100

EXPLANATION

——1700— Line of equal climatic factor

200 MILES

100 200 KILOMETERS

Figure 7. Geographic variation of the climate factor for the 100-year-recurrence-interval
flood. The factor is the ratio of peak-flood discharge that has a probability of exceedance
of 1 percent in any given year to a mathematical description of the physical characteristics
of the drainage basin that could yield the flood; the mathematical description was derived
by regression techniques used on an exhaustive set of drainage characteristics and model

output. Source: Lichty and Liscum, 1978.

Stochastic Models

Because of the inherent imprecision in physically based
hydrologic models, a special class of models, known as
stochastic models, has been developed. Stochastic models
are based on principles of probability and statistics and can
be used to describe either hydrologic phenomena or the errors
that derive from physically based hydrologic models. The
uses of stochastic models are:

(1) To provide language in which assumptions may
be stated about observed time series (Parzen,
1962);

(2) To provide insight into the most realistic and/or
mathematically tractable assumptions to be made
concerning the stochastic processes that are
adopted as models for time series (Parzen, 1962);
and

14 Water Resources and Implications of Climate Uncertainty

(3) To provide a tool for obtaining approximate solu-
tions to the complex problems that arise in mak-
ing water-resources decisions (Moss and Tasker,
1987).

However, for stochastic modeling to remain a useful aspect
of hydrology in the 21st century, its language and
mathematical constructs must be expanded to describe
hydrologic processes that are changing in response to climate:
change.

A priority area for stochastic-modeling research deals
with disaggregation models, which develop statistically
representative data at scales of time and space that are finer
than those of the data that are available to drive the models.
The priority results from the mismatch between the relatively
large grid sizes of the current general circulation models and
the much smaller scales at which most hydrologic analyses


Much is currently known about many of the hydrologic
Processes, particularly as they function in the laboratory or
on small plots of land. The knowledge developed in the
laboratory and on small plots inherently is limited to the lower
end of both the spatial and temporal scales of interest in
hydrology and frequently is isolated from many of the factors
that may be relevant in the natural environments in which
the processes function.

Many of the questions concerning the hydrologic
implications of climate uncertainty cannot be addressed
adequately by improving process understanding at modest
scales. Therefore, the majority of the elements contained in
the fundamental research component of the program will be
oriented toward development of understanding the aggregate
of processes at work over reasonably large and diverse areas
of land—the scale problem (Dooge, 1982).

An example of a process that is reasonably well
understood at the small scale is the concept of infiltration,
which describes the passage of precipitated, ponded, or flow-
ing water from the surface of the Earth into its interior. Much
is known about infiltration from the laboratory or at small
field-plot scales (Dooge, 1982). Rates of infiltration depend
on the nature and water content of the soil or rock that
receives the infiltrated water, the chemical, physical, and
biological character of the source water, and in the case of
Precipitation, the rate at which water is supplied to the
surface. At many larger scales of interest—that is,
agricultural fields or larger areas—most of the factors that
control infiltration will vary significantly. Because of the
complexity of the relations among the controlling factors,
the knowledge of infiltration derived at small scales is
difficult to apply at large scales. This quandary is
compounded by the current inability to collect and interpret
sufficient quantities of precise and accurate data to describe
adequately the spatial variability of the controlling factors.
Thus, gaining more insight on infiltration over medium to
large areas is an essential.element of the program.

Another hydrologic process whose understanding is
impacted by scale is the reverse of infiltration, that is
evapotranspiration, which takes water out of the Earth and
the biosphere and returns it to the atmosphere. In most water-
balance studies, evapotranspiration is computed as the
residual after all other relevant flows and reservoirs have
been taken into account. There are two primary reasons that
it is treated so: (1) evapotranspiration is a highly nonlinear
function of the energy available to transform liquid water
to water vapor at the surface of the Earth or on a plant
surface, and (2) the energy balance on the land surface or
on a plant is highly variable both in space and in time. As
climate changes, the statistical characteristics of the energy
balance will change, as will the availability of water at land
surface. In response to significant shifts in water availability,
the local plant community also can be expected to change
(Eagleson and Segaria, 1985). Therefore, evapotranspiration

8 Water Resources and Implications of Climate Uncertainty

probably will be very sensitive to climate change. Of the
major water balance components, evapotranspiration is the
least documented. Unlike precipitation and runoff, evapo-
transpiration has not been measured systematically across
the Nation. Its character at various spatial and temporal scales
must be determined.

In many regions of the United States, ground water
is an abundant resource that has accumulated over long
periods of time. It is a resource that can be drawn upon at
rates that vary as functions of the volume of ground water
in storage and the rates at which it is replenished. The rate
at which ground water is replenished is known as aquifer
recharge and, to a first approximation, it is equal to the
difference between infiltration and evapotranspiration.
Because these processes are controlled by many interrelated
factors sensitive to scale, it follows that aquifer recharge must
be as well. For ground-water development to proceed in a
wise and measured fashion under climate uncertainty, the
process of aquifer recharge must be better understood.

As a first approximation, the difference between
precipitation and infiltration is surface runoff. Runoff is the
primary source of water for most floods producing serious
property damage and loss of life in the United States. As
a result of its direct linkage to infiltration, the processes
controlling the generation of surface runoff are poorly
understood at spatial scales larger than field plots. Thus, even
if climate change were not a significant issue, research on
the process of runoff from catchments and basins is an area
that warrants renewed support. The added uncertainty
attendant to climate change only serves to augment an existing
need for research on this phenomenon.

Another category of the hydrologic continuum requiring
process-oriented research is extreme hydrologic conditions.
The extremes of the hydrologic continuum, floods and
droughts, have been studied largely in statistical contexts.
Much of water-resource planning is based on the normal or
average conditions over some standard period of in-
strumented observations. Such an approach ignores the ques-
tion of how representative the available data may be of the
true expected conditions. This question is particularly rele-
vant for decisions that entail planning horizons that extend
20 to 100 years into the future.

Historically, water-resource systems have been designed
on the assumption that future climate conditions, hence
floods and droughts, would be similar to those observed in
the systematic record. This assumption, known as station-
arity, has long been controversial in hydrology. If significant
climate change occurs in the coming decades, it will
invalidate the stationarity assumption and force a change in
the procedures for estimating the occurrence of hydrologic
extremes; the 100-year flood of today will not be the same
as that of the mid-21st century. Importantly, the change will
not be attributable simply to a longer record of floods, as
is frequently the case today but, rather, to a shift in the


providing in-situ observations necessary for both sensor
calibration and verifying the interpretation of remotely sensed
data. An example of such support involves ongoing participa-
tion by the USGS in NASA’s First International Satellite
Land Surface Climatology Project Field Experiment at the
Konza Prairie Long Term Ecological Research Site in north-
eastern Kansas, which began in 1987 (Sellers and Hall, 1987,

written commun.). As part of the experiment, the Geological
Survey is operating three surface stations designed to measure
the flux of water vapor and sensible heat to the atmosphere.
These measurements are important to continuing efforts
oriented toward regional-scale estimation of microscale
processes, such as evapotranspiration, from remote-sensing
platforms (fig. 10).

SCALE AND SIMULTANEITY

Satellite 10 meters - 8 kilometers

Airborne flux 15 kilometers

Airborne radiometry
10 meters - 15 kilometers

Flux site
10 meters - 1 kilometer

Canopy, leaf physiology
1 centimeter - 10 meters

Figure 10. Range of scales addressed by the First International Satellite Land Surface
Climatology Project Field Experiment. Source: Brutsaert and other, 1988.

18 Water Resources and Implications of Climate Uncertainty


CONTENTS

Foreword Hl
Abstract 1
Introduction 1
Perspectives on climate, hydrology, and the U.S. Geological Survey 2
Climate variability, change, and uncertainty 2
The climate-hydrology continuum 4
The water-related mission of the U.S. Geological Survey 6
Elements of a program on the hydrologic implications of climate uncertainty 7
Research 7
Process-oriented research 7
Model-oriented research 12
Process models 12
Stochastic models 14
Data collection 15
Land-based data 15
Interface with remote sensing 17
Water-resources interpretive studies 19
Strategy for achieving the program goal 21
References 24

FIGURES

1. Graphs showing annual mean concentrations of atmospheric carbon dioxide
measured at the Mauna Loa Observatory and annual changes in mean
concentrations 3

2. Graph showing relation of annual runoff to precipitation and temperature 4

3. Map showing regions that exhibit a consistent precipitation response signal
to El Niffo-Southern Oscillation episodes 5

4. Graphs showing population growth in California; land under irrigation; water
storage capacity of reservoirs in the Sacramento and San Joaquin river basin;
and historic and projected export of water from the delta by the Federal Central
Valley and State water projects 10

5. Maps showing mean sea-level pressure (in millibars minus 1,000) and monthly
streamflow patterns for winters of 1976-77 and 1982-83 11

6. Characterization of how the spatial variability of a surface condition such as
soil moisture, which varies over a scale of meters, is generalized to a single
value through parameterization 13

7. Map showing geographic variation of the climate factor for the 100-year-
recurrence-interval flood 14

8. Map showing locations of U.S. Geological Survey benchmark stations 16

9. Histogram depicting the percentage of continuously operated stream gages
in 1987, by drainage area 17

10. Sketch depicting range of scales addressed by the First International
Satellite Land Surface Climatology Project field experiment 18


must be performed to meet the needs of water-resources deci-
sionmakers. For example, suppose that one wants to know
the impact of computed values of precipitation on the
likelihood of flooding in a small catchment contained within
the 5° grid of aGCM. Because the catchment is much smaller
than the GCM grid and because the response time of the
catchment is significantly smaller than the time step of the
GCM, the time series of precipitation values from the GCM
must be disaggregated in both time and space to extract the
desired information. Although disaggregation modeling in
the time dimension is relatively advanced at the current
time (Bras and Rodriguez-Iturbe, 1985, p. 147-154), little
progress has been made in the spatial dimension, and none
has occurred in the bidimensional domain of space and time.

