Water—the Nation’s Fundamental Climate Issue

A White Paper on the U.S. Geological Survey Role and Capabilities

Circular 1347

U.S. Department of the Interior

U.S. Geological Survey
Water—the Nation’s Fundamental Climate Issue

A White Paper on the U.S. Geological Survey Role and Capabilities

By Harry F. Lins, Robert M. Hirsch, and Julie Kiang

Circular 1347

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Lins, Harry F., Hirsch, Robert M., and Kiang, Julie, 2010, Water—the Nation’s Fundamental Climate Issue: A White 

Paper on the U.S. Geological Survey Role and Capabilities: U.S. Geological Survey Circular 1347, 9 p., available at 

http://pubs.usgs.gov/circ/1347.
 iii

Contents

Introduction.....................................................................................................................................................1

Understanding Climate and Water..............................................................................................................2

Climate-Sensitive Hydrologic Data....................................................................................................2

Climate-Directed Hydrologic Analyses.............................................................................................2

Water Budget ...............................................................................................................................4

Seasonal Streamflow..................................................................................................................4

Low-Flow Characteristics ..........................................................................................................5

Flood and High-Flow Characteristics .......................................................................................5

Geographical Design.....................................................................................................................................7

References Cited............................................................................................................................................7

Appendix 1. List of Abbreviations................................................................................................................9

Figures

1. Relation of annual runoff to precipitation and temperature ..................................................3

2. Number of streamgaging stations with statistically significant (p ≤ 0.05)

increasing and decreasing trends in annual minimum daily streamflow......................5

3. Annual peak discharges, at the USGS streamgage, Red River of the

North, Grand Forks, North Dakota, 1882 through 2009......................................................6

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square

mile [(ft3

/s)/mi2]

 0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

cubic foot per day (ft3

/d) 0.02832 cubic meter per day (m3/d)

inch per hour (in/h) 0 .0254 meter per hour (m/h)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

mile per hour (mi/h) 1.609 kilometer per hour (km/h) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Conversion Factors
Introduction

Of all the potential threats posed by climatic variability 

and change, those associated with water resources are arguably 

the most consequential for both society and the environment 

(Waggoner, 1990). Climatic effects on agriculture, aquatic 

ecosystems, energy, and industry are strongly influenced by 

climatic effects on water. Thus, understanding changes in the 

distribution, quantity and quality of, and demand for water in 

response to climate variability and change is essential to planning for and adapting to future climatic conditions. A central 

role of the U.S. Geological Survey (USGS) with respect 

to climate is to document environmental changes currently 

underway and to develop improved capabilities to predict 

future changes. Indeed, a centerpiece of the USGS role is a 

new Climate Effects Network of monitoring sites. Measuring the climatic effects on water is an essential component of 

such a network (along with corresponding effects on terrestrial 

ecosystems).

The USGS needs to be unambiguous in communicating with its customers and stakeholders, and with officials at 

the Department of the Interior, that although modeling future 

impacts of climate change is important, there is no more 

critical role for the USGS in climate change science than that 

of measuring and describing the changes that are currently 

underway. One of the best statements of that mission comes 

from a short paper by Ralph Keeling (2008) that describes the 

inspiration and the challenges faced by David Keeling in operating the all-important Mauna Loa Observatory over a period 

of more than four decades. Ralph Keeling stated: “The only 

way to figure out what is happening to our planet is to measure 

it, and this means tracking changes decade after decade and 

poring over the records.”

There are three key ideas that are important to the USGS 

in the above-mentioned sentence. First, to understand what is 

happening requires measurement. While models are a tool for 

learning and testing our understanding, they are not a substitute for observations. The second key idea is that measurement 

needs to be done over a period of many decades. When viewing hydrologic records over time scales of a few years to a few 

decades, trends commonly appear. However, when viewed 

in the context of many decades to centuries, these short-term 

trends are recognized as being part of much longer term oscillations. Thus, while we might want to initiate monitoring of 

important aspects of our natural resources, the data that will 

prove to be most useful in the next few years are those records 

that already have long-term continuity. USGS streamflow and 

groundwater level data are excellent examples of such longterm records. These measured data span many decades, follow 

standard protocols for collection and quality assurance, and 

are stored in a database that provides access to the full period 

of record.

