1

Maggie Brooks

County Executive

COUNTY OF MONROE

STATE OF NEW YORK

Streams under drought (above) and flood (below) conditions.

Open-File Report 2008–1199

August 2008 

Prepared in cooperation with the Monroe County Department of Health

Hydrologic Evidence of Climate Change in 

Monroe County, New York

U.S. Department of the Interior

U.S. Geological Survey

I

ncreasing evidence of climate change has raised concerns that the predicted increases in air temperature and attendant changes 

in precipitation patterns will affect water resources around the world. An analysis of long-term meteorological and streamflow 

records can be used to identify trends that might be indicative of climate change, especially with respect to the magnitude and 

frequency of floods and droughts in western New York, including Monroe County. 

IN BRIEF . . . . 

 Long-term annual mean air temperatures have 

been increasing over the past 40 years, but 

not beyond the historical range as defined by 

temperatures that have been recorded since 1890.

 Annual precipitation totals in the Great Lakes 

Basin within the United States have increased by 

an average of 4.5 inches since 1915.

 The chance that daily precipitation will exceed 

2.0 inches has increased from once in 5 years 

prior to 1963 to nearly once every year since 

1992, and the chance that daily precipitation will 

exceed 2.5 inches has increased from once every 

20 years to almost once every 4 years.

 In urban streams, 7-day high flows and the 

frequency of peak flows are increasing, whereas 

base flows are decreasing.

 In rural streams, base flows and 7-day low flows 

are increasing, whereas 7-day high flows show no 

discernible trend.

 Discrepancies in flow characteristics between 

rural and urban streams are attributed to 

differences in the amounts of impervious areas in 

each basin type.

 Flow characteristics of the Genesee River are 

unique because regulation of the outflow from 

Mount Morris Lake moderates the extreme flows, 

both high and low, that might otherwise occur in 

this river.
2

EXPLANATION

Streamflow-monitoring site

and site number

Black

Creek

Oatka

Honeoye

Allen Creek

Irondequoit

Genesee

River

Creek

Creek

Creek

04229500

04230500

04231000

04232000

0423205010

04232050

Monroe County

Greater Rochester

International Airport

Lake Ontario

04232000

Monroe County

Wayne County

Ontario County

Livingston County 

Orleans County

Genesee County

Stream

County boundary

77°22'30"

43°22'30"

78°

43°22'30"

77°22'30"

43° 78°

43°

Rochester

East 

Rochester

Churchville

Scottsville

Honeoye Falls

Garbutt

0 5 10 MILES

0 5 10 KILOMETERS

NEW

YORK

LOCATION MAP

Monroe

County

Base from U.S. Geological Survey, Seamless Data Distribution System,

accessed in 2008 at http://seamless.usgs.gov, Universal Transverse

Mercator projection, Zone 18

Value of Long-Term Weather and 

Streamflow Records

The National Weather Service (NWS) has collected 

meteorological data in the Rochester, N.Y., area since at least 

1872 (National Oceanic and Atmospheric Administration, 

2007). The NWS station is currently at the Greater Rochester 

International Airport (fig. 1), and the data are available at the 

U.S. Historical Climatology Network (HCN) web site (Williams 

and others, 2007). This data set includes monthly average 

maximum, minimum, and mean air temperatures and total 

monthly precipitation at more than 1,200 sites throughout the 

contiguous United States. Stations are selected for inclusion in 

this network on the basis of length of record, completeness of 

record, number of station relocations, and other station changes 

that could affect the homogeneity of the data. The records are 

subjected to quality-control tests and are adjusted for biases or 

anomalies resulting from “suspect” and “outlier” values (those 

that exceed 3.5 and 5.0 standard deviations from the mean, 

respectively); they also are adjusted for time-of-observation 

differences, changes in and relocation of measurement 

instrumentation, station relocations, and the localized warming 

effects caused by urbanization (Williams and others, 2007).