Another crucial type of stochastic modeling research
involves data-network analysis and design. Most, if not all,
methodologies for the design of hydrologic-data networks
are based on statistical or stochastic descriptions of the
hydrologic phenomena to be monitored. Underlying most of
these methodologies is an assumption of stationarity of the
stochastic processes. It has been demonstrated in many
widespread, but isolated, settings that nonstationarities exist
in hydrologic records (Riggs, 1985). Nevertheless, most
hydrologic services continue to rely on stationarity assump-
tions in the allocation of their data-collection resources. The
potential for anthropogenic climate change has heightened
awareness of the disparity between underlying assumptions
and potential realities in the 21st century.

Moss (1986) presents an approach, dealing with data
collection in a regional or national framework, that pertains
to nonstationarity. However, this approach is in an early stage
of development.

As mentioned earlier, the large, but unknown, uncer-
tainty contained in all currently available climate-change
projections necessitates reliance on scenario analysis, which
is perhaps the most elemental, but still rational, strategy
for dealing with uncertainty. To progress beyond the use of
scenario analysis to a more effective strategy, the uncer-
tainties in climate projections must be quantified, and a
decisionmaking structure for coping with the resulting risks
must be elucidated. The theory for decisionmaking under
uncertainty exists (Raiffa, 1970), but the complex stochastic
nature of the inherent errors contained within the
hydroclimate models needs to be determined before the
theory can be brought to bear.

Data Collection

The collection of data is a universal requirement of
scientific endeavor. Until rather recently, hydrology has been
to a large degree an empirical science; data collection has
been the basis for most of its successes. In hydrology, as
with most other sciences, data are used in two general ways:
(1) the computation of statistics and (2) the calibration and

testing of models. These two categories of data use are not
distinct from each other, however. Often models are
calibrated by means of the statistics of relevant data, while
the computation of many statistics presumes an underlying
stochastic model for the data. Although not distinct, the
differentiation between statistical and modeling uses of data
is useful in describing the role of data collection in studying
the hydrologic implications of climate uncertainty.

Hydrologic-data collection for the computation of
statistics entails the quantification of spatial and temporal
hydrologic phenomena both on and beneath the Earth’s
surface. Monitoring of both the quantity and quality of
the Nation’s water resources for compliance with laws,
compacts, and treaties is a major aspect of this type of data
usage. Because the resources for data collection are not
unlimited, most traditional strategies for statistical data
collection have depended on one of two major approaches:
synoptic or temporal. Seldom are aspects of both significant
ina single strategy. Synoptic approaches rely on occasional
or periodic bursts of data at given times to define the spatial
distribution of the hydrologic phenomena of interest; a well
known synoptic data base from outside hydrologic science
is the decadal U.S. census. Temporal approaches, on the
other hand, rely on less spatial resolution through the
establishment of a network of sites at which the phenomena
of interest are measured continually, or nearly so, through
time. Because many of the needs for hydrologic informa-
tion are site specific, the hydrologic data-collection activities
of the U.S. Geological Survey generally have used temporal
strategies instead of synoptic ones.

Land-Based Data

An example of a temporal network that is relevant in
addressing questions of climate uncertainties is the U.S.
Geological Survey Benchmark Network, consisting of 57
sites at which streamflow and water quality have been
measured for almost 25 years (Cobb and Biesecker, 1971;
Lawrence, 1987). The locations of the benchmark sites are
shown in figure 8. As its name implies, this network was
established to provide the Nation with records of hydrologic
conditions at sites that would be affected minimally by human
activities on their drainage basins. Although the benchmark
concept did not explicitly anticipate the current concerns
about climate change, this network of sites is a critical
component of the data base that will be used to detect and
track climate influences on the Nation’s water resources.

For this purpose, the principal shortcomings of the
benchmark network are (1) the short length of records
currently available, (2) the limited number of sites at which
data are being collected, and (3) the limited suite of variables
that are being measured at each site. Obviously, the first
shortcoming is irreconcilable; one cannot go back in time
to redress it except rarely through paleohydrologic studies.

Data Collection 15


CLIMATE MODELING

EXISTING CONDITIONS

CLIMATE

WATERSHED MODELING

FUTURE SCENARIOS

SEA LEVEL ———>

EVAPOTRANSPIRATION — SOIL MOISTURE — SNOWMELT

RECHARGE

RUNOFF ~-———-> RESERVOIRS

i

GROUND-WATER MODELING

SALTWATER INTRUSION

GROUND-WATER AVAILABILITY

ESTUARY MODELING

<—__—_—_—_———— SALINITY DYNAMICS

SURFACE-WATER AVAILABILITY

L

Figure 12. Primary components of the Delaware River basin study.

STRATEGY FOR ACHIEVING THE
PROGRAM GOAL

The primary facet of a strategy for dealing with the
hydrologic implications of climate uncertainty is the evolu-
tion of the resource balance among the three components of
the program: (1) data collection, (2) research, and (3) inter-
pretive studies. The strategy must be an evolutionary one
because of the high degree of near-term uncertainty in the
climate variables that, along with gravity, drive the
hydrologic cycle. Information that reduces this uncertainty
must be monitored continually by the program administrators,
and, as the new information dictates, the program balance
should be modified to address more effectively the program
goal. In the early phases of the program, the necessity of
feedback of information to develop the short-term plan
dominates the planning process to the extent that long-term
plans can be viewed only in a statistical or probabilistic
context.

The planning process is based on the hypothesis that
a mature program will consist of a modest balance between

research and data collection that will continue to generate
new knowledge and information but that will have as its
major focus the synthesis and interpretation of the existing
knowledge and information across broad ranges of both
hydroclimatic settings and water-resources problems and
opportunities. This hypothesis dictates that a mature program
tends to evolve toward the lower-right quarter of the diagram
given in figure 134. As is shown in figure 13B, the water-
resources activities of the U.S. Geological Survey historically
have gravitated from a data-collection focus to a balance in
the 1980’s that has in excess of 50 percent of its funds
expended for interpretive studies. This traditional evolution
can be attributed to the prevailing assumption that natural
hydrologic processes are in statistical equilibrium at the time
scales of a century or so—stationarity. Under such an
assumption, it is efficient to expend relatively large sums
collecting and analyzing data that will serve as the basis for
projections of future water resources. As the data bases
expand, the marginal utility of the next increment of data
decreases (Moss, 1970), while the hydrologists’ abilities to

Strategy for Achieving the Program Goal 21


8S Rk 8 & 8 & SB

PERCENTAGE OF BASINS
a

10

5,000 250,000

DRAINAGE AREA, IN SQUARE MILES

Figure 9, The percentage of continuously operated stream gages in 1987, by drainage area.
Number of benchmark stations in each drainage area class appears in parentheses above

the respective bar.

it will be deployed as a basic component of the data
element.

As has been noted, there is a strong dependency
between the data and the research elements of the program.
In a mature stage of scientific development, a balance is
achieved in the feedback from one element to the other.
However, because of the major philosophical changes
required to deal with hydrologic implications of signifi-
cantly increased climate uncertainty, many research
components of the program will have to precede the data
components. Therefore, definition of major data components
(for example, ground-water levels or water-quality variables)
will have to evolve as research results are applied in the
interpretive studies.

Interface with Remote Sensing

The movement toward large-scale studies of the Earth,
with increasingly complex treatments of the interactions
among the atmosphere-land-ocean-biota system elements, is
generating a growing demand for a variety of high-quality
and high-density geophysical measurements. In many areas
of research, especially modeling, the data emanating from
existing networks are either inappropriate, geographically
insufficient, or both. Numerous applications now demand
near-continuous spatial data of high resolution (<1 km). To
meet these demands, investigators are making more extensive
use of remotely sensed data. Indeed, the various programs

of the National Aeronautics and Space Administration
(NASA), the National Science Foundation, and the National
Academy of Sciences encompassed under the rubric of Global
Change, all explicitly incorporate a requirement for a perma-
nent network of remote-sensing systems in orbit to
complement both existing and new ground-based data
networks.

There is a clear role and need for remotely sensed data
to support studies relating to climate and hydrology. Many
of the most significant problems in hydrology relate to
understanding the hydrologic cycle and its interactions with
the atmosphere, as well as with the biosphere and lithosphere.
Achieving such an understanding, for areas other than
homogeneous small-scale basins, requires a combination
of in-situ and remotely sensed (airborne and spaceborne)
measurements (National Research Council, 1985). The
remote measurements are essential for providing an inte-
gration, over broad spatial and temporal scales, of the in-situ
observations. Moreover, water, because of how and where
it occurs and the transformations it undergoes, is amenable
to detection in many parts of the electromagnetic spectrum.
This fact makes it a particularly appropriate quantity for
sensing by remote means.

Although U.S. Geological Survey scientists make
extensive use of remotely sensed data in numerous and
varied research activities, the agency is not responsible
for operating and maintaining a data-collection system based
on remote sensing. It supports such systems, however, by

Data Collection 17


of these associations and expanded hydroclimatic analysis
of regional patterns nationwide, and at monthly time scales,
offer potential for water-resource planning and assessment.

Water-quality aspects of the hydrologic continuum
form the final special topic of process-oriented research. In
recent years, water quality has received an increasing
emphasis within the hydrologic-research community.
However, little of that emphasis has been directed toward
the impacts on water quality of climate change. As improved
understanding of the potential for modified rates of
streamflow, ground-water recharge, and evapotranspiration
is developed, this new knowledge will shed light on con-
comitant changes in the concentrations and residence times
of various chemical and biological species that comprise
water quality.

Model-Oriented Research

Mathematical models are numerical representations of
real-world phenomena and the interactions among
phenomena. In hydrology such models are used to represent
the essence of existing, fundamental hydrologic knowledge
and to integrate that knowledge with the hydrologic and
related data that are available within an area of interest.
Hydrologic models are used as research tools, as descrip-
tive devices in interpretive water-resources studies, and as
planning and design instruments in water-resources decision-
making. Each usage is relevant in coping with climate
uncertainty. The proper utilization of hydrologic models for
any purpose requires that the characteristics and limitations
of the models be known and understood.

Hydrologic models are necessarily imperfect represent-
ations of the phenomena that they are constructed to mimic.
Inherent errors in the data derived from such models result
from (1) spatial and temporal scale limitations within the
models’ structures, (2) the imperfect state of the hydrologic
knowledge upon which they are based, (3) the simplifica-
tions required in reducing complicated phenomena to relative-
ly simple mathematical expressions, and (4) errors present
in the input data that drive the models.