The third point from the Keeling quote relates to the 

notion of “poring over the records.” Important trends will 

not generally jump off the computer screen at us. Thoughtful analyses are required to get past a number of important 

but confounding influences in the record, such as the role of 

seasonal variation, changes in water management, or influences of quasi-periodic phenomena, such as El Niño-Southern 

Oscillation (ENSO) or the Pacific Decadal Oscillation (PDO). 

No organization is better situated to pore over the records than 

the USGS because USGS scientists know the data, qualityassure the data, understand the factors that influence the data, 

and have the ancillary information on the watersheds within 

which the data are collected.

To fulfill the USGS role in understanding climatic 

variability and change, we need to continually improve 

and strengthen two of our key capabilities: (1) preserving continuity of long-term water data collection and (2) 

analyzing and interpreting water data to determine how 

the Nation’s water resources are changing. 

Understanding change in water resources to date and predicting change into the future must be done in full recognition 

of the other factors that influence water availability, including 

changes in water use, land use, the design and operation of 

water infrastructure, and the depletion of groundwater. There 

is widespread debate about the relative importance of nonclimatic factors versus climatic factors in determining water 

conditions and characteristics over the coming decades (Lins 

and Stakhiv, 1998). Differentiating climatic from nonclimatic 

effects is, therefore, a critical component of any effective 

Water—the Nation’s Fundamental Climate Issue

A White Paper on the U.S. Geological Survey Role and Capabilities

By Harry F. Lins, Robert M. Hirsch, and Julie Kiang
2 Water—the Nation’s Fundamental Climate Issue

assessment of how climate has, is, and will affect the Nation’s 

water resources. Moreover, such assessments are critically 

dependent upon a quality-assured, spatially and temporally 

comprehensive water-resources database.

For more than 100 years, the USGS has been monitoring 

the Nation’s rivers and groundwater resources, and currently 

maintains the world’s most sophisticated information system 

of surface-water, groundwater, water-quality, and water-use 

data. The USGS is uniquely positioned to play a central role 

in providing both data and analyses to address the recently recognized increment of hydrologic uncertainty associated with 

climatic variability and change (Moss and Lins, 1989).

The USGS draws upon two decades of climate change 

research related to hydroclimatology—the study of hydrologic 

events and conditions within their climatologic context. USGS 

research provides an empirical basis for integrating the physical sources of variability in a hydrologic time series with the 

statistical properties of the varying driving force itself. This 

research also highlights several themes where our incomplete 

understanding of important hydrologic processes and conditions continues to serve as an impediment to the broader incorporation of climate change information in water-resources 

planning and design. Thus, expanding our understanding of 

these processes is key to developing improved capabilities for 

dealing with climate uncertainty in the field of water-resources 

planning and management.

Understanding Climate and Water

Climate affects all aspects of hydrology and water 

resources through the water budget. Among the more critical elements of this issue to the Nation are how climate is 

affecting low flows and drought, high flows and flooding, and 

the seasonality (timing) of streamflow. Each of these factors can only be meaningfully understood where there exists 

a spatially and temporally adequate record of high-quality 

hydrologic observations, such as those derived from the USGS 

streamgaging network.

Climate-Sensitive Hydrologic Data

Information on the flow of rivers is a national asset that 

safeguards lives and property and ensures adequate water 

resources for a healthy economy (Hirsch and Norris, 2001). 

As noted by the National Research Council (1999), “Streamflow data collected by the USGS ... form the cornerstone for 

national, regional, and local efforts ... by providing continued, 

up-to-date information about water conditions and understanding of hydrologic phenomena.” In this context, an important component of the USGS National Streamflow Information 

Program (NSIP) is to provide data that are minimally affected 

by human activities for the study of regional streamflow 

characteristics and assessments of trends due to factors such 

as changes in climate, land use, and water use. Within NSIP, 

the stations providing such data are referred to as sentinel 

watersheds, and most are derived from the existing USGS 

Hydro-Climatic Data Network (HCDN). Sentinel watersheds 

also include the 36 discharge-monitoring stations of the USGS 

Hydrologic Benchmark Network (HBN).

