Figure 1. Selected streamflow-gaging 

stations of the U.S. Geological Survey in 

Arizona.

Precipitation records from the four sites— 

Flagstaff Airport, Sedona Ranger Station, 

Payson, and McNary 2N—show that 

precipitation from October 1995 through 

June 1997 was 46, 48, 75, and 70 percent 

of normal, respectively (National Oceanic 

and Atmospheric Administration, 1996, 

1997). These precipitation stations are at 

or near the headwaters of major rivers. 

Although frontal-storm precipitation and 

subsequent snowpack increased during the 

winter and spring of 1997 (December 

1996 through April 1997) as compared 

with the same period in 1995–96,

precipitation for the four stations was still 

55, 69, 82, and 64 percent of normal, 

respectively, for December 1996 through 

April 1997. Some areas of the State did 

receive substantial monsoonal rainfall 

during the late summer of 1996, but these 

storms typically were localized and of 

short duration and resulted in little runoff 

to replenish reservoir systems

Streamflow

Even though streamflow rates have 

increased in 1997 compared to 1996, the 

average amount of water flowing in the 

major river systems of central Arizona still 

remains below normal. One way to 

compare streamflow conditions of 1996 to 

1997 is to look at the total volume of 

water at streamflow-gaging stations for the 

months December through April, which 

usually produce the most streamflow. 

Water volume commonly is measured in 

acre-feet. One acre-foot is equivalent to 

the volume of water covering 1 acre to a 

depth of 1 foot (325,851 gallons) and is 

commonly considered to be the average 

amount of water used by a household of 

four in one year. Normal volumes of 

streamflow for the Gila River at Calva, 

Salt River near Roosevelt, and Verde 

River below Tangle Creek are 192,200, 

448,600, and 318,600 acre-feet, 

respectively, for December through April 

for the periods of record (table 1). At the 

gaging station, Gila River at Calva, 28,940 

acre-feet of water flowed from December 

1995 to April 1996 compared with 

127,900 acre-feet for the same period in 

1996–97. At the gaging station, Salt River 

near Roosevelt, 66,060 acre-feet flowed 

during December 1995 through April 1996 

compared with 277,600 acre-feet during 

this period in 1996–97. For the gaging 

station, Verde River below Tangle Creek, 

76,520 acre-feet of water flowed between 

December 1995 and April 1996 compared 

with 159,200 acre-feet for this period in 

1996–97.

From October 1, 1995, through June 30, 

1997, runoff recorded at streamflow-gaging 

stations, Gila River at Calva (09466500), 

Salt River near Roosevelt (09498500), 

U.S. Department of the Interior

U.S. Geological Survey

Precipitation and Streamflow

Conditions in Arizona,

October 1, 1995, to June 30, 1997 

Precipitation

 

With the pronounced climate variation in 

the State, moisture conditions can vary from 

drought to flooding. Mean annual precipitation in Arizona ranges from about 4 inches 

in Yuma and other areas along the lower 

Colorado River to more than 30 inches at 

higher elevations in mountainous regions. 

Regional storm systems generate most of the 

precipitation and runoff in the State. These 

storms typically occur as frontal systems 

during the winter and early spring 

(December to April). Precipitation from 

frontal storms usually falls at slow to 

moderate rates over long periods and large 

areas. Isolated summer thunderstorms, or 

monsoon storms, occur during late summer 

(July to September) and provide additional 

precipitation that typically falls quickly in 

localized areas for short periods of time. 

Monsoon storms may cause serious flooding 

in places but typically provide little runoff 

for water supplies. Dissipating tropical 

cyclones or hurricanes occasionally occur 

during late summer and fall and may produce 

significant amounts of runoff but are less 

frequent than other types of storms. 

Consequently, runoff produced by precipitation from frontal-storm systems generally 

is the main source of water for replenishment 

of the reservoirs in central Arizona. From 

October 1, 1995, to June 30, 1997, 

precipitation averaged below normal at four 

selected sites in various areas of the State.

STREAMFLOW-GAGING STATIONS

 1. Gila River at Calva, 09466500

 2. Salt River near Roosevelt, 09498500

 3. Verde River below Tangle Creek, above

 Horseshoe Dam, 09508500

 4. Santa Cruz River near Nogales, 09480500

 5. San Pedro River at Charleston, 09471000

 6. Oak Creek near Sedona, 09498500

 7. White River near Fort Apache, 09494000

 8. East Fork White River near Ft. Apache,

 09492400

 9. Black River near Ft. Apache, 09490500

10. West Clear Creek near Camp Verde,

 09505800

5 4

River

R

Salt

iver

Gila

1

10

3

6

2

7

9 8

Since October 1, 1995, Arizona 

has been experiencing one of the 

driest periods on record. From 

October 1, 1995, to June 30, 1997, 

streamflow averaged 50 percent of 

normal for the Gila, Salt, and Verde 

Rivers. However, scientists are 

recording warm water temperatures 

in the eastern Pacific Ocean, which 

typically indicate a return of the El 

Niño phenomenon. El Niño is 

usually associated with increased 

winter rainfall and drier summers 

for Arizona and is closely 

associated with some of Arizona's 

wettest years (Rasmusson, 1985).

