February 10th US Global Change Seminar: "Assessing Regional Climate Impacts Using Global-Scale General Circulation Models"

[Tony Socci]

           U.S. Global Change Research Program Second Monday Seminar Series


 Assessing U.S. Regional Climate Impacts Using Global-Scale General
                                    Circulation Models


     Is it feasible to use global-scale general circulation models (GCMs) to
     assess climate impacts on regional and local scales?  How reliable are
     these methods and how well do they estimate regional climate factors such
     as rainfall and stream flow?  What can such estimates tell us about the
                            regional scale impacts of climate change?


                                                          Public Invited


                                     Monday, February 10, 1997, 3:15-4:45 PM
                         Rayburn House Office Bldg., Room B369, Washington, DC
                                                   Reception Following


INTRODUCTION

Dr. Joel Scheraga, Director of the Climate, Policy, and Assessment
Division, U.S. Environmental Protection Agency, Washington, DC.

SPEAKERS

Dr. Eric J. Barron, Director of the Earth System Science Center,
Pennsylvania State University, College Park, PA.

Dr. Robert G. Crane, Professor of Geography and Associate Dean for
Education, College of Earth and Mineral Sciences, Pennsylvania State
University, College Park, PA.


                                                      Overview


        Global-scale climate models (GCMs) can be successfully employed in
examining the potential climate impacts of global warming on a regional
scale, using a variety of recently developed techniques.  Regional climate
change results (assuming a doubling of the atmospheric CO2 concentration)
derived from such techniques project, for example, that the northeastern
U.S. will have higher wintertime precipitation while the southwestern U.S.
is projected to be substantially drier during winter.  In summer, warmer
global conditions are predicted to lead to increased precipitation over the
southern U.S.  These results would suggest that the Susquehanna River
Basin, which is being examined closely, would receive higher levels of
precipitation during every season in a doubled CO2 world, with the largest
increases being in spring and summer.

        Global climate models, coupled with careful, regional modeling and
analysis techniques, are the only tool available for providing long-term
predictions of future climate and for assessing the climate implications of
human activities.  These comprehensive models require considerable computer
resources, and consequently, they resolve the Earth's atmosphere and land
surface only at very coarse spatial resolution (hundreds of miles).  Using
this spatial resolution, the ability of global models to produce
simulations of the variables essential for assessing the regional impacts
of global climate change on human or ecological systems is generally
limited.  For example, because precipitation is highly variable in time and
geographic location, the prediction of this critical variable by global
models tends to be inadequate for use in evaluating the regional
consequences of precipitation changes for agriculture and/or water
resources.

        In order to address this fundamental dilemma, two unique approaches
are being explored so that results from global-scale climate models can, in
fact, be successfully transformed into information that is useful in
examining regional-scale changes relating to economic or ecological
interests in a particular area.  The first technique is called "nesting,"
and involves embedding a high resolution, limited-area climate model within
a global-scale General Circulation Model (GCM) of the atmosphere.   This is
now being done for the United States.  With this technique, the prediction
of precipitation, particularly in the central U.S., is substantially
improved compared to the global-scale model.  The model results show a high
correspondence with observations.  Furthermore, the high resolution
precipitation prediction provides a firm foundation for predicting river
flow in major regions of the U.S. such as the Susquehanna River Basin which
feeds into Chesapeake Bay.  This has been demonstrated by an ability to
simulate precipitation over the Basin and to match observed  measurements
of precipitation and water flow when the mesoscale model is coupled to a
hydrologic model.  The reason for the improved prediction of precipitation
in the nested model is directly related to achieving better representation
of the precipitation physics and because of the improved incorporation of
topography.

        Statistical techniques also have significant potential as a method
of "downscaling" (scaling from a coarse resolution model to a high spatial
resolution prediction for a region).  As an example, a set of so-called
"neural net transfer functions" (a set of mathematical expressions)  are
being used to derive high resolution precipitation predictions for the
Susquehanna River Basin based on global-scale GCM predictions of the
circulation and humidity, an approach similar to what is used to derive
local weather forecasts.  The downscaled precipitation is, once again, a
close match to the observed data.

        The improved ability to simulate precipitation using both
downscaling methods and nested models indicates potential for greatly
improved estimates of the regional impacts of climate change.  For this
reason, both techniques are being used to produce precipitation predictions
for the initial case of a warmer world resulting from a doubling of
atmospheric carbon dioxide.  The nested model domain includes the entire
continental United States.  In winter, the northeastern U.S. is predicted
to have higher precipitation (rising from an average of 1-2 mm/day to 2-4
mm/day), and the southwestern U.S. is predicted to be substantially drier.
In summer, the largest changes from a doubled CO2 concentration involve
increased precipitation over the southern U.S.  The neural net technique,
which is centered on the Susquehanna River Basin, indicates higher
precipitation during every season in a doubled CO2 world, with a
substantial increase (32%) in spring and summer.  The smallest increases
occur in the southeastern part of the Basin.  Such increases would have
dramatic effects on river flow, on valley communities, and on the
Chesapeake Bay.


                                                             Biographies

Dr. Eric Barron received his bachelor's degree in geology from Florida
State University in 1973.  He then began the study of oceanography and
climate at the Rosenstiel School of Marine and Atmospheric Sciences at the
University of Miami, receiving his master's degree in 1976 and his Ph.D. in
1980.  His career in climate modeling was initiated with a supercomputing
fellowship at the National Center for Atmospheric Research (NCAR)  in 1976.
In 1980 he accepted a postdoctoral fellowship at NCAR in Boulder,
Colorado, and in 1981 he joined the staff in the Climate Section at NCAR.
In 1985 he returned to the University of Miami as an Associate Professor.
In 1986 he became a member of the Pennsylvania State University faculty as
Director of the Earth System Science Center and an Associate Professor of
Geosciences.  His position currently remains the Director of the Earth
System Science Center and Professor of Geosciences.  Areas of
specialization include, global change, numerical models of the climate
system, and study of climate change throughout Earth history.


Dr. Robert Crane received his bachelor's degree in physical geography from
the University of Reading, England, in 1976.  He did graduate work in polar
climatology, microwave remote sensing, and sea ice-atmosphere interactions
at the University of Colorado's Institute for Arctic and Alpine Research
(INSTAAR) and the National Snow and Ice Data Center, receiving a Master's
degree in 1978 and a Ph.D. in 1981.  As a Research Associate in the
Cooperative Institute for Research in Environmental Sciences (CIRES), he
continued his work on the microwave remote sensing of sea ice.
Subsequently, Dr. Crane spent a year as a visiting professor at the
University of Saskatchewan.  He joined the faculty of the Pennsylvania
State University in 1985.  Dr. Crane held a joint appointment in the
Department of Geography and in the Earth System Science Center from 1985 to
1993, serving as Associate Director of the Center from 1990 to 1993.  He
was appointed Associate Dean for Education in the College of Earth and
Mineral Sciences in 1993, and currently holds the position of Associate
Dean and Professor of Geography.  His areas of specialization include sea
ice-atmosphere interactions, synoptic climatology, and regional-scale
climate change.


                      The Next Seminar is scheduled for Monday, March 3, 1997

Planned Topic: Ecological and Climatic Consequences of Human-Induced
                                  Changes in the Global Nitrogen Balance


For more information please contact:

Anthony D. Socci, Ph.D., U.S. Global Change Research Program Office
Code YS-1, 300 E St., SW, Washington, DC 20546
Telephone: (202) 358-1532; Fax: (202) 358-4103
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:
http://www.usgcrp.gov. Normally these seminars are held on the second
Monday of each month.