HCDN stations were identified to provide a unique 

database of high-quality, climate-sensitive observations, specifically for evaluating climatic effects on streamflow (Slack 

and Landwehr, 1992). For nearly two decades, the observations from these stations have been the principal data used 

by researchers worldwide in studies of United States hydroclimatic patterns, variations, and trends. The criteria used to 

identify these stations have been adopted by hydrological 

services in other countries and, more recently, by the World 

Meteorological Organization’s Commission for Hydrology as 

part of its efforts to establish a global climate-sensitive streamflow database [World Meteorological Organization (WMO), 

2004]. When established in 1992, the HCDN consisted of 

1,659 stations. Over time, many of these stations have been 

discontinued and there are numerous gaps in the geographical distribution of stations, particularly in the western United 

States and at higher elevations. An effort is currently underway to update the listing of HCDN stations using a predictive 

model of climate-sensitive watershed conditions based on 

hydrological alteration criteria (Carlisle and others, 2009).

The Hydrologic Benchmark Network (HBN) was 

established in 1963 to provide long-term measurements of 

streamflow and water quality in areas that are minimally 

affected by human activities. These data are used to study 

long-term trends in surface-water flow and water chemistry 

and as a benchmark against which to identify changes in flow 

and chemistry in developed watersheds (Murdoch and others, 

2005). HBN, HCDN, and the corresponding NSIP sentinel 

watersheds are, therefore, logical and essential elements of the 

incipient USGS Climate Effects Network.

Climate-Directed Hydrologic Analyses

The effect of climate (particularly precipitation and 

temperature) on hydrology (particularly streamflow) has been 

a focus of research among USGS hydrologists for six decades. 

The classic hydroclimatic study by Langbein and others (Geological Survey Circular 52, 1949) graphically related mean 

annual runoff in the United States to mean annual precipitation and temperature, and was a standard reference used in 

water balance work through the 1980s (fig. 1). Some of this 

reference’s more enduring aspects were its illustration of (1) 

how runoff, for a given annual precipitation, decreases as 

temperature increases; (2) how runoff, for a given temperature, 

increases with precipitation; and (3) how the numerical difference between precipitation and runoff, for a given temperature, increases with precipitation and ultimately reaches a 

constant representing the limiting rate of evapotranspiration. 

This work served as the basis for many early climate change, 

water-resources impact studies during the 1980s and early 
Understanding Climate and Water 3

1990s, when the emphasis shifted to studying such interactions 

using numerical models.

During the past 15 years, studies of climate change 

impacts on water have increasingly made use of general 

circulation model (GCM) simulations of future climate states 

[Intergovernmental Panel on Climate Change (IPCC), 1995, 

2001, 2007]. Most such studies use model-simulated temperature and precipitation to draw inferences about water-related 

impacts. As most projected climate change effects related to 

water resources (for example, changes in flooding, drought, 

and the seasonality of snowmelt-generated streamflow) are 

subgrid (local) scale processes, they are not resolved explicitly 

within the models. Rather, they are inferred from the changes 

in temperature and precipitation simulated for the grid cell surrounding the location of interest.

The temperature increases simulated by the models occur 

in response to rising concentrations of atmospheric carbon 

dioxide (CO2

) that, in turn, cause increases in both evaporation and precipitation. This increase in atmospheric heat and 

moisture is frequently referred to as indicating an “enhanced 

hydrological cycle.” Since being reported initially in the 

Second Assessment Report (Intergovernmental Panel on Climate Change (IPCC), 1995), the enhanced hydrological cycle 

has been cited generally as the explanation for why floods 

and droughts are expected to increase with increasing CO2

concentrations. Changes in the timing of snowmelt-generated 

streamflow are mentioned as resulting from increasing winter 

and spring temperatures, whereby mountain snows melt and 

resultant peak streamflows occur earlier in the year. Increasing 

spring and summer season temperatures lengthen the warm 

season and the amount of evaporation, and are expected to 

reduce further the water supply in lakes, reservoirs, and rivers 

by summer’s end.

Are these water-related impacts of CO2

-induced climate 

change already manifesting themselves within the United 

States? Answering this question is much more complicated 

than it may appear. Not all changes occurring in the climate 

system are the result of increased CO2 concentrations. Indeed, 

the extent to which observed climatic variations over the past 

three decades are the result of CO2

 emissions versus changes 

in natural factors (for example, El Niño-Southern Oscillation 

(ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), solar variations, etc.) is unknown. 