.
and Verde River below Tangle Creek 

(09508500) were 48, 43, and 45 percent of 

normal, respectively, as compared with 

mean monthly flows for the period of 

record (POR) for each site (table 1 and 

fig. 2).

Below-normal precipitation conditions 

for October 1, 1995, to September 30, 

1996, are shown by the number of record 

lows for yearly runoff for some of the 

major tributaries to the Salt, Verde, and 

Gila Rivers. These sites include the Santa 

Cruz River near Nogales (09480500, 

POR=67 years), San Pedro River at 

Charleston (09471000, POR=31 years), 

Oak Creek near Sedona (09504420, 

POR=15 years), White River near Fort 

Apache (09494000, POR=40 years), 

Streamflow Monitoring

The U.S. Geological Survey (USGS) 

operates a network of 234 streamflowgaging stations throughout the State. Most 

of these stations are operated with at least 

partial support from more than 20 other 

Federal, State, and local agencies. At 124 

of these stations, the data recorded by the 

gaging stations are relayed by satellite 

telemetry to the USGS offices in Flagstaff, 

Tempe, Tucson, and Yuma. The advanced 

satellite-telemetry technology provides the 

USGS, cooperating agencies, and the 

public with streamflow conditions on a 

near real-time basis. These data are 

required to adequately monitor and manage 

the State's water supply, especially during 

extreme hydrologic conditions, such as 

floods and droughts. Streamflow data and 

other hydrologic information are 

available on the Internet through the 

Arizona District home page at

http://wwwdaztcn.wr.usgs.gov.

December 1997 FS-173-97

For more information contact:

U.S. Geological Survey

520 N. Park Ave., Suite 221

Tucson, Arizona 85719-5035

(520) 670-6671

—Owen R. Baynham, Joseph P. Capesius,

 and Jeff V. Phillips

East Fork White River near Fort Apache 

(09492400, POR=39 years), Black River 

near Fort Apache (09490500, POR = 43 

years), and West Clear Creek near Camp 

Verde (09505800, POR= 32 years) (fig. 1). 

All of the above rivers and streams, except 

the Santa Cruz and San Pedro Rivers, 

originate in either the White Mountains or 

the Mogollon Rim area, where runoff 

results primarily from frontal storms and 

snowmelt. Streamflow can be made up of 

both surface-water runoff from precipitation 

and inputs from ground water. Although 

most of the total flow in these streams 

originates at springs and other ground-water 

sources, the record low flows in 1996 

resulted from extremely low runoff 

(Baynham and Phillips, 1996).

Period

of record

Dec.

1995–Apr.

1996

Dec.

1996–Apr.

1997

Mean of total

flow for Dec.

through Apr.

for period

of record, in

acre-feet

Streamflow,

Oct. 1995

through

June

1997, in

acre-feet

Streamflow,

Oct. 1995

through

June 1997,

as percent

of normal

Normal

streamflow

for 21-month

period Oct.–

June, in

acre-feet

Total streamflow,

in acre-feet

Dec.

1995–Apr.

1996

Dec.

1996–Apr.

1997

Streamflow, as

percent of normal

Table 1. Streamflow data for three major rivers in Arizona

1Provisional data—subject to revision.

Gila River at

 Calva (09466500)

Salt River near

 Roosevelt (09498500)

Verde River below Tangle

 Creek (09508500)

1929–97

1913–97

1945–97

192,200

448,600

318,600

28,940

66,060

76,520

15

15

24

67

62

50

250,100

534,000

363,800

48

43

45

524,600

1,255,000

812,800

1127,900

1277,600

1159,200

Mean monthly

discharge

 water years

1945–97

Mean monthly

discharge, water

years 1913–97

Mean monthly

discharge, water

years 1929–97

Figure 2. Monthly mean discharge for October 1, 1995, to June 30, 1997, and the 

mean-monthly discharge for the period of record at Verde River below Tangle Creek, 

Salt River near Roosevelt, and Gila River at Calva (data for 1997 are provisional 

and are subject to revision).

1995 1996 1997

DISCHARGE, IN CUBIC FEET PER SECOND

500

0

1,250

1,000

0

800

1,600

2,500

0

Selected References

Baynham, O.R., and Phillips, J.V., 1996, Precipitation and 

streamflow conditions in Arizona, winter and spring, 

1996: U.S. Geological Survey Fact Sheet FS–223–96, 

1 sheet.

National Oceanic and Atmospheric Administration, 1996, 

Climatological data, annual summary—Arizona, 1995: 

Ashville, North Carolina, National Climatic Data Center, 

v. 99, no. 13.

––––––1997, Climatological data, annual summary—Arizona, 

1996: Ashville, North Carolina, National Climatic Data 

Center, v. 100, no. 13.

Rasmusson, E.M., 1985, El Niño and variations in climate: 

American Scientist, v. 73, p. 168–177.

Smith, C.F., Duet, N.R., Fisk, G.G., McCormack, H.F., 

Partin, C.K., Pope, G.L., and Rigas, P.D., 1996, Waterresources data, Arizona, water year 1996: U.S. 

Geological Survey Water-Data Report AZ–96–1, 328 p. 

Gila River at Calva, 09466500

Salt River near

Roosevelt, 09498500

Verde River below

Tangle Creek, 09508500

Monthly mean discharge

Monthly mean

discharge

Monthly

mean

discharge

Monthly mean

discharge