May 19th US Global Change Seminar: "Potential Consequences of Global Warming for the Northwestern US: Water Resources and Marine Ecosystems"

Tony Socci tsocci at
Wed May 13 16:42:53 EDT 1998

                      U.S. Global Change Research Program Seminar Series

          Potential Consequences of Global Warming for the Northwestern US:
                          Water Resources and Marine Ecosystems

What are the dominant patterns of climate variability in the Pacific
Northwest?  How has climate variability impacted Pacific northwest
resources?  What are the climate projections, as well as projected impacts,
for the Northwestern US, for the next 50-100 years?  What are the likely
impacts of a general climate warming on water resources and marine
ecosystems in this region?  What impact will these changes likely have on
people living in this region of the US?

                                                         Public Invited

                                      Tuesday, May 19, 1998, 3:15-4:45 PM
          NEW LOCATION - Dirksen Senate Office Bldg., Room 628, Washington, DC
                                                     Reception Following


Melissa Taylor, Deputy Executive Director, National Assessment Coordination
Office, Washington, DC


Dr. Dennis P. Lettenmaier, Department of Civil Engineering, University of
Washington, Seattle, WA

Dr. Nathan Mantua, Department of Atmospheric Sciences, University of
Washington, Seattle, WA


How can we assess the impacts of climate change on the natural resources in
any given region? Lessons learned from the past century of observed climate
impacts on sectors like hydrology and fisheries serve as real-life measures
for vulnerabilities and sensitivities to changing climate parameters.

For at least the past century of climate variability in the Pacific
Northwest, El Niño-Southern Oscillation (ENSO) has been a major driver at
year-to-year time scales, while the Pacific Decadal Oscillation (PDO) has
contributed strongly at decade-to-decade time scales.  Spatially, the ENSO
and PDO patterns have similar signatures in the Pacific Northwest: warm
phases of both patterns are associated with mild winter land and coastal
sea surface temperatures, and below average precipitation, snowpack and
streamflows; cold phases of ENSO and PDO typically bring cool land and sea
surface temperatures, above average snowpack, and abundant water supplies.

                                  Water Resources of the Pacific Northwest

Of the potential effects of global warming, the implications for hydrology
(the natural system by which precipitation makes its way into streams and
eventually the oceans) and water resources (the "built" or managed system
that makes freshwater available for human uses) are among the most
important to society.  In many parts of the world, including much of the
U.S., the demand for consumptive (e.g., water supply) and non-consumptive
(e.g., navigation, hydroelectric power generation, industrial cooling,
instream flow) supplies of fresh water is barely balanced by sustainable
surface and groundwater sources.  In addition, water is essential for crop
growth, and water management is an important factor in the reliability and
sustainability of food supplies.

The hydrology of the Pacific Northwest, like much of the Western U.S., is
dominated by two factors: a Mediterranean climate (most precipitation
occurs in the winter months) and a dominant influence of topography, with
much of the precipitation at high elevations occurring as snow in winter,
which does not contribute to stream flow until the following spring or
summer.  The hydroclimatology of the region is also strongly affected by
the Cascade Mountains.  Rivers east of the Cascades are dominated by spring
snowmelt, with seasonal peak flows occurring in late spring and early
summer. Rivers on the west side are dominated by winter rains, augmented by
spring snowmelt at higher elevations, so that many streams have both a
winter and spring peak.  Furthermore, most major floods on the west side
occur as a result of intense rains and snowmelt in the late fall, while
east side floods occur as a result of a mixture of winter rain-on-snow
events and spring melt.

The water requirements of the Pacific Northwest are met primarily by
surface water.  The major river in the region, the Columbia, is managed by
an extensive system of over 100 reservoirs, which is operated for
irrigation, flood control, hydropower, navigation, recreation, and
fisheries protection and enhancement.  Nonetheless, the total storage in
the Columbia River reservoirs is equivalent to only about a third of the
river's mean annual flow.  Therefore, the reservoir system acts primarily
to store water from the spring high flow period to be released during the
summer and fall; it does not, to any significant extent, store water from
one year to the next.  Reservoirs on smaller west-side streams are likewise
small relative to the mean annual flow of the rivers.  West-side streams
are operated primarily for municipal water supply, fisheries protection and
enhancement, and hydropower.

                                      Climate Impacts on Marine Ecosystems

Climate-induced changes in marine ecosystems trigger a cascade of
ecological impacts throughout the marine food-web.  Such impacts are often
most visible in their impacts on higher-order predators like sea birds,
marine mammals, and commercially popular fish stocks. The effects of
anthropogenic climate change (greenhouse warming) on marine ecosystems will
most likely occur via multi-scale atmosphere/ocean circulation changes, and
not by direct (radiatively driven) heating of the oceans.

