By
D. Briane Adams and Kathy Jacobs
Water-related concerns
are central to this National Assessment because the hydrologic
(water) cycle is a fundamental component of climate, and because water
plays a role in every sector and region in the
U.S. Despite many remaining uncertainties, a significant amount
of research has been done on the connections between
climate change and water resources in the U.S. (a searchable
bibliography of over 850 scientific articles is available
at http://www.pacinst.org).
Water Sector
Assessment Timeline
The
Water Sector Assessment of the National Assessment is rapidly coming
to a close. During the past year, the sector sponsored a
specialty conference on the water resources effects of climate
variability and change that was hosted by the American Water
Resources Association (AWRA). A 400 plus page proceedings
was produced from the conference (information on how to obtain the proceedings can be found
by contacting AWRA through their web site: http://www.awra.org).
The conference produced many scientific papers
that introduce new research, and state of the science papers that have helped assess
the current knowledge of climate effects on water resources.
Subsequent to the conference, many papers were submitted to AWRA's peer
reviewed Journal of the American Water Resources Association
(JAWRA), and were published in the dedicated December 1999 issue
of JAWRA. The April 2000 issue will also be dedicated to the assessment,
and will contain a new set of papers.
The sector has produced a draft of its final report for the National
Assessment Synthesis Team (NAST), which is currently undergoing an internal
review by assessment team members. It is anticipated that the internal
review will be completed by the end of March. The draft report will
then be forwarded to other National Assessment sectors, the National
Assessment
Working Group (NAWG) and the NAST. It will simultaneously be put on
the USGCRP web site for a public comment period (about 30 days) before
final publication of the report. The final report should be available
in June 2000.
Water Concerns All Regions and Sectors
Increases in greenhouse gas concentrations may affect
global temperature and lead to changes in the amount,
timing and geographic distribution of rain, snowfall and
runoff. Changes are also likely
in the timing, intensity and duration of extreme events such as
floods and droughts. Such changes may have greater impacts on
the regions and sectors than changes in average temperature or precipitation.
Higher demand for water may occur in areas where increased temperature
results in higher evapotranspiration. If precipitation patterns
do not offset the effects of higher temperatures, some regions
will experience greater difficulty in meeting their
water supply needs. Key variables in determining
likely impacts and responses include changes in soil moisture
and cloud cover, as well as the response of vegetation to
changes in moisture, temperature and increased carbon dioxide
availability.
While significant concerns in the agricultural, forestry, ecosystem,
energy and human health sectors relate to the basic issue
of water availability, there may be some serious impacts
on water quality as well. There is a direct
relationship between quantity of flows and dilution
of constituents of concern. For example, increased intensity
of rainfall may result in increased erosion and flushing
of contaminants into watersheds. Higher water temperature
will also affect the ecology of wetlands, lakes and streams.
Much less research has been done to date on these issues.
Expected
changes in precipitation often do
not offset increased evapotranspiration, though
regional impacts are likely to vary. Therefore, a rise in
average temperature, even in the context of higher precipitation, is
likely to seriously impact aquatic systems, including
riparian habitats and wetland areas. Certain coastal systems,
prairie potholes and arctic and alpine ecosystems
are thought to be especially vulnerable. Major stresses
within the contiguous U.S. are likely to come from
changes in the mean precipitation as well as increases in intensity.
Health-related
issues that have been linked to changes in the hydrologic
cycle include potential for increases
in water-borne pathogens such as Cryptosporidium and vector-borne
diseases such as encephalitis, as well as outbreaks in marine
pathogens associated with red tide. Hantavirus, a
disease spread by deer mice, has also been linked to ENSO
extreme climate variability. With higher rainfall,
rodent populations tend to increase, which increases the chance of human
contact and disease. Inadequate
water and wastewater infrastructure, common along the Mexican
border and in some rural areas, leads to high
risk for health problems. Since the public has very
high expectations regarding water quality, and perceptions of health
risks are not always accurate, health issues may have a high profile
and require particular attention.
Supply
and Demand Issues
The
primary water resource issue for the U.S. is the distribution
of supply and demand, rather than the total quantity of water available.
The nature of water concerns varies by region across the country.
For much of the western U.S., water resources are
often separated both by time and distance from water demands.
As a result, substantial infrastructure has been
developed to store and transport water supplies
(for example, from the Colorado River and Northern California
to the Southwest and Southern California). There are
more than 80,000 dams and reservoirs in the U.S., and millions
of miles of canals, pipes and
tunnels. Although this infrastructure
is sophisticated and has allowed the development
of urban and agricultural areas, it is also a source
of vulnerability to climate change, partially because it
has been designed based on the
assumptions that future conditions will be
similar to the historically observed climate. Some
argue that the robustness built into the system provides some
margin of safety, but failure to re-evaluate these
assumptions and identify key vulnerabilities may prove to be costly
in the future.
Virtually all indices of vulnerability relative
to water have identified the over-appropriation of western
streams and rivers and over-drafting of groundwater supplies
as key issues. The assessment identified indicators of
water resource vulnerability for the
U.S. and found that the most vulnerable regions
were the high irrigation areas along
the eastern drainage of the Rocky Mountains,
the Central Valley of California, and southern California.