As a point of clarification, model-oriented research is
distinct from model development. Modeling research
addresses the quantification of errors present in the model
output and the search to reduce those errors. In contrast,
model development deals with the initial construction of the
model and its incorporation into a modeling framework.
Components of the model-oriented research element of the
program appear in table 2.

Table 2. Components of model-oriented research

Model form Scale/type
Process..... General circulation.
Mesoscale.
Basin scale.
Stochastic... Disaggregation.
Risk.

Data-network analysis and
design.

12 Water Resources and Implications of Climate Uncertainty

Process Models

To address the full suite of hydrologic implications of
climate uncertainty, models that simulate hydrologic proc-
esses over a wide range of spatial scales are required. At
one end of the spectrum of spatial scale is a class of models
known as general circulation models, which are commonly
referred to as GCM’s and occasionally improperly are called
global climate models. GCM’s depict the circulation of mass
and energy in the atmosphere in three spatial dimensions,
on a global scale, and at varying levels of detail that include
components of oceanic and land-surface processes
(Washington and Parkinson, 1986). In general, attempts are
made in the model to represent all physical processes believed
to be important. The variables used to drive GCM’s include
components of the wind field or vorticity, temperature, and
water-vapor content. Typically, the data are aggregated into
cells of several degrees latitude and longitude around the
globe, and at 6 to 10 levels vertically through the lower
atmosphere. The stored quantities are then stepped forward
in time by applying the equations of motion and the first law
of thermodynamics, so that mass, energy, and momentum
are conserved. The equations also include terms describing
surface friction, radiative and latent heating, and other
physical processes.

One of the most crucial aspects of GCM’s involves the
mathematical description of the interactions between the
Earth’s surface and its atmosphere. Typically, the surface
fluxes of heat, momentum, and moisture are described using
bulk aerodynamic formulas. Land-surface temperature and
soil moisture are commonly calculated by equations
incorporating daily and seasonal heat and moisture storage
and their vertical fluxes. Significantly, although current
GCM’s are structurally complex and computationally
demanding even for the latest generation of supercomputers,
in many respects their representations of the physical proc-
esses and conditions at and immediately below the land
surface are exceedingly simple and inaccurate. Sensitivity
studies indicate that climatic simulations are very sensitive to
changing land-surface processes and properties, particularly
those of the hydrologic cycle.

A critical aspect of general circulation modeling
involves parameterizing the interactions between the surface
and the atmosphere. Parameterization refers to the expression
of the statistical effects of various small-scale (subgrid scale)
transport processes in terms of the large-scale (grid-
scale) variables explicitly resolved by the model (Global
Atmospheric Research Program, 1975). Because of the wide
range of scales of interacting atmospheric processes in rela-
tion to the limited spatial resolution of computational grids
and observation systems, it is technically and economically
impractical to observe or explicitly calculate the effects
of small-scale processes in detail. However. these subgrid
processes are significant, and it is important to relate their
statistical effects to measurable or computable conditions at
larger scales. Because the arbitrary specification of small-
scale effects does not accommodate full interaction with the


by the added atmospheric water, the greenhouse effect will
compound because of the radiative properties of the additional
water vapor. On the other hand, if cloud cover increases
significantly as a result of the increased evaporation, the
clouds will reflect part of the incoming solar radiation and
thus will modulate the greenhouse effect.

Concomitant with changes in temperature, other
climatic factors also can be expected to vary as a result of
the modified atmosphere. Thus, after several decades in
which climatic uncertainty seemed to be decreasing as
knowledge and information increased, it seems that climatic
uncertainty suddenly has increased dramatically.

The Climate-Hydrology Continuum

Unlike climate, the boundaries and definition of
hydrology have been rather broadly accepted for several
decades. A typical definition is:

Hydrology—the science that deals with the waters of the
Earth, their occurrence, circulation, and distribution, their
chemical and physical properties, and their reactions with
their environment, including their relation to living things
(Federal Council for Science and Technology, 1962).

This level of acceptance was not always so. Meinzer
(1942) traces the evolution of the meanings of hydrology
from the beginning of the 20th century, when the U.S.
Geological Survey used ‘‘hydrology”’ to denote only the
study of waters beneath the surface of the Earth. At that time,

60

the study of surface water was referred to as ‘‘hydrography”’
and ‘‘hydrometry.’’

Although many hydrologic studies are conducted from
a perspective that is more akin to weather than climate, there
is a field of endeavor within hydrology that relates directly
to climate, and that is the study of the normal behavior of
aspects of the land phase of the hydrologic cycle. Some of
the earliest reported hydrologic studies were of this type.
Meinzer (1942, p. 14-15) attributes the first studies relating
hydrology to climate to Pierre Perrault and Edme Marriotte,
who were French contemporaries of the 17th century. Each
labored independently to demonstrate that rainfall on the
drainage basin of the Seine River was sufficient to be the
ultimate source of runoff in the river. Their studies were
attempts to add evidence to the theory of the hydrologic cycle
that had been espoused a century and a half earlier by
Leonardo da Vinci.

A more recent, but also classic, study is that of
Langbein and others (1949), which graphically relates the
normal runoff in rivers of the United States to the climate
measures of precipitation and temperature (fig. 2). Some of
the more enduring aspects of the Langbein study were its
illustration of (1) how runoff, for a given annual precipita-
tion, 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

55

MEAN ANNUAL PRECIPITATION, IN INCHES

Parameter is weighted mean
annual temperatures, in
degrees Fahrenheit 4

i 1 i 1 1 1 1

16 18 20 2 24 2 28 30

MEAN ANNUAL RUNOFF, IN INCHES

Figure 2. Relation of annual runoff to precipitation and temperature. Source: Langbein and others, 1949.

4 Water Resources and Implications of Climate Uncertainty


earlier, will be repeated in other hydroclimatic and
demographic settings to test the available methodologies and
data bases prior to a major expansion of this component.
These early studies will treat the study areas more as large-
scale open-air laboratories than as definitive hydrologic
assessments. Hydrologic findings pertaining to climate
uncertainty will be placed in the context of the existing levels
of understanding of the critical issues. As the increments of
knowledge and information accumulate, interpretations can
be revisited, and the caveats on such studies can be reduced.
Eventually, generally accepted procedures can be used, and
interpretive studies of the hydrologic implications of climate
uncertainty will become a major component of the water-
resources activities of the U.S. Geological Survey.

REFERENCES

Ayers, M. A., and Leavesley, G. H., 1988, Assessing the potential
impacts of climate change on the water resources of the
Delaware River basin, work plan—1988-1990: U.S.
Geological Survey Open-File Report 88-478, 36 p.

Barnett, T. P., Dumenil, L., Schlese, V., and Roechner, E., 1988,
The effect of Eurasian snow cover on global climate: Science,
v. 239, p. 504-507.

Bras, R. L., and Rodriguez-Iturbe, I, 1985, Random functions
and hydrology: Reading, Mass., Addison-Wesley Publishing
Company, 559 p.

Bretherton, F. P., 1987, A closer view: Colorado, Earth Quest,
Universities Council on Atmospheric Research: Colorado,
v. 1, no. 2, p. 1-2.

Brutsaert, W., Schmugge, T. J., Sellers, P. J., and Hall, F. G.,
1988, Large-scale experimental technology with remote sens-
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Chase, E. B., Moore, J. E., and Rickert, D. A., 1983, Water
Resources Division in the 1980's: U.S. Geological Survey
Circular 893, p. 4.

Clark, W. C., ed., 1982, Carbon dioxide review 1982: Oxford,
Clarendon Press, 469 p.

Cobb, E. D., and Biesecker,'J. E., 1971, The hydrologic bench-
mark network: U.S. Geological Survey Circular 460-D, 38 p.

Dawdy, D. R., Lichty, R. W., and Bergmann, J. M., 1972, A
rainfall-runoff simulation model for estimation of flood peaks
for small drainage basins: U.S. Geological Survey Profes-
sional Paper 506-B, 28 p.

Dean, W. E., Bradbury, J. P., Anderson, R. Y., and Barnosky,
C. W., 1984, The variability of Holocene climate change:
evidence from varved lake sediments: Science, v. 226,
p. 1191-1194.

Delaware River Basin Commission, 1986, Annual report (silver
anniversary edition) of Delaware River Basin Commission:
New Jersey, 32 p.

Dickinson, R. E., 1984, Modeling evapotranspiration for three-
dimensional global climate models, in Hansen, J. E., and
Takahashi, T., Climate processes and climate sensitivity:

24 Water Resources and Implications of Climate Uncertainty

Washington, D.C., Geophysical Monograph 29, American
Geophysical Union, p. 58-72.

Dooge, J. C. I., 1982, Parameterization of hydrologic processes,
in Eagleson, P.S., ed., Land surface processes in
atmospheric general circulation models: Massachusetts,
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Eagleson, P. S., and Segaria, R. I., 1985, Water-limited equi-
librium of Savanna vegetation systems: Water Resources
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Eddy, J. A., 1976, The Maunder minimum: Science, v. 192,
p. 1189-1202.

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of climate and climate modeling: GARP Publication Series
No. 16, 265 p.

Goldman, C. R., 1988, Primary productivity in Lakes Castle and
Tahoe: long-term trends and year-to-year variation (abstract):
American Society of Limnology and Oceanography Annual
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Hastenrath, S., 1978, On modes of tropical circulation and climate
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p. 2222-2231.

Hirschboeck, K. K., 1988, Flood hydroclimatology, in Baker,
V.R., Kochel, R. C., and Patton, P. C., eds., Flood
geomorphology: New York, John Wiley, 503 p.

Howard, K. A., and Smith, G. I., 1978, Climate variations and
its effects on our land and water: Part C, Geological Survey
climate plan: U.S. Geological Survey Circular 776-C, 15 p.

Johnson, R. C., Imhoff, J. C., and Davis, H. H., 1980, Users
manual for hydrologic simulation program—Fortran (HSPF):
EPA 600/9-80-015, 678 p.

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no. 9., p. 1116-1123.

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123 p.

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p. 463-471.