Figure 1. Locations of streamflow-monitoring sites and streams in Monroe County, N.Y. (Site-identification 

number, drainage area, and period of record for each site are given in table 1.)
3

1860 1880 1900 1920 1940 1960 1980 2000 2020

ANNUAL PRECIPITATION, IN INCHES

15

20

25

30

35

40

45

50

Locally weighted smooth line

YEAR

1880 1900 1920 1940 1960 1980 2000 2020

TEMPERATURE, IN DEGREES FAHRENHEIT

42

43

44

45

46

47

48

49

50

Locally weighted smooth line

1860

YEAR

Annual mean air temperatures in Monroe County have 

fluctuated as much as 8 degrees Fahrenheit from 1890 through 

2005, according to data from Williams and others (2007). The 

apparent increase in temperature over the past 4 decades is 

within the historical range of temperatures shown in figure 2. 

Unlike the air-temperature records, the records of annual 

precipitation at Rochester from 1872 through 2005 (Williams 

and others, 2007) indicate an upward trend since about 1950 

that currently exceeds historic levels (fig. 3). This trend has 

been verified through an analysis of annual mean precipitation 

records collected at 34 HCN stations across the Great Lakes 

Basin within the United States, including western New York, 

from 1915 through 2004 that indicates a 4.5-inch increase in 

annual precipitation during that 90-year period (Hodgkins and 

others, 2007).

Rainfall quantity or intensity during individual storms 

may be a more informative indicator of changes in precipitation 

patterns, and the effects of such changes, than total annual 

precipitation. Short-term extreme events are the most likely to 

produce large, potentially destructive flows. A comparison of the 

upward trend in annual precipitation from 1948 through 1963 

with that from 1992 through 2007 indicates that (1) the average 

number of days per year on which precipitation exceeded 

0.5 inch has increased from 16 to 22; (2) the chance that daily 

precipitation will exceed 2.0 inches has increased from once 

in 5 years to nearly once every year; and (3) the occurrence of 

daily precipitation in excess of 2.5 inches has increased from 

once every 20 years to about once every 4 years. These apparent 

increases in the frequency of large precipitation quantities could 

contribute to larger peak stormflows than have occurred in 

the past.

Figure 2. Annual mean of monthly mean air 

temperatures at the National Weather Service 

meteorological station, Rochester, N.Y., 1890–2005. 

(Based on data from Williams and others, 2007) 

(The locally weighted smooth line in figure 2 and 

the similar scatterplots that follow highlight the 

central tendency of the data.)

Figure 3. Annual precipitation measured at the 

National Weather Service meteorological station, 

Rochester, N.Y., 1872–2005. (Based on data from 

Williams and others, 2007)
4

Table 1. Streamflow-monitoring sites in Monroe County, N.Y.

[USGS, U.S. Geological Survey; mi2, square miles. Locations are shown in fig. 1]

USGS 

site-identification

number

Site name Drainage area

(mi2) Period of record

04229500 Honeoye Creek at Honeoye Falls 196 1945–70; 1972–2007

04230500 Oatka Creek at Garbutt 200 1945–2007

04231000 Black Creek at Churchville 130 1945–2007

04232000 Genesee River at Rochester 2,467 1902–2007

04232050 Allen Creek near Rochester 30.1 1959–2007

0423205010 Irondequoit Creek above Blossom Road, Rochester 142 1980–2007

Possible Effects of an Increase 

in Precipitation

The possible effects of the apparent recent increase in 

precipitation on the water resources of the county have not been 

defined. The U.S. Geological Survey, in cooperation with the 

Monroe County Department of Health, however, has monitored 

streamflow and water quality in many streams in Monroe County 

for several decades. Six of these streams—Honeoye, Oatka, 

Black, Allen, and Irondequoit Creeks, and Genesee River (fig. 1; 

table 1)—have been monitored for periods ranging from 26 years 

(Irondequoit Creek) to more than 75 years (Genesee River).

Long-term streamflow records can reveal changes and 

trends that cannot be identified in records that cover shorter 

periods of time. Streamflow characteristics that can best be 

defined from long-term records are the magnitude and frequency 

of peak flows, the percentage of total streamflow that represents 

base flow (the ground-water component of streamflow), and 

the duration of low and high flows (the percentage of time that 

flow in a stream is likely to equal or exceed some specified 

value). Trends in these characteristics for the six streams 

and their relation to climate change in Monroe County are 

discussed below.