However, existing streamflow data provide the requisite 

empirical basis for understanding both short-term (seasonal to 

decadal) hydrologic variations and long-term (multidecadal 

to centennial) hydrologic trends, and for testing hypotheses 

regarding the hydrologic response to climate change. These 

same data also make it possible to differentiate hydrologic 

changes due to climate from those resulting from other 

important forcing factors, such as urbanization, groundwater 

development, dam building, changes in the area of irrigated 

agriculture, changes in the area of row-crop agriculture, and 

changes in water withdrawals or consumption.

The following four topical segments represent issues of 

critical concern to the Nation’s water-resources planning and 

MEAN ANNUAL PRECIPITATION, IN INCHES

60

55

50

45

40

35

30

25

20

15

MEAN ANNUAL RUNOFF, IN INCHES

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Parameter is weighted mean

annual temperatures, in

degrees Fahrenheit

30°

40°

50°

60°

70°

80°

Figure 1. Relation of annual runoff to precipitation and temperature. [Source: Langbein and others, 1949.]
4 Water—the Nation’s Fundamental Climate Issue

management communities, and have been highlighted as possibly being adversely impacted by simulated changes in climate. The USGS has conducted a number of studies on these 

issues during the past two decades (many of which are cited), 

but never in the context of a systematic or comprehensive 

program of investigations. As a result, substantive and crucial 

gaps remain in each issue area, particularly with respect to 

understanding operative climate forcing. Collectively, the 

contents of these topical segments constitute a unique program 

of hypothesis testing on key assumptions associated with 

climate change impacts on water resources. Critical questions 

and issues that the USGS proposes to address are highlighted 

in bold print.

Water Budget

Over time, changes in mean discharge can pose substantial problems, but can also pose opportunities for waterresources managers. Although the effect of climatic change on 

hydrologic extremes has tended to receive the most attention, 

Lins and Cohn (2003) analyzed the sensitivity of streamflow 

to changes in precipitation and found that the precipitation 

sensitivity of mean streamflow is much greater than that of 

flood flows. They also found that the greater the return period 

of the flood, the lower the precipitation sensitivity. This finding suggests that changes in climate are more likely to produce 

changes in the mean state of hydrological regimes than in 

hydrological extremes. From a water-resources planning and 

management perspective, therefore, the more crucial questions 

to answer may be associated with how to take advantage of 

opportunities posed by potential increases in mean discharge, 

as well as how to prepare appropriately for the threats posed 

by potential decreases in mean discharge.

 The following questions identify the types of information that USGS researchers need to provide to be of maximum 

value to water managers: Have multidecadal changes in 

mean discharge occurred and, if so, are these variations 

distinct from observed centennial changes? Have changes 

occurred in the relation of annual or seasonal discharge to 

annual or seasonal precipitation? To date, few studies have 

attempted to document such changes, and those that have, generally have done so at scales not appropriate for resource planning and design purposes. There are 352 hydrologic accounting units in the United States, and not only are these units the 

basis for managing NSIP, they are the basis for planning and 

managing the Nation’s water-resources infrastructure as well. 

Thus, answers to the above two questions need to be sought 

at the hydrologic-accounting unit level.

Seasonal Streamflow

Water-resources systems are designed and managed in 

consideration of the prevailing seasonal characteristics of 

precipitation, both the amount and type, and their effect on 

seasonal streamflow. In most water-resources regions of the 

United States, streamflow decreases to its minimum value in 

September, coincident with the end of the water year.1 Exceptions are the Souris-Red-Rainy and Upper Colorado waterresource regions where snow and river ice in mid-winter cause 

the annual minimum to occur in February (Lins and Slack, 

2005). Maximum streamflow is more temporally variable, 

occurring over the 5-month period from February (California water-resource region) to June (Missouri water-resource 

region), and generally reflects the timing of snowmelt and (or) 

the month of maximum rainfall.

