ALASKA

U.S. Department of the Interior

U.S. Geological Survey

Water Temperature of Streams in 

the Cook Inlet Basin, Alaska, and 

Implications of Climate Change

Water-Resources Investigations Report 01-4109

Prepared as part of the

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM
Cover photograph: View of the Deshka River on June 26, 2001, by Robert Ourso, U.S. Geological Survey.
U.S. Department of the Interior

U.S. Geological Survey

Water Temperature of Streams in 

the Cook Inlet Basin, Alaska, and 

Implications of Climate Change

By REBECCA E. KYLE and TIMOTHY P. BRABETS

Water-Resources Investigations Report 01-4109

Prepared as part of the 

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Anchorage, Alaska 

2001
U. S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

The use of trade, product, or firm names in this publication is for 

descriptive purposes only and does not imply endorsement by 

the U.S. Government.

For additional information: Copies of this report may be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

4230 University Drive, Suite 201 Box 25286

Anchorage, AK 99508-4664 Denver, CO 80225-0286

Internet URLs:

Alaska Water Resources: http://ak.water.usgs.gov

Cook Inlet Basin NAWQA: http://ak.water.usgs.gov/Projects/Nawqa/

National NAWQA: http://water.usgs.gov/nawqa/nawqa_home.html
iii

FOREWORD

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that helps enhance and protect the 

overall quality of life, and facilitates effective management of water, biological, energy, and mineral 

resources. Information on the quality of the Nation’s 

water resources is of critical interest to the USGS 

because it is so integrally linked to the long-term availability of water that is clean and safe for drinking and 

recreation and that is suitable for industry, irrigation, 

and habitat for fish and wildlife. Escalating population 

growth and increasing demands for the multiple water 

uses make water availability, now measured in terms of 

quantity and quality, even more critical to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. Shaped by and coordinated with ongoing 

efforts of other Federal, State, and local agencies, the 

NAWQA Program is designed to answer: What is the 

condition of our Nation’s streams and ground water? 

How are the conditions changing over time? How do 

natural features and human activities affect the quality 

of streams and ground water, and where are those 

effects most pronounced? By combining information 

on water chemistry, physical characteristics, stream 

habitat, and aquatic life, the NAWQA Program aims to 

provide science-based insights for current and emerging water issues. NAWQA results can contribute to 

informed decisions that result in practical and effective 

water-resource management and strategies that protect 

and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 

50 of the Nation’s most important river basins and 

aquifers, referred to as Study Units. Collectively, these 

Study Units account for more than 60 percent of the 

overall water use and population served by public 

water supply, and are representative of the Nation’s 

major hydrologic landscapes, priority ecological 

resources, and agricultural, urban, and natural sources 

of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments thereby build local knowledge 

about water-quality issues and trends in a particular 

stream or aquifer while providing an understanding 

of how and why water quality varies regionally and 

nationally. The consistent, multi-scale approach helps 

to determine if certain types of water-quality issues are 

isolated or pervasive, and allows direct comparisons 

of how human activities and natural processes affect 

water quality and ecological health in the Nation’s 

diverse geographic and environmental settings. 

Comprehensive assessments on pesticides, nutrients, 

volatile organic compounds, trace metals, and aquatic 

ecology are developed at the national scale through 

comparative analysis of the Study-Unit findings. 

The USGS places high value on the communication and dissemination of credible, timely, and 

relevant science so that the most recent and available 

knowledge about water resources can be applied in 

management and policy decisions. We hope this 

NAWQA publication will provide you the needed 

insights and information to meet your needs, and 

thereby foster increased awareness and involvement in 

the protection and restoration of our Nation’s waters. 

The NAWQA Program recognizes that a national 

assessment by a single program cannot address all 

water-resource issues of interest. External coordination 

at all levels is critical for a fully integrated understanding of watersheds and for cost-effective management, 

regulation, and conservation of our Nation’s water 

resources. The Program, therefore, depends extensively on the advice, cooperation, and information 

from other Federal, State, interstate, Tribal, and local 

agencies, non-government organizations, industry, 

academia, and other stakeholder groups. The assistance 

and suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water

v

CONTENTS

Abstract .......................................................................................................................................................................................1

Introduction.................................................................................................................................................................................1

Purpose and Scope ............................................................................................................................................................2

Methods of Study ..............................................................................................................................................................4

Description of the Study Area.....................................................................................................................................................4

Water-Temperature Characteristics ............................................................................................................................................5

Kenai Peninsula.................................................................................................................................................................8

Anchorage Area ................................................................................................................................................................8

Susitna River Basin.........................................................................................................................................................10

Future Trends in Water-Temperature Characteristics...............................................................................................................11

Climate Change...............................................................................................................................................................11

Water-Temperature Model..............................................................................................................................................12

Calibration and Verification..................................................................................................................................13

Stream-Temperature Projections and Implications...............................................................................................17

Summary ...................................................................................................................................................................................22

References Cited .......................................................................................................................................................................23

FIGURES

Figure 1. Map showing location of water-temperature and climate sites in the Cook Inlet Basin, Alaska ...........................3

Figure 2. Graph showing comparison of discharge between a glacial and a nonglacial stream ............................................5

Figure 3 Graph showing beginning and ending year of available data for water-temperature-measurement sites ..............8

Figure 4. Graph showing average daily maximum and minimum water temperatures for six sites on the 

Kenai Peninsula.......................................................................................................................................................9

Figure 5. Graph showing average daily maximum and minimum water temperatures for three sites in Anchorage ............9

Figure 6. Graph showing average daily maximum and minimum water temperatures for five sites on the 

Susitna River.........................................................................................................................................................10

Figure 7. Graph showing average daily maximum and minimum water temperatures for the Chulitna River near 

Talkeetna, Alaska (site 40)....................................................................................................................................11

Figure 8. Graph showing average daily maximum and minimum water temperatures for the Yentna River near 

Susitna Station, Alaska (site 109) .........................................................................................................................11

Figure 9. Schematic representation of the logistic function parameters (from Mohseni and others, 1998) ........................12

Figure 10. Graph showing relation of distance between a water-temperature site and its associated air-temperature 

site to Nash-Sutcliffe coefficient...........................................................................................................................17

Figure 11. Graph showing relation between percent of watershed covered by glaciers and Nash-Sutcliffe coefficient.......17

Figure 12. Graph showing relation between weekly average water temperature and weekly average air temperature 

for Ship Creek below powerplant at Elmendorf Air Force Base at Anchorage, Alaska.......................................17

Figure 13. Graph showing relation between weekly average water temperature and weekly average air temperature 

for Chester Creek at Arctic Boulevard at Anchorage, Alaska ..............................................................................17

Figure 14. Map showing water-temperature sites in the Cook Inlet Basin with predicted water temperatures greater 

than 3 degrees Celsius...........................................................................................................................................21

TABLES

Table 1. Observed water-temperature ranges for five species of salmon in four freshwater life stages...............................2

Table 2. Water-temperature sites in the Cook Inlet Basin, Alaska .......................................................................................6

Table 3. Climate stations used with water-temperature-regression model .........................................................................13

Table 4. Results from water-temperature-regression model...............................................................................................14

Table 5. Water-temperature regression-model parameters .................................................................................................18

Table 6. Predicted water temperatures due to climate change ............................................................................................20
vi

CONVERSION FACTORS AND VERTICAL DATUM

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=1.8 °C+32

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) — a geodetic 

datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called 

Sea Level Datum of 1929.

MAPPING SOURCES:

Base map modified from U.S. Geological Survey 1:250,000 State base maps.

U.S. Geological Survey Digital Line Graphs published at 1:2,000,000.

Publication projection is Albers Equal Area.

Standard parallels are 55ο00’ and 65ο00’, central meridian –154ο00’, latitude of projection origin 50ο00. 

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2)
1

Water Temperature of Streams in the Cook Inlet Basin, 

Alaska, and Implications of Climate Change

By Rebecca E. Kyle and Timothy P. Brabets

Abstract

Water-temperature data from 32 sites in the 

Cook Inlet Basin, south-central Alaska, indicate 

various trends that depend on watershed characteristics. Basins with 25 percent or more of their 

area consisting of glaciers have the coldest water 

temperatures during the open-water season, midMay to mid-October. Streams and rivers that drain 

lowlands have the warmest water temperatures. A 

model that uses air temperature as input to predict 

water temperature as output was utilized to simulate future trends in water temperature based on 

increased air temperatures due to climate warming. Based on the Nash-Sutcliffe coefficient, the 

model produced acceptable results for 27 sites. For 

basins with more than 25 percent glacial coverage, 

the model was not as accurate. Results indicate 

that 15 sites had a predicted water-temperature 

change of 3 degrees Celsius or more, a magnitude 

of change that is considered significant for the 

incidence of disease in fish populations.

