U.S. Department of the Interior

U.S. Geological Survey

Potential implications of a warmer future for 

the Colorado River ecosystem

Kimberly L. Dibble

Annual Reporting Meeting

Phoenix, AZ

January 13, 2020

U.S. Department of the Interior

U.S. Geological Survey
Presentation Outline

 Drivers of water temperature in the CRe

 What drives water temperatures in Grand Canyon and 

across the CRe?

 Present and future river temperatures

 How will climate change, drought, and reservoir 

storage decisions influence future river temperatures?

 Implications of warmer temperatures on fish

 How has river temperature shaped post-dam aquatic 

communities, and how may they change in the future?
FY18-20 Project Elements, Study Objectives, 

and LTEMP Resource Goals

 Project Element E1: Temperature and nutrients in the 

CRe – patterns, drivers, and improved predictions

 Study Objective: Modify previous models for predicting CRe

temperatures to reflect exponential (rather than linear) warming.

 LTEMP Resource Goals: Identify processes that drive spatial 

and temporal variation in nutrients and temperature within the CRe

and establish quantitative and mechanistic links among these 

ecosystem drivers, primary production, and higher trophic levels.

 Natural Processes (#3), Humpback Chub (#1), Other Native Fish 

(#1), Rainbow Trout Fishery (#2)

 Builds off data collected during Project Element H.4 

(FY13-14) and Project Element 9.8 (FY15-17 Workplan)
Lake Powell thermal stratification

Vernieu et al. 2005
Lake Powell elevation as a driver of temperature

Lake Powell storage strongly influences river temperature 

downstream from Glen Canyon Dam

1060 1080 1100 1120

8

12

16

20

24

28

Summer Release Temperature ( C)

 Lake Powell S 

Pre-Dam

 Natural

Post-Dam

 Altered

Minimum Power Pool

COLD

early 1

COOL

mid 2000s

WARM

late 1960s

Dibble et al., In Review, Ecol Apps

175

150

125

100

75

50

25

0

28 24 20 16 12 8

Penstocks Relative to Crest (m)

Withdrawal Depth Rela 

Lake Powell Temperature at Depth (C)

COLD

COOL

WARM

Dibble et al., In Review, Ecol Apps

Preliminary Data – Do Not Cite
Warmer reservoir releases contain less nutrients

Deemer and Yackulic, Unpub. Data Deemer and Yackulic, Unpub. Data

Phosphorus concentrations are elevated in bottom water

Warmer withdrawals may decrease nutrient availability fish 

Preliminary Data – Do Not Cite
To model future river temperatures, we 

modified the current CR temperature model

Tributary 1 (warmer)

Release Temperature Temperature & Discharge

Air Temperature

Discharge at dam Water Temperature

(downstream)

River Kilometer

Predicted Water Temperature in July ( C)

0 100 200 300 400 500

12 16 20 24 28

*

Predicted River Temperature (°C)

12 14 16 18 20

Distance from Dam (km)

Tributary 2 (colder)

Temperature & Discharge

September October November

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Residual Error (

C)

Linear (current)

Exponential (new)

Preliminary Data – Do Not Cite
FY 2013-14 & FY 2015-17 Workplans

= Data on Hand

+ USGS WaterSmart Funding

FY13-14; Project Element H.4

Dibble et al. 2018, EBF

FY15-17; Project Element 9.8

Dibble et al., 2015, Ecol Apps

Wikimedia Commons, Creative Commons Copyright, Author: Shannon1; 

https://commons.wikimedia.org/wiki/File:Coloradorivermapnew1.jpg
Current 

thermal 

regime

Dibble et al., In Review, Ecol Apps 

Photos: J. Tomelleri

15 465

Flow

m3s-1

Upper Basin

• Short tailwaters

• Warm summer 

thermal regime

Lower Basin

• Long tailwaters

• Cold summer thermal 

regime

Preliminary Data – Do Not Cite
Fish community distribution and abundance

1. Species-Level Information

Colorado Pikeminnow

Roundtail Chub

Red Shiner

Smallmouth Bass

Humpback Chub

Rainbow Trout

Native

Non-Native

2. Relative Abundance

Extirpated

Not 

Present

Rare

Abundant

Common

Common

25%

50%

100%

0%

50%

gray

Photos: J. Tomelleri

Preliminary Data – Do Not Cite
Fish 

community 

dynamics 

relative to 

current thermal 

regime

Dibble et al., In Review, Ecol Apps 

Photos: J. Tomelleri

Cold-water non-native 

salmonids common to 

abundant in tailwaters

Warm-water non-native 

fish common to abundant 

in Upper Basin

Warm-water native fish 

rare or extirpated in basin 

Humpback chub abundant

in Grand Canyon despite 

cold water temperatures

Preliminary Data – Do Not Cite
Humpback Chub decadal 

scale trends in abundance 

relative to temperature

Dinosaur National 

Monument

Desolation/Gray 

Canyons

Black Rocks

Westwater

Canyon

Little Colorado River (Eastern 

Grand Canyon)