Concern has been raised that in a scenario where the 

climate is warmer than today’s climate, reservoir contents in 

regions where streamflows are primarily snowmelt driven, 

rather than rainfall driven, could be reduced earlier in the 

summer than at present, leading to reduced water availability during the season of peak water demand. This reduction 

in availability would result from a combination of increased 

evaporation and transpiration from warmer temperatures and a 

lengthening of the warm season, as well as increased irrigation demand. Moreover, several recent studies have shown 

that in mountainous areas of the Western United States and 

in northern New England, the midpoint in the total volume of 

streamflow for the first 6 months of the calendar year appears 

to be occurring 1 to 3 weeks earlier than in the past (Dettinger 

and Cayan, 1995; McCabe and Clark, 2005; Stewart and others, 2005; Hodgkins and Dudley, 2006); however, no reduction 

in summer season flows has been observed (Lins and Slack, 

2005).

Tracking and understanding the reasons for such shifts 

are important because of the impact they can have on waterresources and aquatic ecosystems management. For example, 

reservoir rule curves, which were developed using streamflow 

observations from decades ago, may need to be modified to 

ensure the maintenance of adequate municipal and agricultural 

water supplies, in-stream flow for aquatic ecosystems, or to 

provide flood protection. Despite the insights gained from 

recent USGS research, numerous questions remain. Are the 

shifts that are currently taking place important to water 

management (water supply, flood mitigation, and aquatic 

ecosystem integrity)? If not, why not, and how long would 

a shift have to continue before it becomes important to 

these kinds of issues? Although climate change has been 

implicated as the likely cause for the observed hydrologic 

changes, to what extent could multidecadal climatic-oceanic oscillations or changes in groundwater development 

or water use be responsible for these observed changes?

Being able to differentiate and quantify the water-resources 

response to both climatic and nonclimatic drivers of hydrologic change is critical for any effective program of adaptive 

water management.

1

 The 12-month period from October through September. The water year is 

designated by the calendar year in which it ends and which includes 9 of the 

12 months. For example, the year ending September 30, 1992, is called the 

“1992 water year.”
Understanding Climate and Water 5

Low-Flow Characteristics

The characteristics of low flows in rivers and streams are 

important metrics for water managers who must meet a growing number of water-supply requirements, particularly when 

low flows persist over an extended period as during drought. 

Low flows are also critical for managing water quality where 

pollutant concentrations must be maintained below regulatory 

thresholds required by the Clean Water Act. Low flows, which 

regularly occur during late summer in most of the United 

States, can be affected by changes in precipitation, evapotranspiration, and, in snow-melt dominated areas, by shifts 

in seasonality (that is, late winter and spring temperatures). 

Annual low flows are distinct from drought flows primarily 

in terms of their temporal duration and magnitude. The IPCC 

(1995, 2001, 2007) model simulations indicate drying in 

midcontinental areas during the summer and the possibility of 

more severe droughts. However, empirical studies of trends in 

low flows have not shown evidence of a general decrease in 

low flows (Svensson and others, 2005). Indeed, several studies 

have found substantial increases in low flows in the United 

States over the past half century (Lins and Slack, 1999; 2005; 

McCabe and Wolock, 2002; fig. 2).

Explaining variations and changes in low streamflow is 

complicated by the fact that low flows are sensitive to nonclimatic factors, particularly to manmade water storage, water 

use, and groundwater depletion. The following research questions are critical to gaining additional insight into how and to 

what extent climate is affecting low flows: Is there a pattern 

of change in 1-day, 7-day, 14-day, or 28-day low flows? Are 

we seeing an unexpected number of new record low flows 

(more than expected or less than expected by chance)? If 

low flows are changing, what are the relative influences 

of changing water use, groundwater depletion, reservoir 

storage, or intrabasin transfers on low flows? To what 

extent is it possible to predict regional low flows seasonally 

and annually based on North Atlantic and North Pacific 

sea-surface temperatures as hypothesized by McCabe and 

others (2004)?

Flood and High-Flow Characteristics

Floods are the most costly natural hazard in the United 

States, causing an average of 140 fatalities and $5 billion in 

damages each year (O’Connor and Costa, 2003). Any change 

in the factors that affect flood hazards can, therefore, dramatically impact the Nation’s social and economic well-being. 

Increased urban and suburban development on flood plains 

has, for example, substantially increased the mortality and 

economic losses from floods (Pielke and Downton, 2000). 

