U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3081

September 2005

Hydrologic Conditions in Arizona During 1999–2004:

A Historical Perspective

Printed on recycled paper

Introduction

Arizona’s climate is prone to extreme 

changes that range from persistent 

droughts to frequent local and regional 

flooding. These changes are evident in 

hydrologic data collected. Streamflow 

records indicate that a drought in 

Arizona during 1999–2004 was the 

worst drought since the early 1940s and 

possibly earlier. Droughts result from 

a decrease in the number of already 

infrequent storms that bring moisture to 

Arizona. The drought conditions in the 

Southwestern United States over the last 

several years, and especially in Arizona, 

have resulted in several large summer 

fires, a decrease in potable water for 

some smaller communities, and depleted 

water available for surface water as well 

as ground-water recharge. An unusually 

wet December 2004 and January 2005 

in Arizona has interrupted the multiyear 

drought. Dry conditions, however, still 

prevail in parts of Arizona. It is difficult 

to conclude, therefore, whether the 

drought is over or if it will persist.

Historical and Current Hydrologic 

Conditions

Although the spatial and temporal 

extent of droughts is somewhat difficult 

to determine, three severe droughts 

during the 20th century were recognized 

in a 1989 U.S. Geological Survey 

National Water Summary (Paulson and 

others, 1991). The periods of significant 

statewide droughts, as indicated by 

records from several streamflow-gaging 

stations, were recognized as 1932–36, 

1942–64, and 1974–77 (figs. 1 and 2; 

table 1). 

This document utilizes long-term 

data from streamflow-gaging stations 

to compare the severity of the current 

drought to those indicated by Paulson and 

others (1991; fig. 2).

Climatology in Arizona

Precipitation in Arizona is biseasonal, 

having both winter and summer 

regimes (Hereford and others, 2002). 

The moisture comes from three major 

sources: (1) Pacific winter frontal storms 

that can produce significant snowpack 

in northern Arizona as well as flooding 

in the central and southern parts of 

Arizona, (2) subtropical Pacific moisture 

(dissipating hurricanes or tropical storms)

that is generally warmer and can produce 

regional flooding of large magnitude, 

and (3) convective storms that occur 

throughout the State during the summer 

months. The location and intensity of 

convective storms are difficult to predict 

as the storms can form quickly and 

produce large amounts of precipitation 

in localized areas. They also generally 

result in flooding in smaller basins and 

urban areas, but are not significant for 

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50 MILES

Little Colorado

Lower

Colorado

Bill

Williams

Verde

Phoenix Metropolitan Area

Yuma

Tucson

SANTA

CRUZ 

PIMA 

YUMA 

LA PAZ 

MOHAVE 

COCONINO 

UTAH

ARIZONA 

NEVADA 

COLORADO

NEW MEXICO 

COCHISE 

GRAHAM PINAL 

GILA 

MARICOPA 

NAVAJO APACHE 

YAVAPAI 

GREENLEE

Flagstaff

Paria

Virgin

San Juan Upper

San Juan

Whitewater Draw

Rio Sonoyta

Santa Cruz

San Pedro

Upper Gila

Salt Agua Fria

Lower Gila

CALIFORNIA

MEXICO

TUCSON

MESA

PRESCOTT

WILLIAMS

ROOSEVELT SALT RIVER

VERDE

RIVERTONTO CREEK

PARIA RIVER

GILA RIVER

SAN CARLOS RIVER

AGUA FRIA RIVER

SANTA CRUZ RIVER

SAN FRANCISCO RIVER

LITTLE COLORADO RIVER

EXPLANATION

RIVER-BASIN BOUNDARY

LONG-TERM GAGING STATION

MEDIUM TO LONG-TERM

 GAGING STATION

LONG-TERM PRECIPITATION 

 STATION 

Figure 1.  Locations of 10 long-term streamflow-gaging stations, 10 medium- to long-term gaging

stations, and 5 long-term precipitation stations.
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SAN CARLOS RIVER (09468500) 

SALT RIVER (09498500)

SAN FRANCISCO RIVER (09444500)

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2,500

GILA RIVER (09448500)

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160

120 SANTA CRUZ RIVER (09480500)

ANNUAL STREAMFLOW, IN CUBIC FEET PER SECOND

1920 1930 1940 1950 1960 1970 1980 1990 2000

production of higher flows in main-stem 

river systems (Paulson and others, 1991).

Additional Information on 

Hydrologic Conditions in Arizona, 

1999–2004

Precipitation data acquired by the 

National Weather Service can serve as an 

indicator of drought and flood conditions. 

Data acquired at five long-term precipitation stations in different parts of 

Arizona indicate that precipitation during 

the last 6 years was below the long-term 

average (fig. 3).

Streamflow in water years (WY) 

1999–2004 was compared to historical 

streamflow data for 20 streamflowgaging stations in Arizona for this report 

(table 2 and fig. 1). Included in the 20 

stations are 10 long-term stations, as well 

as an additional 10 medium- to longterm stations (fig. 1). These 20 stations 

are considered index stations because 

they have medium to long periods of 

record and are little affected by flow 

diversions. The data for the period 

1999–2004 for these 20 stations, when 

compared to historical data, indicate 

WY 2000 and WY 2002 were two of the 

driest years during the period of record. 

