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OCR for page 111
Climatic Change
and Water Supply:
How Sensitive is
the Northeast?
7
INTRODUCTION
HARRY E . S CH WARZ
Clark University
Water supply is an essential service that requires profes-
sional water managers to plan continuously and carefully
as system expansion is costly and time-consuming. Re-
duced to its simplest terms, water-resources planning
with its water-supply component is a search for the most
cost-effective means of striking a balance between sets of
estimated demand with sets of estimated supply. Further,
however, water-supply plans must also take into con-
sideration constraints imposed by the larger environment
within which the water manager operates: limitations
imposed by law, custom, institutions, fiscal capabilities,
and long-time horizons appropriate to political
decision-making. Indeed the time scales for the water-
resources planner and the political system are dramati-
cally out of synchronization. In most small jurisdictions,
for example, the short-range future is tomorrow. Mid-
range futures come before the next election, and long-
range just beyond that election. Usually, only larger
cities, regional jurisdictions, states, or the federal gov-
emment can look at planning horizons of 2~50 years. In
terms of local decision-making, what might occur in 100
years is almost entirely without significance.
In this context, the professional water manager's lot is
not a happy one. His customers castigate him in the event
of even short-term water shortages, while the academic
community, particularly economists and environmen-
talists, accuse him of habitually overestimating demand
and overbuilding facilities. Further, his operation and
construction plans rest on uncertain estimates of demand
based, in turn, on equally uncertain population and eco-
nomic development projections. Even the range of varia-
tion in his supply is based on predictions made from
historical data and statistical manipulations.
Hence, it is understandable that the introduction of yet
another element of uncertainty—climatic change—leaves
the water manager still more vulnerable to accusations
that he did not correctly consider the unforeseeable in
making his calculations. The water-resources planner
needs better information to assess the importance of cli-
matic change as a valid planning factor and its acceptabil-
ity in the public decision-making process. The probability
of climatic change could be considered a goad to action or
OCR for page 112
112
additional fuel for the "let's wait and see" style of
facilities planning.
THE REGIONAL SETTING
For more than 10 years, uncertainties about the validity of
demand projections, fiscal and environmental constraints,
and simple procrastination have stalled all major projects
that would increase water supplies in the northeastern
United States. In 1972, the North Atlantic Regional Water
Resources Study (NAR) found that water-quality mainte-
nance and water supply for public, industrial, and pow-
erplant cooling purposes were the most important water-
resource problems of the northeastern United States
(NAS, 1972a). Intuitively, water supply is likely to be far
more sensitive to climatic change than water quality
maintenance, although the latter might also be adversely
affected. Future water needs for additional municipal use
based on today's experience were estimated to range from
a low of 1400 million gallons per day (mad) (61.3 m3/sec)
in 1980 to a high of 10,600 mad (464 m3/sec) in 2020 (NAR,
1972a). Even greater quantities have been estimated to be
needed for industrial and power cooling.
The northeastern United States as defined in the NAB
study encompasses all river basins within the United
States draining into the Atlantic Ocean north from the
Virginia-North Carolina border, the Lake Champlain
drainage, and the St. Lawrence River drainage in the
United States south of the junction of the St. Lawrence
River and the international border. This land area of
about 167,000 square miles (432,500 km2) includes all or
parts of 13 states and the District of Columbia. The region
contains about 5 percent of the nation's land area, but it
holds about 25 percent of its population and produces
nearly 30 percent of its wealth (NAR, 1972a).
On the average, some 1200 water suppliers in the
region presently furnish 5.5 billion gallons per day (bad)
(241 m3/sec) and serve more than 47 million people or 88
percent of the area's total population. About 4.7 bad (206
m3/sec) is used in domestic supplies. The remainder
serves industrial, commercial, and municipal purposes.
About 76 percent of the water used in these supplies
comes from surface waters, the remainder from ground-
water. Depending on which projection of growth is
realized, populations are likely to require 9.5 to 10.9 bad
(416 to 478m3/sec) by the year 2000 and from 13.1 to 16.0
bad (574 to 701 m3/sec) by 2020. By far the major share of
this water will come from surface sources with reservoirs
as the major device for collecting supply (NAR, 1972b).