Magnitude and Frequency of Peak Flows

Flooding in Monroe County is not new, but whether the 

magnitudes of peak flows are increasing, or whether floods are 

occurring more frequently than in the past, can be determined 

through an examination of peak-flow records. Because not all 

apparent increases in the magnitude and frequency of peak 

flows can be attributed to climate change, these records must 

be scrutinized to identify anomalies and their causes. For 

example, urbanization of a watershed can affect peak flows. 

The magnitude of peak flows and the damages associated with 

flooding typically are greatest in urbanized areas, especially 

where floodplains have been developed. Regulation of 

streamflow also can affect long-term peak-flow records. Past 

flooding on the lower Genesee River, such as the historic floods 

of 1865, 1916, and 1942, is unlikely to recur because the Mount 

Morris Dam, constructed on the river near Mount Morris, N.Y., 

in 1951, provides flood protection for downstream communities.

The floods of 1960 and 1974 on Allen Creek and numerous 

floods during the past decade on Allen and Irondequoit Creeks 

are examples of regional flood events that caused extensive 

damage to property in the developed areas of the county. 

Evidence of increased flooding can be seen in the peak-flow 

records of these two streams. During 1998–2006, Irondequoit 

Creek had eight peak flows that exceeded 1,800 ft3/s (cubic 

feet per second), each of which exceeded the highest flow 

recorded during the previous 16 years (fig. 4). Peak flows on 

Allen Creek, which has a smaller, more developed drainage 

basin than Irondequoit Creek, also seem to be occurring more 

frequently than in the past (fig. 5). Although the number of 

peak flows exceeding 900 ft3/s on Allen Creek during the last 

20 years (1986–2006) is equal to the number that occurred 

during 1960–80 (14 peak flows), only three of those flows 

exceeded 1,300 ft3/s during the earlier period, whereas seven 

flows equaled or exceeded that rate during the later period. 

These apparent increases in the magnitude and frequency of 

floods on Irondequoit and Allen Creeks in the last 20 years can 

be attributed partly to the increase in impervious area (roads, 

parking lots, and buildings) that has accompanied development 

in each basin, but an increase in the frequency of storms 

that produce large amounts of precipitation also could be a 

major factor.
5

0

900

1,800

2,700

3,600

1982.03.141984.05.291987.11.291991.03.041992.08.281994.03.221996.05.121998.07.092000.06.132004.09.092006.07.12

DATE (YEAR.MONTH.DAY)

DISCHARGE, IN CUBIC FEET PER SECOND

100

500

900

1,300

1,700

2,100

2,500

2,900

3,300

1960.03.301967.11.231970.04.021973.03.041976.05.201978.09.181981.02.231984.05.291987.11.291992.03.271996.01.191999.01.242003.03.212004.12.102006.07.28

DATE (YEAR.MONTH.DAY)

DISCHARGE, IN CUBIC FEET PER SECOND

Figure 4. Annual peak flows and secondary peaks greater than 900 cubic feet per second on Irondequoit Creek above 

Blossom Road, Rochester, N.Y., 1982–2007.

Figure 5. Annual peak flows and secondary peaks greater than 450 cubic feet per second on Allen Creek near Rochester, N.Y., 

1960–2007.
6

Streamflow Separation

Streamflow can be separated 

into its two flow components—

base flow and storm runoff—by 

several methods, each of which 

systematically draws connecting 

lines between the low points 

of the streamflow hydrograph 

(Sloto and Crouse, 1996). The 

local-minimum method, which 

often is used to identify these 

low points, can be visualized 

as connecting the lowest points 

on the hydrograph with straight 

lines, as illustrated (right). Base 

flow values for each day between 

the selected local minimums are 

estimated by linear interpolation. 

