Modeling of Climate Variability and
Change in the Western United States
L. Ruby Leung
Pacific Northwest National Laboratory
MTNCLIM 2005
Chico Hot Springs, Pray, MT
March 1-4, 2005
Challenges
• Climate is an important driver of mountain resources
including water and ecosystems
• Predictions are needed for managing resources and
risks: Seasonal-to-interannual, decadal and long term
trends
• Climate models are commonly used for prediction or
projection: What are the challenges?
• Climate forcing and feedback are not fully understood
and represented
• Climate exhibits large inherent temporal and spatial
variability: Small signal to noise ratio
• The extreme matters: Floods/droughts, heat waves
Interannual Variability (CA)
DJF
Snowpack
Precipitation
GCM Simulated Precipitation and Snowpack
Downscaling by Regional Climate Modeling
Global Domain
Regional Domain
Multiple Nesting
El Nino Precipitation Anomaly
RCM simulation of 1980-2000 driven by NCEP reanalysis
Anomaly calculated based on 6 El Nino cases minus 20 year mean
Observation
RCM Simulation
NCEP Reanalysis
Leung et al. 2003, J. Clim.
Needs to predict changes in circulation and
represent orographic effects
Cascades
ist
o
M
Dry
Sierra
Observed Streamflow Variability
CRB/SSJ
Olympic Peninsula
West of Cascades
How Well Can We Simulate Regional Precipitation?
Seasonal Cycle of Precipitation
Northwest & Columbia
California
Great Basin
Colorado River
Rio Grande
Missouri River
Arkansas River
South Central
Great Lakes Drainage
Upper Mississippi
Lower Mississippi
East Coast
Observation
RCM driven by GCM
Ohio River
Distribution of Rain Rates
Northwest & Columbia
California
Arkansas River
Great Basin
Colorado River
Great Lakes Drainage
Upper Mississippi
Missouri River
Lower Mississippi
Ohio River
Rio Grande
South Central
Extreme Daily Precipitation (DJF)
Observation
RCM
GCM
Climate Change Signals (2050s – present)
Precipitation
RCM
GCM
Temperature
Leung et al. 2004, Climatic Change
Extreme Precipitation/Snowpack Changes
Lead to significant changes in streamflow affecting hydropower production, irrigation,
flood control, and fish protection
Streamflow in Yakima River Basin
9000
Streamflow (cfs)
8000
7000
6000
Current
Future 1
Future 2
Future 3
5000
4000
3000
2000
1000
0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Model projects similar change in the next
50 years as observed in the past 50
Large reduction in snowpack
Mote et al.
Snowmelt flow starts earlier
Iris Stewart, Dan Cayan and Mike Dettinger
Why regions of larger warming differ?
Precipitation
RCM
GCM
Temperature
Leung et al. 2004, Climatic Change
Global and Regional Simulations of Snowpack
Regional Simulation
Global Simulation
Snow-albedo feedback is important for increased
warming at higher elevation
Larger Signal-to-Noise Ratio at High Elevation?
RCM
GCM
Temperature
Precipitation
Use of Climate Scenarios
PCM
GCM
SD+BC
SD
PCM
GCM
DD
RCM
I
SD+BC
Hydrology
VICModel
SD
} Is this step needed?
I
Hydrology
VICModel
Note:
DD – Dynamical Downscaling
I – Spatial Interpolation
SD – Statistical Downscaling
BC – Bias Correction
A
B C
A’ B’ C’
Larger hydrologic impacts using RCM
scenarios than GCM
Wood et al. 2004 Climatic Change
Warm Season Changes
Meehl and Tebaldi (2004)
Temperature/Rain Frequency
Leung and Gustafson 2005
Stagnation/Ventilation
Assessing Uncertainty
• PRUDENCE is a European program to assess
uncertainty in climate change projections by using
multiple GCMs and RCMs
• Main conclusions: (1) seasonal mean changes are
largely determined by GCMs; and (2) changes in
detailed patterns and extremes are largely
determined by RCMs
NARCCAP
North American Regional Climate
Change Assessment Program
Linda O. Mearns, NCAR
Ray Arritt, Iowa State, George Boer, CCCma, Daniel Caya, OURANOS,
Phil Duffy, LLNL, Filippo Giorgi, Abdus Salam ICTP, William Gutowski, Iowa State,
Isaac Held, GFDL, Richard Jones, Hadley Centre, Rene Laprise, UQAM,
Ruby Leung, PNNL, Jeremy Pal, ICTP, John Roads, Scripps,
Lisa Sloan, UC Santa Cruz, Ron Stouffer, GFDL, Gene Takle, Iowa State,
Warren Washington, Tom Wigley, NCAR, Francis Zwiers, CCCma
NARCCAP PLAN
A2 Emissions Scenario
MM5
HADAM3
GFDL
CCSM
1960-1990 current
Provide boundary conditions
Iowa State/
PNNL
RegCM3
UC Santa Cruz
ICTP
CRCM
Quebec,
Ouranos
link to European
Prudence
HADRM3
Hadley Centre
CGCM3
2040-2070 future
RSM
Scripps
WRF
PNNL/
NCAR
Summary
• Coupled global and regional climate models generally
reproduce some basic features of climate variability
(seasonal cycle, rain rates, extreme precipitation)
• Climate signals (temperature, extreme precipitation,
snowpack) seem to be amplified in the mountain regions
(snow-albedo feedback, increased water holding capacity,
threshold effect)
• However, signal-to-noise ratio does not necessarily
increase at the higher elevation
• Potential climate change effects in the western U.S.
include: large reduction in snowpack, shift in seasonal
runoff, increase in extreme precipitation and runoff,
increased frequency of heat waves and stagnation,
reduced ventilation and rainfall frequency