Average annual runoff from the region is 163 bad (714
m3/sec) 123 bad (5389 m3/sec) available 90 percent of the
time (U.S. Water Resources Council, 1968~. Seasonal var-
iability, which is generally moderate, can be high in
individual basins. Months of high flow are usually March
and April, the lowest flow tending to occur in August and
September. At the extreme end of the scale, at the height
of the drought in the early 1960's, runoff in the affected
HARRY E . S C HWARZ
area was from between 45 and 60 percent of normal. The
total drought period lasted 51 months.
Despite the fact that average annual draft on the waters
of the region is less than one third of the annual runoff
that can be expected to occur 95 percent of the time,
severe local shortages have occurred in the past and are
likely to occur again in the future. Recurrence of a major
drought, coupled with the projected increases in demand,
would cause larger and more widespread disruptions than
have been experienced in the region so far.
This possibility is extremely significant in light of the
fact that three metropolitan areas, Washington, New York,
and southeastern New England, account for more than 70
percent of the total present average public water supply
now furnished in the northeastern United States. From
the foregoing it is obvious that water supply is a problem
of tremendous magnitude in the northeastern United
States and that water supply for these metropolitan re-
gions is of particular concern.
EVALUATION OF CLIMATIC CHANGE
There are two major ways in which climatic change af-
fects water supply. One is the effect it may have on
demands such as lawn irrigation or the use of showers.
Second is the effect on water sources such as streamflows
or groundwater recharge. Of these, the second is likely to
be far more important to metropolitan water management
in the Northeast. Therefore, this paper will deal predom-
inantly with changes in water sources and within these
restrictions with streamflow, the most common source of
metropolitan water supplies here.
Four parameters, singly or in combination, could be
used as indicators of climatic change. They are the first
three moments of the distribution of streamflow and per-
sistency and the tendency of dry years to follow dry years
and wet to follow wet. Records of streamflow allow us,
within the limits imposed by their shortness, to estimate
these parameters if we assume some specific distribution
function as properly descriptive of streamflow. Climatic
change, as expressed in streamflow, can then be de-
scribed as a significant change in one or more of these
four parameters and maybe even in the distribution func-
tion. This last change, however, is unlikely to be detected
in practical human time space; and, therefore, changes in
the four parameters, mean, standard deviation, skew, and
persistency, would suffice to characterize climatic
change.
To evaluate the effect of climatic change on the water
supply systems of the Northeast, the most effective ap-
proach would be to project the direction and magnitude of
such change, to translate this into streamflow records, and
then to use these records to analyze the response of the
present and projected future major water-supply systems
to forecast change. Unfortunately, this straightforward ap-
proach is not feasible. While the specter of major changes
in climate has been held before the public for a long time
OCR for page 113
Climatic Change and Water Supply: How Sensitive is the Northeast?
and while serious scientists have long debated this prob-
lem, the result of the debate has not been very helpful for
the solution of problems faced by water-resources plan-
ners and managers. The one conclusion available to prac-
ticing professionals is that changes in climate are likely.
However, the magnitude and timing and even the sign of
the changes are unknown.
Under the present state of climatic forecasting and our
ability to translate climatic data into streamflow, such an
approach is not feasible. Furthermore, the possibility to
construct long-term hydrologic records from secondary
sources appears limited in the Northeast, although a con-
sistent 239-year record of precipitation and temperature
has been produced by Landsberg et al. (19681. Unfortu-
nately, the errors associated with converting precipitation
into streamflow are much higher than rainfall-runoff
modelers have led us to believe (Todin and Wallis, 1974~.
Thus other ways must be attempted to assess the sensitiv-
ity of northeastern water supply systems to climatic
change.
Three possibilities appear feasible: (1) to review indi-
vidual cases and, on the basis of their previous response
to existing climatic anomalies and on the basis of ques-
tioning some of the water managers, speculate on the
response to climatic change; (2) to select certain broad
criteria of water systems and speculate on the effect
climatic changes might have on each; and (3) to select a
method of synthetic streamflow generation, use gener-
ated streamflow as a decoupled surrogate for climate,
arbitrarily vary parameters, and observe the effect of
these variations on the safe yield that could be developed
from this streamflow record.
Within the space and time limitations of this paper, all
three will be attempted.
