U.S. Department of the Interior 

U.S. Geological Survey

Fact Sheet FS 2005-3003

January 2005

Historical Trend in Ice Thickness on the Piscataquis River, near DoverFoxcroft, Central Maine

Introduction 

Systematic changes in water-resource 

variables can provide evidence for hydrologic response to climate change. Coherence among indicators within a region may 

be the most compelling evidence for 

change. Recent studies have shown that 

average dates of river ice-out (Dudley and 

Hodgkins, 2002) and high spring river discharge (Hodgkins and others, 2003) 

became earlier in New England during the 

20th century. The growing season has 

lengthened in New England (Cooter and 

LeDuc, 1995) and numerous plant and animal indicators also are consistent with 

trends towards earlier spring warming 

(Walther and others, 2002) throughout the 

Northern Hemisphere during the 20th century. 

The U.S. Geological Survey has historical records of river-discharge measurements, including measurements made 

during the winter, when rivers are typically 

ice-covered in Maine. Ice thickness can be 

estimated from the relation between the 

distance from the water surface to the bottom of the ice (which was systematically 

recorded) and ice thickness (which was 

recorded for a subset of the data). The purpose of this study was to assess the suitability of river-ice thickness as a sensitive 

hydrologic indicator for detecting climate 

change and to test for trends in this indicator over time. The Piscataquis River near 

Dover-Foxcroft in central Maine was studied because it is free from any significant 

human influences that could affect flow 

and a long-term record (1912 to 2001) was 

available. Methods and data sources are 

described in Huntington and others (2003).

Key Findings

Ice thickness was found to be a sensitive indicator of climate variability during 

the 1912 to 2001 measurement period. A 

distinct, overall trend towards thinning of 

river ice was found (fig. 1). Average ice 

thickness decreased by about 23 cm (about 

9 inches) during this period (fig. 1) (Huntington and others, 2003). This change in 

ice thickness was equivalent to a decrease 

of about 46 percent. Ice thickness was significantly correlated with winter air temperature, the date of river ice-out, and the 

timing of high spring flow on the Piscataquis River.

Average winter air temperature 

increased during the 20th century, but there 

was a distinct period of cooling from about 

1950 through 1975 (fig. 2). This trend 

reversal during the 3rd quarter of the 20th 

century, and the corresponding pause in the 

ice-thickness trend, are consistent with 

regional cooling during the 3rd quarter of 

the 20th century (Intergovernmental Panel 

on Climate Change, 2001). The increasing 

winter temperature trend of about 1.7oC 

during the 20th century is significant, and 

these warming trends are similar to those 

reported for the larger regional area (Intergovernmental Panel on Climate Change, 

2001).

The increase in air temperature over 

time, including the trend reversals in the 

3rd quarter of the 20th century and the corresponding decrease in ice thickness suggests a strong sensitivity of ice thickness to 

regional climate change. Decreases in ice 

thickness, advances in the timing of river 

and lake ice-out, and advances in timing of 

spring discharge are likely to have consequences for aquatic biota that are sensitive 

to changes in ice dynamics (Beltaos and 

Prowse, 2001). Collection of long-term 

water-resource data is essential for understanding the response of natural systems to 

climate change. Improving our understanding of the sensitivity of water-resource 

variables to climate change provides a 

U.S. Geological Survey gaging station on the Piscataquis River near Dover-Foxcroft

Changes in water resources over time may affect public and private water 

supplies and the health of aquatic ecosystems. The U.S. Geological Survey 

is studying the relation between climate and water-resource variables in 

Maine and New England to provide resource managers, the scientific community, and the public with better information about the sensitivity of water 

resources to climate change and variability. The long-term collection and 

availability of high-quality water-resources data are crucial to these efforts.
U.S. Department of the Interior 

U.S. Geological Survey

Fact Sheet FS 2005-3003

January 2005

foundation to develop predictive models 

that can be used by resource managers. 

References

Cooter, E. J., and LeDuc, S., 1995, Recent 

frost date trends in the northeastern 

U.S.: International Journal of Climatology, v. 15, p. 65-75.

Beltaos, S., and Prowse, T. D., 2001, Climate impacts on extreme ice-jam 

events in Canadian Rivers: Hydrological Sciences, v. 46, p. 157-181.

Dudley, R.W., and Hodgkins, G. A., 2002, 

Trends in streamflow, river ice and 

snowpack for coastal rivers in Maine 

during the 20th century: U.S. Geological Survey Water-Resources Investigations Report 02-4245, 26 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. 244-252.

Huntington, T. G., Hodgkins, G. A., and 

Dudley, R. W., 2003, Historical trend 

in river ice thickness and coherence in 

hydroclimatological trends in Maine: 

Climatic Change, v. 61, p. 217-236.

Intergovernmental Panel on Climate 

Change, 2001, Climate Change 2001, 

The Scientific Basis: Cambridge University Press, Cambridge, 881 p.

Walther, G.-P., Post, E., Convey, P., Menzel, A., Parmesan, C., Beebee, T. J. C., 

Fromentin, J. -M., Hoegh-Guldberg, 

O., and Bairlein, F., 2002, Ecological 

responses to recent climate change: 

Nature, v. 416, p. 389-395.

—By Thomas G. Huntington, Glenn A. 

Hodgkins and Robert W. Dudley

For more information please contact:

District Chief

U.S. Geological Survey

196 Whitten Road

Augusta, Maine 04330

Telephone: (207) 622-8201

Email: dc_me@usgs.gov

Website: http://me.water.usgs.gov Figure 2. Historical trend in winter air temperature and smoothed line showing the 

average of seven U.S. Historical Climatology network stations in Maine.

Figure 1. Historical trend in ice thickness and smoothed line measured on 28 February 

(+/-14 days) on the Piscataquis River near Dover Foxcroft.