Annual discharge for almost all sites for 

individual years from 1999 to 2004 was 

well below long-term average conditions, 

indicating statewide drought conditions 

since the beginning of WY 1999 (October 

1998). Annual discharge exceeded the 

long-term average only 6 times at the 20 

sites from WY 1999 through WY 2004 

(table 2). Annual discharge for the 20 

sites over this same period of time was 

less than 10 percent of the average 

annual discharge 17 times and less 

than 50 percent 83 times. The drought 

of 1999–2004 is considered the most 

severe drought in Arizona since the early 

1940s and possibly earlier (table 1). The 

average streamflow during three drought

periods—1942–64, 1974–77, and 

1999–2004—was compared to average 

streamflow for the 10 long-term index 

stations. Streamflow at the stations was 

45 percent of the long-term flow during 

1999–2004, 53 percent during 1974–77, 

and 68 percent during 1942–64 (fig. 2). 

Data for 1932–36 were insufficient for 

comparisons with data for 1999–2004.

STREAMFLOW-GAGING STATIONS IN NORTHERN AND CENTRAL ARIZONA, 1939–2004—Drought periods

shown in gold; horizontal line indicates long-term average. Record for the Paria River begins in 1923; data for

1923–38 not shown.

Figure 2.  Annual mean streamflow at 10 long-term streamflow-gaging stations in Arizona.

STREAMFLOW-GAGING STATIONS IN CENTRAL AND SOUTHERN ARIZONA, 1914–2004—Drought periods

shown in gold; horizontal line indicates long-term average. Record for the Salt River begins in 1913; data for

1913 not shown. Gaps in plots after 1914 indicate data are not available.

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100

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200

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500

1,000

1,500

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AGUA FRIA RIVER (09512500)

PARIA RIVER (09382000)

VERDE RIVER (09508500)

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400

600

800

TONTO CREEK (09499000)

1940 1950 1960 1970 1980 1990 2000

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40

60

80

LITTLE COLORADO RIVER (09384000)

ANNUAL STREAMFLOW, IN CUBIC FEET PER SECOND
Although streamflows generally 

were low in Arizona during 1999–2004, 

floods during the winter of 2005 were 

substantial—to the point of filling 

reservoirs in central Arizona. The 

climate of Arizona, however, naturally 

tends to extremes—large floods and 

severe drought conditions are common. 

Determining whether this was an 

interruption to a longer drought, or the 

beginning of wetter years in Arizona, 

Table 1. Chronology of major and other memorable floods and droughts in Arizona, 1862–2005

 [Modified from Paulson and others, 1991]

Flood or 

drought

Date Area affected Remarks

Flood Jan. 19–23, 1862 Gila and Colorado Rivers Severe at Yuma. Wet year in Verde and Bright Angel Basins, but not in upper 

Salt River Basin

Flood Feb. 18–26, 1891 Central Highlands Phoenix and Yuma flooded. In Clifton, 18 deaths, $1 million in damage

Flood Nov. 27–30, 1905 San Francisco to Verde Rivers Several severe to moderate floods, particularly at Phoenix and along the lower 

Gila River

Flood Jan. 19–22, 1916 Central Highlands Intense rain on melting snow produced large flows in central Arizona; 4 deaths, 

$300,000 in damage

Flood Aug. 21, 1921 Phoenix (Cave Creek) Six inches of rain in 2 days flooded 4,000 acres and the State capital building; 

$240,000 in damage

Flood Sept. 27–29, 1926 San Pedro River and Mexico Tropical storm. Peak flow 2–3 times any other in 70 years; $450,000 in damage

Drought 1932–36 Statewide Effects differed among basins

Flood Mar. 14–15, 1941 Central Arizona One of several storms that caused general runoff and filled reservoirs

Drought 1942–64 Statewide Severe long-term drought interrupted by several wet periods

Flood Sept. 26–28, 1962 Brawley and Santa Rosa Washes 1 death; $3 million in damage, mostly to agriculture near Casa Grande

Flood Dec. 22 1965 to 

Jan. 2, 1966

Verde, Salt, and Gila Rivers and 

Rillito Creek

First large flow through Phoenix since reservoirs were built on Verde River (1939); 

$10 million in damage

Flood Dec. 5–7, 1966 Grand Canyon to southwestern 

Utah

Mudflows and channel erosion damaged Indian ruins that had been undisturbed for 

800 years

Flood Sept. 5–7, 1970 Tonto Creek to Hassayampa River Labor Day weekend floods in recreation areas. Reservoirs stored most runoff; 

23 deaths, $8 million in damage

Flood Oct. 17–21, 1972 Upper Gila River Tropical storm; 8 deaths, $10 million in damage