>From the perspective of marine ecosystems, Pacific interdecadal climate
shifts between warm and cold climate phases (Pacific Decadal Oscillation)
have been linked to decade-to-decade changes in Pacific salmon production
from western Alaska all the way to central California.  In addition,
shorter-lived El Niño-related changes to the marine environment have caused
temperature and spatial dislocations in the distribution of many open-ocean
bird and fish species, as well as important changes in overall ecosystem
productivity.  Common to both El Nino- and PDO-related marine climate
fluctuations are regionally specific swings in primary and secondary
productivity (via phyto- and zooplankton production, respectively) that
trigger a cascade of ecological impacts throughout the marine food web.
Generally speaking, processes important to marine ecosystems take place at
regional and smaller scales.  Global-scale climate models now used to
investigate the impacts of increased concentrations of greenhouse gases
globally, are not yet as useful at these regional and smaller scales.
Based upon observed climate impacts on marine ecosystems, the following
impacts are likely to occur as a response to future anthropogenic climate
change: 1) species distributions will change;
2) there will be winners and losers; warm phases of the PDO correspond to
high productivity in the Gulf of Alaska and low productivity in the
California Current (and vice-versa with the cold phase of the PDO); 3)
ecosystem surprises are to be expected; and 4) if present day El Nino and
PDO-like warm episodes are a model for future climate changes, warm water
pelagic fish (e.g., albacore, mackerel, sardines) will become more common
in nearshore and higher latitude waters of the northeastern Pacific.

                    Water Resources in the Pacific Northwest in a Warmer World

The dominant effect of a warmer climate on the streams of the Pacific
Northwest would be that less wintertime precipitation would fall as snow
and more would fall as rain, resulting in decreased snowpack accumulation,
and therefore increased winter flows and decreased spring and summer flows.
This pattern would alter the flow patterns away from spring peaks and
toward a rainfall-dominated peak in the winter. This change would, in
general, create more stress on reservoir systems, as the natural storage of
snowpacks would have to be replaced with reservoir storage to meet current
water demands.  Furthermore, the potential would exist for increased fall
and winter flooding, especially in west-side streams, and perhaps in some
smaller east side streams that are not generally susceptible to winter
floods in the current climate. Consequences of these changes for water
resource management include the need for more deliberate spillage in
west-side rivers and the possibility for decreased water supply in summer,
given reservoir storage limitations.

In order to understand these consequences more fully, the climate scenarios
from three atmospheric General Circulation Models (GCMs) were used in
conjunction with regional hydrologic and reservoir models to assess the
impacts of the scenarios on Pacific Northwest hydrology and water
resources.  Notwithstanding that current GCMs cannot provide detailed
regional-scale, watershed-specific information, modeling studies can,
nonetheless, indicate the general nature of the response of the hydrology,
and managed water resource systems, to changes in the region's climate.

The model studies show that the projected shifts in the timing of runoff
(associated primarily with temperature), and volumes of runoff (associated
primarily with changes in precipitation) would have important implications
for energy production, fish protection, and irrigation water supply in the
region.  The changes in seasonal timing of runoff associated with the
warmer climate scenarios tend to be advantageous for hydropower production
during the winter high demand period, but may jeopardize subsequent
reservoir refill and hydropower production for the following year.   In one
of the climate scenarios, however, considerably reduced precipitation would
result in failure to meet firm-energy production requirements more often
under current climate conditions.  The changes in the seasonal pattern of
streamflow generally would have negative implications for fish protection,
especially, for instance, in terms of the reliability of the Columbia River
reservoir system to meet the statutory minimum flow requirements for McNary

The ability of the reservoir system to meet irrigation demands generally
would decline under the climate warming scenarios; particularly those
accompanied by significant decreases in streamflow volumes. These changes
would be especially important in the upper Snake River basin, in part
because of the high irrigation demands there, and in part because the
seasonal pattern of Snake River streamflows is more sensitive to climate
warming than is the main stem of the Columbia. Recreation would be impacted
as well. Recreation benefits for the Columbia River reservoirs depend on
high reservoir levels during the summer, targets which would be more
difficult to meet with reduced spring streamflows. On the other hand, the
severity of spring floods would generally be reduced in the Columbia River

   El  Nino and the PDO: Real-Life Models of Climate-Driven Changes in
                                  Marine Ecosystems

A growing body of research has shown a close connection between
fluctuations in the northeastern Pacific marine ecosystems and large scale
features of Pacific climate. Large amplitude, year-to-year climate
fluctuations, often associated with El Nino/La Nina, have dramatic impacts
on marine ecosystems in the northeast Pacific.  Typical El Nino-related
environmental changes include a warming of the coastal upper ocean, raised
sea levels, increased poleward coastal currents, and a deepening of the
ocean surface layer.  Off the west coast of the continental US, these
frequent warming events often lead to a reduction in phytoplankton and
zooplankton production, which in turn sets the stage for dramatic crashes
in overall fishery productivity.  Large die-offs have been observed among
higher-level predators like sea-birds, marine mammals, and some salmon
populations during the strong climate warming events of 1983 and 1997/98.

