Introduction Study Area

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3128

March 2012

Introduction

General Circulation Model (GCM) simulations of future 

climate through 2099 project a wide range of possible 

scenarios (Intergovernmental Panel on Climate Change, 2007). 

To determine the sensitivity and potential effects of long-term 

climate change on the freshwater resources of the United 

States, the U.S. Geological Survey Global Change study, 

“An integrated watershed scale response to global change in 

selected basins across the United States” was started in 2008. 

The long-term goal of this national study is to provide the 

foundation for hydrologically based climate-change studies 

across the nation.

Fourteen basins for which the Precipitation Runoff Modeling System (PRMS) has been calibrated and evaluated were 

selected as study sites. PRMS is a deterministic, distributedparameter watershed model developed to evaluate the effects 

of various combinations of precipitation, temperature, and land 

use on streamflow and general basin hydrology. Output from 

five GCMs and four emission scenarios were used to develop 

an ensemble of climate-change scenarios for each basin. These 

ensembles were simulated with the corresponding PRMS 

model. This fact sheet summarizes the hydrologic effects and 

sensitivity of the PRMS simulations to climate change for the 

Cathance Stream Basin at Edmunds, Maine (U.S. Geological 

Survey streamflow-gaging station 01021230; fig. 1) presented 

in the project summary report (Markstrom and others, 2012) 

and a journal article (Hay and others, 2011).

Study Area

The Cathance Stream is an 85-square kilometer (km2) basin in 

Washington County, eastern Maine, on the coast of the Atlantic 

Ocean. The stream is a tributary to the Dennys River. The basin 

is rural and its rolling topography predominantly is forested with 

wetlands, lakes, ponds, blueberry agriculture fields, clear cuts, 

partial cuts, regenerating forest, and light residential development. The climate is temperate, with mild summers and cold 

winters; normal mean annual air temperature is about 7 degrees 

Celsius (oC), with mean monthly air temperatures ranging from 

about –29 o

C in January to about 19 oC in July. Mean annual 

precipitation is approximately 114 centimeters (cm) and is 

distributed fairly evenly throughout the year. Mean annual 

evapotranspiration (loss of water to the atmosphere by evaporation from the soil and transpiration from plants) is about 46 cm.

The Dennys River and Cathance Stream are important 

habitat for wild Atlantic salmon. Currently (2011), wild 

Atlantic salmon populations are protected under the U.S. 

Endangered Species Act of 1973 (16 USC Sec. 1531) and are 

the subject of a comprehensive recovery program. The U.S. 

Geological Survey, in cooperation with the Maine Department 

of Marine Resources Bureau of Sea Run Fisheries and Habitat, 

began a study in 2004 to characterize the quantity, variability, 

and timing of streamflow in the Dennys River (Dudley, 

2008). The study included the development and evaluation 

of a distributed-parameter watershed model (PRMS). The 

watershed modeling work supports several tasks directed at 

developing water-use management plans for Atlantic salmon 

rivers and development of comprehensive flow monitoring in 

these basins. Improved water-resources information supports 

Atlantic salmon protection efforts.

Watershed Scale Response to Climate Change—Cathance 

Stream Basin, Maine
General Circulation ModelsGeneral Circulation Models Given the uncertainty in climate modeling, it is desirable to use more than one GCM to obtain a range of potential future climatic 

conditions. Monthly precipitation and temperature output from five GCMs were processed (table 1).

01021230

High 4,314

Low -79

EXPLANATION

Base from U.S. Geological Survey digital data, 2011 1:100,000

Albers Equal-Area Conic projection

Standard parallels 29°30'N and 45°30'N

Central meridian 96°00'W, Latitude of origin 23°00'N

Horizontal coordinate information is referenced to the

World Geodetic System of 1984 (WGS 84)

Elevation in meters

U.S. Geological Survey streamflow-

 gaging station and identifier

44°52'

67°28'

26'

24'

54'

56'

58'

22'

20'

18'

45°

Cathance

Lake

Cathance Stream

67°16'

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

01021230

INDEX MAP

MAINE

Study area

Figure 1. Precipitation Runoff Modeling System study locations, Cathance Stream Basin, Maine, and location of U.S. 

Geological Survey streamflow-gaging station 01021230 with a drainage area of 85 square kilometers and elevation 

range from 46 to 174 meters.

Table 1. General Circulation Model (GCM) projections used in this study.