Water Resources in the Twenty-First Century—A Study
of the Implications of Climate Uncertainty

By Marshall E. Moss and Harry F. Lins

Abstract

The interactions of the water resources on and within the
surface of the Earth with the atmosphere that surrounds it are
exceedingly complex. Increased uncertainty can be attached to the
availability of water of usable quality in the 21st century, therefore,
because of potential anthropogenic changes in the global climate
system. For the U.S. Geological Survey to continue to fulfill its mis-
sion with respect to assessing the Nation’s water resources, an
expanded program to study the hydrologic implications of climate
uncertainty will be required. The goal for this program is to develop
knowledge and information concerning the potential water-
resources implications for the United States of uncertainties in
climate that may result from both anthropogenic and natural
changes of the Earth’s atmosphere. Like most past and current water-
resources programs of the Geological Survey, the climate-
uncertainty program should be composed of three elements: (1)
research, (2) data collection, and (3) interpretive studies. However,
unlike most other programs, the climate-uncertainty program
necessarily will be dominated by its research component during
its early years.

Critical new concerns to be addressed by the research com-
ponent are (1) areal estimates of evapotranspiration, (2) hydrologic
resolution within atmospheric (climatic) models at the global scale
and at mesoscales, (3) linkages between hydrology and climatology,
and (4) methodology for the design of data networks that will help
to track the impacts of climate change on water resources. Other
ongoing activities in U.S. Geological Survey research programs will
be enhanced to make them more compatible with climate-
uncertainty research needs.

The existing hydrologic data base of the Geological Survey
serves as a key element in assessing hydrologic and climatologic
change. However, this data base has evolved in response to other
needs for hydrologic information and probably is not as sensitive
to climate change as is desirable. Therefore, as measurement and
network-design methodologies are improved to account for climate-
change potential, new data-collection activities will be added to the
existing programs. One particular area of data-collection concern
pertains to the phenomenon of evapotranspiration.

Interpretive studies of the hydrologic implications of climate
uncertainty will be initiated by establishing several studies at the
river-basin scale in diverse hydroclimatic and demographic settings.
These studies will serve as tests of the existing methodologies for
studying the impacts of climate change and also will help to define
subsequent research priorities. A prototype for these studies was
initiated in early 1988 in the Delaware River basin.

INTRODUCTION

Recently, climate has attained the status that Charles
Dudley Warner long ago claimed for the weather; that is,
“everybody” talks about it. But counter to the old saw about
weather, ‘‘somebody’’ is doing something about the climate
of the Earth—‘‘somebody’’ is changing it. However, it is
uncertain whether the changes at any point or at any time
will be beneficial or detrimental. At this time, the only
certainty pertaining to climate change is that its potential
impacts on humankind will be pervasive. Describing the trend
within the scientific community toward more integrated
interdisciplinary studies of the Earth to cope with the
uncertainties of change, Bretherton (1987) states:

This movement gains a sense of urgency from signs
that human activities are altering our global environ-
ment in unprecedented ways, with consequences for
our children and grandchildren that we are barely able
to comprehend. Although some of the changes may
well be beneficial, others may not. Without an
adequate understanding of what is happening, all are
likely to be stressful.

Among the resources most likely to be impacted significantly
is water.

Water is one of the physical elements that must be
studied intensively in order to develop a better understand-
ing of the potential for climatic change. Thus, the hydrologist
is a necessary component in developing the science of global
environmental change in addition to serving as a linkage to
the water-resources decisionmakers, who need the anticipated
new knowledge to decrease the stress that Bretherton so aptly
describes. Traditionally, the U.S. Geological Survey (USGS)
has played a significant role in the development of the
world’s hydrologic knowledge and information. However,
the water-resources mission of the Geological Survey,
discussed in more detail subsequently, cannot be effectively
fulfilled in the 21st century without active participation in
the national and international programs investigating global
climate change. This document provides a basis for planning
the evolution of the Geological Survey water-resources

Introduction 1


11. Map showing physiography of the Delaware River basin 20

12. Diagram showing primary components of the Delaware River basin study 21

13. Diagrams showing resource balance among the three components of the
climate-uncertainty program 22

TABLES

1. Themes and issues in process-oriented research 7
2. Components of model-oriented research 12
3. Research status and priorities 23

vi


larger scale resolvable state of the atmosphere, parameteriza-
tion is required.

To illustrate the problem associated with specifying
subgrid processes at the grid scale, consider how a typical
GCM treats soil moisture (fig. 6). At the Earth’s surface,

Figure 6. Characterization of how the spatial variability of
a surface condition such as soil moisture, which varies over
a scale of meters, is generalized to a single value through
parameterization.

the moisture content of the top 15 cm of soil is a highly
variable quantity, responding to differing vegetation, soils,
and geomorphological characteristics. Over an area the size
of a 5° latitude by 5° longitude grid square, a map of soil-
moisture content would appear as a complex mosaic. Yet,
the input to the GCM is a single value for the entire grid
square. Clearly, for most of the globe’s land surface, this
is a poor representation of soil-moisture conditions.
Linking hydrology and climate through GCM’s is very
difficult. Accounting for the myriad of interacting processes,
including precipitation, interception, infiltration, runoff, and
evapotranspiration, with any degree of precision or realism
is very complicated, and procedures for handling these
intricacies are largely underdeveloped or totally lacking.
Significantly, hydrologists, especially those involved
in surficial-process and ground-water modeling, have been

addressing many of these same problems and can make major
contributions toward their solution. Whereas atmospheric
modelers have focused their attention primarily on processes
over characteristic scales ranging from 10,000 to
100,000 km?, hydrologic modelers have dealt with smaller
scale processes, those occurring over field (<1 km?) or
catchment (100-1,000 km?) areas. Importantly, hydrologists
have had to confront many of the same basic issues to
parameterize field-scale processes in catchment-scale
models. Although adequate solutions have not been
found always, those processes significantly affecting
catchment response have been identified. Thus, the
hydrologic community has acquired important insights
necessary in guiding parameterizations from catchment scales
up to GCM-grid scales.

An intermediate step of great significance has been
undertaken by atmospheric modelers to enhance the realism
of subgrid-scale processes by application of a finer mesh grid.
This work, generally referred to as mesoscale modeling, is
a spatially and temporally limited form of general circula-
tion modeling. Their basic physical and mathematical found-
ations are the same, although more detail is incorporated
at the mesoscale. Pielke (1984) defines mesoscale as hav-
ing a characteristic horizontal spatial scale of 10 km? to
50,000 km? with a time scale of about 1 to 12 hours. Clearly,
this scale of analysis is much more consistent with that used
in hydrology and affords a sound basis for substantial
interaction between the atmospheric and hydrologic model-
ing communities. The mesoscale class of models, with the
inherent ability to nest within the broader GCM’s, provides
a likely pathway for incorporating more realistic hydrologic
conditions into climate simulations at the global scale.
Perhaps more important for hydrologists, however, is the
potential for improving the output of catchment models by
using the output of mesoscale models as input.

At the smaller end of the spatial scale are the basin
or catchment models commonly used by hydrologists. The
actual information content of such model outputs has seldom.
been investigated, however, and their sensitivities to vary-
ing climate conditions are generally unknown. One excep-
tion is the small-catchment rainfall-runoff model developed
by the U.S. Geological Survey (Dawdy and others, 1972).
Lichty and Liscum (1978) have devised a procedure for
estimating the information about flood-recurrence intervals
that the model can extract from weather records. A factor,
illustrated in figure 7, also has been mapped that defines the
impact of existing climate conditions on flood frequencies
in small catchments of the United States east of the Rocky
Mountains. Studies of this sort will be carried out for other
models and for characteristics other than floods, and the pro-
cedures will be extended to estimate the impacts of climate
change on the models’ abilities to generate hydrologic
information.

Research 13


350

345
340
335
330
325
320
315
3104
305

CARBON DIOXIDE, IN PARTS PER MILLION

300

3.0

254

2.04

154

1.04

0.5

CARBON DIOXIDE, IN PARTS PER MILLION

0.0

1960 1965

1970

Figure 1. Annual mean concentrations of atmospheric carbon dioxide measured at the Mauna
Loa Observatory (A) and annual changes in mean concentrations (B).

greenhouse gases in the atmosphere (Clark, 1982). In 1985,
a group of eminent scientists convened in Villach, Austria,
to discuss this problem. They reached a consensus that
the global-mean temperature would increase by 1.5 to
4.5° Celsius during the first half of the 21st century (World
Climate Programme, 1986). However, because of the
dynamic nature of the Earth’s oceans and atmosphere, such
a change will not occur uniformly over the surface of the

Earth. Some areas will warm in excess of the global mean,
others less, and probably some will cool.

An important aspect of the greenhouse effect is the
potential for positive or negative feedbacks among the
phenomena that cause either exacerbation or modulation of
the initial effect. For example, increased energy within the
atmosphere will cause added evaporation of water from the
Earth’s surface. If cloud cover is not increased significantly

Perspectives on Climate, Hydrology, and the U.S. Geological Survey 3


Another example is the development of an in-situ
instrument package for measuring the dielectric properties
of snow and ice. The Snow and Ice Dielectrics System,
developed collaboratively by the Environmental Research
Institute of Michigan and the U.S. Geological Survey, is
specifically designed to facilitate the spatial extrapolation of
snow water-equivalent estimates derived from airborne
passive microwave measurements of snow. Activities such
as these undoubtedly will expand as large-scale integrated
studies of the Earth focus to a greater degree on increasing
the detail and versatility of remotely sensed data.

Water-Resources Interpretive Studies

The success of any program designed to study the
hydrologic implications of climate uncertainty must be
measured in terms of information utility. It is essential that
the information generated by a program be carefully matched
to the level and scale at which actual policies and decisions
affecting the Nation’s ability to cope with the uncertainty are
made. In terms of water resources, an appropriate areal scale
for information synthesis is the major river basin or regional
aquifer. Accordingly, the U.S. Geological Survey has
initiated a pilot study of the Delaware River basin (Ayers
and Leavesley, 1988) (1) to test its capabilities to develop
information on the implications of climate uncertainty
regarding a number of interrelated aspects of the basin’s
hydrology; (2) to determine the utility of such information
for basinwide water-resources planning in the 21st century;
(3) to assess methodological performance and needs for
enhancing the utility of such studies; and (4) to evaluate future
data requirements for tracking potential impacts of climate
change.