EXAMPLES OF METROPOLITAN WATER-
S U PPLY PROB LE M S
The Washington Metropolitan Region in Virginia, Mary-
land, and the District of Columbia covers about 2800
square miles (7242 Imp. With a population of about 2.4
million, it is the ninth largest metropolitan area in the
United States. Population projections postulate a likely
growth of this area to 5.2 million people by 2000 and 6.8
million by 2020. This population generates a water de-
mand averaging 390 mad (17 m3/sec) on its water supply
today and a demand of 720 mad (31.5 m3/sec) and 925 mad
(41.5 m3/sec) projected for the years 2000 and 202O, re-
spectively (Northeastern United States Water Supply
Study, 1975~.
The major share of the present water demand, about 60
percent, is supplied by the generally unregulated flow of
the Potomac River. The remainder comes from reservoirs
on the Patuxent and Occoquan Creek. The two latter
rivers are almost fully developed, and the Potomac can, in
its present unregulated stage, barely supply present
summer peak demands. Plans for the future foresee a
~3
mixture of regulation of the Potomac, local reservoirs,
interconnections of water-supply systems, emergency re-
strictions, use of water-saving devices in new construc-
tion, and reuse of water from the Potomac estuary and
advanced waste-treatment plants (Northeastern United
States Water Supply Study, 1975~.
To date, the existing water-supply sources and the
institutions managing them have generally been success-
ful. Even during the droughts of the 1930's and 1960's,
restrictions did not pass the minor nuisance levels. This
situation will not continue, however. Growth to date has
been sufficient to outstrip the safe yield of the region's
water sources under drought conditions, and even the
most optimistic believers in controlled growth cannot
show that continued increases in demand, albeit smaller
ones than officially estimated, are likely. Planners have
predicted this situation for a long time, and expansion
plans go back to the 1940's; yet the response has been
greater on rhetoric than on action. Only the suburban sys-
tems have made many significant improvements in source
development, and there has been none at all in the last 10
years.
While water planners blame the environmentalists and
the environmentalists blame the pigheadedness and lack
of imagination of the water engineers, the reasons are
more fundamental. One is the diversity of objectives
relating to the social and economic development of the
region. The other is that the existing institutions are
geared to deal with relatively short-term problems in a
political climate that demands that decisions be made for
clearly visible reasons to achieve immediate results. The
water problem of the area is not obviously visible. It is a
long-range problem and its possible solutions are based
on uncertain assumptions in both the demand and water
aspects assumptions that are based on often unpopular
political decisions such as growth control or on statistical
distributions of natural events that may or may not be
valid.
In the face of these difficulties in decision making on
water-supply development in which steps leading toward
stabilization of supply and increases in water reuse are
taken extremely slowly and under constant opposition
from one side or the other, it would be hard to imagine that
the process could include, with some realism, estimates
of climatic change that are even more uncertain, less
understood, and further in the future than annual and
monthly variability now used in water-planning studies.
The New York Metropolitan Area covers 9345 square
miles (24,200 km2) in the states of New lersey, New York,
and Connecticut. It includes not only New York City but
a number of municipalities with populations exceeding
150,000 and several hundred smaller communities. The
area is not only a population center but contains a large
number of manufacturing plants and the nation's largest
concentration of financial, trade, professional, and com-
munication services. Population is now estimated at
about 19 million and expected to reach nearly 24 million
by 2000 and nearly 27 million by 2020. Water demands
OCR for page 114
114
today average 2760 mad (121 m3/sec) and are expected to
reach 4050 mad (177 m3/sec) and 5120 mad (224 m3/sec)
in 2000 and 2020, respectively. New York City's water-
supply system provides more than 65 percent of today's
demand, but its share is expected to shrink to less than 60
percent by 2020 (Northeastern United States Water Sup-
ply Study, 1975~.
The New York metropolitan area is at present supplied
by a large number of water-supply systems. The system
that serves the city is by far the largest. It draws its
supplies from a series of reservoirs located in the Croton,
Catskill, and Upper Delaware watersheds. Other systems
within the area use the streams of north and central New
lersey and western Connecticut. Safe yield of many of
these water-supply systems is today barely sufficient to
meet demands. The drought of the 1960's required strin-
gent emergency restrictions. No major new water sources
have been developed since the drought, and a compara-
ble period of low supply starting today would likely have
even greater effects.