GCM Center and country of origin

BCC–BCM2.0 Bjerknes Centre for Climate Research, Norway

CSIRO–Mk3.0 Australia’s Commonwealth Scientific and Industrial Research Organization, Australia

CSIRO–Mk3.5 Australia’s Commonwealth Scientific and Industrial Research Organization, Australia

INM–CM3.0 Institute for Numerical Mathematics, Russia

MIROC3.2 National Institute for Environmental Studies, Japan
Results

Climate-change fields were derived by calculating the 

change in climate from current (water years 1988–1999) to 

future conditions simulated by each GCM. The 20C3M simulation for water years 1988–1999 was used to represent current 

climatic conditions. This 12-year period of record was chosen 

based on the overlap of the available historical records from 

the 14 basins included in the national study. Climate change 

fields (percentage changes in precipitation and degree changes 

in temperature) were computed for 12-year moving window 

periods (from 2001–2099) using the 20C3M (1988–1999) and 

the A1B, B1, and A2 emission scenarios. A 12-year moving 

window, starting in 2001 and ending in 2099, results in 1,320 

future scenarios [(88, 12-year climatologies, 1 per year starting 

with 2001–2012 and ending with 2088–2099) x (3 emission 

scenarios) x (5 GCMs)].

Climate-change scenarios were generated for PRMS by 

modifying PRMS precipitation and temperature inputs with the 

mean monthly climate change fields derived from the GCMs, 

resulting in 1,320 PRMS-input files. Table 3 shows the change 

(slope) and adjusted R2

 (adjR2) for the least squares fit to the 

trend line for selected output variables from the PRMS projections. The slope indicates the change in the selected variable by 

year. The adjusted R2

 value gives an indication of the variability 

in the central tendency of the trend line.

Figure 2 shows a summary of the projected range in 11-year 

moving mean daily values of maximum temperature (fig. 2A), 

minimum temperature (fig. 2B), and precipitation (fig. 2C) by 

emission scenario. The first year of each 12-year simulation was 

used as PRMS initialization and is not included in the results. 

The three solid-colored lines indicate the 11-year moving mean 

values (x-axis indicates center of 11-year window) for the three 

future emission scenarios (central tendency of the five GCMs 

for each emission scenario). The projected range shown for each 

emission scenario indicates the range of potential future climatic 

conditions simulated by the five GCMs. All GCM simulations 

project steady increases in maximum and minimum temperature (table 3), with uncertainties associated with these GCM 

projections increasing with time. Both maximum and minimum 

temperatures show the smallest projected annual changes for the 

B1 emission scenario. Projected annual changes in precipitation 

are variable, with projected increases in the central tendencies 

by the end of the 21st century for the A1B and A2 emission 

scenarios (table 3).

Results

PRMS simulates spatially distributed streamflow, components of flow (surface, subsurface, and groundwater), snowpack 

conditions, and many other hydrologic components of interest. 

Figure 3 shows the projected range in 11-year moving mean 

daily values of streamflow by emission scenario. The central 

tendencies of the PRMS simulations using the emission scenarios project decreases in mean annual streamflow for the A1B 

and A2 emission scenarios (table 3), though the uncertainties 

associated with these streamflow projections are large.

Because of the increase in temperatures, the percentage 

of precipitation that falls as snow (fig. 4A), snowpack water 

equivalent (fig. 4B), and snowmelt (fig. 4C) are projected to 

decrease in the basin on an annual basis, with high variability 

(table 3). The changes in snowpack accumulation and melt will 

in turn affect the seasonal amount and timing of streamflow.

Displaying basin mean streamflow by month (fig. 5) illustrates the projected change in the seasonal distribution of 

streamflow resulting from projected changes in snowpack 

accumulation and melting (fig. 4). The solid red lines in figure 

5 show PRMS-simulated mean monthly streamflow for current conditions (1989–1999). The boxplots represent the range 

in projected mean monthly streamflow for the five GCMs 

and three scenarios for 2030 (green, 2025–2035), 2060 (tan, 

2055–2065) and 2090 (blue, 2085–2095). Large increases in 

streamflow are projected for January through March, while 

large decreases are projected for April through June. The timing of peak streamflow for current conditions (1989–1999, 

red line) occurs in April. By the end of the 21st century, peak 

timing of streamflow could occur as early as January based on 

the projections in figure 5. The range of values indicated by the 

The GCM outputs were obtained from the World Climate Research Programme’s Coupled Model Intercomparison Project 

phase 3 multi-model dataset archive, which was referenced in the Intergovernmental Panel on Climate Change Fourth Assessment 

Special Report on Emission scenarios (Intergovernmental Panel on Climate Change, 2007). For each GCM, one current (water 

years 1988–1999) and three future emission scenarios were used and are described in table 2. 

Table 2. Climate-change emission scenarios simulated by the General Circulation Models in this study.

