways.
FloodsMar. - June 1983Statewide except south less than 10 to 50 Greatest snowmelt floods known except in Humboldt River basin where exceeded in 1984.
FloodJuly 1983Las Vegas Valley, Muddy RiverUnknown
FloodsApr. - June 1984Centered in Humboldt River drainage.>100 along middle and lower Humboldt River.Greatest snowmelt floods known in Humboldt River basin.
FloodsJuly- Sept. 1984Las Vegas ValleyUnknownLives lost, 5.
FloodsFeb. 1986Sierra Nevada drainages10 to 50Greatest discharge in main rivers since 1963.
Drought1987-88Statewide, especially Sierra Nevada drainages.About 10About equal to 1976-77 drought.


Figure 1. Areal Extent of Floods in Nevada. Click on image to view a larger version.

To portray the intensity and duration of floods, six streamflow-gaging stations were selected on streams having diverse drainage-area size (9.2 to 5,010 square miles) and geographic distribution and little, if any, regulation or diversion of streamflow. Streamflow data are collected, stored, and reported by water year (a water year is the 12-month period from October 1 through September 30 and is identified by the calendar year in which it ends). Floodflow data before the 1960's from gaging stations in central and southern Nevada are unavailable; therefore, knowledge of floods in those parts of the State during that time is limited.

In west-central Nevada, along the main stems of the Truckee, Carson, and Walker Rivers, the most severe floods have resulted from winter rains in the Sierra Nevada lasting several days to more than a week. During major storms, the main stems of the Truckee and Carson Rivers generally reach flood stage, although the magnitude of flow in one river can be considerably different from that in the other river. Floods along the Walker River frequently occur at the same time as those along the Truckee and Carson Rivers; however, floods along the Walker River generally are caused by snowmelt rather than by rain because of the higher basin altitude.

After a stormy early December, intense rainfall in the Sierra Nevada during December 21-24, 1955 (water year 1956), caused widespread flooding along the Truckee, Carson, and Walker Rivers. Rainfall, which melted some of the snow, and snow-fall totaled 10-13 inches (as liquid water) in the headwaters. Of the three river basins, the Carson was the hardest hit - from the head-waters to Carson City, the flood is the largest known (U.S. Geological Survey, 1963, p. A13-A17).Total damage along the three rivers was estimated at $4 million (U.S. Geological Survey, 1963, p. A78).

Storms throughout a 10-day period in February 1986 caused severe flooding along the Truckee and Carson Rivers and to a lesser extent along the Walker River. The storms causing the floods were similar meteorological to those in December 1955 and February 1963, but in 1986 the rains continued for a longer period, and the snow level was at a significantly lower altitude. Maximum precipitation for the period was 12 inches in valley areas, 20 inches in the foothills of the Sierra Nevada, and 30 inches in the higher mountains. The precipitation was unprecedented for durations of as many as 10 days. Flows in the Truckee River in the Reno-Sparks area and in the Carson River at Carson City were the greatest since 1963. Downstream on the Carson River near Fort Churchill, the flow was the greatest since record keeping began in 1911.

In northern Nevada from November to March, flooding at the two representative gaging stations-Martin Creek near Paradise Valley and Humboldt River at Palisade may not be significant even though major floods are occurring along the Truckee, Carson, and Walker Rivers. Of the five largest floods on Martin Creek, only two-February 1963 and February 1986- occurred at the same time as one of the five largest floods occurred on the Carson River. None of the five largest floods on the Humboldt River at Palisade correspond in time to the largest floods of major rivers draining the Sierra Nevada.

On rare occasions, principally in large drainages of northern and eastern Nevada, flooding is caused by rapid midwinter thawing combined with light to moderate rain. The largest (February 1910) and fourth-largest (February 1962) floods measured on the Humboldt River at Palisade resulted from such conditions. Not much is known about the 1910 flood. The February 1962 flood was mostly in the upper Humboldt River basin. At Elko, minimum temperatures were not appreciably below freezing, and daily maximums were about 50 degrees Fahrenheit for a week. Rainfall of about 1.5 inches, combined with the snowmelt caused by warm weather, resulted in floods having recurrence intervals of 50-100 years (Thomas and Lamke, 1962).

Peak discharges of snowmelt floods from April to June do not rank as severe along the main stems of major Sierra Nevada rivers. However, along the main stem of the Humboldt River, peak discharges of snowmelt floods in 1984 and 1983 were the second and third largest, respectively, for the period of record. The floods of April-June 1984 on the Humboldt River were caused by melting of an unprecedented snowpack in the entire basin. In addition to the magnitude of the floods, the total volume of runoff for water year 1984 was more than twice any volume recorded in the years before 1983. Damage to bridges, highways, and agriculture was the most severe in history. The airport at Lovelock was not usable for several months because of water on the runway.