Perhaps even more important to the northeastern Pacific marine ecology are
the decade-to-decade environmental shifts associated with the Pacific
(inter)Decadal Oscillation (PDO).  The PDO has been described as an
interdecadal El Nino-like pattern of climate variability.  Warm phases of
the PDO bring decadally-persistent El Nino-like environmental changes.
Long-lived (20 to 30 year) climate fluctuations associated with the PDO
have been linked to dramatic and persistent changes in the large marine
ecosystems of the North Pacific Ocean.  Since the late 1970's (the last
switch from cold to warm PDO regimes) these changes include crashes in
Alaska Murre (sea-birds) and Stellar Sea Lion populations, significant
reductions in Halibut growth rates, sharp declines in Alaska King Crab and
shrimp fisheries, altered salmon migration routes, and an era characterized
by record salmon production in Alaska but very low salmon production in
Washington, Oregon, and California.

Climate-related changes to streamflow regimes will also play a major role
in determining the future of Pacific salmon.  The PDO-related changes in
salmon abundance previously noted are thought to result mostly from changes
in the marine environment.  For Alaska salmon, the typical positive PDO
year brings enhanced streamflows and nearshore ocean conditions favorable
to high productivity.  Generally speaking, the converse appears to be true
in the Pacific Northwest.

The specter of a greenhouse climate with warmer, wetter winters and warmer,
drier summers in the Pacific Northwest suggests significantly reduced
snowpack.  Such streamflow regimes would be less favorable for salmon than
those now observed with El Nino and PDO.  Such scenarios paint a picture of
an increased frequency of scouring, nest-damaging fall and winter floods,
with reduced flows and elevated stream temperatures in the critical low
flow summer periods.


Dennis Lettenmaier is a hydrologist with interests in continental and
global-scale land surface hydrology, and smaller-scale sensitivity of
catchment hydrologic processes to land cover change.  He is presently
involved in several projects seeking to improve the representation of the
land surface, especially the representation of streamflow and
evapotranspiration, in climate and numerical weather prediction models.  He
is a Professor of Civil Engineering at the University of Washington, where
he has been on the faculty since 1976.

Since 1995 Dr. Lettenmaier has worked with NOAA's Joint Institute for the
Study of the Atmosphere and Oceans (JISAO) at the University of Washington,
where he participates in a NOAA Global Change project, "An Integrated
Assessment of the Dynamics of Climate Variability, Impacts, and Policy
Response Strategies for the Pacific Northwest", as the hydrology and water
resources team leader.  He has participated in several assessments of the
effects of climate change on  hydrologic and water resources, including the
1989 EPA Report to Congress, for which he directed the study on California
Water Resources, and a recent U.S. Army Corps of Engineers study of the
climatic sensitivity of six water resources systems throughout the
continental U.S.  He is a Fellow of the American Geophysical Union and the
American Meteorological Society.

Dr. Lettenmaier received his Ph.D. degree from the University of
Washington's  Department of Civil Engineering in 1975.

Nathan Mantua is an atmospheric scientist whose interests are in
understanding ocean-atmosphere climate dynamics.  He is presently involved
in interdisciplinary studies related to climate variability,
seasonal-to-interannual climate prediction, and the human and ecological
dimensions of climate change.

Since 1995 Dr. Mantua has worked with NOAA's Joint Institute for the Study
of the Atmosphere and Oceans (JISAO) at the University of Washington where
he has played a key role in a NOAA/ Global Change project  titled "An
Integrated Assessment of the Dynamics of Climate Variability, Impacts, and
Policy Response Strategies for the Pacific Northwest."  This study is an
interdisciplinary effort focused on understanding the role of climate
information in resource management.  The JISAO team is investigating both
short- and long-term climate issues, the former in terms of the use of
seasonal-to-interannual climate predictions, the latter in assessing the
Pacific Northwest's vulnerability to potential anthropogenic climate

Dr. Mantua has also had a life-long involvement with the commercial and
sport salmon fishing industries, and as a result, has a unique
understanding of the connections between climate and fishery science.  His
versatility in these two fields has led to a number of collaborations with
fisheries scientists at the University of Washington and at other research
institutions.  He was recently appointed to the Scientific Steering
Committee (SSC) for the international Global Oceans Ecosystems Dynamics
(GLOBEC) program, a NOAA/NSF (Global Change)-sponsored effort devoted to
better understanding the role of climate variations in marine ecosystems.

Dr. Mantua received his Ph.D. degree from the University of Washington's
Department of Atmospheric Sciences in 1994, and shortly thereafter, was
awarded a NASA Global Climate Change Fellow.

The Next Seminar is scheduled for Thursday, June 11, 1998

Planned Topic: Projected Atmospheric and Climatic Implications of Asian

For more information please contact:

Anthony D. Socci, Ph.D., U.S. Global Change Research Program Office, 400
Virginia Ave. SW, Suite 750, Washington, DC 20024; Telephone: (202)
314-2235; Fax: (202) 488-8681 E-Mail: TSOCCI at USGCRP.GOV.

Additional information on the U.S. Global Change Research Program (USGCRP)
and this Seminar Series is available on the USGCRP Home Page at:  A complete archive of seminar summaries is also
posted at this site.  Normally these seminars are held on the second Monday
of each month.

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