INTRODUCTION

Water temperature is one of the most significant 

factors in the health of a stream ecosystem (Ward, 

1963). Depending on the type of stream and its location, the natural flora and fauna often establish themselves in ranges delineated by temperature. The study 

of water temperature has many immediate practical 

applications, such as determining the environmental 

impacts due to anthropogenic sources (Smith, 1972) 

and the health of stream biota (Peterson and others, 

1977; Alderice and Velsen, 1978; Edwards and others, 

1979; Baltz and others, 1987; Eaton and Scheller, 

1996; Scheller and others, 1999). Stream temperature 

can have detrimental effects on various species populations by influencing physical, chemical, and biological water properties (Smith, 1972). For example, 

if stream temperatures are low (between 4°C and 

0°C), fish growth slows (Edwards and others, 1979). 

If temperatures are significantly lower than typical 

seasonal temperatures, fish egg development may 

be stunted (Alderice and Velsen, 1978). In contrast, 

a stream-temperature rise could be unfavorable for 

a certain species of fish if it encourages predators, 

disease, or competitors or exceeds the threshold 

of tolerance. For example, fish will leave a stream 

reach that becomes increasingly warm (Smith, 1972; 

Eaton and Scheller, 1996). Biochemical activity 

increases with warmer water temperatures, which in 

turn increases the demand for oxygen. Warm water 

with low dissolved oxygen may create an oxygendeprived environment.

Stream temperature is an important physical factor of Pacific salmon habitat, and its effects on various 

salmon life stages have been extensively researched 

(Bell, 1973; Alderice and Velsen, 1978; Murray 

and McPhail, 1988; Groot and Margolis, 1991). To 

maximize survival, each species of Pacific salmon has 

adapted to specific spawning times and temperatures 

in order that incubation and emergence occur at 

the most favorable time of the year (table 1). Chum 

salmon (Oncorhynchus keta) have been observed at 

temperatures above 20°C. The U.S. Environmental 

Protection Agency (1976) water-quality criteria for 

coho salmon (Oncorhynchus kisutch) assert a maximum weekly mean temperature of 18°C for growth 

and 24°C for survival. The physiologically optimum 

water temperature for salmon depends on the species, 

the life stage, and the season (Carmen Olito, Alaska 

Department of Fish and Game, written commun., 

2000). 
2

Table 1. Observed water-temperature ranges for five species of salmon in four freshwater life stages 

[Data from R&M Consultants Inc., 1981; values in degrees Celsius]

Species Migration Spawning Incubation Rearing

Total range for 

all life stages

Coho 2.0–15.6 2.0–17.0 1.3–14.0 4.1–5.7 1.3–17.0

Pink 4.0–15.6 7.0–18.4 0.5–15.0 4.4–15.7 0.5–18.4

Chum 1.5–21.0 1.8–16.0 0.0–15.0 1.3–16.2 0.0–21.0

Sockeye 2.5–17.8 4.9–13.0 2.0–14.3 4.4–15.7 2.0–17.8

Chinook 4.0–16.0 5.6–13.9 1.5–16.0 4.4–15.7 1.5–16.0

Carpenter and others (1992) noted that one of the 

initial effects of climate warming would be changes 

in recreational and commercial fisheries. Because 

fish are cold-blooded animals, their metabolic rates 

rise with increasing water temperature. As natural or 

artificial events shift temperatures away from optimal 

ranges for fish species, their populations are affected. 

Fish will actively seek habitats in their preferred 

temperature range. However, these temperature 

preferences would still be near the warm side of the 

fish’s fatal temperature limits (Regier and others, 

1996). Fish living in freshwater at the mid- to high 

latitudes are predicted to be the most affected 

by increased warming at the poles (Rombough, 

1996). These temperature changes may stress some 

fish populations.

Cold-water fish usually cease to grow at temperatures above 20°C because of their increased 

metabolic rate. Carpenter and others (1992) noted that 

all phases of fish life histories will quicken due to 

environmental warming. Stream temperature can trigger important physiological and behavioral changes 

in fish life cycles. Temperature increases may affect 

the process of transition from freshwater to saltwater 

(smolting) in juvenile salmonids as well (McCormick 

and others, 1996). Adult cold-water fish species may 

cease to migrate or die unspawned if exposed to 

long periods of warmer than usual temperatures 

(Bell, 1973). Cold-water fishes are more sensitive 

to temperature fluctuations during the early stages 

of their life than as juveniles or adults (Rombough, 

1996). Chatters and others (1991) noted that the survival of adult chinook salmon is usually reduced in 

warmer water.

Cool- and warm-water fish will benefit from 

warmer waters by the northern expansion of their 

geographical limit because some of these species do 

not feed when the water temperature reaches a critical 

minimum level, so their northern distribution is 

limited by their physiological ability to survive 

winter starvation (Shuter and Post, 1990). Conversely, 

warmer water and increased metabolism will lead 

to fish population declines if there is an insufficient 

food source (Carpenter and others, 1992). It is 

generally agreed that the fish populations most 

affected by global warming will be cold-water fishes 

living in habitats near the southern limits of their 

range. Crawshaw and O’Connor (1997) concluded that 

increased stream temperatures generally reduce the 

survival of adult salmon by fostering disease. Chatters 

and others (1991) stated that a temperature change 

of 3°C or less would have little effect on the incidence 

of disease, but changes in fish quantity and well-being 

are expected for temperature changes over 3°C.

Five species of Pacific salmon use many of the 

streams and rivers in the Cook Inlet Basin (fig. 1, 

table 1) for spawning and rearing; continued global 

warming may alter their spawning and rearing habitat. 

These salmon populations are of considerable 

economic significance to area communities. In 1997, 

the Cook Inlet area accounted for 50 percent of the 

State’s sportfishing angler-days (an angler-day is 

equivalent to 12 hours of fishing by one person or a 

combination of persons). The Kenai River, considered 

Alaska’s most popular sportfishing river, sustains 

one of the State’s most valuable salmon fisheries. 

In 1997, the Kenai River accounted for 12 percent of 

the angler-days statewide (Howe and others, 1998).

Purpose and Scope

This study is part of the Cook Inlet Basin 

National Water-Quality Assessment (NAWQA) 

Program. The U.S. Geological Survey (USGS)
3

Figure 1. Location of water-temperature and climate sites in the Cook Inlet Basin, Alaska. 

CONTINENTAL

CONTINENTAL

MARITIME

TRANSITIONAL

TRANSITIONAL

MARITIME

75 100 MILES

100 KILOMETERS

50

75

25

25 50

0

0

149°

60°

63°

146°

63° 

152° 

60° 

154° 

A L A S K A RANGE

Susitna River

COOK INLET

Harding Ice Field

Killey 

River

Skilak

Lake

Glacier

Water body

 3 EXPLANATION 70

7

82

55

16

17

23 27 29

46 83

43

42 44

85

41

86

40

87 39

93

92

84

36

91 90 38

89 88

Water-temperature site and number

Climate-zone boundary

Anchorage

Kenai

Soldotna

Talkeetna River

Talkeetna

Yentna River

Caswell

Climate site and number

48

s

109

▲

▲ ▲ ▲

▲▲

▲

▲▲

▲

▲

▲

▲

▲

▲

▲▲

▲▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲▲

3

▲

▲

5

5

6

1

7

4

2

3

▲

Homer

Gulkana

Cantwell

Chulitna River

Lodge

Study

unit

ALASKA
4

implemented the NAWQA program in 1991, and work 

in the Cook Inlet Basin Study Unit began in 1997. 

The purpose of the Cook Inlet Basin NAWQA study 

is twofold: (1) describe the status and trends in the 

quality of water resources in the Cook Inlet Basin 

and (2) provide an understanding of factors affecting 

water quality and aquatic ecosystems. Because water 

temperature is an important factor influencing the 

quality of aquatic habitats, an investigation describing 

the present and future patterns of water temperature 

within the Cook Inlet Basin was conducted.

This report (1) compiles all available watertemperature data that have been collected in the 

Cook Inlet Basin, (2) analyzes those data to determine 

differences between individual streams and rivers, 

(3) tests the accuracy of a water-temperature model, 

(4) uses the model to simulate future trends in water 

temperature, and (5) describes how predicted future 

trends might affect fish habitat. The scope of this study 

is limited to the Cook Inlet Basin, Alaska.

Methods of Study

Some of the variables that influence water temperature are solar radiation, air temperature, the source 

of water input to a stream (such as snowmelt or glacier 

ice melt), and vegetative cover. The methods used in 

this study were (1) compilation and analysis of watertemperature data from streams located in the Cook 

Inlet Basin, (2) compilation of basin characteristics 

(such as percent glacier for watersheds with streamtemperature data), (3) compilation of air-temperature 

data from selected climatological stations within 

the Cook Inlet Basin, (4) calibration and verification 

of a water-temperature model, and (5) utilization 

of the water-temperature model with climate-change 

scenarios for Alaska.

DESCRIPTION OF THE STUDY AREA

The following description of the Cook Inlet 

Basin is taken from Brabets and others (1999) and 

Glass (1999). The Cook Inlet Basin covers 39,325 mi2

(square miles). Altitude ranges from sea level to the 

highest point in North America, Mount McKinley, 

at 20,320 ft (feet). Because of its large size and 

range in altitude, the Cook Inlet Basin has three 

climate zones: the Continental, Transition, and 

Maritime Zones (fig. 1). The Continental Zone has 

greater temperature highs and lows than the other 

climate zones and is characterized by an average 

annual temperature of –5.5°C and an average annual 

precipitation of about 20 inches. The average annual 

temperature in the Transitional Zone is about -5°C 

and average annual precipitation is about 30 inches. 