0

50

100

150

200

250

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

BASE FLOW

STORM

RUNOFF

DAY

STREAMFLOW, IN CUBIC FEET PER SECOND

Base Flow and Stormflow

Streams in the northeastern United States continue to flow 

even during prolonged periods of dry weather. The explanation 

for this phenomenon lies in the relation between surface runoff 

and ground water. Water in the soil and bedrock over which 

streams flow slowly makes its way from underground storage 

in pores and fractures into surface-water channels. This groundwater contribution to surface flow, which is called base flow, 

occurs all the time, but can be obscured by streamflow’s other 

major component, storm runoff. As the term implies, storm 

runoff results from precipitation and snowmelt that flows 

overland or through stormwater-drainage systems into stream 

channels. Storm runoff creates high water levels and turbid 

conditions in a stream; base flow is characterized by clear water 

flowing in streams during long, dry periods. Computerized 

streamflow-separation techniques (such as the program of 

Sloto and Crouse, 1996) can be used to separate the base-flow 

component from the stormflow component in a streamflow 

record and provide another streamflow characteristic that can be 

analyzed to further assess evidence of climate change in western 

New York.

Most of the flow in streams in western New York, on an 

annual basis, consists of base flow despite the large volume of 

storm runoff that can be carried downstream during major floods. 

Streamflows in three rural streams in Monroe County—Oatka, 

Black, and Honeoye Creeks (fig. 1)—have been monitored since 

1945. The flows of Oatka and Black Creeks reflect undisturbed 

runoff processes, whereas those of Honeoye Creek are affected 

by withdrawals for water supply and regulation of outflows from 

Hemlock and Canadice Lakes. Nevertheless, base flow appears 

to have been increasing in all three creeks during their respective 

60-year periods of record, although the percentage of flow that 

consists of base flow has remained relatively stable (figs. 6–8).

A striking difference between the 60-year trends for these 

three rural streams and that for Allen Creek, which drains an 

urbanized basin, can be seen by comparing figures 6 through 

8 with figure 9. Whereas the rural streams (figs. 6–8) show 

an upward trend in base flows, Allen Creek (fig. 9) shows a 

decrease since about 1980 and a steep downward trend in base 

flow as a percentage of total flow—a pattern not seen in the 

data from the rural streams. The differences between the urban 

site (Allen Creek) and the rural sites are even more pronounced 

when the periods of record of the rural streams are shortened to 

coincide with that of Allen Creek (1961–2005). The downward 

trend in the Allen Creek base flows presumably reflects this 

basin’s large amount of impervious area, which facilitates rapid 

runoff to storm sewers or nearby stream channels and inhibits 

infiltration of precipitation that would otherwise replenish the 

ground-water system. Thus, a decrease in ground-water storage 

due to urbanization is expressed as a decrease in base flow. A 

similar analysis of the Irondequoit Creek data, which cover a 

shorter period of record than the Allen Creek data, did not show 

any clear trends. 
7

1940 1950 1960 1970 1980 1990 2000 2010

BASE FLOW, IN CUBIC FEET PER SECOND

50

100

150

200

250

300

BASE FLOW AS PERCENT OF TOTAL FLOW

0

20

40

60

80

Base flow 

Base flow as percent of total flow

Locally weighted smooth line

YEAR

1940 1950 1960 1970 1980 1990 2000 2010

BASE FLOW, IN CUBIC FEET PER SECOND

20

40

60

80

100

120

140

160

BASE FLOW AS PERCENT OF TOTAL FLOW

0

20

40

60

80

Base flow

Base flow as percent of total flow

Locally weighted smooth line

YEAR

1940 1950 1960 1970 1980 1990 2000 2010

BASE FLOW, IN CUBIC FEET PER SECOND

0

30

60

90

120

150

180

BASE FLOW AS PERCENT OF TOTAL FLOW

0

20

40

60

80

Base flow 

Base flow as percent of total flow

Locally weighted smooth line

YEAR

0

10

20

30

40

50

Base flow 

Base flow as percent of total flow

Locally weighted smooth line

1940 1950 1960 1970 1980 1990 2000 2010

BASE FLOW, IN CUBIC FEET PER SECOND

BASE FLOW AS PERCENT OF TOTAL FLOW

0

20

40

60

80

YEAR

Figure 7. Annual mean base flow and base flow as a 

percentage of total flow, Black Creek, 1946–2005.

Figure 6. Annual mean base flow and base flow as a 

percentage of total flow, Oatka Creek, 1946–2005.

