U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005-3019

March 2005

Changes in Streamflow Timing in New England 

During the 20th Century

... from the National Streamflow Information Program

Printed on recycled paper

This Fact Sheet is one in a series that highlights information or recent research findings from the USGS 

National Streamflow Information Program (NSIP). The investigations and scientific results reported in this 

series require a nationally consistent streamgaging network with stable long-term monitoring sites and a 

rigorous program of data quality assurance, management, archiving, and synthesis. NSIP produces multipurpose, unbiased surface water information that is readily accessible to all.

Introduction

The amount, timing, and form 

of precipitation (rain, sleet, or 

snow) directly affect the amount 

and timing of runoff into riv- ers and streams, particularly in 

northern and mountainous areas. 

If air temperatures were to warm 

in the future, the warming could 

decrease the fraction of precipita- tion occurring as snow or speed 

the start of spring snowmelt caus- ing streamflow to occur earlier 

in the year with potential conse- quences for some aquatic life and 

human activities. Using longterm streamflow records from the 

U.S. Geological Survey (USGS) 

National Streamflow Information 

Program, it is possible to evaluate 

changes in the timing of stream- flow of New England streams. 

Streamflow Data

The USGS started measuring 

streamflow in the United States 

about 115 years ago. Today, 

USGS streamflow data are available for thousands of streamgages 

throughout the Nation (http://

waterdata.usgs.gov/usa/nwis/sw). 

Long-term, nationally consistent 

data-collection and reporting tech- niques increase the utility of these 

data for analysis of important 

local, regional, and national water 

issues, and make possible the con- fident analysis of historical data, 

including changes in the timing of 

seasonal streamflow (Hodgkins

High streamflow on the St. John River in northern Maine, spring 2003.

Both the magnitude and timing of streamflow can be affected 

by watershed urbanization and 

reservoir operations. A subset 

of the USGS streamflow database, the USGS Hydro-Climatic 

Data Network (HCDN) (Slack 

and Landwehr, 1992) excludes 

streamflow records in which the 

effects of substantial land-use 

changes or regulation are present, 

and contains streamflow data most 

appropriate for climate studies. Of 

the approximately 1,600 HCDN 

streamgages in the Nation, 76 

monitor rivers in New England. 

 In order to avoid the undue

influence of short-term fluctuations, relatively long streamflow 

records (on the order of 50+ years) 

are needed for climate studies, and 

to be relevant to current conditions, these records should extend 

to recent years. Of the 76 HCDN 

streamgages in New England, 27 

have 50 years or more of continuous record including the 50 

years from 1951 to 2000. These 

27 streamgages have an average 

period of record of 68 years and 

New England (fig. 1).

are well distributed throughout 

and others 2003).
Changes in Streamflow 

Timing

The measures of streamflow 

timing used for this study were 

the dates by which half of the total 

volume of water (center of volume) for winter/spring (January 1 

to May 31) and fall/winter (October 1 to December 31) seasons 

flowed past a streamgage. These 

measures were computed for every 

year of record at all 27 HCDN 

streamgages. 

Significant trends toward 

earlier winter/spring streamflow 

were evident in the data for all 11 

streamgages where snowmelt has 

the greatest effect on streamflow. 

These 11 streamgages measure 

flow from northern and moun- tainous areas in Maine and New 

Hampshire. Data from three of the 

remaining 16 streamgages in the 

Figure 1. Location of the 27 streamgaging stations used in this study and summary of 

trend-test results.

rest of New England also exhibited trends toward earlier winter/

spring streamflow. Data from 4 

of the 27 streamgages exhibited 

significant trends in the timing of 

fall/winter streamflow; these data 

also tended toward earlier streamflow.

Plots of the center-of-volume 

data indicate significant annual 

variability but also reveal more 

specific information about the 

trends. For example, the dates for 

the winter/spring streamflow at 

Piscataquis River in central Maine 

has varied by approximately 6 

weeks over the period of record 

(fig. 2), however since about 1970, 

the date has tended to occur earlier 

in the year and now occurs about 2 

weeks earlier than in 1970. Plots 

of moving-average trend lines for 

the 13 streamgages with the longest streamflow records also show 

similar, coherent patterns (fig. 3). 

While some trends toward increasing dates (later winter/spring 

streamflow) are evident at several 

streamgages prior to about 1970, 

far more substantial, consistent, 

and steeper trends toward decreasing dates (earlier streamflow) 

occur at the northern and mountainous stations after about 1970. 

Over the last 30 years, winter/

spring streamflows have become 

earlier by 1 to 2 weeks in northern 

and mountainous areas of New 

England. Changes in the timing 

of flows in southern New England 

are not as consistent. 

While the cause of the earlier 

streamflow is not fully known, the 

year-to-year variability in the tim- ing of winter/spring streamflow is 

strongly correlated to the year-toyear variability of March through 

April air temperatures and to a 

lesser extent, changes in January 

precipitation. Trends toward ear- lier streamflow in northern New 

England also are consistent with 

the findings of other studies of 

last-frost dates, lilac-bloom dates, 

lake-ice breakup dates, and spring 

air temperatures.

Changes in the timing of win- ter/spring streamflow in northern 

and mountainous parts of New 

England may have implications 

for some aquatic species and 

human activities. These changes 

may affect different life stages 

of aquatic organisms in streams 

and in coastal estuaries. Management of water-supply reservoirs 

may also need to adapt to changes 

in the arrival of spring snowmelt 

runoff. More research is needed 

to evaluate these changes. Both 

research and potential operational 

responses, however, will depend 

on the continued collection of 

streamflow data.
1900 1920 1940 1960 1980 2000

YEAR

DATE

Mar 11

Mar 21

Mar 31

Apr 10

Apr 20

Apr 30

May 10

Figure 2. Annual winter/spring center-of-volume dates for the Piscataquis River in central Maine, and a moving-average trend line through the dates.

Figure 3. Average winter/spring center-of-volume dates for the 13 HCDN streamgages in 

New England with the longest periods of record.

Rivers in northern and mountainous areas

Rivers in southern areas

1900 1920 1940 1960 1980 2000

DATE

Mar 11

Mar 21

Mar 31

Apr 10

Apr 20

Apr 30

May 10

YEAR

For additional information, contact:

Glenn A. Hodgkins

U.S. Geological Survey

196 Whitten Road

Augusta, ME

(207)622-8201 (ext. 121) or

gahodgki@usgs.gov

Robert W. Dudley

U.S. Geological Survey

196 Whitten Road

Augusta, ME

(207)622-8201 (ext. 115) or

rwdudley@usgs.gov

References

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, Vol. 278, p. 244-

252.

Slack, J.R., and Landwehr, J.M., 

1992, Hydro-climatic data 

network (HCDN): A U.S. 

Geological Survey Streamflow 

data set for the United States for 

the study of climatic variations, 

1874-1988: U.S. Geological 

Survey Open-File Report 92-

129, Reston, Virginia.