Because the Delaware River basin does not encompass
the full range of hydrologic phenomena susceptible to climate
change, this study is envisioned as the first of several
geographically distinct pilot assessments that logically should
precede a comprehensive attack on the problem of evaluating
the Nation’s water resources in the 21st century. The
following summary of the Delaware River Basin study
provides an example of the scientific complexity associated
with such comprehensive, but meaningful, interpretive
analyses.

The Delaware River basin encompasses 12,765 mi? and
crosses four distinct physiographic provinces (fig. 11). Its
runoff processes are quite diverse, and man’s influence on
the movement and storage of water adds considerable
complexity to the basin system. The Delaware River serves
as a major source of water for an estimated 20 million
people both in and outside the basin (Delaware River Basin
Commission, 1986).

The availability of water to users is based on many
complex systems of reservoirs for storage and pipes, tunnels,
and canals for diversion and delivery. The two largest
diversions out of the basin are through the New York City
aquaduct system to New York City and the Delaware and

Raritan Canal to northeastern New Jersey. The freshwater
portion of the tidal river below Trenton, the Delaware
estuary, serves as a source of ground-water recharge for
aquifer systems supplying water to southern New Jersey as
well as a water-supply source for the city of Philadelphia
and many industries by direct diversion. It is critical for these
supplies that the Delaware Estuary along these reaches
remain potable, even during periods of prolonged low flow
(droughts).

Salinity problems in the estuary have historically been
associated with New York City diversion rights. The U.S.
Supreme Court (1931; 1954) required the city system to
maintain certain instream flows at Montague, N.J., to
provide both an adequate water supply and salinity controls
in the estuary, an issue of considerable concern to
downstream interests. Further, ‘‘Good Faith’’ agreements
have included instream flow requirements at Trenton, N. J.
During the drought of record in 1961-65, and twice since
1980, emergency water-use restrictions have been placed on
basin water users to meet basic water-supply demands and
instream-flow requirements.

Such experiences illustrate the susceptibility of the
basin’s water-supply to climate variability and empha-
size how longer term climate uncertainty poses potentially
serious problems for the Delaware River basin. Moreover,
they provide insight on how poorly understood the potential
effects are of climate change on the water supplies of the
basin, including the ability to maintain instream-flow
requirements.

The Delaware River basin study is designed to
investigate the hydrologic response of the basin (fig. 12),
under the existing management infrastructure, to possible
climatic conditions in the mid to late 21st century. Specific
objectives include defining the spatial and temporal variability
of current and projected climate conditions on four important
aspects of water availability within the basin. These are
(1) the streamflows and storage associated with the New
York City and other basin reservoir systems, (2) the ability
to maintain instream flow requirements, (3) the upstream
movement of saline water in the Delaware estuary associated
with changes in sea level and freshwater inflows, and (4)
the resulting potential intrusion of saline water into aquifers
adjacent to the estuary.

Although the Delaware River basin is a unique
hydrologic system within the United States, the interpretive
assessment of this basin is intended to serve as a prototype
for similar studies across the Nation. Clearly, other regions
will have a different mix of physical system, water-supply,
legal, and economic problems attendant with a climate
change, but the general approach to evaluating those prob-
lems should be applicable. That approach, involving the
coupling of advances in process research and data collec-
tion with existing hydrologic capabilities, is a robust yet
flexible design. It should provide a sound framework for
analysis regardless of the hydrologic region or type of climate
change.

Water-Resources Interpretive Studies 19


TWENTY-FIRST CENTURY—

A STUDY OF THE IMPLICATIONS
OF CLIMATE UNCERTAINTY



addressed. For example, Barnett and others (1988) have
demonstrated the effect that added snow cover and subsequent
increased soil moisture in Eurasia have on deterring the
subsequent monsoon in South Eastern Asia. This same study
shows strong correlations between Eurasian snow cover and
the atmospheric conditions over all of North America.

A common characteristic of each of the above examples
is that significant levels of uncertainty exist with respect to
the exact forms of the interdependence of climate and
hydrology and also with respect to the parameters that
quantify the interdependence at any given time and location.
Therefore, current uncertainties pertaining to the availability
and quality of water resources in the 21st century must be
viewed as a manifestation of the climatic uncertainty
described in the previous section.

Because new hydrologic uncertainties exist and the
current level of scientific understanding does not permit their
quantification, scenario analysis (Lave and Epple, 1985) has
become an accepted tool for exploring potential impacts.
Scenario development in the climate-change arena has
been based on three separate, but potentially comple-
mentary, approaches: (1) reconstruction of prehistoric
climates from geologic evidence (paleoclimatology),
(2) analysis of aberrant-climate periods in recorded history,
and (3) computation of future conditions using physically
based three-dimensional General Circulation Models
(GCM’s). Lamb (1987) has described some of the short-
comings of each of these three. However, any one of today’s
scenarios points to potential disruptions in certain parts of
the water-based economies of the world, while providing
added opportunities for other parts. Within the United States,
this mix of potential disruptions and opportunities is no more
evident than it is on the global scale; the potential for
disruption may be greater in the United States than in many
other countries, however, because the relatively mature
development of our water resources makes them more
vulnerable to perturbations.

Because of the potential for major impacts on social,
economic, and environmental conditions in the United States,
and because of the uncertainties concerning those impacts,
major scientific studies are being planned and some already
have begun. These studies are being carried out both at the
national and global scales.

The Water-Related Mission of the
U.S. Geological Survey

The water-related activities of the U.S. Geological
Survey are executed by its Water Resources Division. The
stated mission of Water Resources Division is to provide the
hydrologic information needed for managing the Nation’s
water resources (Chase and others, 1983). This information
is developed by conducting hydrologic research, by collecting

6 Water Resources and Implications of Climate Uncertainty

basic hydrologic and water-use data, and by performing
interpretive studies of the Nation’s water resources at various
scales from local to national. These three program com-
ponents are interfaced with the Nation’s information users
through the release of publications and hydrologic data and
through data-coordination, cataloging, and retrieval services.

For almost 100 years, the Geological Survey has been
providing hydrologic information to the Nation that is
essential for coping with water-supply uncertainty and for
protecting the citizenry from the devastations of floods and
droughts. For a shorter period of time, the Nation also has
depended on the Geological Survey’s information to set and
implement policies for dealing with the degradation of the
quality of its water resources. Thus, the Geological Survey
is well positioned by tradition, as well as by the scientific
momentum of its current activities, to play a key role in
providing information to address the recently recognized
increment of ‘hydrologic uncertainty associated with the
potential for global climate change. In fact, it will be
impossible for the Geological Survey to continue to meet its
mission responsibilities in the 21st century if the potential
impacts of climate change are not taken properly into
account.

Although the Geological Survey has not been one of
the major Federal participants in the climate-change activities
of the last decade, it has not been isolated from them either.
In 1976, the Geological Survey convened a workshop to
stimulate discussion of the effects of climate variation on the
land and water resources of the Nation (Smith, 1978a,b).
As a result of the workshop, a Geological Survey climate
plan was developed (Howard and Smith, 1978) that to date
has been implemented only to a modest degree. The plan
is consistent with the responsibilities of the Geological Survey
as specified in the first U.S. National Climate Program Plan,
a document called for in the National Climate Program Act
(Public Law 95-367) and prepared by the National Climate
Program Office of the National Oceanic and Atmospheric
Administration in conjunction with other Federal agencies.
However, as more knowledge and information have
accumulated and as Federal agency activities have shifted,
the National Climate Program Plan has been revised
(National Climate Program Office, 1988), and the respon-
sibilities of the Geological Survey have increased to that of
a lead agency for the study of the interactions between climate
and hydrology.

For the Geological Survey to become a focal point for
hydrology in the climate-change arena, the significant, but
diffuse, climate-related activities that currently are being con-
ducted within the Water Resources Division need to be
brought into perspective; their roles relevant to a common
goal need to be evaluated, and weaknesses and critical gaps
need to be identified. By carrying out these steps and
rectifying weaknesses and gaps as resources can be made
available, the Geological Survey indeed will have a program


ultimately reaches a constant representing the limiting rate
of evapotranspiration. Although in more recent years there
has been an increasing emphasis placed on studying such
conditions using numerical models, Langbein’s fundamental
points have endured. The study continues to this day as a
mainstay in the definition of impacts of climate change on
streamflow (Revelle and Waggoner, 1983).

A rapidly emerging field of study within hydrology
focuses on flooding and related sedimentary processes that
occurred during the period from the mid- to late Holocene
up to the advent of systematic stream gaging. Such paleoflood
studies are having significant impacts on flood-probability
estimation. For example, Webb (1985) determined that the
frequency of large floods on the Escalante River in south-
central Utah was at a maximum 1,100 to 900 years ago and
that the largest flood, occurring approximately 950 years ago,
was seven times larger than the maximum recorded at any
of the river’s gaging stations. These flood-frequency changes,
in turn, have produced changes in the Escalante’s upstream
alluvial channel. Valley-margin stratigraphy representing
1,600 years of deposition indicates that since 1,100 years
ago, when large floods were at a maximum, a marshy flood
plain gave way to a dry, fire-swept meadow wherein a 24-m-
wide and 2.5-m-deep arroyo formed.

Although this arroyo filled with sediments between 500
and 400 years ago, floods between 1909 and 1940 recut the
arroyo to up to 100 m wide and 17 m deep. Although land

use practices have clearly been associated with signif-
icant changes in watershed and flood-plain conditions,
there also has been a subtle climate shift that has in-
creased the amount of summer precipitation and intensity of
storms.

Another example, relevant to both floods and droughts,
is their relation to large-scale atmospheric and oceanic
phenomena. The occurrence and magnitude of the aperiodic
EI Nifto-Southern Oscillation (ENSO) phenomenon, which
spans the South Pacific Basin, have been shown to relate
to climatic and hydrologic anomalies from Asia (Shukla
and Paolino, 1983) to South America (Hastenrath, 1978;
Ropelewski and Halpert, 1987) and to the western and
southeastern parts of the United States (Ropelewski and
Halpert, 1986) (fig. 3). Such associations, although statis-
tically significant, are often weak, and their physical basis
is poorly understood. Considerably more research is neces-
sary before such associations can be used in warning of
extreme hydrologic events.