Figure 8. Annual mean base flow and base flow as a 

percentage of total flow, Honeoye Creek, 1946–2005.

Figure 9. Annual mean base flow and base flow as a 

percentage of total flow, Allen Creek, 1961–2005.
8

A

1940 1950 1960 1970 1980 1990 2000 2010

FLOW, IN CUBIC FEET PER SECOND

10

20

30

40

50

60

7-day low flow

Locally weighted smooth line

YEAR

B

1940 1950 1960 1970 1980 1990 2000 2010

FLOW, IN CUBIC FEET PER SECOND

0

500

1,000

1,500

2,000

2,500

3,000

3,500

7-day high flow 

Locally weighted smooth line

YEAR

Figure 10. Seven-day (A) low and (B) high flows, Oatka Creek, 1946–2005.

Seven-Day Low and High Flows

A streamflow statistic that is commonly used by 

hydrologists to describe low and high flows is the 7-day mean 

low or high flow—the minimum or maximum average daily 

mean flow for any 7-consecutive-day period in a given year. 

These 7-day flows can be more representative of a stream’s 

flow conditions than instantaneous or daily flow values. Given 

that base flow represents from 60 to 70 percent of the annual 

streamflow in Monroe County streams, the upward trends for the 

7-day low flows for the three rural streams (Oatka, Black, and 

Honeoye Creeks), which range from less than 1 ft3/s in Honeoye 

Creek to more than 10 ft3/s in Oatka Creek (figs. 10–12), are not 

surprising. A similar trend was reported for 27 streamflow sites 

throughout the Great Lakes Basin (within the United States) 

that are considered to be relatively free of human influences 

(Hodgkins and others, 2007). The plots in figures 10 and 11 

show no discernible trends in the 7-day high flows on Oatka or 

Black Creeks, but the plot for Honeoye Creek (fig. 12) shows a 

slight increase in the 7-day high flows. The periodic spikes in 

the 7-day low flows and the deviations in the trend lines of the 

data from Honeoye Creek compared with those from the other 

two streams presumably are a result of regulation of the outflows 

from Hemlock and Canadice Lakes to the creek. 

Unlike the 7-day low- and high-flow data shown for 

the two unregulated rural streams—Oatka and Black Creeks 

(figs. 10–11)—the data for the urbanized Allen Creek Basin 

show a downward trend in 7-day low flows and an upward trend 

in 7-day high flows (fig. 13). Like the difference between the 

base-flow data for Allen Creek (fig. 9) and those for the rural 

streams (figs. 6–8), the differences between the 7-day low- and 

high-flow trends for Allen Creek and those for the rural streams 

can be attributed to the large amount of impervious area in the 

Allen Creek Basin. No discernible trends were detected in 7-day 

low and high flows for Irondequoit Creek.

The trends identified here for the unregulated rural 

streams in Monroe County are consistent with results of a 

study of streamflow trends at 395 climate sensitive streamflow 

monitoring sites in the conterminous United States (Lins and 

Slack, 1999). That study identified (1) upward trends in annual 

minimum and median flows similar to those found for base 

flows and 7-day low flows in Monroe County, and (2) the 

absence of a predominant trend in high flows, similar to the 

absence of such a trend for the Monroe County 7-day high flow 

data. In addition, an analysis of streamflow data from 400 sites 

in the conterminous United States (McCabe and Wolock, 2002) 