The Maritime Zone is the wettest of the three zones, 

with an average annual temperature of about 8.3°C 

and an average annual precipitation of about 70 inches 

(Hartman and Johnson, 1978). Evaporation in the 

Cook Inlet Basin is minimized by the relatively 

cool climate, high humidity, and cloud cover that 

predominate over the Cook Inlet Basin. Average 

annual precipitation for the entire Cook Inlet Basin 

is about 44 inches, and precipitation in the basin 

ranges from 20 to 240 inches annually. High 

mountainous areas (which account for 58 percent of 

the Cook Inlet land area) receive the greatest amount 

of precipitation; conversely, the lowland areas receive 

the least. From November to March, precipitation 

generally falls as snow. In extremely high mountains, 

snow is deposited year-round on glaciers and ice 

fields.

Glaciers cover approximately 11 percent (4,200 

mi2

) of the land area of Cook Inlet Basin. Most glaciers 

are located on the Alaska Range, Harding Ice Field, 

and western Cook Inlet (fig. 1). Year-round basal ice 

temperatures near 0°C classify glaciers in the basin 

as temperate. These glaciers store massive amounts of 

water as ice, and the amount of glacial melt is dependent on the extent of warm meteorological conditions. 

Streams that have as little as 5 percent glacial ice 

within their basin have distinct characteristics compared to stream basins with no glaciers. The most 

disparate feature is mean daily discharge. For example, 

in a comparison of a basin with glaciers (Susitna 

River near Denali) and a basin without glaciers 

(Ninilchik River at Ninilchik), both glacial and nonglacial streams have low stream discharge through the 

winter because of ice formation, unless ground-water 

recharge occurs (fig. 2). In April or May, rapid warming triggers ice breakup and snowmelt that increases 

streamflow. During the warm and dry summer period, 

the discharge of nonglacial streams declines while 

the flow of glacier-fed streams remains high due to 

the continuous melting of snow and ice upstream.
5

Figure 2. Comparison of discharge between a glacial and a nonglacial stream.

Susitna River near Denali (site 36) (glacial)

Ninilchik River at Ninilchik (site 7) (nonglacial)

J F MAMJ J A SO ND J F MAMJ J A S O N D J F M A M J J A S O ND

1978 1979 1980

25,000

0

5,000

10,000

15,000

20,000

DAILY MEAN DISCHARGE FOR SUSITNA RIVER 

NEAR DENALI, IN CUBIC FEET PER SECOND

1,000

0

200

400

600

800

DAILY MEAN DISCHARGE FOR NINILCHIK RIVER 

NEAR NINILCHIK, IN CUBIC FEET PER SECOND

Although glaciers delay the decline of high seasonal 

flows, the unit discharge for streams in basins with 

glacial ice coverage is generally larger than for 

streams in basins without glacial ice.

WATER-TEMPERATURE 

CHARACTERISTICS

Water-temperature data, specifically longterm data, for the Cook Inlet Basin are sparse. Many 

measurement sites are concentrated in one area and 

may not represent all the different types of streams and 

rivers in the basin. As water-temperature data were 

examined, it was common to find records with few 

complete weekly water-temperature measurements. 

Streams draining into west Cook Inlet are underrepresented. Ice formation affected the quality of 

observed data. In their study on changes in thermal 

habitat of Great Lakes fish due to global warming, 

Magnuson and others (1990) noted that the validity 

of their results lies in the quality of their data and the 

structure of their models. Thus, the importance of 

quality and quantity of baseline data cannot be overemphasized, and conclusions resulting from this study 

should be reevaluated as more data is collected in this 

region.

Water-temperature information for 32 sites in 

the Cook Inlet Basin (fig. 1, table 2) were obtained 

from the Alaska Power Authority (APA) studies 

for the Susitna River Hydroelectric Project (R&M 

Consultants, Inc., 1981), the Alaska Department 

of Fish and Game (ADFG) (1983, 1984), and the 

U.S. Geological Survey National Water Information 

System (NWIS). Data from all sources were collected 

from 1969 through 2000, although the period of record 

varied from stream to stream (fig. 3). The shortest 

records extended 2 years and the longest period of 

record was 7 years for site 27. Due to the difficulty 

of collecting water-temperature data during winter, 

most sites have water-temperature data only for the 

open-water period, which is generally from mid-May 

to mid-October (table 2). 

The distribution of sites with water-temperature 

data is not uniform (fig. 1). As a result of environmental studies conducted for proposed hydropower 

facilities in the early 1980’s, there are 20 sites in 

the Susitna Basin, the largest number of sites in any 

of the basins of Cook Inlet. Water-temperature data 

collected at other sites include the Anchorage urban 

area (3 sites) and the Kenai Peninsula (7 sites). Based 

on the data from these sites, general observations can 

be made about the water-temperature characteristics of 

these three areas. 
6

Table 2. Water-temperature sites in the Cook Inlet Basin, Alaska[USGS, U.S. Geological Survey; ft, feet; AK, Alaska; ADF&G, Alaska Department of Fish and Game; APA, Alaska Power Authority; --- drainage area not determin

Map

number 

(figure 1)1

USGS station 

number or 

latitude/longitude Station name

Elevation 

(ft)

Data 

source

Period 

of record2

Drainage area 

(square miles)

3 15239000 Bradley River near 

Homer, AK

1,054 USGS 1979–86

seasonal

54 

70 15239070 Bradley River near tidewater near Homer, AK 25 USGS 1986–99 yearly --- 

7 15241600 Ninilchik River at 

Ninilchik, AK

30 USGS 1998 

yearly

131 

82 60o11’00”

151o00’00”

Nikolai Creek near Kasilof, AK

180 USGS 1990–92

seasonal

--- 

55 15266110 Kenai River below 

Skilak Lake outlet near Sterling, AK

240 USGS 1998

yearly

1,206 

16 15266300 Kenai River at 

Soldotna, AK

35 USGS 1998

yearly

1,951 

17 15266500 Beaver Creek near 

Kenai, AK

48 USGS 1969–75

yearly

51 

48 15294450 Chuitna River near 

Tyonek, AK

160 USGS 1976–78

seasonal

131 

23 15274000 South Fork Campbell Creek 

near Anchorage, AK

260 USGS 1998

yearly

29.4 

27 15275100 Chester Creek at 

Arctic Boulevard at Anchorage, AK

16 USGS 1981–86

1998yearly

27.3 

29 15276570 Ship Creek below powerplant at Elmendorf Air Force 

Base at Anchorage, AK

80 USGS 1971–80

yearly

113 

46 15294350 Susitna River at Susitna 

Station, AK

40 USGS 1977–83

seasonal

19,400 

83 61o34’00”

150o25’00”

Susitna River above Yentna River near Susitna Station, AK

40 ADF&G;

APA

1982–83seasonal

E 13,200 

43 15294010 Deception Creek near 

Willow, AK

250 USGS 1978–85

seasonal

48 

42 15294005 Willow Creek near 

Willow, AK

350 USGS 1979–86 

seasonal

166 

44 15294100 Deshka River near 

Willow, AK

80 USGS 1999

yearly

591 
7

84 15281500 Camp Creek near Sheep 

Mountain Lodge, AK

2,950 USGS 1996

seasonal

1.09 

85 15292780 Susitna River at 

Sunshine, AK

300 ADF&G; 

APA

1982–83seasonal

11,100 

41 15292700 Talkeetna River near 

Talkeetna, AK

400 ADF&G; 

APA

1982–83seasonal

1,996 

86 62o23’00”

150o08’00”

Susitna River near Talkeetna, AK

400 ADF&G; 

APA

1982–83seasonal

E 6,534 

40 15292400 Chulitna River near 

Talkeetna, AK

500 USGS 1982–86

seasonal

2,570 

87 62o37’00”

150o00’00”

Susitna River at Curry, AK

550 ADF&G; 

APA

1982–83seasonal

E 6,534 

88 62o38’00”

147o22’00”

Oshetna River near Cantwell, AK

2,100 ADF&G; 

APA

1982–83seasonal

--- 

89 62o38’00”

147o26’00”

Goose Creek near Cantwell, AK

2,100 ADF&G; 

APA

1982–83seasonal

--- 

38 15291500 Susitna River near 

Cantwell, AK

1,900 USGS 1971–74

1980–86seasonal

4,140 

39 15292000 Susitna River at 

Gold Creek, AK

678 USGS 1974–75

1977–85seasonal

6,160 

90 62o46’00”

147o56’00”

Kosina Creek near Cantwell, AK

1,600 ADF&G; 

APA

1982–83seasonal

--- 

93 62o47’18”

149o39’36”

Indian River near Gold Creek, AK

750 ADF&G; 

APA

1982–83seasonal

--- 

91 62o49’00”

148o15’00”

Watana Creek near Cantwell, AK

1,500 ADF&G; 

APA

1982–83seasonal

--- 

92 62o50’00”

149o22’35”

Portage Creek near Gold Creek, AK

900 ADF&G; 

APA

1982–83seasonal

--- 

36 15291000 Susitna River near 

Denali, AK

2,440 USGS 1974–82

seasonal

950 

109 15294345 Yentna River near 

Susitna Station, AK

80 USGS 1981–86

seasonal

6,180 

1The Cook Inlet NAWQA study unit established a uniform numbering system for all surface water sites located in the study basin. 

