Prepared in cooperation with the Maine Department of Transportation

Modeled Future Peak Streamflows in Four Coastal Maine Rivers

Ducktrap River near Lincolnville, coastal Maine, April 4, 2009

Introduction

To safely and economically design bridges and culverts, it 

is necessary to compute the magnitude of peak streamflows that 

have specified annual exceedance probabilities (AEPs). These 

peak flows are also needed for effective floodplain management. 

Annual precipitation and air temperature in the northeastern 

United States are in general projected to increase during the 

21st century (Hayhoe and other, 2007). It is therefore important 

for engineers and resource managers to understand how peak 

flows may change in the future. This Fact Sheet, prepared in 

cooperation with the Maine Department of Transportation, 

presents a summary of modeled changes in peak flows at four 

basins in coastal Maine on the basis of projected changes in air 

temperature and precipitation. The full Scientific Investigations 

Report (Hodgkins and Dudley, 2013) is available at http://pubs.

usgs.gov/sir/2013/5080.

Methods

To estimate future peak streamflows at the four basins in 

this study (fig. 1), historical air temperature and precipitation 

in the basins were adjusted by different amounts and input 

to a hydrologic model of each study basin. To encompass 

the projected changes in climate in coastal Maine by the end 

of the 21st century, air temperatures were adjusted by four 

different amounts, from -3.6 oF (-2 oC) to +10.8 oF (+6 oC) of 

observed temperatures. Precipitation was adjusted by three 

different percentage values from -15 percent to +30 percent 

of observed precipitation. The 20 combinations of adjusted 

temperature and precipitation values (includes the no-change 

scenarios) were input to Precipitation-Runoff Modeling System 

(PRMS) watershed models (Leavesley and others, 2005; 

Leavesley and others, 1983), and annual daily maximum peak 

flows were calculated for each combination. Modeled annual 

U.S. Department of the Interior

U.S. Geological Survey June 2013

U.S. Geological Survey Fact Sheet 2013–3021
SOMERSET PENOBSCOT

OXFORD

FRANKLIN

WASHINGTON

YORK

PISCATAQUIS

HANCOCK

WALDO

KENNEBEC

CUMBERLAND

KNOX LINCOLN

ANDROSCOGGIN

AROOSTOOK

SAGADAHOC

Base from U.S. Geological Survey and Maine Office of

Geographic Information Systems digital files,

North American Datum of 1983,

Universal Transverse Mercator projection, Zone 19

Scale: 1:1,500,000

0 10 20 30 40 MILES

0 20 30 40 KILOMETERS 10

Pleasant

 River

Royal River

Narraguagus

 River

Sheepscot River

UNITED STATES

CANADA

STATES

CANADA

UNITED

45°

44°

70° 69° 68°

CANADA

UNITED STATES

NEW QUEBEC BRUNSWICK

NEW HAMPSHIRE

VERMONT

MAINE

NEW YORK

MASSACHUSETTS

LOCATION MAP

Area enlarged

Study basins

County boundary

EXPLANATION 

ATLANTIC OCEAN

Gulf of Maine

ATLANTIC OCEAN

Gulf of Maine

Figure 1. Map showing location of river basins selected for study in coastal Maine.
daily maximum peak flows from the adjusted temperature 

and precipitation changes were then compared to unadjusted 

(historical) modeled peak flows. Peak flows with 50-percent and 

1-percent AEPs (equivalent to 2-year and 100-year recurrence 

interval peak flows, respectively) were calculated for the four 

basins in the study using the modeled annual daily maximum 

peak flows. Modeled peak flows with 50-percent and 1-percent 

AEPs and adjusted temperatures and precipitation were 

compared to unadjusted (historical) modeled values.

Results

Annual daily maximum peak flows increase or decrease 

at the four study basins, depending on whether temperature 

or precipitation is adjusted. Increases in air temperature (with 

no change in precipitation) lead to decreases in peak flows, 

whereas increases in precipitation (with no change in air 

temperature) lead to increases in peak flows. As the magnitude 

of air temperatures increase in the four basins, peak flows 

decrease by larger amounts. If precipitation is held constant 

(no change from historical values), 17 to 26 percent decreases 

in peak flow occur when temperature is increased by 7.2°F. 