Western Grand Canyon

Upper Basin

Grand Canyon Temperature Trends

1995 2000 2005 2010 201

11

15

19

23

27

Average Peak Summer Temperature ( C)

Grand Canyon

Upper Basin

11 15 19 23 27

0%

25%

50%

75%

100%

Relative Abund 

Average Peak Summer Temperature (C)

Grand Canyon Upper 

Decadal Scale Trends in

Dibble et al., In Review, Ecol Apps

Photos: J. Tomelleri

Preliminary Data – Do Not Cite
Warm-water non-native fish in Upper Basin

Upper Colorado River Endangered Fish Recovery Program & San Juan River Basin Recovery Implementation Program Fact Sheet 2017, https://www.coloradoriverrecovery.org/general-information/general-publications/stand-alone-2017-web.pdf 

Humpback Chub Bonytail Colorado Pikeminnow Razorback Sucker

Bestgen and Hill 2016

Photos: J. Tomelleri

UCREFRP & SJRBRIP Fact Sheet 2017

UCREFRP & SJRBRIP Fact Sheet 2017
What are basin-wide expectations for the future?

Air

*

Increased air temperature 

(2.6oC) 

Decreased flow

(17%)

*

Udall and Overpeck 2017 **

** High emissions: business-as-usual, SRES A2 and RCP8.5; Moderate emissions: somewhat reduced by mitigation, SRES A1B and RCP4.5
Potential future Lake Powell release 

temperatures (LTEMP EIS)

Dibble et al., In Review, Ecol Apps 

Drier hydrology traces based on mean annual inflows indicate release 

temperatures in summer have the potential to reach ~20 °C

h00 h00 h00

Preliminary Data – Do Not Cite
To what degree will changes in air temperature, 

discharge, and storage drive future river temperatures?

Increased air 

temperature 

(2.6oC) 

Decreased Colorado 

River flow

(17%)

Phillip Martin

National Geographic 2014

Decreased 

reservoir 

storage
Future 

thermal 

regime

Preliminary Data – Do Not Cite Dibble et al., In Review, Ecol Apps 
Effects of warmer water on rainbow trout

FY15-17; Project Element 9.8

Warmer 

Water Year

Smaller adults

Dibble et al. 2018, EBF

Warmer 

Summer

Recruitment 

increases

Dibble et al. 2018, EBF

02

05

02

05

05

02

Drift Biomass Inflation Factor

Dodrill et al. 2016, CJFAS, with modifications

Warmer temperatures = smaller 

adult trout with current foodbase

Preliminary Data – Do Not Cite
Effects of warmer water on humpback chub

Positive effect 

on growth 

(transition to 

larger fish)

Yackulic et al. 2018, Ecology

Positive effect 

on growth

CR

LCR

Dzul et al. 2016, CJFAS

Expansion into 

Western Grand Canyon

VanHaverbeke et al. 2018, Southwestern Naturalist
Warm-water non-native fish invasion into GC?

1060 1080 1100 1120

8

12

16

20

24

28

Summer Release Temperature ( C)

 Lake Powell S 

Pre-Dam

 Natural

Post-Dam

 Altered

Minimum Power Pool

COL

early 1

COOL

mid 2000s

WARM

late 1960s

Dibble et al., In Review, Ecol Apps 

0 200 400 600 800 1000 1200

10

14

18

22

26

30

Summer Water Temperature ( 

C) 

River Kilometer

Fontenelle Reservoir

Flaming Gorge Reservoir Lake Powell Lake Mead Northern Pike WalleyeSmallmouth Bass

Striped Bass

Channel Catfish

Growth

tolerance

optimum

Average releases, historic climate

Average releases, climate change

Cold releases, climate change

Cool releases, climate change

Warm releases, climate change

Pre-dam thermal regime, climate change

Dibble et al., Unpub. Data

Grand Canyon

Preliminary Data – Do Not Cite
Potential ecological outcomes of a warmer CRe

Potential mainstem 

spawning and higher 

growth of native fish

Humpback Chub Razorback Sucker

Potential boost in 

invertebrate taxa; 

better food base

Caddisflies Midges

Potential nutrient decline 

(warmer, epilimnetic), 

implications for food base

Diatoms Midges

Potential rainbow trout 

decline, replacement by 

piscivorous non-native fish

Smallmouth Bass

Northern Pike

Preliminary Data – Do Not Cite
Acknowledgements

Funding

 USBR Glen Canyon Dam 

Adaptive Management Program

 USGS WaterSMART Program

Coauthors

 Charles Yackulic, USGS

 Jack Schmidt, Utah State 

University

 Ted Kennedy, USGS

 Kevin Bestgen, Colorado State 

University

Data

 Colorado Division of Water 

Resources

 U.S. Army Corps of Engineers 

 U.S. Bureau of Reclamation, 

Hydromet

 USDA NRCS National Water and 

Climate Center

 Upper Colorado River 

Endangered Fish Recovery 

Program

 USFWS San Juan River Basin 

Recovery Implementation 

Program

 USGS BioData and WaterWatch

 Tom Gushue, USGS, GIS Support