For a complete list of stations and numbers see http://ak.water.usgs.gov/Projects/Nawqa.

2Data from sites operated seasonally span the open-water period, generally mid-May to mid-October. 

Table 2. Water-temperature sites in the Cook Inlet Basin, Alaska—Continued[USGS, U.S. Geological Survey; ft, feet; AK, Alaska; ADF&G, Alaska Department of Fish and Game; APA, Alaska Power Authority; --- drainage area not determin

Map

number 

(figure 1)1

USGS station 

number or 

latitude/longitude Station name

Elevation 

(ft)

Data 

source

Period 

of record2

Drainage area 

(square miles)
8

Figure 3. Beginning and ending year of available data for water-temperature-measurement sites. 

1965

1970

1975

1980

1985

1990

1995

2000

3 70 7 82 55 16 17 48 23 27 29 46 83 43 42 44 84 85 41 86 40 87 88 89 38 39 90 93 91 92 36

PERIOD OF RECORD

WATER-TEMPERATURE SITES

109

Kenai Peninsula

Water-temperature-measurement sites in the 

Kenai Peninsula are located in all three climate 

zones—Maritime, Transitional, and Continental 

(fig. 1). Sites on the Bradley River are located in the 

Maritime Zone and reflect the influence of glaciers. 

Site 3 on the Bradley River monitors a basin with 

36 percent of its area consisting of glaciers. Inflow 

of glacial meltwater throughout July and August 

maintains the water temperature between 4°C and 

9°C (fig. 4). Farther downstream, the effects from 

additional water from tributary basins with no 

glaciers have a general warming effect on the river, 

as indicated by the data at site 70. Water temperature 

at this site ranges from about 5°C to 11°C during July 

and August.

Beaver Creek (site 17) and the Ninilchik River 

(site 7) (fig. 4) represent streams in lowland areas. 

Water temperatures in these streams remain at 0°C 

throughout the winter. During and after snowmelt, 

water temperature rises throughout early to midsummer and begins to cool in late summer. Fluctuations 

in water temperature are most likely linked with air 

temperature or rainfall.

Water-temperature data are available for two 

sites on the Kenai River. Site 55 is located downstream 

from the outlet of Skilak Lake. Skilak Lake has a 

somewhat moderating effect on the water temperature 

(fig. 4). Water temperature gradually falls to 0°C 

from October to January. Water temperatures at the 

downstream site, Kenai River at Soldotna (site 16), 

are slightly lower than at the upstream site and are 

probably affected by inflow from the Killey River, 

a glacierized watershed located between the two sites.

Anchorage Area

Water-temperature data are available for three 

streams in the Anchorage area, each of which drains 

an area having a different land use. South Fork Campbell Creek (site 23) drains primarily an undisturbed, 

high elevation watershed. Chester Creek (site 27) 

drains an urbanized, residential watershed. Both 

of these basins are approximately 30 mi2 in area. 

Water-temperature data for Ship Creek, which drains 

a 113 mi2 watershed, is collected downstream from 

the outfall of a powerplant. 

South Fork Campbell Creek is the coldest of 

the three streams (fig. 5). Most of the flow at this 

site is either runoff from the upper mountains in the 

basin or ground water. Chester Creek is the warmest 

of the three streams during the summer. This may 

be because of urban development within the basin or 

because the lower part of the basin drains lowlands. 
9

Figure 4. Average daily maximum and minimum water temperatures for six sites on the Kenai Peninsula. WATER TEMPERATURE, IN DEGREES CELSIUS

May June July Aug Sept 0

12

2

4

6

8

10

May June July Aug Sept 0

12

2

4

6

8

10

Bradley River near Homer (site 3)

Bradley River at tidewater (site 70)

O N D J F MA M J J AS

0

20

5

10

15

Kenai River below Skilak Lake (site 55)

Kenai River at Soldotna (site 16)

O ND J F MA MJ J A S

0

20

5

10

15

O N D J F MA M J J AS

0

20

5

10

15

Beaver Creek (site 17)

Ninilchik River (site 7)

O ND J F MAMJ J AS

0

20

5

10

15

DAILY MAXIMUM

DAILY MAXIMUM

DAILY MAXIMUM

DAILY MINIMUM

DAILY MINIMUM

DAILY MINIMUM

Figure 5. Average daily maximum and minimum water temperatures for three sites in Anchorage. 

O N D J F M A M J J A

0

20

5

10

15

WATER TEMPERATURE, 

IN DEGREES CELSIUS

Ship Creek (site 29)

Chester Creek (site 27)

South Fork Campbell Creek (site 23)

S O N D J F M A M J J A S 0

20

5

10

15

DAILY MAXIMUM DAILY MINIMUM
10

At Ship Creek, the outflow from the powerplant has 

a noticeable effect on water temperature during the 

winter. Temperatures at this site range from 2°C to 

about 11°C, while water temperature at Chester Creek 

and South Fork Campbell Creek remains near 0°C. 

During the summer, as additional water enters Ship 

Creek from snowmelt, effects of outflow from the 

powerplant on water-temperature decrease.

Susitna River Basin

The Susitna River Basin encompasses about 

one-half of the Cook Inlet drainage basin and is the 

largest watershed in the study area. In the early 1980’s, 

a number of studies took place in the Susitna River 

Basin as part of an environmental assessment for the 

proposed Susitna Hydroelectric Project. Thus, watertemperature data are available for many sites in the 

basin, 20 in all (fig. 1), and provide a good overview 

of the water-temperature characteristics from the headwaters to the mouth.

Site 36, the Susitna River near Denali, monitors 

a 950 mi2 watershed 25 percent of which consists of 

glaciers. Glacial meltwater dominates the discharge 

at this site during the summer runoff period (fig. 2). 

Daily minimum water temperature ranges from 0.5°C 

to 5.0°C, (fig. 6) and daily maximum water temperature during the summer ranges from 2°C to 8.5°C. 

At site 38, the Susitna River near Cantwell, water temperatures are not influenced by glacial meltwater to 

the same extent as at site 36. Glaciers comprise 7 percent of the 4,140 mi2 drainage area upstream of the 

Susitna River near Cantwell site. Flow is dominated 

by nonglacier-fed streams. Daily minimum water temperatures at this site ranged from about 2°C to 11°C, 

and daily maximum temperature ranged from 4°C to 

12.5°C. Downstream of this site, the Susitna River 

near Gold Creek site (site 39) monitors drainage from 

6,160 mi2

, of which 5 percent consists of glaciers. 

At this site there is less influence due to glacier melt 

than at sites 38 and 36, and water temperatures are 

generally higher than at the upstream sites throughout 

the summer.

Figure 6. Average daily maximum and minimum water temperatures for five sites on the Susitna River. 

May June July Aug Sept

0

14

2

4

6

8

10

12

WATER TEMPERATURE, IN DEGREES CELSIUS

EXPLANATION

Susitna River near Denali (site 36)

Susitna River near Cantwell (site 38)

Susitna River at Gold Creek (site 39)

Susitna River at Sunshine (site 85)

Susitna River at Susitna Station (site 46)

May June July Aug Sept

0

14

2

4

6

8

10

12

WATER TEMPERATURE, IN DEGREES CELSIUS

DAILY MAXIMUM

DAILY MINIMUM
11

Downstream of the Susitna River near Gold 

Creek, two major tributaries enter the Susitna 

River—the Chulitna River and the Talkeetna River. 

The Chulitna River drains an area of 2,570 mi2

and 27 percent of the watershed consists of glaciers. 

The Talkeetna River drains an area of 1,996 mi2

and 7 percent of the area consists of glaciers. Watertemperature characteristics of the Chulitna River 

near Talkeetna (site 40) (fig. 7) are quite similar to 

those at the Susitna River near Denali site (site 36) 

(fig. 7), reflecting the influence of glacial meltwater. 

Water temperatures throughout the runoff season are 

less than 10°C. The combined effects of the Chulitna 

and Talkeetna Rivers are noticeable at site 85, the 

Susitna River at Sunshine (fig. 6). Water temperatures 

at this site generally are lower than the water temperatures of the Susitna River at Gold Creek (site 39) 

from July through September, when glacial melt is at 

its peak. 