Emission scenario Description/assumptions

20C3M 20th century climate used to determine baseline (1989–1999) conditions

A1B Rapid economic growth, a global population that peaks in mid-21st century and rapid introduction of new and 

more efficient technologies with a balanced emphasis on all energy sources

B1 Convergent world, with the same global population as Emission scenario A1B, but with more rapid changes in 

economic structures toward a service and information economy that is more ecologically friendly

A2 Heterogeneous world with high population growth, slow economic development, and slow technological change
EXPLANATION

Emission Scenarios

A2 A1B B1

Maximum

Mean from five General Circulation Models

Minimum

Center of 11-year window

Maximum temperature,

degrees Celsius

A. Basin mean maximum temperature

2020 2040 2060 2080

12

13

14

15

16

17

18

12

13

14

15

16

17

18

Center of 11-year window

Minimum temperature,

degrees Celsius

B. Basin mean minimum temperature

2020 2040 2060 2080

0

1

2

3

4

5

6

0

1

2

3

4

5

6

Center of 11-year window

Precipitation, millimeters per day

C. Basin mean precipitation

2020 2040 2060 2080

3.4

3.6

3.8

4.0

3.4

3.6

3.8

4.0

Center of 11-year window

Streamflow,

cubic meters per second

Basin mean streamflow

2020 2040 2060 2080

1.4

1.6

1.8

2.0

2.2

1.4

1.6

1.8

2.0

2.2

EXPLANATION

Emission Scenarios

A2 A1B B1

Maximum

Mean from five General Circulation Models

Minimum

Figure 2. Projected range in 11-year moving mean daily values 

of (A) maximum temperature, (B) minimum temperature, and 

(C) precipitation by emission scenario.

Figure 3. Projected range in 11-year moving mean daily values of streamflow by emission scenario.

Table 3. Projected change by year (slope) and adjusted R2 (adjR2) based on the central tendencies of the five General Circulation Models for the three 

carbon emission scenarios for selected Precipitation Runoff Modeling System (PRMS) output variables.

[Blue indicates a significant negative trend and yellow indicates a significant positive trend (p<0.05) accounting for lag-1 autocorrelation].

PRMS output variable

Emission scenario

A1B

Emission scenario

A2

Emission scenario

B1

slope adjR2 slope adjR2 slope adjR2

Maximum temperature in degrees Celsius 0.033 0.99 0.038 0.98 0.018 0.98

Minimum temperature in degrees Celsius 0.035 0.99 0.041 0.98 0.020 0.98

Precipitation in millimeters per day 0.0019 0.56 0.0019 0.58 0.0016 0.40

Streamflow in cubic meters per second -0.0029 0.78 -0.0038 0.84 -0.0012 0.35

Percent snow in percent per day -0.12 0.98 -0.13 0.99 -0.07 0.95

Snowpack water equivalent in millimeters per day -0.28 0.95 -0.29 0.98 -0.17 0.94

Snowmelt in millimeters per day -0.0039 0.95 -0.0047 0.97 -0.0021 0.93
boxplots in figure 5 illustrates the high degree of uncertainty 

associated with the magnitude of these projected streamflow 

changes, in all but the summer months. This trend is consistent 

with projected decreases in snowpack water equivalent (fig. 6). 

Snowpack is expected to decrease because of more snowmelt 

and more precipitation falling as rain during the winter (November through March) months. This advance in spring snowmelt 

runoff has been documented in the historical record with winterspring streamflow becoming significantly earlier in northern 

and mountainous sections of Maine during the 20th century 

(Dudley and Hodgkins, 2002; Hodgkins and others, 2003; 

Hodgkins and Dudley, 2006a). Over a 50-year historical period, 

18 of 23 snow-course sites in and near Maine had a significant 

decrease (p < 0.1) in late-winter snowpack depth, or an increase 

in snowpack density (Hodgkins and Dudley, 2006b). PRMSmodel results indicate these trends are expected to continue.

Month

Snowpack water, millimeters

Basin mean snowpack water

 Feb. Apr. June Aug. Oct. Dec.

0

50

100

150

200

0

50

100

150

200

Center of 11-year window

Percent snow

A. Basin mean percent snow

2020 2040 2060 2080

5

10

15

20

25

30

5

10

15

20

25

30

Center of 11-year window

Snowpack water, millimeters

B. Basin mean snowpack water

2020 2040 2060 2080

0

10

20

30

40

50

0

10

20

30

40

50

Center of 11-year window

Snowmelt, millimeters per day

C. Basin mean snowmelt

2020 2040 2060 2080

0.6

0.8

1.0

1.2

0.6

0.8

1.0

1.2 EXPLANATION

Emission Scenarios

A2 A1B B1

Maximum

Mean from five General Circulation Models

Minimum

Figure 4. Projected range in 11-year moving mean daily values 

of (A) percentage of precipitation that falls as snow, (B) snowpack 

water equivalent, and (C) snowmelt by emission scenario.

Month

Streamflow,

cubic meters per second

Basin mean streamflow

 Feb. Apr. June Aug. Oct. Dec.