Studies of additional sources of water supply show that
the most important source for the area would be the
Hudson River either by high-flow skimming or reservoir
development on one or more of its tributaries. The second
regional source, particularly for the New jersey portion, is
the Delaware River, through the controversial Tocks Is-
land project. Lesser sources are in the smaller streams of
New lersey and Connecticut and groundwater in New
lersey and on Long Island. Metering of the New York
City supply is also considered as a method to reduce
demand (Northeastern United States Water Supply Study,
1975).
Here again, acrimonious debates have taken the place
of action. Arguments over the merits of the Tocks Island
area as a park or as a reservoir have been decided in favor
of park development, removing the Delaware River as an
expansion source for the New York-New Jersey met-
ropolitan area. Equally, reservoir development in the
Adirondacks had been practically outlawed by action of
New York's electorate. Water-supply interconnections in
New Jersey, installed during the drought, have been
disconnected. As a result, the region is more susceptible
to shortages now, and its choices for the future have been
significantly narrowed. Institutional arguments between
the state of New York and New York City, the emotional
issue of New York City metering, and the city's monetary
problems further complicate the situation. A Hudson
River high-flow skimming project coupled with metering
in the city appears to have some chance to be im-
plemented and to solve New York City and state of New
York water problems 10 years hence. In New Jersey,
there is as yet no plan.
Even with a Hudson source development, the region's
water system would be sensitive to climatic changes that
change the runoff regimen of the source streams. Three
points make it so. First, the Delaware's delicate balance
between upstream diversions to New York City and the
HARRY E. SCHWARZ
downstream needs for municipal and industrial water
supply and estuarine salinity control could be easily
upset by a relatively small reduction in long-term average
runoff or the occurrence of long droughts. This balance is
codified by existing legal decisions and interstate
agreements; climatic change would bring changes here
too, as discussed in Chapter 4. Second, the amounts avail-
able from highflow skimming of the Hudson, with con-
sideration of both salinity control and fish spawning and
migration, depend on the time-flow distribution. Changes
in that distribution through climatic change could upset
yield estimates. Third, groundwater yield on Long Island
is directly related to local rainfall. Consistent short falls,
for example, would rapidly reduce aquifer yield or in-
crease the danger of saltwater intrusion.
The southeastern New England Metropolitan area in
Massachusetts and Rhode Island encompasses 357
municipalities with an estimated population of 6.5 mil-
lion today. Population projections foresee a growth to 8.5
and 9.7 million for the years 2000 and 2020, respectively.
Water demands in this area were 749 mad (33 m3/sec) in
1965, and these demands are projected to increase to 1519
mad (66 m3/sec) in 2000 and to 1893 mad (83 m3/sec) in
the year 2020 (Northeastern United States Water Supply
Study, 1975).
This area is served today by 369 public water systems
with a combined safe yield of 970 mad (42 m3/sec). The
Metropolitan District Commission (MDC) system serving
Boston and 41 nearby communities is by far the largest.
Its supplies are drawn from tributaries of the Connecticut
and the Merrimack through the Quabbin, Wachusetts,
and Sudbury reservoirs. Other supplies come from the
basins of the Ipswich, North, Taunton, Pawtuxet,
Blackstone, Thames, and Powcatuck Rivers. Impound-
ments in these basins are the usual source of the water
supplies. Present demands are approximately equal to
safe yield, although the demand in the MDC system ex-
ceeds its safe yield by almost 1 percent now. During the
drought of the 1960's, reservoir levels in the MDC system
were very low, and drought of a longer duration would
have caused significant shortages. Other communities in
the area resorted to emergency restrictions, some of quite
stringent nature.
Ongoing planning includes additional diversion of
water from the Connecticut Basin and the Merrimack
Basin, either through high-flow skimming or reservoir
development, as well as through new reservoirs in the
other aforementioned streams in the area and groundwa-
ter development (Northeastern United States Water Sup-
ply Study, 1975~.
The major problem here is that there is a different con-
stituency for the source area western Massachusetts-
and for the user area Boston. These constituencies
are economically and socially divergent and see little
need to accommodate each other. To this must be
added the perception of the supply. The reservoirs are
full right now, and the drought is forgotten. Climatic
OCR for page 115
Climatic Change and Water Supply: How Sensitive is the Northeast?
changes that would produce longer dry and wet periods
would tend to inhibit development further, as little can be
completed even during a 5- or 6-year drought, and 10
years or longer of normal or above normal supply would
allow people to forget the lessons of the last drought
completely.