The last major tributary to the Susitna River 

downstream of Sunshine is the Yentna River. The 

Yentna River Basin is 6,180 mi2, 15 percent of which 

consists of glaciers. Water-temperature data do not 

indicate any significant glacial influence, with daily 

maximum summer water temperatures ranging from 

5°C to 12°C (fig. 8). Site 46, the Susitna River at 

Susitna Station, monitors drainage from 93 percent of 

the Susitna River Basin. The highest daily maximum 

water temperatures of the main stem of the Susitna 

River were recorded at this site and ranged from 5°C 

to 13.5°C (fig. 6). 

Figure 7. Average daily maximum and minimum water 

temperatures for the Chulitna River near Talkeetna, 

Alaska (site 40). 

May June July Aug Sept

2

10

4

6

8

WATER TEMPERATURE, IN DEGREES CELSIUS

Daily 

maximum

Daily 

minimum

FUTURE TRENDS IN WATER-TEMPERATURE 

CHARACTERISTICS

Climate Change

Alaska has experienced the largest regional 

warming of any State in the United States, with a rise 

in average annual temperature of about 3°C since 

the 1960’s and 4.5°C in winter (Alaska Regional 

Assessment Group, 1999). There has been extensive 

melting of glaciers and thawing of permafrost during 

this period. Warming also has been associated with an 

increase in precipitation of about 30 percent between 

1968 and 1990 (Alaska Regional Assessment Group, 

1999). The Alaskan regional warming is part of a 

larger warming trend throughout the Arctic. 

General Circulation Models (GCMs) have been 

used to project future climates in Alaska. The two 

most widely used GCMs are the Canadian Climate 

Model (CCM) (Canadian Centre for Climate Modeling and Analysis, no date) and the Hadley Center 

Model (HCM) (Hadley Centre for Climate Prediction 

and Research, no date). Both GCMs have projected 

trends toward a warmer and wetter climate. For 

Cook Inlet, the Canadian model projects the largest 

warming trends, with an increase in air temperature 

ranging from 5°C to 10°C by the year 2100, whereas 

the Hadley model projects an increase in air temperature ranging from 4°C to 6.5°C by 2100. Precipitation 

is projected to increase between 20 and 25 percent. 

Alaska’s fisheries can be expected to be affected as the 

climate continues to warm (Alaska Regional Assessment Group, 1999).

Figure 8. Average daily maximum and minimum water 

temperatures for the Yentna River near Susitna Station, 

Alaska (site 109). 

Daily 

maximum

Daily 

minimum

2

14

12

10

4

6

8

WATER TEMPERATURE, IN DEGREES CELSIUS

May June July Aug Sept
12

Water-Temperature Model

Multiple factors influence stream temperature. 

Climatological factors include air temperature, solar 

radiation, and precipitation (as both snow and rain); 

hydrological factors include discharge and channel 

form; and geological factors include base-flow 

contributions, such as ground-water seepage and channel form (Smith and Lavis, 1975; Webb and Nobilis, 

1997). Physical land-surface characteristics of the 

basin, including forest cover, glacial influence, aspect, 

and elevation additionally affect stream temperatures 

(Johnson, 1971). The most significant environmental 

factors that influence stream temperature depend on 

time scale. For example, Mohseni and Stefan (1999) 

found that in daily time scales, the upstream water 

temperature has more influence on water temperature 

than current weather conditions at a certain stream site; 

therefore, the use of traveltime or lag should be considered. When the time scale is increased to a weekly or 

annual scale, the air/water temperature equilibrium is 

more significant and a timelag is not necessary. Eaton 

and Scheller (1996) noted that a weekly time scale is 

traditionally and adequately used to assess changes in 

fish habitat and growth conditions.

In a study done in England, Crisp and Howson 

(1982) found that a linear regression of mean air temperature with mean stream temperature accounted for 

87–95 percent of the variance in water temperatures. 

Regression equations that included rainfall and discharge made only small improvements, ranging from 

5 to 13 percent. In addition, air temperatures from 

distant stations did not significantly reduce the accuracy of water-temperature models (Crisp and Howson, 

1982; Mohseni and others, 1998).

Linear-regression models for stream temperatures 

are easy to develop, but also have some limitations. 

At very high and low air temperatures, the water/air 

temperature relationship does not stay linear. At 

high temperatures, evaporative cooling allows the 

water body to lose more heat and stream temperature 

no longer increases linearly with air temperature. 

Conversely, a separate function is needed for water 

temperature when air temperatures dip below freezing 

(Mohseni and others, 1998). Also, spring stream 

temperatures are strongly affected by snowmelt and 

runoff. Autumn temperatures are generally higher 

than spring temperatures because of the general lack 

of snow, less streamflow, and, in late autumn, the 

release of latent heat from ice formation (Webb and 

Nobilis, 1997).

Studies on the influence of air temperature on 

water temperature are ongoing and numerous. Many 

different models of stream temperature have been 

developed, such as heat advection/dispersion transport 

models, models based on the concept of equilibrium 

temperature and processes of surface-heat transfer, 

seasonal and sinusoidal functions with respect to time, 

and linear regressions of air and stream temperature 

(Ward, 1963; Edinger and others, 1966; Brown, 1969; 

Johnson, 1971; Song and others, 1973; Crisp and 

Howson, 1982; Sinokrot and Stefan, 1993; Stefan 

and Preud’homme, 1993; Mohseni and others, 1998;

Pilgrim and others, 1998).

Mohseni and others (1998) developed a nonlinear-regression model that uses a logistic function 

to determine weekly stream temperatures; this model 

overcame several of the previously mentioned limitations. The model creates an S-shaped graph (fig. 9) 

that has a more gradual slope at extreme temperatures, 

which is the typical shape of the logistic function and 

is represented as follows:

where

Ts is the estimated weekly stream temperature, 

Ta is the average weekly air temperature, 

μ is the estimated minimum stream temperature, 

α is the estimated maximum stream temperature, 

γ is a measure of the steepest slope of the function, and 

β is the air temperature at the inflection point.

Ts μ α μ –

1 e

γ β Ta ( ) – +

= + ------------------------------ , (1)

Figure 9. Schematic representation of the logistic function 

parameters (from Mohseni and others, 1998). 

Ts

Ta

Inflection 

Point

γ = (θ)

μ

β

θ

0

α

Ts = μ + 

α − μ

1 + e γ (β - Ta)
13

At air temperatures below 0°C, the regression 

line for water temperature levels out at 0°C, as does 

observed water temperature before water undergoes 

a phase change into a solid; on the other end, the 

regression line flattens out, reflecting the process of 

evaporative cooling. Hysteresis is accounted for by 

separating the regression into two functions that represent rising and falling temperatures. (Hysteresis is the 

tendency for stream-temperature increases to lag airtemperature increases and for stream-temperature 

decreases to lag air-temperature decreases.) The rising 

limb function is used for the period starting the week 

in which the mean air temperature is at a minimum 

and ending the week in which the mean air temperature is at a maximum. The falling limb function then 

begins and lasts until the mean air temperature is at a 

minimum. The model was tested and provided acceptable results for 584 USGS sites (Mohseni and others, 

1999). 

Mohseni’s model was used for this study, 

although in cooler climates such as Alaska the 

characteristics that make the nonlinear-regression 

model more accurate than a linear-regression model 

might be diminished. The largest deviations of 

observed temperatures from temperatures simulated 

by the model occurred at air temperatures above 0°C 

and below 12°C. Air temperatures in Alaska tend to 

fall in this temperature range at a higher frequency 

than air temperatures in the 48 contiguous States. 

In areas with significant snowmelt, air- and watertemperature data are less correlated. Also, the presence 

of glaciers in the watershed may exacerbate this 

phenomenon (Mohseni and Stefan, 1999). 

Ice, snow, and glaciers are prominent in Alaska 

and may influence the insensitivity of some runoff 

to air-temperature changes (Smith and Lavis, 1975; 

Kobayashi, 1985; Webb and Noblis, 1997). Finally, air 

temperatures in Alaska may not warm sufficiently to 

register the signature from evaporative cooling and 

thus necessitate an S-shaped logistic function (Crisp 

and Howson, 1982; Mohseni and Stefan, 1999).

Calibration and Verification

Daily mean, maximum, and minimum airtemperature information were acquired from the 

National Climate Data Center (no date) for seven 

climate stations (table 3). The overall period of record 

spanned the years 1957 through 2000. Individual airtemperature records contained a minimum of 3 years 

of data, a maximum of 43 years of data, and a median 

of 29 years of data. Air temperatures of these seven 

climate stations ranged from -34°C to 32°C.

Water- and air-temperature data were compiled 

and converted into mean weekly temperatures. Mean 

weekly temperatures were computed using the Julian 

Day calendar year, where day 1 is January 1 and 

December 31 is either day 365 or day 366, depending 

on whether a year is a leap year. The last week 

of the year comprises the normal 7-day week plus 

the remaining 1 or 2 days, for a total of 8 or 9 days. 

Data were not used if there were more than two 

daily measurements missing from each week. The 

number of weekly temperature-data values for each 

site ranged from 22 (at site 83) to 573 (at site 70) 

with a median of 67 weeks (table 4). Initially, the 

nearest air-temperature site was used for a given 

water-temperature site. If the results from the watertemperature model were not satisfactory, the next 

closest air-temperature site was used, because the 

data from the next closest site might better reflect the 

weather patterns that exist at the water-temperature 

site owing to factors such as topographic effects. 