Moreover, as noted earlier, climate model simulations have 

been interpreted as indicating that more and larger floods will 

occur in response to a warming-induced, enhanced hydrological cycle. To date, numerous studies of annual maximum (daily mean) streamflow have found no evidence of an 

increasing trend in high streamflow (Lins and Slack, 1999; 

2005; McCabe and Wolock, 2002; Douglas and others, 2000; 

and Kundzewicz and others, 2005). One study, using different data (annual maximum based on monthly mean streamflow) and methods, reported an increase in the frequency of 

floods having an exceedance probability <0.01 during the 

20th century (Milly and others, 2002). A concern associated 

with all of these studies, however, is that annual maximum 

streamflow records include many observations that are not 

true (out-of-bank) floods. A more representative dataset for 

Number

of Stations

Number

of Stations

Number of Increasing Trends

BEGINNING YEAR

1940 1960 1980 2000

2000

1980

1960

1940

ENDING YEAR

180

140

100

60

20

Number of Decreasing Trends

BEGINNING YEAR

1940 1960 1980 2000

2000

1980

1960

1940

ENDING YEAR

180

140

100

60

20

Figure 2. Number of streamgaging stations with statistically significant (p ≤ 0.05) increasing and decreasing trends in annual minimum 

daily streamflow for various periods at least 10 years in length during 1941 through 1999. [Source: McCabe and Wolock, 2002.]
6 Water—the Nation’s Fundamental Climate Issue

assessing flood trends is the USGS peak flow file, maintained 

within the USGS National Water Information System (NWIS) 

(http://nwis.waterdata.usgs.gov/usa/nwis/peak). Peak flow 

data represent the maximum instantaneous discharge of water 

passing a streamgage during each year; although it should be 

noted that in any given year, even these values may not necessarily represent a true (out-of-bank) flood as most streams do 

not experience flooding every year.

An example of a peak flow record is shown in figure 3 for 

the USGS streamgage on the Red River of the North at Grand 

Forks, North Dakota, for the period 1882–2009. The history 

of flooding at this site and others in the region is complex. 

The graph demonstrates the importance of having long-term 

flow records and carefully and thoroughly examining those 

records. For example, an analysis of this record for the period 

1930–2009 would conclude that there is a substantial upward 

trend in flood discharges that appears to continue to the present. An association between this trend and contemporaneous 

increases in greenhouse gas concentrations or land-use change 

would seem highly plausible if only this part of the record is 

considered. However, if the entire period of record is assessed, 

the conclusion is quite different. Considering the entire period, 

a more likely conclusion is that floods arise from at least two 

substantially different statistical populations. One population 

has very large annual peak discharges that prevailed in the 

years from 1882 to about 1900 and again after about 1942; the 

other population has much smaller peaks that occurred from 

about 1900 to 1942. Thus, in considering the entire period 

of record, it becomes apparent that very large floods were 

common well before the onset of large increases in greenhouse gases or extensive land modifications. In this case, the 

data strongly support persistence in climate states as the key 

mechanism for increased peak flows, rather than a human forcing of change.

One of the most important contributions that the USGS 

can make to understand better climatic variability and change 

is to explore the numerous streamflow records that have been 

collected over the past century, and in some instances longer, and examine flood flows, average flows, seasonal flows, 

and low flows. Critically, this exploration needs to include 

Figure 3. Annual peak discharges, at the USGS streamgage, Red River of the North, Grand Forks, North Dakota, 1882 through 2009. 

Figure also includes (in blue) a locally weighted smoothed estimate of the changes in the mean flood magnitude over the period of 

record.

1880 1900 1920 1940 1960 1980 2000

WATER YEAR

DISCHARGE, IN CUBIC FEET PER SECOND

0

50,000

100,000

150,000
References Cited 7

investigations of both the patterns of change and their relation 

to a wide range of potential driving variables, including such 

atmospheric, oceanic, and terrestrial features such as El Niño 

and the Pacific Decadal Oscillation, as well as greenhouse 

gas concentrations, and land-use changes in the basin. Waterresources managers and those responsible for flood-plain 

management and land-use decisions, are looking for answers 

to how streamflow is changing and where it may be headed in 

the future. Analysis of datasets, such as the example of annual 

peak flows from the Red River of the North, is of paramount 

importance in support of understanding the implications of 

climatic variability and change for water resources and waterrelated hazards.