In a discussion of the problems of water supply and
climatic change with the Chief of the Water Divisions of
the Metropolitan District Commission, that official re-
marked that long-term changes in climate reflected in the
availability of water would increase or decrease the vul-
nerability of this supply system but would not change his
basic problem. "We look ahead, but not necessarily act on
that look" is the way he put it (Matera, 1976~. A decrease
in the mean annual yield would be in his opinion most
detrimental to Boston's water supply. Increased persis-
tency, longer periods of less flow, would be the next most
damaging manifestation of climatic change.
EVALUATION OF METROPOLITAN WATER
SUPPLIE S
There is a set of attributes that appears common to all the
examples of major water-supply problem areas that can be
used to evaluate the effect of climate change. While these
attributes are common to all, the importance of each varies
from area to area. Nine such attributes are considered
here. First, there are four that are related to the resource
itself: yield from unregulated streamflow, yield from res-
ervoirs, yield from groundwater, and quality of raw wa-
ter. The next two related to the effectiveness of water-
supply works: overall systems reliability and effective-
ness of regional interconnections. The last three involve
the management of water supply: magnitude and control
of demand, cost of operation, and pressure on the water-
supply system to expand and its ability to respond to
change.
These attributes of metropolitan water-supply systems
can then be evaluated against the four parameters of
climatic change mentioned in the previous section. An
additional characteristic of climatic change should also be
considered. This is the speed with which these changes
become manifest. Reactions to such changes are likely to
be considerably different if change manifests itself over
the span of a few years or comes gradually over periods as
long as 20, 50, or even 100 years.
A speculative effect matrix could be constructed show-
ing the effects of the enumerated manifestations of cli-
matic change on the nine attributes of water systems.
Table 7.1 presents such a matrix.
A SIMULATION APPROACH
A third way to evaluate the possible significance of cli-
matic changes would be through the use of synthetic
~5
hydrology. Using streamflow as a surrogate for climate,
alternative hydrologic scenarios could be constructed to
cover a wide range of possibilities, permitting an evalua-
tion of system sensitivity to change.
There are two major problems to this approach. First,
the relationship between climatic variations, the way
climatologists see them, and streamflow is largely unde-
fined. This is particularly true when a specific stream and
location on that stream must be considered. The second
problem is the selection of a generating algorithm. Sev-
eral streamflow generation models exist, each having its
partisans and detractors within the hydrologic commu-
nity.
For the initial analysis of this paper, it was assumed that
monthly streamflow adequately described the water re-
source and that its variations could be represented by a
skewed logarithmic lag-one Markovian model. Such a
model can be characterized by four parameters. These are
mean, standard deviation, skew, and serial correlation
coefficients. These parameters can be used to generate
streamflow traces representing alternative futures. By
varying these four parameters, we can simulate some of
the effects of climatic change on systems response. A
computer program developed by Leo R. Beard and the
Hydrologic Engineering Center is available that allows
generation of such alternative synthetic streamflow rec-
ords using observed or modified statistics (U.S. Army
Corps of Engineers, 1971~.
Using the aforementioned mathematical model and
computer program, alternative streamflow records were
generated for the Potomac River at the Point of Rocks
gauge, where the drainage area is 9651 square miles
(24,996 amp. Statistics were computed from the existing
record. Records from 1895 to 1970 were used to compute
the logarithmic mean, standard deviation, skew, and se-
rial correlation coefficient for each month. These statistics
were then used to generate a 1000-year record and eight
alternative "climatically changed" 1000-year records. For
each of the alternative records, one set of statistics was
varied. Table 7.2 shows the assumptions used for each
data generation and the highest and lowest 1-month,
6-month, and 54-month flows, as well as the long-term
average.
As no estimates of likely climatic change were avail-
able, the variations in statistics were arbitrarily chosen.
As can be seen from Table 7.1, variations in the standard
deviation not only greatly increase the range of monthly
flows, they also increased the mean flow. Changes in the
mean generally shift the entire population of data, and
increases in the serial correlation coefficients have rela-
tively little influence. A change of the skew coefficient
had a far greater effect on the one-month extremes than on
the longer and more critical high- or low-flow periods, a
result to be expected since monthly correlations of the
generating algorithm were rather small.