Table 3. Climate stations used with water-temperature-regression model

[Source: National Climate Data Center (no date); ft, feet]

Map number 

(figure 1) Station name

Elevation 

(ft) Latitude Longitude

Period of 

record used

1 Anchorage 114 61o11’00” 150o00’00” 1969–2000

2 Cantwell 655 63o24’00” 148o54’00” 1983–1986

3 Chulitna River Lodge 427 62o49’00” 149o54’00” 1970–2000

4 Gulkana 478 62o09’00” 145o27’00” 1996–2000

5 Homer 27 59o39’00” 151o29’00” 1979–2000

6 Kenai 84 60o35’00” 151o14’00” 1969–2000

7 Talkeetna 105 62o19’00” 150o06’00” 1957–2000
14

Table 4. Results from water-temperature-regression model[Values are for the open-water period, mid-May to mid-October; oC, degrees Celsius; AK, Alaska]

Map 

number 

(figure 1) Station name

Observed 

minimum 

weekly water 

temperature 

(oC)

Observed 

maximum 

weekly water 

temperature

(oC)

Observed 

mean air 

temperature 

(oC)

Observed 

mean water 

temperature 

(oC)

Number 

of weeks 

of data

Nash

Sutcli

coeffic

3 Bradley River near 

Homer, AK

0.0 11.1 9.5 6.0 219 0.68 

70 Bradley River near 

tidewater near Homer, AK

0.0 11.9 9.6 6.5 573 .93 

7 Ninilchik River at 

Ninilchik, AK

0.0 14.3 6.1 8.1 64 .93 

82 Nikolai Creek near 

Kasilof, AK

0.0 12.8 9.2 5.2 87 .64 

55 Kenai River below 

Skilak Lake outlet near Sterling, AK

0.0 12.4 8.0 9.4 51 .93 

16 Kenai River at 

Soldotna, AK

0.0 12.6 7.5 9.1 67 .91 

17 Beaver Creek near 

Kenai, AK

0.0 12.6 8.6 7.6 232 .92 

48 Chuitna River near 

Tyonek, AK

0.0 16.6 9.1 8.6 74 .80 

23 South Fork Campbell 

Creek near Anchorage, AK

0.0 10.7 10.1 6.5 48 .98 

27 Chester Creek at 

Arctic Boulevard at Anchorage, AK

0.0 14.9 10.4 9.7 285 .97 

29 Ship Creek below powerplant at Elmendorf Air Force 

Base at Anchorage, AK

0.2 15.9 10.4 9.0 438 .75 

46 Susitna River at 

Susitna Station, AK

0.2 14.2 12.2 10.3 93 .92 

83 Susitna River above 

Yentna River near Susitna Station, AK

0.0 11.8 12.2 8.6 22 .98 

43 Deception Creek near 

Willow, AK

0.0 14.1 10.1 7.8 127 .90 

42 Willow Creek near 

Willow, AK

0.1 12.7 10.3 7.1 149 .84 
15

44 Deshka River near 

Willow, AK

0.0 20.6 13.4 10.8 57 0.84 

84 Camp Creek near 

Sheep Mountain Lodge, AK

0.0 6.9 9.2 3.4 122 .68 

85 Susitna River at 

Sunshine, AK

0.2 12.1 9.0 7.7 29 .97 

41 Talkeetna River near 

Talkeetna, AK

0.2 11.2 9.8 7.6 28 .96 

86 Susitna River near 

Talkeetna, AK

0.2 13.3 10.8 9.3 33 .95 

40 Chulitna River near 

Talkeetna, AK

0.2 8.5 11.3 5.8 67 .66 

87 Susitna River at 

Curry, AK

1.1 14.1 11.0 9.5 28 .95 

88 Oshetna River near 

Cantwell, AK

0.8 12.2 11.0 8.1 30 .95 

89 Goose Creek near 

Eureka, AK

0.4 12.2 9.7 7.4 27 .90 

38 Susitna River near 

Cantwell, AK

0.0 11.8 10.8 8.1 100 .98 

39 Susitna River at 

Gold Creek, AK

0.1 12.6 10.4 8.1 96 .84 

90 Kosina Creek near 

Cantwell, AK

0.1 12.7 10.8 8.4 26 .94 

93 Indian River near 

Gold Creek, AK

1.6 11.9 11.2 7.4 30 .80 

91 Watana Creek near 

Cantwell, AK

0.6 11.5 11.1 7.4 28 .94 

92 Portage Creek near 

Gold Creek, AK

1.0 11.6 11.0 6.5 30 .75 

36 Susitna River near 

Denali, AK

0.0 8.4 11.2 5.0 163 .68 

109 Yentna River near 

Susitna Station, AK

1.3 11.8 11.7 8.5 85 .81 

Table 4. Results from water-temperature-regression model—Continued[Values are for the open-water period, mid-May to mid-October; oC, degrees Celsius; AK, Alaska]

Map 

number 

(figure 1) Station name

Observed 

minimum 

weekly water 

temperature 

(oC)

Observed 

maximum 

weekly water 

temperature

(oC)

Observed 

mean air 

temperature 

(oC)

Observed 

mean water 

temperature 

(oC)

Number 

of weeks 

of data

Nash

Sutcli

coeffic
16

Regression equations were determined for each 

of the stream sites by using the formatted weekly 

stream- and air-temperature data as input to the 

model developed by Mohseni and others (1998). 

The observed and simulated data were then visually 

and statistically interpreted and analyzed. The NashSutcliffe coefficient (NSC) (Nash and Sutcliffe, 1970; 

Mohseni and others, 1998) was the main determinant 

of goodness of fit, and can be considered the proportion of variation explained: 

where

NSC is the Nash-Sutcliffe coefficient, 

Tsim is the simulated water temperature, 

Tobs is the observed water temperature, and 

Tobs is the mean observed water temperature.

NSC 1

Tsimi

Tobsi( – )

2

i = 1

n

∑

Tobs Tobsi( – )

2

i = 1

n

∑

= – ------------------------------------------------ , (2)

Root mean squared error (RMSE) expresses the 

standard error of prediction and was also evaluated:

RMSE

Tsimi

( Tobsi)

2 –

i = 1

n

∑

n – 4 = ------------------------------------------------ (3)

However, the RMSE statistic was used cautiously 

because outliers can have a large effect on the value. 

A perfect correlation between observed and simulated 

data would have a NSC of 1 and a RMSE of zero. 

For most stations, the period of weekly temperatures was from mid-May to mid-October, the openwater season. Thus, the water-temperature model 

was applied only to this period of data. Most stations 

had minimum weekly water temperatures between 0 

and 1°C (table 4). Ship Creek (site 29), located downstream from a powerplant outfall, was within this 

range for 1 week, although most of the weekly minimum water temperatures were above 1°C. Maximum 

weekly water temperature during the open-water 

period showed a wide variation, from 6.9°C at Camp 

Creek (site 84) to 20.6°C at the Deshka River (site 80). 

Comparisons of the average air and water temperatures for the open-water season indicate that the three 

sites with 25 percent or more of their upstream drainage area consisting of glaciers (Bradley River [site 3], 

Chulitna River [site 40], Susitna River near Denali 

[site 36]) are on some of the coldest rivers, although 

the air temperature for the associated climate site was 

near the average. The sites with the highest mean 

water temperature were on Chester Creek (site 27), the 

urbanized stream in Anchorage; the Susitna River 

near Susitna Station (site 46), near the mouth of the 

Susitna River; and the Deshka River (site 80), a river 

that drains extensive wetlands.

The NSC ranged from 0.64 to 0.98 (table 4); 

26 sites had a NSC of 0.75 or higher, which indicates 

a good fit between predicted and observed stream 

temperatures. Five sites had an NSC between 0.64 

and 0.68. The average distance between a watertemperature site and a climatological station was 

35.4 miles. The closest air- and water-temperature 

stations were 3.1 miles apart, and 98.8 miles separated 

the most distant paired stations. Distance between airand water-temperature stations did not substantially 

influence the quality of fit of the water-temperatureregression model (fig. 10). 

Sites in glaciated stream basins were relatively 

evenly distributed throughout the study area. The 

glacial streams examined have from 5 to 36 percent 

of their drainage basins covered by glaciers. Three 

sites, Bradley River (site 3), the Chulitna River (site 

40), and the Susitna River near Denali (site 36), have 

25 percent or more of their upstream drainage basins 

covered by glaciers. These streams have some of 

the lowest average water temperatures for the openwater period, most likely due to the large amount of 

glacial meltwater that enters the rivers. Nash-Sutcliffe 

coefficients for these three sites were relatively low—

0.68, 0.66, and 0.68, respectively (table 4). In general, 

with decreasing glacial coverage, the effects from 

glaciers on water temperature are diminished, and the 

Nash-Sutcliffe coefficients are higher (fig. 11).