If temperature is held constant, large increases (greater than 

25 percent) in peak flow result from a 15-percent increase in 

precipitation, and very large increases (greater than 50 percent) 

occur with a 30-percent increase in precipitation. The largest 

decreases in peak flows at the four basins result from 15-percent 

decreases in precipitation combined with temperature increases 

of 10.8°F. The largest increases in peak flows generally result 

from 30-percent increases in precipitation combined with 3.6 °F 

decreases in temperatures. 

In many cases when temperature and precipitation 

both increase, small increases or decreases in annual daily 

maximum peak flows result. For likely changes projected for 

the northeastern United States for the middle of the 21st century 

(temperature increase of 3.6 °F and precipitation increases of 

0 to 15 percent), peak-flow changes at the four coastal Maine 

basins in this study are modeled to be evenly distributed 

between increases and decreases of less than 25 percent. 

Changes in peak flows with 50-percent AEPs for adjusted 

temperatures and precipitation are similar to changes in 

annual daily maximum peak flow. Changes in peak flows with 

1-percent AEPs (table 1) are similar in pattern to changes in 

annual daily maximum peak flow, but some of the changes 

Table 1. One-percent annual exceedance probability peak-flow changes based on changes in precipitation and 

air temperature.

[Peak-flow changes in percent; light blue shading represents peak flow increases of 25 to 50 percent, blue represents flow increases greater than 50 percent, 

light orange represents decreases of 25 to 50 percent, orange represents decreases of greater than 50 percent; °F, degrees Fahrenheit]

Temperature Changes

-3.6°F No change + 3.6°F + 7.2°F + 10.8°F

01022260 Pleasant River near Epping, Maine

-15 percent precipitation change -4.1 -32.8 -51.4 -56.7 -61.5

No precipitation change 38.5 0.0 -28.6 -34.6 -40.1

+15 percent precipitation change 99.3 40.1 -1.1 -10.3 -14.3

+30 percent precipitation change 162.2 90.1 48.2 28.7 14.1

01022500 Narraguagus River at Cherryfield, Maine

-15 percent precipitation change -15.8 -25.1 -36.7 -42.5 -42.4

No precipitation change 9.6 0.0 -11.6 -21.4 -19.7

+15 percent precipitation change 39.6 26.0 10.6 0.0 4.1

+30 percent precipitation change 72.1 55.4 39.0 28.1 32.5

01038000 Sheepscot River at North Whitefield, Maine

-15 percent precipitation change -23.5 -26.7 -33.1 -45.4 -50.5

No precipitation change 15.0 0.0 -5.3 -15.5 -17.4

+15 percent precipitation change 51.7 29.0 25.5 12.6 7.8

+30 percent precipitation change 83.9 58.1 57.1 42.2 34.3

01060000 Royal River at Yarmouth, Maine

-15 percent precipitation change -31.5 -29.2 -36.6 -43.2 -47.6

No precipitation change 12.6 0.0 -11.3 -14.1 -22.5

+15 percent precipitation change 54.2 50.4 44.0 34.5 12.8

+30 percent precipitation change 110.1 93.8 94.6 94.7 68.9
associated with increasing precipitation are much larger than 

changes in annual daily maximum peak flow. 

The decrease in modeled peak flows with increasing air 

temperature, given no change in precipitation amount, is likely 

caused by decreases in winter snowpack (the snow on the 

ground that accumulates during a winter). Substantial decreases 

in maximum annual winter snowpack water equivalent 

(the amount of water in a snowpack if it were melted) are 

modeled to occur with increasing air temperatures at the four 

basins in the study. Maximum annual snowpack in coastal 

Maine is modeled to decrease by about 50 percent with a 

3.6 oF temperature increase, by about 75 percent with a 7.2 oF 

temperature increase, and by about 85 percent with a 10.8 oF 

temperature increase (assuming no change in precipitation). 