The 1000-year synthetic records generated were pro-
cessed through a computer program developed by the
OCR for page 116
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118
TABLE 7.2 Alternative Streamflow Records for Potomac River at Point of Rocks
Average Flow in Cubic Feet per Second
HARRY E. SCHWARZ
1-Month 6-Month 54-Month
- Total
Basis for Record Generation Highest Lowest Highest Lowest Highest Lowest Record
76-year historical record
Actual record 1895-1970 68,359 706 26,225 943 12,171 6205 9061
1000-year simulated records
Observed statistics
Standard deviation increased 10~o
Standard deviation increased 20%
Log mean decreased logo
Log mean decreased 20~o
Serial correlation coefficient increased logo
Serial correlation coefficient increased 20`Yo
Skew coefficient increased +0.5
Skew coefficient increased -0.5
80,529
112,808
128,932
70,647
43,104
75,762
75,786
167,855
57,011
439
273
192
329
284
358
358
736
159
34,437 1132
36,728 866
42,514 761
28,464 893
25,306 789
32,136 936
31,901 882
51,001 1223
25,720 823
13,528 5455 9076
15,871 5353 9428
17,214 5270 9813
12,846 4896 8152
11,412 4344 7339
14,449 5376 9073
14,636 5315 9073
16,996 5356 9233
12,748 5579 8938
author for the NAB study and adapted for use here by
Bruce Morris, a student at Clark University. This program
subjects the flow of the river under study to varying levels
of drafts while varying the amount of usable storage in the
system from O to that amount needed to meet all drafts
without a month of failure. The program tabulates for
each combination of draft and storage the number of
months in which the target draft could not be furnished,
the number of shortage periods of various length, the
highest and the average shortage, and other information.
Relationships between draft, storage, percent chance of
meeting demand, and the different assumptions of statis-
tical variations were then analyzed. The result of this
analysis was generally disappointing to those who be-
lieve that climatic change should radically alter the
water-supply planning process. No clear picture of the
susceptibility of large water-supply shortages attributable
to a specific statistical parameter developed. For instance,
if 95 percent assurance of supply is required, the Potomac
in its present state can supply about 1400 cubic feet/see
(cis) (938 mad or 130 m3/sec). With the most unfavorable
alternative tested, the yield was 1100 cfs (737 mad or 122
m3/sec) or a reduction of about 20 percent. With the same
unfavorable trace, the full 1400 cts were assured 91 per-
cent of the time. The trace that produced this change
assumed a reduction of the log-mean by 20 percent. The
other alternative traces have less influence on the yield of
the free-flowing river. Figure 7.1 shows the plot between
draft and percentage of time the draft requirements can
be fulfilled.
Adding storage into the system complicates the analysis
and makes it even less satisfactory. The number of points
now available for analysis of the apparently most impor-
tant relationship, that between storage, draft, and
shortages, is small; and storage and shortages vary from
run to run even with the same statistics because of the
random component in the data generation. Therefore,
plots can only be sketched by smoothing and with a
resulting reduction in accuracy. There are strong indica-
tions, however, that major increases in standard deviation
are as important as reductions in log-mean. There are
furler indications that sensitivity to changes in the
streamflow trace increases with the degree of develop-
ment and with a decrease in the level of acceptable risk.
In other words, the increase in storage needed to com-
pensate for alternative scenarios and to maintain a spe-
cific draft increases with the size of the draft and with a
decrease in the acceptable shortage index.
The results of this analysis can be accepted only as very
preliminary. Various phenomena observed, such as the
changes in mean flows accompanying changes in stan-
dard deviations, need further analyses. Also, other
generating algorithms, including non-Markovian models,
should be studied. Work toward this end has been ini-
tiated by the author in cooperation with lames Wallis and
others.
CONCLUSION
What does all this mean to those who must plan and
manage the water supply of the northeastern United
States? Apparently it has no importance to them now.
There is not yet sufficient knowledge of climatic change
or its effect on water supply to suggest any rational
change in public policy. If, in addition, we add in the
uncertainty of the timing of possible climatic changes,
then it becomes even more certain that current planning
does not have to be concerned with climatic change. On
balance, it is the more easily perceived uncertainties at
OCR for page 119
Climatic Change and Water Supply: How Sensitive is the Northeast?