Forty-seven percent, or 15 of the 32 sites, 

exhibited hysteresis (table 4). This figure is similar to 

the 43 percent of the streams in the contiguous United 

States that exhibit noticeable hysteresis (Mohseni and 

others, 1998). The majority of sites exhibiting hysteresis were located in the Kenai Peninsula. Ship Creek 

below the powerplant at Elmendorf Air Force Base 

(Site 29) is an example of extreme hysteresis (fig. 12). 

Some possible reasons for hysteresis are the melting 

of the snowpack during the spring, which results in 

cold water entering a stream as air temperature rises, 

or the input of warm water from a powerplant during 

the winter season, which maintains artificially warmer 

water temperatures as the air temperature falls.
17

Figure 10. Relation of distance between a watertemperature site and its associated air-temperature

site to Nash-Sutcliffe coefficient.

Figure 11. Relation between percent of watershed covered 

by glaciers and Nash-Sutcliffe coefficient. 

The regression-model parameters are shown 

in table 5. Compared to the study by Mohseni and 

others (1998), air temperature at the inflection point 

(β, [fig. 9 and eq. 1]) and the steepest slope (γ) varied 

more in Alaska. The estimated minimum stream 

temperature (μ) was less varied because most streams 

cool to near 0°C. A typical example is site 10, Chester 

Creek at Arctic Boulevard at Anchorage (fig. 13). 

The plot for the simulated water temperature exhibits 

the typical S-shaped curve, starting at 0°C and then 

decreasing in slope at higher temperatures as the 

effects of evaporative cooling begin. Regression 

equations with the lowest quality of fit were, on 

average, for cooler streams.

0 20 40 60 80 100 120

DISTANCE BETWEEN WATER-TEMPERATURE

 AND AIR-TEMPERATURE SITES, IN MILES

1.0

0.6

0.7

0.8

0.9

NASH-SUTCLIFFE COEFFICIENT

0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

NASH-SUTCLIFFE COEFFICIENT

0

40

10

20

30

PERCENT OF WATERSHED COVERED BY GLACIERS

Figure 12. Relation between weekly average water 

temperature and weekly average air temperature for 

Ship Creek below powerplant at Elmendorf Air Force 

Base at Anchorage, Alaska. 

Figure 13. Relation between weekly average water 

temperature and weekly average air temperature for 

Chester Creek at Arctic Boulevard at Anchorage, Alaska.

Stream-Temperature Projections and Implications

According to the Canadian Climate Model and 

the Hadley Center Model, the largest increases in air 

temperature will occur during the winter, and only modest increases will occur during the summer. The mean 

annual increase will be 7.2°C in the northern half of the 

Cook Inlet Basin and 8.5°C for western Cook Inlet and 

the Kenai Peninsula. Both models assume a doubling 

of carbon dioxide. The predicted air-temperature 

increases were added to the air-temperature records 

used at each site, and the predicted stream temperatures 

were determined by use of the regression equations 

determined by the water-temperature model. Only 

the 27 sites with an NSC of 0.75 or higher were used. 

-5 0 5 10 15 20

AIR TEMPERATURE, IN DEGREES CELSIUS

2

18

4

6

8

10

12

14

16

WATER TEMPERATURE, IN DEGREES CELSIUS

Rising

Falling

-30 -20 -10 0 10 20

AIR TEMPERATURE, IN DEGREES CELSIUS

WATER TEMPERATUARE, IN DEGREES CELSIUS -1

4

9

14

Number of data points = 285

Nash-Sutcliffe coefficient = 0.97
18

Table 5. Water-temperature regression-model parameters

[All values in degrees Celsius (°C); AK, Alaska]

Map 

number 

(figure 1) Station name

alpha, α 

(°C)

beta, β 

(°C)

gamma, γ 

(°C)

mu, μ 

(°C)

3 Bradley River near Homer, AK 12.8 18.4 0.1 0

70 Bradley River near tidewater near Homer, AK 13.1 12.0 0.3 0.3

7 Ninilchik River at Ninilchik, AK 14.5 6.6 0.6 0

82 Nikolai Creek near Kasilof, AK 16.4 11.6 0.3 0

55 Kenai River below Skilak Lake outlet near Sterling, AK 12.4 7.0 0.5 1.0

16 Kenai River at Soldotna, AK 14.3 8.9 0.3 0

17 Beaver Creek near Kenai, AK 13.7 7.5 0.3 0

48 Chuitna River near Tyonek, AK 18.7 10.0 0.3 0

23 South Fork Campbell Creek near Anchorage, AK 10.9 10.3 0.3 0.1

27 Chester Creek at Arctic Boulevard at Anchorage, AK 16.0 8.6 0.2 0

29 Ship Creek below powerplant at Elmendorf 

Air Force Base at Anchorage, AK

17.0 11.1 0.1 1.6

46 Susitna River at Susitna Station, AK 16.0 8.9 0.2 0

83 Susitna River above Yentna River near 

Susitna Station, AK

13.0 7.1 0.2 0

43 Deception Creek near Willow, AK 16.1 11.9 0.3 0

42 Willow Creek near Willow, AK 14.3 10.6 0.2 0.1

44 Deshka River near Willow, AK 27.1 18.1 0.2 0

84 Camp Creek near Sheep Mountain Lodge, AK 7.5 11.0 0.2 0.1

85 Susitna River at Sunshine, AK 12.5 7.1 0.3 0

41 Talkeetna River near Talkeetna, AK 11.8 7.0 0.2 0

86 Susitna River near Talkeetna, AK 13.8 7.8 0.3 0

40 Chulitna River near Talkeetna, AK 9.4 7.7 0.2 0

87 Susitna River near Curry, AK 16.1 9.4 0.2 0

88 Oshetna River near Eureka, AK 13.5 11.3 0.2 0

89 Goose Creek near Eureka, AK 13.1 9.2 0.3 0.1

38 Susitna River near Cantwell, AK 12.6 8.1 0.2 0

39 Susitna River at Gold Creek, AK 13.8 9.7 0.2 1.1

90 Kosina Creek near Eureka, AK 13.6 9.3 0.3 0

93 Indian River near Gold Creek, AK 13.8 12.5 0.3 0

91 Watana Creek near Gold Creek, AK 12.5 10.1 0.3 0

92 Portage Creek near Gold Creek, AK 16.0 18.0 0.1 0

36 Susitna River near Denali, AK 9.5 10.5 0.2 0

109 Yentna River near Susitna Station, AK 12.7 8.2 0.2 0
19

Similar to the method used by Mohseni and others 

(1999), an error analysis was conducted. There 

are errors associated with the projection of air 

temperatures by the General Circulation Models and 

errors in the stream-model simulations. The error 

analysis was a one-tail paired Student’s t test at the 

95 percent confidence level between the mean of the 

errors for water temperature:

where

Tsim = simulated water temperature, 

Tobs = observed water temperature, 

χ

1

1

n = --

n

Σ

i =1

TsimiTobsi – , (4)

and the means of the changes under the 2 × CO2

climate scenario:

where

T2 × CO2 = water temperature under the 2 × CO2

climate scenario. If the t test failed at the 95 percent 

level, then the site has significant changes in stream 

temperature under the 2 × CO2 climate scenario.

χ

2

1

n = --

n

Σ

i=1

TsimiT2 CO2 × – , (5)

Results from the climate-change simulation 

indicate that mean water temperature for all the sites 

would increase (table 6). Differences between mean 

observed and climate-change water temperatures 

range from 1.2°C at site 23 to 7.1°C at site 48. The 

changes in weekly minimum water temperature ranged 

from 0.0°C to 6.4°C. The regression model indicated 

that only one site, Deshka near Willow 

(site 44), would have a maximum weekly water 

temperature higher than 20°C, but the observed 

temperature for that week was over 20°C as well. 

Results of the t test indicated statistical significance 

for all 27 sites.

Fifteen sites had a difference of means between 

observed and climate-change water temperatures 

of more than 3°C (fig. 14), which is significant, 

according to Chatters and others (1991), in influencing 

the incidence of disease in fish. However, it should 

be noted that water-temperature changes would be 

gradual and fish might adapt to the 3°C change 

or might move to a cooler portion of the stream. 

A characteristic of sites with climate change equal 

to or greater than 3°C is that they are generally 

warmer, because there are fewer glaciers in their 

watersheds.

Fish survival depends on a number of factors, 

such as food supply, habitat conditions, predators, 

pathogens, and competitors (Regier and others, 1996). 

A temperature change greater than or 3°C in the 

Pacific Northwest is expected to increase the 

incidence of disease in fish (Chatters and others, 

1991). It is unlikely that fatal temperatures for salmon 

will be reached in the Cook Inlet Basin with a 

doubling of carbon dioxide, but the incidence of 

infection within salmon fisheries may rise.

It is important to note that the climate-change 

estimations for streams are based on stream-temperature data from the open-water season and the 

assumption that there will be no future change in the 

physical setting of the stream (Mohseni and others, 

1999). Three indirect factors affecting the change in 

stream temperature caused by global climate warming 

not considered by the water-temperature-regression 

model are (1) forest or vegetation cover change, 

(2) alternative sources of cooler or warmer water (i.e., 

natural and artificial reservoirs), and (3) precipitation. 