In small drainages throughout the State and also in large drainages in southern Nevada, flash floods may occur from May to October as a result of intense rainfall on relatively small areas. In Eldorado Canyon (a normally dry tributary to the Colorado River, 50 miles southeast of Las Vegas) nine people were killed in a flash flood on September 14, 1974. The flood destroyed 5 mobile homes and damaged many others, obliterated a restaurant, and destroyed 38 vehicles, 19 boat trailers, 23 boats, half of the boat-docking facilities, and the gas dock. The flash flood was caused by intense basinwide rain and hail of as much as 3 inches in 30 minutes (Glancy and Harmsen, 1975). Similar floods in Las Vegas in 1975 (Katzer and others, 1976), 1983, and 1984 killed several people and resulted in significant property damage.

Streamflow data collected at the three representative gaging stations in central and southern Nevada indicate that flooding there has been caused by diverse sources. The largest floods in South Twin River near Round Mountain have been caused by snowmelt. Along Steptoe Creek near Ely the largest flood resulted from a summer storm and the second largest from spring snowmelt. In Lee Canyon near Charleston Park, a channel that has had no flow in about one-half of the years of record, floods have occurred almost exclusively in the summer.


Figure 2. Areal Extent of Droughts in Nevada. Click on image to view a larger size version.

Drought in Nevada is superimposed on chronic arid conditions. In contrast to a flood, the onset of a drought is characterized by gradual intensification. For most of Nevada, which depends mostly on streamflow for water supply, a drought is considered to be a period of 2 or more consecutive years in which streamflow is much less than average.

The same six gaging stations used for floods were selected to portray the severity and duration of droughts. The areal extent of the droughts shown in Figure 2, were determined from an analysis of streamflow at gaging stations that form the statewide network. Because streamflow data for central and southern Nevada have been available only since the 1960's, records of hydrologic drought in those areas are few.

A major drought, possibly the most severe and longest of this century, occurred throughout northern Nevada from 1928 to about 1937. Extended periods of deficient streamflow in the Humboldt River basin indicate an earlier beginning for the drought in that area. During the drought, streamflow exceeded the average in only 1 or 2 years at gaging stations for which data are available. Drought during the 1930's was especially severe in the Humboldt River basin. Drought conditions were somewhat alleviated in Sierra Nevada drainages such as the Carson River in 1932 and 1937.

Two moderate droughts affected most of Nevada during the 1950's and early 1960's: 1953-55 and 1959-62. The drought of 1959-62 probably was the second most severe in this century. As is common, both droughts were ended by floods (Table 1).

During 1976-77, streamflow in the major rivers draining the Sierra Nevada and, to a lesser extent, in the Humboldt River and its tributaries was far less than average. Because of substantial development and population increase since the 1950's, drought and potential mitigation were becoming major concerns. During previous droughts, the major concern was adequacy of water supply for irrigation. The 1976-77 drought brought into focus such additional issues as adequacy for residential needs, necessity for water meters in the Reno area, suitability of fish habitat in rivers, and the potential for Lake Tahoe as a water supply. The return to average and greater than average supplies in 1978-80 helped to delay the resolution of some of those issues.

After an extremely wet period during 1982-86 in northern and western Nevada. a severe drought began in the fall of 1986 (beginning of water year 1987). Although the drought of 1987-88 had about the same severity as the drought of 1976-77, continued growth and development have heightened the concerns about the effects of the most recent drought.

After the extremely dry years of 1987 and 1988, precipitation and streamflow in most of the major river basins of northern and northwestern Nevada returned to near normal in 1989. Streamflow was slightly greater than average in the Humboldt River and near average in the Truckee and Carson Rivers but remained significantly less than average in the Walker River. As of 1989, it is uncertain whether the drought has ended or will continue.

In the southern part of the State, streamflow is meager and unreliable as a result of the arid climate; the only perennial stream in the area is the Colorado River, which is regulated in the reach bordering Nevada. The gaging station on Lee Canyon near Charleston Park has recorded only sporadic streamflow for many years; this typical near absence of data for ephemeral streams makes definition of hydrologic droughts in dry areas difficult.

As is true for floods, the effects of droughts are not constant with time. Continued population growth and land and resource development in the State ensure that floods and droughts of a severity that was troublesome decades ago will have a much greater effect in the future.

Selected References

Glancy,P.A., and Harmsen,L., 1975, A hydrologic assessment of the September 14, 1974 flood in Eldorado Canyon, Nevada: U.S. Geological Survey Professional Paper 930, 23p.

Thomas,C.A., and Lamke,R.D., 1962, Floods of February 1962 in southern Idaho and northeastern Nevada: U.S. Geological Survey Circular 467, 30p.

U.S. Geological Survey, 1963, Floods of December 1955-January 1956 in the far western States: U.S. Geological Survey Water-Supply Paper 1650-A,B, 736p.

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