Recently, the USGS implemented procedures for assessing the quality of its peak flow records, and for identifying and 

correcting errors in the records. An appropriate flood database 

now exists that can be used to help discern if a pattern of 

change in observed annual peak discharges has occurred. In 

particular, the questions of greatest interest include: Is there 

a pattern of change in annual flood peak discharges or 

flood volumes? Is there a change in the timing of annual 

peak discharges? Is there a change in the number of largest floods (as defined by exceedances of a particularly 

high threshold)? Are there an unexpected number of new 

record peaks (either more or less than would be expected 

by chance)? Can the role that dams play in changing 

high-flow characteristics be quantified? Can any observed 

changes in peak flows be related unambiguously to changes 

in climatic factors and (or) land-use factors?

Geographical Design

Obtaining answers to the questions highlighted in the 

previous section requires a mix of national and regional 

investigations. Hydroclimatic patterns and events across the 

United States are a response to highly varying, but geographically persistent, air-mass boundary conditions. Of particular 

regional interest is the mountainous West, the Northern Plains 

(Dakotas), and the Northeast, where snowpacks and seasonal 

river ice create enhanced hydroclimatic sensitivities that can 

presage critical water-resources variations and change. The 

gradient from the Continental Divide to just east of the 100th 

meridian is a highly engineered water-resources environment, with substantially different characteristics from north 

to south. A suite of comparative east-west transects across the 

High Plains would provide valuable insight into water balance 

and low-flow variations. Similarly, gradients from the Appalachians to the Atlantic Coastal Plain, the upper Midwest to 

the Northern Plains, north-south across the semiarid to arid 

Intermountain West, and the hurricane-prone areas from Texas 

to New England each have unique climate-driven waterresources issues that vary considerably from year to year, and 

where documentation of longer term variations and changes is 

critical to ensuring the reliability of the Nation’s water supply. 

In addition to geographically focused studies, there also is a 

need for issue-oriented investigations that can capitalize on 

unique characteristics of particular river basins. Issues associated with basins having a large amount of storage in relation 

to flow, as in the Colorado River Basin; a high percentage of 

urbanization, such as in the Delaware River Basin; or a high 

percentage of agriculture or irrigated agriculture, such as in the 

Missouri River Basin, all pose situations that can be difficult 

to analyze yet be of enormous consequence to the Nation’s 

economy and resource security. In this regard, studies that 

focus on reference sites, such as the incipient USGS Climate 

Effects Network and the USGS Hydrologic Benchmark Network, are vital to identifying and differentiating climatically 

driven variations and trends from human-induced landscape 

effects.

In summary, the USGS is uniquely poised to make a 

major contribution to the understanding of the role that climatic variability and change can have on our Nation’s water 

resources and aquatic ecosystems. The key attributes that 

will enable the USGS to make that contribution are: (1) the 

ability to ensure the continued monitoring of a wide range of 

hydrologic systems (particularly those that already have long 

records and limited influences of man on the landscape); and 

(2) the capacity to substantially increase efforts to analyze 

existing records to understand changes that are taking place 

and to differentiate the relations of water resources to climate 

variation, climate change, and direct human activities on the 

landscape. “The only way to figure out what is happening to 

the planet is to measure it, and this means tracking changes 

decade after decade and poring over the records” (Keeling, 

2008). This statement should be the guiding principle by 

which the USGS Climate Effects Network is implemented.

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Appendix 1. List of Abbreviations 9

WMO (World Meteorological Organization), 2004, Commission for Hydrology, 12th Session: Abridged Final Report 

with Resolutions and Recommendations: WMO-No. 979, 

Geneva, 55 p.

Appendix 1. List of Abbreviations

AMO Atlantic Multidecadal Oscillation

CO2 carbon dioxide

ENSO El Niño-Southern Oscillation

GCM general circulation model

HBN USGS Hydrologic Benchmark Network

HCDN USGS Hydro-Climatic Data Network

IPCC Intergovernmental Panel on Climate Change

NSIP USGS National Streamflow Information 

Program

NWIS USGS National Water Information System

PDO Pacific Decadal Oscillation

USGS U.S. Geological Survey

WMO World Meteorological Organization
Manuscript approved for publication March 16, 2010.

Prepared by the Reston Publishing Service Center.

Edited by Marilyn A. Billone.

Design and layout by Patricia H. Packard.

For more information, please contact

Dr. Harry F. Lins, U.S. Geological Survey, 415 National Center,

Reston, VA 20192 hlins@usgs.gov.