0

1

2

3

4

5

6

0

1

2

3

4

5

6

EXPLANATION

Baseline

Conditions

(1989-1999)

2030

(2025-2035)

2060

(2055-2065)

2090

(2085-2095)

Whisker, 90th percentile

Upper quartile line, 75th percentile

Median line, 50th percentile

Lower quartile line, 25th percentile

Whisker, 10th percentile

Outlier

Figure 5. Mean daily streamflow values by month for baseline conditions and projected range (2030, 2060, and 2090) using the five General 

Circulation Models and three emission scenarios.

Figure 6. Mean daily snowpack water equivalent values by month for 

baseline conditions and projected range (2030, 2060, and 2090) using the 

five General Circulation Models and three emission scenarios.
Conclusion and

 Discussion Selected References Conclusion and Discussion

The Cathance Stream tributary of the Dennys River Basin, 

and other coastal river basins in Maine, are important habitat 

for a variety of aquatic species including endangered Atlantic 

salmon. The broader-scale consequences of climate change 

on the flow regimes of rivers in Maine, like Cathance Stream, 

likely will affect ecosystems. The ecological implications of 

changes in the timing of winter-spring streamflow in Maine are 

not well understood. One possible effect may be a change in 

Atlantic salmon survival rates. If the peak spring migration of 

juvenile salmon from freshwater rivers (which is controlled by 

photoperiod, temperature, and flow) becomes out of phase with 

optimal environmental conditions in the rivers, the estuaries, or 

the ocean, salmon survival could drop substantially (McCormick 

and others, 1998). Changes in the timing of spring river flows 

also may effect fresh-water mixing in estuarine ecosystems. 

Earlier snowmelt and increases in summer evapotranspiration 

rates (not shown) could shorten the annual periods of standing 

water pools which are used by amphibians for breeding in forested depressional wetlands (called vernal pools). The scientific 

techniques described in the fact sheet can be augmented with 

other techniques in developing the science needed to address the 

effects of climate change on water resources and ecosystems.

Selected References

Dudley, R.W., 2008, Simulation of the quantity, variability, and 

timing of streamflow in the Dennys River Basin, Maine, by 

use of a precipitation-runoff watershed model: U.S. Geological Survey Scientific Investigations Report 2008–5100, 44 p.

Dudley, R.W., and Hodgkins, G.A., 2002, Trends in streamflow, 

river ice, and snowpack for coastal river basins in Maine 

during the 20th century: U.S. Geological Survey WaterResources Investigations Report 02–4245, 26 p.

Hay, L.E., Markstrom, S.L., and Ward-Garrison, C.D., 2011, 

Watershed-scale response to climate change through the 

twenty-first century for selected basins across the United 

States, Earth Interactions, v. 15, 37 p.

Hodgkins, G.A., Dudley, R.W., and Huntington, T.G., 2003, 

Changes in the timing of high river flows in New England over the 20th century: Journal of Hydrology, v. 278, 

p. 242–250.

Hodgkins, G.A., and Dudley, R.W., 2006a, Changes in the timing of winter–spring streamflow in eastern North America, 

1913–2002: Geophysical Research Letters, v. 33, L06402, 

doi: 10.1029/2005GL025593.

Hodgkins, G.A., and Dudley, R.W., 2006b, Changes in latewinter snowpack depth, water equivalent, and density in 

Maine, 1926–2004: Hydrological Processes, v. 20, p. 741–751.

Intergovernmental Panel on Climate Change, 2007, Summary 

for policymakers, in Climate change 2007—The physical 

science basis, Contributions of Working Group 1 to the 

Fourth Assessment Report of the Intergovernmental Panel 

on Climate Change: Cambridge and New York, Cambridge 

University Press, 18 p.

Markstrom, S.L., Hay, L.E., Ward-Garrison, C.D., Risley, J.C., 

Battaglin, W.A., Bjerklie, D.M., Chase, K.J., Christiansen, 

D.E., Dudley, R.W., Hunt, R.J., Koczot, K.M., Mastin, M.C., 

Regan, R.S., Viger, R.J., Vining, K.C., and Walker, J.F., 2012, 

An integrated watershed scale response to climate change 

for selected basins across the United States: U.S. Geological 

Survey Scientific Investigations Report 2011–5077, 142 p.

McCormick, S.D., Hansen, L.P., Quinn, T.P., and Saunders, 

R.L., 1998, Movement, migration, and smolting of Atlantic 

salmon (Salmo salar): Canadian Journal of Fisheries and 

Aquatic Science, v. 55 (Suppl. 1), p. 77–92. By Robert W. Dudley, Lauren E. Hay, 

Steven L. Markstrom, and Glenn A. Hodgkins

For more information visit the following Web sites:

http://wwwbrr.cr.usgs.gov/projects/SW_MoWS/

http://me.water.usgs.gov/

http://www.usgs.gov/climate_landuse/