Decreases in maximum winter snowpack for temperature 

increases of 7.2 oF or 10.8 oF occur regardless of changes 

in precipitation. 

The modeled changes in peak flows (annual daily 

maximum peak flows and 1-percent and 50-percent AEP peak 

flows) caused by changing precipitation and air temperatures are 

consistent with previous studies from other parts of the world. 

Increased peak flows resulting from increases in precipitation at 

the four basins in this study are consistent with projections for 

many parts of the world (Bates and others, 2008). Decreased 

peak flows from increased temperatures have been shown in 

some areas of the world where increased temperatures lead 

to decreased snowpacks and resulting decreased snowmelt 

runoff (Arora and Boer, 2001; Voss and others, 2002; Hamlet 

and Lettenmaier, 2007). In some other areas, loss of winter 

snowpack may lead to increased flood risk because of increased 

effective watershed areas from elevational shifts in the snow 

line (Hamlet and Lettenmaier, 2007; Tohver and Hamlet, 2010).

References Cited

Arora, V.K., and Boer, G.J., 2001, Effects of simulated climate 

change on the hydrology of major river basins: Journal of 

Geophysical Research, v. 106, p. 3335–3348.

Bates, B.C., Kundzewicz, Z.W., Wu S., and Palutikof, J.P., 

eds., 2008, Climate change and water: Technical paper of 

the Intergovernmental Panel on Climate Change, IPCC 

Secretariat, Geneva, 210 p.

Hamlet, A.F., and Lettenmaier, D.P., 2007, Effects of 20th 

century warming and climate variability on flood risk in the 

western U.S.: Water Resources Research, v. 43, no. 6, 17 p.

Hayhoe, K., Wake, C.P., Huntington, T.G., Luo, L., Schwartz, 

M.D., Sheffield, J., Wood, E., Anderson, B., Bradbury, J., 

DeGaetano, A., Troy, T.J., and Wolfe, D., 2007, Past and 

future changes in climate and hydrological indicators in the 

U.S. Northeast: Climate Dynamics, v. 28, p. 381–407.

Hodgkins, G.A., and Dudley, R.W., 2013, Modeled future peak 

streamflows in four coastal Maine rivers: U.S. Geological 

Survey Scientific Investigations Report 2013–5080, 18 p.

Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, 

L.G., 1983, Precipitation–runoff modeling system—

User’s manual: U.S. Geological Survey Water-Resources 

Investigations Report 83–4238, 207 p.

Leavesley, G.H., Markstrom, S.L., Viger, R.J., and Hay, L.E., 

2005, U.S. Geological Survey Modular Modeling System 

(MMS) Precipitation-Runoff Modeling System (PRMS) 

(MMS–PRMS), in Singh, V., and Frevert, D., eds., Watershed 

Models: Boca Raton, Fla., CRC Press, p. 159–177.

Tohver, I., and Hamlet, A.F., 2010, Impacts of 21st century 

climate change on hydrologic extremes in the Pacific 

Northwest region of North America: Chapter 7 in Final 

Report for the Columbia Basin Climate Change Scenarios 

Project, Climate Impacts Group, Center for Science in the 

Earth System, Joint Institute for the Study of the Atmosphere 

and Ocean, University of Washington, Seattle, 20 p.

Voss, R., May, W., and Roeckner, E., 2002, Enhanced resolution 

modeling study on anthropogenic climate change—Changes 

in extremes of the hydrological cycle: International Journal of 

Climatology, v. 22, p. 755–777.

By Glenn A. Hodgkins and Robert W. Dudley

Sheepscot River at North Whitefield, Maine, April 19, 2011

For more information, please contact:

Robert Lent, Office Chief

USGS New England Water Science Center,

Maine Office

196 Whitten Road

Augusta, Maine 04330

Telephone: (207) 622-8201

http://me.water.usgs.gov