The above examples demonstrate the dependence of
several hydrologic variables on climate factors, but the
interrelation is not always so unidirectional; studies of the
oasis effects of irrigated lands have demonstrated the feed-
back from living plants, the water surface, and moist soil
to modify local microclimates (Oke, 1978). However, the
potential magnitudes of the feedbacks for large-scale
hydrologic phenomena are just now beginning to be

180°

Insufficient
station data

i) for analysis

EXPLANATION

409) f Wet

te
[jon

604 a —

Figure 3. Regions exhibiting a consistent precipitation response signal to El Ni flo-Southern Oscillation episodes. Source:

Ropelewski and Halpert, 1987.

The Climate-Hydrology Continuum 5


Manabe, S., 1981, Simulation of climate by general-circulation
models with hydrologic cycles, in Eagleson, P. S., ed., Land
surface processes in atmospheric general circulation models:
New York, Cambridge University Press, p. 19-66.

Martin, M. M., 1987, Ground-water flow in the New Jersey Coastal
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253 p.

Meinzer, O. E., 1942, Introduction, in Hydrology (O. E. Meinzer,
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Moss, M. E., 1970, Optimum operating procedures for a river
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Moss, M. E., and Tasker, G. D. 1987, The role of stochastic
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National Climate Program Office, 1988, National climate program
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National Research Council, 1983, Fundamental research on
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1985, A strategy for earth science from space in the 1980’s

and 1990's, Part II: Atmosphere and interactions with the

solid earth, oceans, and biota: Washington, D.C., National

Academy Press, 149 p.

1986, Global change in the geosphere-biosphere: Initial
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Nichols, F. H., Cloern, J. E., Luoma, S. N., and Peterson, D. H.,
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Oke, T. R., 1978, Boundary layer climates: London, Methuen and
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Parzen, E., 1962, Stochastic processes: California, Holden-Day,
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Peterson, D. H., Cayan, D. R., Dileo-Stevens, J., and Ross, T. G.,
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Hogg, W., eds., The influence of climate change and climate
variability on the hydrologic regime and water resources,
IAHS Publication No. 168, p. 45-62.

Pielke, R. A., 1984, Mesoscale meteorological modeling: New
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US GOVERNMENT PRINTING OFFICE 1989 ~ 242-338 - 226/80083

Raiffa, H., 1970, Decision analysis; introductory lectures on choices
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Revelle, R. R., 1983, Probable future changes in sea level resulting
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climate: Washington, D.C., National Academy Press,
p. 433-448.

Revelle, R. R., and Waggoner, P. E., 1983, Effects of a carbon
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D.C., National Academy Press, p. 419-432.

Riggs, H. C., 1985, The changing environment, in Streamflow
characteristics: The Netherlands, Elsevier Science Publishers,
Chapter 10, p. 177-206.

Ropelewski, C. F., and Halpert, M. S., 1986, North American
precipitation and temperature patterns associated with the
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v. 114, p. 2352-2362.

1987, Global and regional scale precipitation patterns
associated with the El Nirio/Southern Oscillation: Monthly
Weather Review, v. 115, p. 1606-1626.

Shukla, J., and Paolino, D. A., 1983, The southern oscillation and
long-range forecasting of the summer monsoon rainfall over
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Smith, G. I., 1978a, Climate variation and its effects on our land
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References 25


activities in light of the potential for climate change in a
decadal timeframe.

This document is the synthesis of ideas derived from
discussions with many of the authors’ colleagues both from
within and from outside the U.S. Geological Survey. The
authors particularly would like to acknowledge the contribu-
tions of Mark Ayers, Julio Betancourt, Fred Nichols, Dave
Peterson, and Tom Winter.

PERSPECTIVES ON CLIMATE, HYDROLOGY, AND
THE U.S. GEOLOGICAL SURVEY

The concept of climate is an evolving one, and today
there are usages within the scientific community for this term
that are at variance with each other. Therefore, a working
definition for the purposes of this document is provided here:

Climate—the unconditioned, statistical (probabilistic)
description of the sequence of measures of a suite of
properties that describe the atmospheric components of
the environment of a locality or region.

In other words, climate comprises the likelihoods,
independent of weather-forecasting skill, of such properties
as sunshine or percentage of cloud cover, amount and
intensity of precipitation, or the magnitude and direction of
wind. Weather is a realization or happening at any particular
instant from within the realm of possibilities described by
the appropriate climate descriptions for that instant.

Both climate and weather impact the study of the
Earth’s water resources, which is known as hydrology.
Hydrology, through its linkage with climate, entails the statis-
tical description of water-related environmental conditions;
but it also, through its relation with weather, involves an
accounting of the individual realizations in time of such
conditions. Thus, conceptually, the term ‘‘hydrology’’ refers
to a broader field of study than either climatology or
meteorology. In this regard, hydrology is more analogous
to the term ‘‘atmospheric sciences,”” which encompasses both
climatology and meteorology. With these distinctions drawn,
it is possible to define a role for the Geological Survey in
the study of the hydrologic implications of climate
uncertainty.

Climate Variability, Change, and Uncertainty

The classical definition of climate was a quasi-static
one; climate was described by the normal or most common
weather conditions. It was recognized that climate could
change on a time scale of centuries to millennia, but the
averages of limited historical data were the best key to what
might happen weatherwise in the future. Such an approach
suffered from several shortcomings. First, the averages or
norms of weather properties do not comprise a sufficient set
of statistics to describe the atmospheric environment. The

2 Water Resources and implications of Climate Uncertainty

variability and particularly the extremes of weather are often
more useful for climate applications than are norms. Second,
examination of longer historical records demonstrated that
periods of deviation of weather from its norms could last
significantly longer than could be explained on a statistical
basis. The Little Ice Age is such an example (Eddy, 1976).
Third, for many areas of the world, the periods of data
collection are too short and the numbers of meteorological
stations are too few to accurately describe the local climate,
even on a quasi-static basis. Thus, study of any climate-
related phenomenon such as water resources must contend
with significant uncertainty even before the consideration of
potential anthropogenic change of the Earth’s atmosphere.

Climate varies periodically on at least three temporal
scales: (1) daily, (2) annually, and (3) over geological ages.
Over the daily cycle, changes in insolation and temperature
are as distinct as night and day; over the annual cycle, clouds,
precipitation, and winds may vary seasonally as well; and
at the geologic time scale, ice sheets wax and wane causing
drastic swings in all climate parameters. The changes
associated with each of these periods can be attributed
primarily to the distribution of incident solar radiation across
the Earth’s surface. However, another factor that causes
variation in the Earth’s climate is the makeup of its
atmosphere, which controls the amount of energy that passes
from the Earth back into space. Radiative gases in the
atmosphere, like carbon dioxide, methane, ozone, and water
itself, are called greenhouse gases. Analogous to the glass
panes in the gardener’s greenhouse, these gases permit the
passage of the Sun’s short-wave energy in to the Earth but
deter the longer wave energy reradiated by the Earth from
dissipating into space. Thus, the greenhouse gases temper
the Earth’s climate by retaining energy within the
atmosphere.

Since the Industrial Revolution, the use of energy has
increased immensely. For the last century much of that
energy has come from the consumption of fossil fuels like
coal, petroleum, and natural gas. A byproduct of the con-
sumption of fossil fuels is carbon dioxide, which is released
to the atmosphere. The concentration of carbon dioxide in
the atmosphere has been measured at the top of Mauna Loa
in Hawaii since 1958; figure 1A illustrates the significant
increase in this gas, which frequently has been cited as a
likely cause of climatic change. Increasing the carbon dioxide
in the atmosphere is analogous to increasing the thickness
of the glass panes in a greenhouse—each results in a more
efficient deterent to the loss of long-wave energy. Retention
of more energy within the atmosphere eventually will result
in a global increase in temperature. Perhaps even more
disturbing than the increase in atmospheric carbon dioxide
is the sporadic but increasing rate at which it is increasing,
as is shown in figure 1B.

The climatic impacts of increasing concentrations of
carbon dioxide will be compounded by increases in other


EXPLANATION
@ Hydrologic benchmark station

Figure 8. Locations of U.S. Geological Survey benchmark stations.

However, items 2 and 3 will be ameliorated as part of the
data-collection element of the program.

Climate data for the benchmark drainage basins are
sporadic in time and in space; this facet of the network limits
its utility for studying climate-hydrology interactions. The
first priority for increased data collection under this program
will be the installation of permanent climate stations on each
benchmark drainage basin. Because of the climate variability
over areas within the range of the benchmark drainage basins
(approx 5-2,500 km?), several climate stations may be
desirable in many of the basins. However, the network-design
methodology for specifying the ideal number and locations
of climate stations for each basin currently does not exist.
Therefore, a single climate station will be installed on each,
and deployment of other stations will await the methodology
that is to be developed in the research element of the
program.

Even though new sites can be added to the benchmark
network as funds are made-available, any new site will never
be as powerful in tracking the impacts of potential climate
changes as would the original sites. The information
contained in the charter sites never can be recovered fully
for the new sites. Nevertheless, if significant climate change
is not too immediate, time remains for the establishment of
significant data bases at new locations. Criteria for the new
sites, both the number of sites and the characteristics of the
individual sites, also will be developed within the research
element of the program.

16 Water Resources and Implications of Climate Uncertainty

A histogram of the percentage of continuous stream
gages in the United States by area of their drainage basin, as
determined from the files of the National Water Data
Exchange (Williams and Knecht, 1981), appears in figure
9. The drainage basins of the benchmark network fall on the
smaller end of the spectrum of gaged watersheds. Because
of the incongruity between the spatial resolution of general
circulation models and that of the Benchmark Network, the
benchmark sites will contribute only a minor amount of
information for the calibration and testing of general circula-
tion models. Another set of stations at a more appropriate
areal scale will be needed for this purpose. Currently, the
Geological Survey is making a detailed search of the existing
data base to identify stations that either are active now or
could be reactivated to provide the requisite data for model
testing and for evaluation of the hydrologic information
content of the outputs of the GCM’s. It is anticipated that
both reactivation of some discontinued stations and the
establishment of some new ones will be required to develop
an adequate data base to achieve these ends.

