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Ten-Year Simulations
of
U.S. Regional Climate
Z. Pan, W. J. Gutowski, Jr., R. W. Arritt,
E. S. Takle, F. Otieno, C. Anderson, M. Segal
Iowa State University
J. H. Christensen, O. B. Christensen
Danish Meteorological Institute
Copenhagen, Denmark
START Temperate East Asia Regional Center
(February 2000)
Outline
 Overview
 Comparison with Observations
 Precipitation
 Tmin, Tmax
 Biases as norms for evaluating climate change
 Precipitation
 Tmin, Tmax
 Conclusions
START Temperate East Asia Regional Center
(February 2000)
Outline
 Overview
START Temperate East Asia Regional Center
(February 2000)
Simulations
Model
Observed
RegCM2
NCEP
Hadley
Reanalysis Centre
(1979-1988) (~1990’s)
HIRHAM
(DMI)
“
GCM-control GCMScenario
“
Hadley
Centre
(2040-2050)
“
Domain
Purpose
 Evaluate RCM performance
 Compare RCM and GCM projections
 Assess U.S. regional climate change
uncertainty
Outline
 Overview
 Comparison with Observations
 Precipitation
 Tmin, Tmax
START Temperate East Asia Regional Center
(February 2000)
RegCM2
Bias
VEMAP
JAN
JUL
-4
-2
0
+2
+4
+6
[mm/d]
Self-Organizing Maps
Set of maps
• Trained to distribution of data
• Give 2-D projection of higher order
map space
• Show characteristic data structures
• Are approximately continuous
“Robert Johnson” box: (31-35 N, 85-90 W)
Precipitation Regions
Upper
Miss.
Range: 600 - 970 mm
Range: 650 - 850 mm
Range: 590 - 870 mm
Tmin/Tmax Problem:
Model elevations different from observing stations
O
O
O
O
O
Tmin/Tmax Problem:
Model elevations different from observing stations
O
O
O
O
O
“Solution”:
Interpolate to common elevation using dT/dz = - 6.5 K/km
(common = real world @ 1/2 deg)
10 Year Mean Maximum Temperature - RegCM2
-12.5
-2.5 +2.5
+12.5
+22.5
[C]
10 Year Mean Maximum Temperature - DMI
-12.5
-2.5 +2.5
+12.5
+22.5
[C]
10 Year Mean Minimum Temperature - RegCM2
-12.5
-2.5 +2.5
+12.5
+22.5
[C]
10 Year Mean Minimum Temperature - DMI
-12.5
-2.5 +2.5
+12.5
+22.5
[C]
Outline
 Overview
 Comparison with Observations
 Precipitation
 Tmin, Tmax
 Biases as norms for evaluating climate change
 Precipitation
 Tmin, Tmax
START Temperate East Asia Regional Center
(February 2000)
Possible Comparisons?
Reanalysis
HadCM
Cont/Scen
Driving
RegCM2
OBS
HIRHAM
HadCM
Cont/Scen
Differences
Definition of Biases
Reanalysis
RegCM2
OBS
RCM (performance) bias
Definition of Biases
Reanalysis
RegCM2
Inter-model
bias
HIRHAM
Definition of Biases
Reanalysis
RegCM2
Forcing
bias
HadCM
RegCM2
Definition of Biases
RegCM2
HadCM
G-R
nesting
bias
HadCM
Climate Change
HadCM
control
RegCM2
Change
HadCM
scenario
RegCM2
Climate Change
P
Change
Control
Scenario
Climate Change
P
Max Bias
Control
Change
Scenario
Analysis Regions
Definitions
Seasonal-regional biases
PRCM
1 N m
o
  Pi  Pi 
N i1
Po, Pm are observed, model
precipitation
N is total grids in the region
Climate change ratio
Rchng
Pchng

Max ( PRCM , Pforc, Pitmd )
RegCM2
7
Rchng
6
winter
spring
summer
autumn
5
4
3
2
1
0
PNW
CA
MW
NE
Region
Rchng
Pchng

Max ( PRCM , Pforc, Pitmd )
NS
HIRHAM
7
6
winter
spring
summer
autumn
Rchng
5
4
3
2
1
0
PNW
CA
MW
Region
NE
SE
Include here
Tmin/max transparencies
Degree-days
Wind power
Outline
 Overview
 Comparison with Observations
 Precipitation
 Tmin, Tmax
 Biases as norms for evaluating climate change
 Precipitation
 Tmin, Tmax
 Conclusions
START Temperate East Asia Regional Center
(February 2000)
Conclusions
 RegCM2 simulates broad-scale regional features
fairly well.
 Interannual variability in RegCM2 (and HIRHAM)
is less than observed.
 Specific regions and seasons pose special
challenge to RegCM2, e.g., south-central US
 Timing of events good
 Magnitude poor
 Moisture transport problem?
START Temperate East Asia Regional Center
(February 2000)
Conclusions
 Climate change is 1-3 times larger than biases in
most seasons and regions
 summer ratios are always less than 1
 Ratio of climate change to biases is especially
large in the California region
 Differences between RCM and GCM imply room
for RCMs to add value to GCM simulations
START Temperate East Asia Regional Center
(February 2000)
Conclusions
 Regional warming signal is less robust than
precipitation change
 Future warming projection has large inter-model
differences
 Warming greater for Tmin than Tmax
 Warming greater for winter than summer
START Temperate East Asia Regional Center
(February 2000)
Acknowledgments
 Primary Funding:
Electric Power Research Institute (EPRI)
 Additional Support:
U.S. National Oceanic and Atmospheric
Administration
U.S. National Science Foundation
START Temperate East Asia Regional Center
(February 2000)
EXTRA SLIDES
Definition of Biases
 RCM (performance) bias - difference between
reanalysis-driven RCM simulation and observations
 forcing bias - difference between runs driven by GCM
control climate and driven by reanalysis
 inter-model bias - difference between runs from
different RCMs (HIRHAM minus RegCM2), both
driven by reanalysis
 G-R nesting bias – difference between GCM run and
RCM run driven by GCM output, both for current
climate.