Forest cover affects stream temperatures by reducing 

the magnitude of extremes and reducing the seasonal 

variations in temperature (Johnson, 1971). If a basin 

is logged or the vegetation removed, studies have 

shown that significant increases in water temperature 

will occur (Brown and Krygier, 1970). Outflows from 

dams and lakes add water to stream systems that alter 

the heat balance equilibrium and reduce the sensitivity 

of the stream temperature to climatological changes. 

Increases in air temperature would most likely 

increase the temperature of ground water entering 

streams. Ripley (1987) hypothesized that the most 

direct effects of climate change on hydrological 

regimes will be through changes in precipitation. 

The hydrologic cycle will intensify and may change 

weather patterns, so some parts of the world will 

receive more rain and snow as other parts experience 

a decline in precipitation. In some areas, increased 

streamflow will enhance the thermal capacities of 

streams and make streams less susceptible to atmospheric conditions, and the reverse will be true for 

areas with decreased streamflow (Meisner, 1990). 
20

Table 6. Predicted water temperatures due to climate change

[Values in degrees Celsius. AK, Alaska]

Map 

number 

(figure 1) Station name

Minimum 

weekly 

temperature

Change in 

minimum 

temperature

Maximum 

weekly 

temperature

Change in 

maximum 

temperature

Mean 

water 

temperature

Change in 

mean water 

temperature

70 Bradley River near tidewater near 

Homer, AK

0.2 0.2 12.9 1.0 10.2 3.7

7 Ninilchik River at Ninilchik, AK 0.0 0.0 14.5 0.2 13.4 5.3

55 Kenai River below Skilak Lake 

outlet near Sterling, AK

1.0 1.0 12.4 0.0 11.8 2.4

16 Kenai River at Soldotna, AK 0.0 0.0 13.9 1.3 11.5 2.4

17 Beaver Creek near Kenai, AK 0.0 0.0 13.6 1.0 12.9 5.3

48 Chuitna River near Tyonek, AK 0.1 0.1 18.3 1.7 15.7 7.1

23 South Fork Campbell Creek near 

Anchorage, AK

1.2 1.2 9.4 - 1.3 7.7 1.2

27 Chester Creek at Arctic Boulevard at 

Anchorage, AK

0.0 0.0 15.6 0.6 13.6 3.9

29 Ship Creek below powerplant at Elmendorf Air Force Base at Anchorage, AK4.0 3.8 12.2 - 3.7 10.8 1.8

46 Susitna River at Susitna Station, AK 3.9 3.7 15.2 1.0 13.8 3.5

83 Susitna River above Yentna River near 

Susitna Station, AK

3.5 3.5 12.6 0.8 11.3 2.7

43 Deception Creek near Willow, AK 0.0 0.0 15.4 1.3 12.2 4.4

42 Willow Creek near Willow, AK 0.3 0.2 13.6 0.9 11.4 4.3

44 Deshka River near Willow, AK 0.1 0.1 24.6 4.0 16.2 5.4

85 Susitna River at Sunshine, AK 0.5 0.3 12.3 0.2 10.4 2.7

41 Talkeetna River near Talkeetna, AK 3.2 3.0 11.6 0.4 10.2 2.6

86 Susitna River near Talkeetna, AK 0.5 0.3 13.6 0.3 11.9 2.6

87 Susitna River at Curry, AK 6.9 5.8 15.4 1.3 13.7 4.2

88 Oshetna River near Cantwell, AK 4.4 3.6 12.8 0.6 10.9 2.8

89 Goose Creek near Cantwell, AK 3.7 3.3 13.0 0.8 11.3 3.9

38 Susitna River near Cantwell, AK 0.0 0.0 12.4 0.6 11.0 2.9

39 Susitna River at Gold Creek, AK 1.7 1.6 13.5 0.9 11.6 3.5

90 Kosina Creek near Cantwell, AK 3.7 3.6 13.5 0.8 12.0 3.6

93 Indian River near Gold Creek, AK 2.2 0.6 13.4 1.5 11.2 3.8

91 Watana Creek near Cantwell, AK 3.1 2.5 12.3 0.8 10.8 3.3

92 Portage Creek near Gold Creek, AK 3.8 2.8 10.3 - 0.2 8.1 1.6

109 Yentna River near Susitna Station, AK 7.7 6.4 12.3 0.5 11.5 3.0
21

Figure 14. Water-temperature sites in the Cook Inlet Basin with predicted water temperatures greater than 3 degrees Celsius.

149°

60°

63°

146° 

63°

152° 

60°

154°

A L A S K A RANGE

Susitna River

COOK INLET

Harding Ice Field

70

7

17

27

46

43

44 42

87

39

93

91 90

89

Anchorage

Kenai

Soldotna

Talkeetna River

Talkeetna

Yentna River

Caswell

48

MARITIME

▲ ▲

▲ ▲

▲

▲

▲

▲

▲▲

▲

▲

▲

▲

▲

CONTINENTAL

CONTINENTAL

MARITIME

TRANSITIONAL

TRANSITIONAL

75 100 MILES

100 KILOMETERS

50

75

25

25 50

0

0

Glacier

Water body

EXPLANATION

Water-temperature site and number—

 With predicted climate change more

 than 3 degrees Celsius

Climate-zone boundary

3

▲
22

Webb and Nobilis (1997) suggest that the 

relationship between air and river temperatures is 

better described as similar responses to seasonal 

changes of two mediums with slightly different 

thermal capacities. The nonlinear-regression model 

may describe the air-temperature dependency of water 

temperature, but little is explained. Air temperature 

may not be an adequate predictor of the effects of 

climate change on the stream environment (Jager and 

others, 1999), but using an air-temperature-based 

model may be a useful and simple way to estimate 

current and future water temperatures if all other 

variables are held constant.

Conversely, semiquantitative reviews of sparse 

climate data from more remote subarctic regions are 

important in contributing to the understanding of 

climate change as it affects the entire globe. Global 

warming is expected to be greatest at higher latitudes. 

Alaska has undergone the most climate warming of 

all the States in the United States since 1960 (Alaska 

Regional Assessment Group, 1999). Temperature 

modeling and estimation is also valuable for rough 

predictions of climate-change effects on the survival 

and distribution of organisms in local ecosystems. 

As models to predict effects of temperature upon 

freshwater communities (Brett, 1971; Baltz and 

others, 1987; Christie and Regier, 1988; Eaton and 

Scheller, 1996; Rombough, 1996; Scheller and others, 

1999) are developed, the prediction of water temperatures in streams will become ever more important 

(Crisp and Howson, 1982). The use of temperature 

models is practical for filling in gaps of data and 

estimating past temperatures, as well as for predicting 

temperatures in succeeding years.

SUMMARY

Water temperature is a valuable measure and 

descriptor of physical, chemical, and biological 

characteristics of streams and rivers in the Cook 

Inlet Basin in south-central Alaska. Fish health 

and populations, in particular, are greatly affected 

by water-temperature conditions. Existing watertemperature data in the Cook Inlet Basin has been 

compiled and analyzed. Major findings are:

• Water temperature from sites in the Kenai 

Peninsula is dependent on basin characteristics. Streams and rivers such as Beaver 

Creek and the Ninilchik River that drain 

lowland areas have higher water temperatures than watersheds that contain glaciers, 

such as the Bradley River. The Kenai River 

downstream of Skilak Lake has higher water 

temperature in the winter than near its 

mouth at Soldotna.

• In the Anchorage area, South Fork Campbell 

Creek, which drains a relatively high 

elevation watershed, has the coldest water 

temperature; Chester Creek, an urbanized 

basin, has warmer temperatures; and Ship 

Creek, downstream from a powerplant, has 

the warmest temperatures in the winter.

• The Susitna River is the largest river in the 

Cook Inlet Basin. In the headwaters of the 

basin, glaciers dominate the basin, and, as a 

result, water temperatures during the openwater season remain at 8.5°C or lower. Proceeding downriver, the Susitna River gradually warms until it reaches the Chulitna and 

Talkeetna Rivers. The input from these two 

rivers lowers the water temperature. From 

this point, water temperature gradually 

increases.

• Mohseni and others (1998) developed a 

nonlinear-regression model for predicting 

water temperature from air temperature. The 

model was applied to data collected in 

the Cook Inlet Basin in Alaska. Twentyseven sites had a Nash-Sutcliffe coefficient 

of 0.75 or higher, indicating a good fit of 

the model. Sites on streams with greater 

than 25 percent of their basin consisting of 

glaciers produced a poor simulation because 

glacial meltwater keeps the streams cold in 

summer, when air temperatures are rising.

• Global circulation models predict air 

temperature increases of between 7.2°C 

and 8.5°C for the Cook Inlet Basin. These 

increased air temperatures were used 

as input to the temperature-regression 

equations developed for 27 sites to simulate 

future trends in water temperature. Fifteen 

sites had a predicted water-temperature 

change of 3°C or more, which is considered 

significant for the incidence of disease in 

fish populations.
23

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