concluded that the increase in low flows of streams in the eastern 

United States has not been gradual or continuous, but rather an 

abrupt step increase that occurred during the early 1970s. This 

step increase can be seen in the base flows for Oatka, Black, and 

Honeoye Creeks (figs. 6–8) and in the 7-day low flows for Oatka 

and Black Creeks (figs. 10–11).
9

A

1940 1950 1960 1970 1980 1990 2000 2010

FLOW, IN CUBIC FEET PER SECOND

0

2

4

6

8

10

12

14

16

7-day low flow 

Locally weighted smooth line

YEAR

B

1940 1950 1960 1970 1980 1990 2000 2010

FLOW, IN CUBIC FEET PER SECOND

0

500

1,000

1,500

2,000

2,500

7-day high flow

Locally weighted smooth line

YEAR

A

1940 1950 1960 1970 1980 1990 2000 2010

FLOW, IN CUBIC FEET PER SECOND

0

2

4

6

8

10

7-day low flow

Locally weighted smooth line

YEAR

B

1940 1950 1960 1970 1980 1990 2000 2010

FLOW, IN CUBIC FEET PER SECOND

0

500

1,000

1,500

2,000

2,500

3,000

7-day high flow 

Locally weighted smooth line

YEAR

FLOW, IN CUBIC FEET PER SECOND

0

2

4

6

8

10

12

14

16

18

7-day low flow 

Locally weighted smooth line

A

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

FLOW, IN CUBIC FEET PER SECOND

0

50

100

150

200

250

300

350

400

7-day high flow 

Locally weighted smooth line

B

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

Figure 11. Seven-day (A) low and (B) high flows, Black Creek, 1946–2005.

Figure 12. Seven-day (A) low and (B) high flows, Honeoye Creek, 1946–2005.

Figure 13. Seven-day (A) low and (B) high flows, Allen Creek, 1961–2005.
10

A

1920 1950 1980 2010

FLOW, IN CUBIC FEET PER SECOND

0

200

400

600

800

1,000

1,200

7-day low flow

Locally weighted smooth line

YEAR

B

1920 1950 1980 2010

FLOW, IN CUBIC FEET PER SECOND

5,000

10,000

15,000

20,000

25,000

30,000

7-day high flow

Locally weighted smooth line

YEAR

1920 1935 1950 1965 1980 1995 2010

BASE FLOW, IN CUBIC FEET PER SECOND

500

1,000

1,500

2,000

2,500

3,000

3,500

Base flow 

Locally weighted smooth line

YEAR

0

10,000

20,000

30,000

40,000

50,000

1902.03.031915.02.261925.02.251934.03.051943.01.011952.03.121961.04.261970.04.041979.03.061988.04.041997.03.272006.03.14

DATE (YEAR.MONTH.DAY)

DISCHARGE, IN CUBIC FEET PER SECOND

Mount Morris Dam 

completed in 1951

Figure 14. Seven-day (A) low and (B) high flows, Genesee River at Rochester, N.Y., 1920–2005.

Figure 16. Annual mean base flows on Genesee River at 

Rochester, N.Y., 1920–2005.

Figure 15. Peak flows on Genesee River at Rochester, N.Y., 

1902–2007.

Effects of Genesee River Regulation on 

Streamflow Characteristics

All previously discussed hydrologic characteristics of 

streams in Monroe County are applicable to the Genesee River, 

with one qualification: flow of the Genesee River has been 

regulated by the dam at Mount Morris since its completion in 

1951 and, to a lesser degree, by Rushford Lake in Allegany 

County and Conesus Lake in Livingston County. In contrast 

to the minor effects of regulation of outflow from Hemlock 

and Canadice Lakes on flows in Honeoye Creek, regulation 

of outflow from Mount Morris Lake has resulted in a marked 

decrease in both the 7-day low and high flows (fig. 14), as 

well as the number and magnitude of damaging floods in the 

Rochester area (fig. 15). The apparent increase in annual mean 

base flow in the Genesee River since 1920 (fig. 16) is consistent 

with that identified in other streams in Monroe County, but the 

upward trend downstream from Mount Morris Lake after 1951 

presumably reflects sustained flows from dam releases rather 

than any effect of climate change. 
11

For more information on the USGS--the 

Federal source for science about the 

Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names 

is for descriptive purposes only and 

does not imply endorsement by the 

U.S. Government.

For additional information write to:

New York Water Science Center

U.S. Geological Survey

30 Brown Rd.

Ithaca, N.Y. 14850

Information requests:

(518) 285-5602

or visit our Web site at:

http://ny.water.usgs.gov

Summary

The long-term annual mean air-temperature record from 

the National Weather Service station at the Rochester, N.Y., 

airport indicates an apparent increase over the past 4 decades; 

however, this increase does not differ substantially from the 

historical range of temperatures during the last century. Annual 

precipitation totals are increasing, and this increase is reflected 

in the peak flows of streams in urbanized basins and in the base 

flows and 7-day low flows of two rural, unregulated streams—

Oatka and Black Creeks—in Monroe County, N.Y. The 

magnitudes of recent peak flows, since about 1997, appear to be 

comparable to those of earlier peaks, but the frequency of peak 

flows appears to be increasing, at least in the urbanized basins. 