100
90
FIGURE 7.1 Potomac River at Point of
Rocks. Draft-duration relationship without
storage.
- o
O_
Q 80—
. _
a:
en
. _
~ 70—
. _
o
a'
cn
a'
cat
a)
cat
60—
50
40 -'
hand that are the appropriate guides to policy-making. If
this study has any relevance to ongoing water-supply
planning, it might reinforce the need for flexibility in
plans and argue for a more adequate safety margin in the
development of water supplies.
The conclusions of this chapter are as follows:
1. A full understanding of the possible relationships
between climatic changes and water supply, its planning,
and management is a desirable goal.
2. At minimum, a range of likely climatic-change
scenarios should be available to the water-resources
planner.
3. Much more detailed and complete analyses are re-
quired to assess the sensitivity of existing or projected
water supplied to climatic variations. Such work should:
(a) Consider several streams throughout the region.
(b) Test different models for streamflow generation
including those that preserve skewness directly without a
logarithmic transformation and those,that allow for
/
119
all other
futures tested
log M -1 C)% I\
I\\
109 M - 20% \\ \
1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 10
Draft in 1000 cfs
greater long-term persistence than is possible with the
Markov model used in this study.
(c) Postulate smaller increments between alterna-
tives and make a far greater number of iterations for each
alternative so that observed differences cannot be at-
tributable to noise in the data.
(d) Use more detailed models of urban water-supply
systems, including economic loss functions.
Beyond these preliminary results, it is appropriate to
speculate on the changes in water-supply planning and
decision-making occasioned by findings that significant
climatic change is at hand or that such changes are of no
consequence. In the latter case, unwarranted con-
siderations should not be allowed to complicate and delay
water supply plans and their implementation. If, how-
ever, significant climatic changes are likely, present
planning methods must take them into account.
The most straightforward incorporation of information
on climatic change would be the development of a series
OCR for page 120
120
of water-resource projections analogous to Bureau of the
Census population projections. These could be prepared
on a national basis and then adapted to specific regional
characteristics and uses. In this fashion, consistency
could be maintained, while variations dictated by specific
local circumstances could still be considered. Such alter-
native projections would complicate the hydrologic
studies needed for water-supply planning and manage-
ment, but the institutional decision process would not be
significantly changed for near-term and midterm con-
siderations. Should really large climatic changes appear
likely for Me more distant future, political decision-
makers must be sensitized to deal with long-range plan-
ning fixtures and their associated increase in uncertain-
ties.
REFERENCES
Landsberg, H. E., C. H. Yu, and L. Huang (1968~. Preliminary
Reconstruction of a Long Time Series of Climatic Data for the
Eastern United States, Tech. Note BN-571, Sept.
HARRY E. SCHWARZ
Matera, J. (1976~. Director, Division of Water Supply, Metropoli-
tan District Commission, Boston, Mass., personal communica-
tion.
NAR (1972a). North Atlantic Regional Water Resources Study,
Coordinating Committee, North Atlantic Regional Water Re-
so~4rces Study Report, Fords Atlantic Div.? U.S. Arrny Corps of
Engineers, New York, June.
NAR (1972b). North Atlantic Regional Water Resources Study,
Coordinating Committee, North Atlantic Regional Water Re-
sources Study,Append~x R. Water Supply' North Atiantic Div.,
U.S. Army Corps of Engineers, New York, June.
Northeastern United States Water Supply Study (1975~. Interim
Report~ritical Choices for Critical Years, Norm Atlantic
Div., U.S. Army Corps of Engineers, New York, Nov.
Todin, E., and J. R. Wallis (1974~. Using cars for duly or longer
period rainfall-runoR modeling, paper presented at Workshop
on Mathematical Models in Hydrology, Pisa, Italy, Dec.
U.S. Army Corps of Engineers (1971~. Hydrologic Engineenng
Center, HECK Monthly Streamflow Simulation, Davis, Celia,
Feb.
U.S. Water Resources Council (1968~. The Nation's Water Re-
sources, U.S. Government Pnnfing Office' Washington, D.C.
Representative terms from entire chapter:
water supply