One area in which hydrologic data generally are not
available for either statistical or modeling purposes is that
of evapotranspiration. The reason for this is that a cost-
effective methodology does not exist to generate the data
of the desired temporal and spatial scales. Early in the
research element of the program, high priority will be given
to the development of the missing methodology. Once
the methodology has been demonstrated to be successful,


Research
dominates

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oS 50 ¥.
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Data Interpretive
collection studies
dominates dominate
100 0
0 50 100

INTERPRETIVE STUDIES

INTERPRETIVE STUDIES

Figure 13. Resource balance among the three components of the climate-
uncertainty program: (A) areas of single-component dominance and (B) pro-
gram evolutions.

22 Water Resources and Implications of Climate Uncertainty


FOREWORD

The uncertainty associated with global-climate change and attendant implica-
tions for water and land resources represents one of the major scientific challenges
of the 20th century. The geophysical and geochemical complexities inherent to the
study of climate change are enormous. Disciplines from within the atmospheric,
hydrospheric, terrestrial, and biological sciences are compelled now, as never before,
to cooperate in studying the climate system, especially the intricate interactions of the
processes comprising it.

For more than a decade, the U.S. Geological Survey has been an active partici-
pant in Federal programs designed to enhance scientific understanding of climate
variability and change as well as the social, economic, and political implications of
such change. Recent revisions to the U.S. National Climate Program Plan call for a
significant increase in the role and responsibilities of the Geological Survey. To meet
the challenge of enhanced participation in the study of climate, the Survey is cur-
rently engaged in the development of new programs that build upon and expand our
previous efforts.

One of the most fundamental aspects of this expansion involves the develop-
ment of new insights into the potential water-resources implications of climate
change. A better understanding of the global-hydrologic cycle is frequently cited as a
critical climate research need. ‘Water Resources in the Twenty-First Century—A
Study of the Implications of Climate Uncertainty’ presents the elements of the
Geological Survey’s program for studying climate and hydrology. It incorporates the
Survey’s strong and traditional approach that couples research, data collection, and
interpretive studies. We believe that it demonstrates the strength of the U.S. Geo-
logical Survey's commitment to the national and international attempts to understand
the nature and effects of climate change.

Dallas L. Peck
Director


character of the causal factors of flooding. In a situation of
climate change, shifts in the likelihood of flooding or
droughts would be continual, lasting to the time at which
the climate change has ceased. Consequently, data-based
descriptions of floods and droughts will be of limited utility
unless a better understanding of the causal processes and their
rates of change relative to ongoing climate change is attained.

A third class of problems requiring process-oriented
research involves complex hydrologic environments such as
the unsaturated zone, lakes, regions of snow and ice, and
estuaries. Each of these environments plays an important role
in the hydrologic cycle, and the dynamics associated with
each often are poorly understood.

For example, the characterization of the transport of
water, as vapor or liquid, and other climatically significant
gases through the unsaturated zone is crucial to understanding
how the zone functions as a source or sink of such substances.
To amplify this point, preliminary studies in Nevada have
recently indicated that the unsaturated zone is a methane
sink, yet in the past it has been characterized as a methane
source. On a molecule-per-molecule basis, methane is a much
more efficient greenhouse gas than carbon dioxide, and
methane also is increasing in the atmosphere (National
Research Council, 1986). Thus, the question of whether the
unsaturated zone is a modulator or an intensifier of climate
change vis-a-vis methane cycling is an important one that
is yet to be answered.

Lakes integrate the hydrologic system of their water-
shed because they are in direct contact with each of the three
major water components: atmospheric water, streamwater,
and ground water. Therefore, lakes reflect changes in the
supply of water, chemicals, and other materials that enter
them from their airshed and watershed. In addition,
depending on the residence time of water and chemicals in
lakes, internal chemical and biological processes further
modify the character of lakes. Because of the wide variety
of lake sizes, geologic settings, and watershed-area to lake-
area ratios, lakes can be used to assess climate variability
and the impact of that variability on their watersheds over
time scales ranging from days to years (Goldman, 1988).

Perhaps the greatest role lakes have in the linkage of
climate and hydrologic processes is their ability to capture
the historical record of hydrologic processes in their
sediments. Lake sediments are comonly used to study past
hydrologic, climatic, and land use changes, primarily for the
last 13,000 years (Dean and others, 1984), and in some cases
for many tens of thousands of years.

Snow-covered areas on land, and ice on both land and
sea, are extremely sensitive barometers of climate variability
and change. Perhaps more importantly, these areas exert a
major influence on the Earth’s radiation budget as well as
on atmospheric and oceanic circulations. Seasonal variations
in the areal extent of snow are the most significant
contributors to global albedo changes. Albedo refers to the

ratio of radiant energy reflected by a surface to that incident
upon it. The presence or absence of snow, which has the
highest albedo of any natural feature on the Earth’s surface
(80-90 percent), dramatically affects the absorption of solar
radiation and, therefore, surface air temperature. Snow also
provides the water-supply base for parts of the Western
United States. Answers to questions regarding how climate
change will affect the spatial distribution and timing of snow-
fall and consequent water-supply conditions and resource-
allocation strategies must be sought. Similarly, numerous
questions associated with snow and ice dynamics must be
answered to measure and to model more accurately snow
and ice volumes and interactions with other hydrologically
significant variables. Moreover, more detailed information
on the characteristics and dynamics of glaciers, continental
ice sheets, and sea ice is essential for deriving better estimates
of climatic and hydrologic conditions, including changes in
sea level, from climate models.

River-estuarine systems, the meeting place of fresh-
water and saltwater, are among the world’s most complex
hydrodynamic, chemical, and biological environments. They
are also, as a result, exceedingly sensitive to climatic and
anthropogenic influences. These systems, which typically
support large population centers, provide much of the water
needed for domestic consumption, industry, and agriculture
(irrigation) (fig. 4). Developing an understanding of how the
river-estuarine environment varies in association with
variations in climate and human activity is essential for
effective resource management.

One of the more obvious estuarine responses to climate
variability and change, having major societal and economic
importance, relates to instream movement of the freshwater-
saltwater interface. Saltwater intrusion can seriously degrade
coastal land and water resources. The projected acceleration
in the rise of sea level in the 21st century (Revelle, 1983)
will promote upstream shifts in the position of the interface
and increase the landward intrusion of saltwater, thus
endangering municipal freshwater supplies from rivers and
ground-water reserves. In some regions, reduced streamflows
also could increase the demand for coastal ground-water
withdrawals and generate a need to deepen and widen
shipping channels.

In addition to the relatively direct impact of climate
change on coastal water resources, there are a number of
more complex and subtle interactions among the estuarine
hydrodynamic, chemical and biological realms. Such
processes include changes in river-borne sediment transport
and deposition and changes in estuarine biogeochemistry.
Preliminary research indicates that realistic modeling of these
interactions is highly dependent on the development of
nonsteady-state formulations of estuarine physics and
associated biogeochemistry with flow.

The final categories of the hydrologic continuum for
which expanded process-oriented research is needed include

Research 9


processes and also the quantitative assessment of their
variability (Hirschboeck, in press; Lins, 1985a,b).
Recent research indicates that specific regions of the
globe respond in a consistent manner to large-scale atmos-
pheric and oceanic circulations. These consistent responses,
or teleconnections, provide a basis for predicting areas of
water deficits and surpluses attendant to climate change. The
concept of teleconnections, introduced by Walker (1923) and

refined by Namias (1981), actually refers to the statistical
cross-correlation between atmospheric anomaly patterns
separated by synoptic (1,000-2,500 km) to hemispheric
distances. Some of the best documented teleconnections, the
Pacific/North American, the Central North Pacific, and the
Southern Oscillation patterns, for example, have been clearly
associated with distinct patterns of streamflow variability in
western North America, as shown in figure 5. Refinement

A. WINTER SEA LEVEL PRESSURE PATTERN

EXPLANATION
Monthly Streamflow

Below average
| Above average

September

EXPLANATION
Monthly Streamflow

Below average
@ Above average

Figure 5. Mean sea-level pressure (in millibars minus 1,000) and monthly
streamflow patterns: (A) winter 1976-77 and (8) winter 1982-83. “Below
average” refers to the lower quartile flow and “above average” to the upper
quartile of flow. Source: Peterson and others, 1987.

Research 11


DEPARTMENT OF THE INTERIOR
DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY
Dallas L. Peck, Director

Library of Congress Cataloging-in-Publication Data

Moss, Marshall E.
Water resources in the twenty-first century.

(U.S. Geological Survey circular; 1030)

Bibliography: p.

Supt. of Docs. no.: I 19.4/2:1030

1. Climatic changes—United States. 2. Water-
supply—United States. I. Lins, Harry F. Ul. Title.
I, Series.

QC981.8.C5M67 1989 553.7 88-600420

Free on application to the Books and Open-File Reports Section,
U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225


EXPLANATION

—++— Basin boundary
——— Physiographic
boundary

DMONT as"
a £
a

Wn vw do,

T
NY TAU.

25 MILES
0 25 KILOMETERS
|

aie

1
Figure 11. Physiography of the Delaware River basin.

20 Water Resources and Implications of Climate Uncertainty


WATER RESOURCES IN THE
TWENTY-FIRST CENTURY—

A STUDY OF THE IMPLICATIONS
OF CLIMATE UNCERTAINTY

By Marshall E. Moss and Harry F. Lins

US. GEOLOGICAL SURVEY CIRCULAR 1030

Cover photograph by Peter L. Kresan,
University of Arizona


perform interpretive studies using the historical data bases
increase. Thus, under the assumption of stationarity, there
is a natural tendency to evolve from data collection to
interpretation. During this evolution, research has been
viewed primarily as a modest investment to address future
contingencies.

The potential for climate change provides an impetus
to the proposed program to start from a different sector than
have the traditional water-resources programs. As was
described previously, the lack of sufficient understanding of
the major interactions of the hydrosphere with the atmosphere
contributes significantly to the level of uncertainty regarding
the future characteristics of both. Development of this
understanding is requisite for useful projections of future
hydrologic conditions as well as for understanding the
apparent changes that may be detected as a result of existing
data-collection activities. Thus, research will be the domi-
nant component of the climate uncertainty program during
its early stages, as shown in figure 13B. As research
contributes additional understanding, both interpretive studies
and data collection will have a strong basis for increased
levels of effort.