Drought 1974–77 Statewide Most severe in eastern Arizona

Flood July 17, 1974 Safford (Holyoke Wash) Thunderstorm produced flow of 1,740 cubic feet per second from 0.85-square-mile 

drainage basin

Flood Oct. 1977 to Feb. 1980 Central and southeastern Arizona Seven regional floods. Phoenix declared a disaster area three times; 18 deaths, 

$310 million in damage

Flood July 26, 1981 Tucson (Tanque Verde Falls) Flash flood at recreation area on Sunday; 8 deaths. Two larger peak discharges in the 

same week were not noticed

Flood June 20 to Aug. 7,1983 Colorado River Upper basin rain and snowmelt. First reservoir spill since Hoover Dam was built 

(1935); $80 million in damage

Flood Oct. 1–3, 1983 Santa Cruz to San Francisco 

Rivers

Record floods on 18 streams; two peak discharges doubled 65-year-old records; 

8 deaths, $226 million in damage

Flood Winter 1993 Statewide Resulted from extremely intense El Niño; breach of Gillespie Dam on Gila River

Drought 1999–present (2005) Statewide Extensive and abundant fires (Rodeo-Chedeski fire, for example) and decreased water 

supplies statewide

(Figure 3 and table 2 on next page)

therefore, is difficult. Data acquired at 20 

medium- to long-term streamflow-gaging 

stations, however, indicate the period 

1999–2004 was the driest since the early 

1940s and possibly earlier.

—Jeff V. Phillips and

Blakemore E. Thomas

References

Hereford, R., Webb, R.H., and Graham, S., 

2002, Precipitation history of the Colorado 

Plateau region: U.S. Geological Survey 

Fact Sheet 119–02, 4 p.

Paulson, R.W., Chase, E.B., Roberts, R.S., 

Moody, D.W., 1991, National Water 

Summary 1988–89, Hydrologic events 

and floods and droughts: U.S. Geological 

Survey Water-Supply Paper 2375, 

p. 181–188.
Table 2.  Percentage of average annual discharge for 20 selected streamflow-gaging stations during water years 1999–2004

Site Number Site Name Period of 

Record

Percentage of average annual mean discharge for

indicated water year

1999 2000 2001 2002 2003 2004

1 09382000 Paria River at Lees Ferry 1924–2004 109 41 96 39 57 62

2 09512500 Agua Fria River near Mayer 1940–2004 49 17 38 40 34 17

3 09508500 Verde River below Tangle Creek 1946–2004 51 36 65 32 68 40

4 09499000 Tonto Creek above Gun Creek, near Roosevelt 1941–2004 24 8.0 58 3.1 52 17

5 09384000 Little Colorado River above Lyman Lake 1941–2004 65 17 88 15 33 44

6 09498500 Salt River near Roosevelt 1914–2004 40 22 70 23 70 41

7 09468500 San Carlos River near Peridot 1930–2004 29 18 45 11 56 17

8 09444500 San Francisco River at Clifton 1928–2004 67 26 150 33 37 44

9 09448500 Gila River at head of Safford Valley 1921–2004 62 29 130 31 38 49

10 09480500 Santa Cruz River near Nogales 1931–2004 45 12 205 4.0 5.0 1.6

11 09490500 Black River near Fort Apache 1958–2004 31 13 73 15 66 40

12 09496500 Carrizo Creek near Show Low 1952–2004 18 11 28 35 55 26

13 09424450 Big Sandy River near Wikieup 1967–2004 5.0 3.8 61 4.1 13 44

14 09397500 Chevelon Creek below Wildcat Canyon 1948–2004 17 6.7 80 0 48 24

15 09504500 Oak Creek near Cornville 1941–2004 55 41 63 34 83 55

16 09510200 Sycamore Creek near Fort McDowell 1961–2004 5.0 .61 52 .23 36 2.7

17 09505350 Dry Beaver Creek near Rimrock 1961–2004 25 5.0 48 .8 77 20

18 09485000 Rincon Creek near Tucson 1953–2004 25 17 190 4.4 14 45

19 09497980 Cherry Creek near Globe 1966–2004 35 16 53 12 35 16

20 09379200 Chinle Creek near Mexican Water 1965–2004 110 19 49 74 34 43

Figure 3.  Annual precipitation at five long-term stations in Arizona. Drought periods shown in

gold; horizontal line represents long-term average. Gaps in plots after 1910 indicate data are not

available.

Current streamflow conditions in

Arizona can be obtained from

http://waterdata.usgs.gov/az/nwis/rt

Historical streamflow conditions can be

obtained from

http://waterdata.usgs.gov/az/nwis/sw

For more information contact:

U.S. Geological Survey

Arizona Water Science Center

520 N. Park Ave., Suite 221

Tucson, Arizona 85719

Telephone: (520) 670-6671 x261

Fax: (520) 670-5592

E-mail: jvphill@usgs.gov

az.water.usgs.gov

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ANNUAL PRECIPITATION, IN INCHES

ROOSEVELT

MESA

TUCSON

WILLIAMS

PRESCOTT