Base flows and 7-day low flows are increasing as expected 

from the increasing amounts of precipitation, yet 7-day high 

flows show no discernible trends. In contrast, streamflow in the 

urbanized Allen Creek Basin, the hydrology of which is affected 

by its large amount of impervious area, shows downward trends 

in base flow and in 7-day low flows, and an upward trend in 

7-day high flows. These differences between the urban and rural 

streams persist even when coincident periods of record are used 

in the analysis. Flow conditions in the Genesee River are unique 

because the regulation of outflow from Mount Morris Lake 

has decreased the number and magnitude of damaging floods 

downstream in the Rochester area and also has diminished the 

7-day low and high flows in that reach.

By William F. Coon

References Cited

Hodgkins, G.A., Dudley, R.W., and Aichele, S.S., 2007, 

Historical changes in precipitation and streamflow in the 

U.S. Great Lakes Basin, 1915–2004: U.S. Geological Survey 

Scientific Investigations Report 2007–5118, 31 p.

Lins, H.F., and Slack, J.R., 1999, Streamflow trends in the 

United States: Geophysical Research Letters, v. 26, no. 2, 

p. 227–230.

McCabe, G.J., and Wolock, D.M., 2002, A step increase in 

streamflow in the conterminous United States: Geophysical 

Research Letters, v. 29, no. 24, p. 38–1 to 38–4.

National Oceanic and Atmospheric Administration, 2007, 

National Climatic Data Center, accessed October 1, 2007, at 

http://www.ncdc.noaa.gov/oa/ncdc.html

Sloto, R.A., and Crouse, M.Y., 1996, HYSEP—A computer 

program for streamflow hydrograph separation and analysis: 

U.S. Geological Survey Water-Resources Investigations 

Report 96–4040, 46 p.

Williams, C.N., Jr., Menne, M.J., Vose, R.S., and Easterling, 

D.R., 2007, United States historical climatology network 

monthly temperature and precipitation data: Oak Ridge, 

Tenn., Carbon Dioxide Information Analysis Center, Oak 

Ridge National Laboratory, U.S. Department of Energy, 

ORNL/CDIAC–118, NDP–019, accessed October 10, 2007, at 

http://cdiac.ornl.gov/epubs/ndp/ushcn/usa_monthly.html
Water-level monitoring equipment 

at a U.S. Geological Survey 

streamflow-monitoring station.

Benefit of Long-Term Weather and Hydrologic Records

Climate ultimately affects every aspect of life on earth, including human health and well-being. Recent changes 

in climate have increased the frequency and intensity of floods, droughts, and wildfires, and also have resulted in 

increased crop failures, outbreaks of disease, and insect damage to crops and structures. The National Weather Service 

has maintained a long-term weather station at the Greater Rochester International Airport, while the U.S. Geological 

Survey (USGS), in cooperation with other Federal and State agencies and the Monroe County Department of Health, 

has operated a network of streamflow-monitoring sites in the County. The data from these sites can be analyzed to 

determine if and how the local weather is changing and how climate change might affect the local water resources. 

Analyses of the long-term precipitation and streamflow records indicate that Monroe County’s average annual 

precipitation is increasing, and that the amount of water flowing in local streams has increased accordingly. Despite 

this trend, drought remains an annual possibility. The observed changes in the amount, timing, and distribution of rain, 

snow, and runoff pose a challenge to the management of water resources, infrastructure, and services. Whether the 

identified seasonal and annual trends in streamflow will continue into the future or are merely short-term expressions of 

long-term natural cycles that will eventually reverse direction is unknown, but continued meteorological and streamflow 

monitoring is vital to the forecasting of future climatic conditions and their implications, and to the preparation of 

strategies to minimize the attendant risks to human life and damage to property and infrastructure.