As shown in table 3, the research needs for this
program are partitioned into three categories. The first
category, which is called critical, consists of endeavors that
currently are underrepresented to a debilitating degree if the
program goal is to be addressed in a timely manner. It is
noticable that, with one exception, each of these endeavors
deals with links between the atmospheric and hydrologic
sciences. Because each will be carried out at the disciplinary
frontier of hydrology, each increased activity should be
planned to take advantage of and interact with complemen-
tary activities of other Federal agencies and interdisciplinary,
international programs.

The exception to the hydrology-atmosphere interface
in this research category is network design. This endeavor
is critical because the data-collection component cannot be
fully effective until better knowledge and methodologies are
available to guide investments in data.

The second category of research endeavors includes
facets of existing activities that only may need some redirec-
tion and (or) added support to assume their proper role in
the program. With the exception of perhaps paleohydrology
and biogeochemical cycles, entries in this category are
traditional strengths of U.S. Geological Survey hydrologic
research.

The final category contains lakes and estuaries, which
have been significant components of U.S. Geological Survey
research in the past but that will require added emphasis in
the decade of the 1990’s and beyond. Studies currently
are being conducted within the Survey to define more
specifically the research needs and opportunities in each
of these areas.

Table 3. Research status and priorities

Status Research

Critical concerns...

Evapotranspiration.
Droughts.
Modeling (general circulation
and mesoscale).

o Parameterization.

o Spatial disaggregation.
Hydroclimatology.
Network design.
Snow and ice.

Infiltration.

Runoff.

Unsaturated zone.
Floods.

Recharge.
Paleohydrology.
Biogeochemical cycles.
Water quality.

Lakes.
Estuaries.

Ongoing concerns.............

Evolving concerns..........-++

As was discussed above, the data-collection component
of the program initially will not be of the same magnitude
as the research component. However, there are two data-
collection activities that merit particular concern. The first
of these is augmentation of the benchmark network to provide
baseline information for tracking hydrologic change. Modest
initial expansion likely would be followed by additional
increases as knowledge, methodology, and technology are
developed.

The second critical endeavor for data collection is a
network for estimating areal evapotranspiration. Although
such a network is an immediate need, methodology and
technology limit our abilities to deploy the requisite cost-
effective measurement systems. Interagency collaboration,
such as is currently being carried out in the Konza Prairie
of Kansas (Brutsaert and others, 1988), will be required both
to redress the technological shortcomings as well as to
implement the ultimate solution. The Geological Survey has
a key role to play in both aspects.

The program component with the greatest potential for
growth is interpretive studies. As information and under-
standing from the other two components of the program
accumulate, the demand for interpretive studies can begin
to be met. Indications are that the demand for this type of
product already exists as a result of the publicity that climate
change has received recently. However, current ability to
provide substantive interpretations of the implications of
climate change is extremely limited. Thus, a cautious
approach to performing interpretive studies is in order.
Studies like that in the Delaware River basin, described

Strategy for Achieving the Program Goal 23


on the hydrologic implications of climate uncertainty. The
goal for this program is:

To develop knowledge and information concerning the
potential water-resources implications for the United
States of uncertainties in climate that may result from
both anthropogenic and natural changes of the Earth’s
atmosphere.

Knowledge and information, as referred to in this goal,
encompass fundamental research into the linkages of climate
and hydrology, collection of basic data, and the development
of technology that facilitates interpretation of the data in light
of the research findings. Although the goal is water-resources
driven, this program cannot be isolated from current and
future advances in climatology, biology, geochemistry,
geology, or any of a multitude of interdependent sciences.
Nor can the national focus of the goal be interpreted as a
limitation to consider only U.S. science and U.S. data bases.
The Water Resources Division must be more involved in
international scientific endeavors, like the International
Geosphere Biosphere Programme and the World Climate
Programme, that portend significant progress toward its
goal.

ELEMENTS OF A PROGRAM ON THE
HYDROLOGIC IMPLICATIONS OF CLIMATE
UNCERTAINTY

Elements from each of three major categories of the
traditional activities of the Water Resources Division of the
Geological Survey—research, data collection, and inter-
pretive studies—are essential in a comprehensive program
designed to address the hydrologic implications of climate
uncertainty. Maintenance of the proper balance of activities
among the three categories at each stage of its evolution will
be a key to the program’s effectiveness. The final chapter
of this document discusses the program balance; the present
chapter describes its composition within each of the above
categories.

Research

Like climate, the word research has a diversity of
meanings even within the scientific community. Therefore,
for clarity of presentation, the following definition is used
in this document:

Research—the development of understanding through the
conceptualization and testing of new ideas.

More specifically, hydrologic research is the develop-
ment of understanding about (1) the paths along which water
moves on and in the land masses of the Earth, (2) the rates
of movement along various paths, (3) the chemical, bio-
logical, and physical character of the constituents transported

by the water, (4) the controls on the rates of movement of
and interactions among water and its transported constituents
imposed by the atmosphere, the geosphere, the biosphere,
and the oceans, and, conversely, (5) the impacts on the
atmosphere, geosphere, and biosphere caused by the presence
or absence of water in or on the land.

The research component of the program is partitioned
into two types: (1) fundamental or process oriented and
(2) model oriented. Because one type of research often builds
on the results of research of the other type, most research
projects carry out activities in both categories at any given
time. Thus, the line delimiting these categories of research
often is difficult to distinguish even within any particular
project. However, the categories have utility in describing
the elements of the proposed program.

Process-Oriented Research

Process-oriented research, as used herein, refers to the
development of increased understanding about how the
processes that control the land phase of the hydrologic cycle
interact and how they interact with other processes that they
impact. Because of the intrinsic interconnectivity among
elements of the Earth’s environmental system, the hydrologic
impacts of climate change ultimately will depend on
adjustments in the lithosphere and biosphere, as well as in
the atmosphere. Therefore, the study of any single component
or pair of components of the Earth’s complex system in isola-
tion from others has inherent limitations. Many of the inter-
connections are poorly understood, and thus fundamental
research is needed. Such research will provide insights into
likely changes in advance of their appearance in the environ-
ment and subsequently will facilitate development of timely
guidance for coping with the changes. A list of the primary
elements to be addressed by process-oriented research is
provided in table 1.

Table 1. Themes and issues in process-oriented research

Theme Specific issues
Problems of scale...........:+00++ Infiltration.
Evapotranspiration.

Aquifer recharge.
Surface runoff.
Floods.
Droughts.
Unsaturated zone.
Lakes.

Snow and ice.
Estuaries.

Extreme conditions.............00++

Complex environments. ........++-

Biogeochemical cycles.
Paleohydrology.
Hydroclimatology.
Water quality.

Special topics.......sseesseeesseeess

Research 7


30

A. CALIFORNIA POPULATION /

7
L fd
Projected 7

MILLIONS
Nn
S

T T

o
T

EN}

B. AREA UNDER IRRIGATION

MILLIONS OF
HECTARES
N
T

fe) 1
40
2 C. RESERVOIR CAPACITY ,
Ww a
Tn Projected—7" +
S /
g 20+ a 4
x
OoL
a 1
er) 1 I 1 1 iJ
© D. DELTA EXPORT
,
a BE Projected =” 4
i ,
Go
st Lt
oY 7
o>
YG ab 4
oO a
0
a) b 4
o)
(0) 1 1 1 1 1 1 1 i
1860 1900 1940 1980
YEAR

Figure 4. Population growth in California (A); land under
irrigation (8); water storage capacity of reservoirs in the
Sacramento and San Joaquin river basin (Q); and historic and
projected export of water from the delta by the Federal
Central Valley and State water projects (D). Source: Nichols
and others, 1986.

biogeochemical cycles, paleohydrology, hydroclimatology,
and water quality. A growing body of evidence indicates that
the rate of cycling of greenhouse gases through the
hydrosphere, atmosphere, biosphere, and lithosphere has the

10 Water Resources and Implications of Climate Uncertainty

potential to perturb the global climate and that climate
change, conversely, can produce feedbacks to change
significantly rates of cycling. Carbon dioxide and methane
are just two of the greenhouse gases that play a significant
role in the study of climate change. Nitrous oxide, ozone,
and industrial halocarbons also are related intimately to
climate and the hydrologic cycle. Because these gases impact
on and are impacted by the water resources of a region and,
more broadly, of the globe, the study of biogeochemical
cycles must be an integral part of the study of the hydrologic
implications of climate uncertainty.

Paleohydrology, the study of geologic and biologic
evidence of past hydrologic events, is another special
research topic,of increasing fundamental importance with
respect to climate change. The aim of paleohydrology is to
describe hydrologic variations that span intervals beyond the
range of instrumental records, from glacial-interglacial cycles
to seasonal anomalies, and to identify their causes. The need
to study past evidence of climatic and hydrologic change is
derived from the brevity of most instrumental records, which
are commonly shorter than the planning horizons for applied
hydrology and water-resources management. Moreover, it
is important to place the relatively brief systematic record
in its proper perspective over the longer historic and geologic
past. The different response times and sensitivities of the
atmosphere and oceans (from weeks to centuries) suggest
that high-frequency phenomena (interannual variability) are
transient responses to a continuously varying climate system.
Because the full impact of an anthropogenically induced
warming may take centuries to develop, an understanding
of long-term climate dynamics may be necessary to model
the evolution of equilibrium environmental conditions.

High-resolution proxy data, that is, geologic and other
surrogate records, are indispensible for improving estimates
of the annual mean, annual variance, and long-term per-
sistence of hydrologic phenomena. However, proxy records
suitable for hydrologic analysis are limited both in geographic
coverage and interpretive methodological development.
Presently, interannual proxy records are restricted to tree
rings, sediment varves (both marine and lacustrine), coral
bands, ice layers, and written records. The continued
development and expansion of meaningful and usable high-
resolution and spatially diverse proxy time series are essential
elements of the research program to supplement inadequacies
that exist in the recorded data base.

Hydroclimatology, the study of hydrologic events and
conditions within their climatologic context, is another special
topic of process-oriented research. It encompasses large-scale
interactions between the atmosphere and hydrosphere.
Hydroclimatology, by focusing on atmospheric forcing,
provides a mechanism for integrating the physical sources
of variability in a hydrologic time series with the statistical
properties of the varying driving force itself. This integration
has the benefit of enhancing our understanding of hydrologic