The overall index indicates that the most vulnerable watersheds are
in the West, Southwest and Great Plains.
Water
supply issues in the eastern U.S. relate to aging infrastructure
and inadequate storage capacity during times of drought.
Flood control issues are also of concern.
In general, local surface water and groundwater supplies
are available for domestic and industrial use without major water transfers
between basins, but excess reservoir capacity
to respond to drought is quite limited. In some areas, such
as New York City, reservoir function is threatened by upstream
development. New York and other cities also have serious
problems with water main breaks causing flooding and other
damage on a regular basis.
Economic
Context
This assessment has focused on identifying
areas of existing stress and vulnerability and on evaluating new problems
that climate change may bring. It should be noted that even in
the absence of climate change, adapting to existing stresses (such
as aging infrastructure, inadequate water supplies for areas
of rapid growth, etc.) and increased pressures from population
growth would be expensive.
It is estimated that the annualized water-related
costs associated with the demands of an increasing population are
likely to approach $13.8 billion by 2030.
The impacts of climate change on these costs depend on the
nature of the changes. The estimated costs include
investments in new water supplies and conservation measures, as
well as the impacts on stream flows and irrigated
lands. The costs would be much higher if climate change were to
significantly decrease water availability (as with the Canadian
Climate model) or affect the magnitude and timing of extreme
events. This is because the current infrastructure and management
practices are designed based on the historical
climate conditions.
Socioeconomic
and Institutional Context
Population pressures, increasing urbanization,
land use practices and climate change are all likely
to increase stress on water supply systems. The need
to reserve water for in-stream uses,
endangered species protection, recreation and American
Indian water rights settlements also places new demands
on a water rights system that in many parts of the
country is already seriously stressed.
As society changes, its value system also evolves. Placing
more value on protection of fish and wildlife habitat and recreational
values may force institutional change at the same time that new stresses
are appearing due to climate change. Although there is substantial
uncertainty in the projections of changes in runoff that are derived
from the climate models, socioeconomic conditions may be even less predictable.
There is a need for more flexible
institutional arrangements and more effective ways of
making water policy decisions in order to adapt
to changing conditions (not just changes in
climate, but multiple existing stresses). The legal
framework for water rights varies from state to state,
with nearly infinite permutations at the
local level. The one characteristic that is
typical of most institutions related to water is inability
to respond well to changing socioeconomic
and environmental conditions. This is primarily
because institutions tend to reflect existing
water right holders' interests, and substantial investments
are made based on expectations regarding availability
of supplies. Devising new legal and related
institutions that can introduce the necessary
flexibility into water management
without destabilizing investors' expectations,
while at the same time incorporating
public values (ecological, recreational, aesthetic, etc.) is a
significant challenge.
Some innovative institutions are developing in
response to specific problems. For example, the water banks established
in California to respond to drought, and in Arizona to respond to long-term
supply reliability issues offer some protection to
existing water rights while
providing much-needed flexibility. Water banks
generally provide opportunities for short-term transfers of
agricultural water supplies to municipal
end users on a willing buyer/willing seller basis.
In the case of the Arizona Water Banking Authority,
excess Colorado River water is being stored underground through
recharge projects to offset future shortfalls
in supply. This opportunity is expected to be
available on an interstate basis among the Lower Colorado
Basin states in the near future.
Similar types of contingency planning between
jurisdictions and water rights holders could prove beneficial
in responding to short-term emergencies. Longer-term
changes in climatic conditions that would
require permanent changes to legal systems could be more problematic.
Many have argued that an open market in water
rights would help resolve conflict and increase efficiency
because water would flow to the highest and best use based
on willingness to pay. It is widely acknowledged that market-related
solutions may relieve some water supply problems, especially in
the western U.S. However, water marketing
is an imperfect solution. Of particular concern
are third party impacts in water transfers, and overall equity
issues. Water markets are developing in many states, but
they are generally regulated markets in order
to protect the public interest. Mechanisms exist
to identify economic values for non-market goods
and services, but water rights for non-market
values such as ecosystems, aesthetics and recreation
have difficulty competing with major economic forces. There
is also a risk that disproportionate burdens will be placed on
the social groups that can least
afford it (such as rural farming communities, Native Americans and communities
along the Mexican border with inadequate infrastructure).
Legal experts say true (unregulated) markets have seldom existed
for water rights and there are good reasons
for believing that they seldom will. This is because water, like
air, is viewed as a "public good," which means that
people cannot realistically be excluded from using it, at least
on a subsistence basis. There is reluctance
to pay the full cost of water, including the replacement cost;
people are generally charged only the cost for capture and distributing
water. Key factors in developing a workable market are determining
whether the market will enable consumers to meet their needs and whether
government regulation and assistance at the margins can correct for
market failures.
For more information, contact:
D.
Briane Adams, Staff Hydrologist, USGS; 3850 Holcomb Bridge Road, Suite
160, Norcross, GA 30092-2204; Telephone: (770) 409-7700; Voice Mail:
(770) 409-7708; FAX: (770) 409-7725; E-mail: dadams@usgs.gov;
Homepage: http://www.usgs.gov
National
Assessment 
