Alan F. HamletDennis P. Lettenmaier
Amy K. Snover
JISAO Center for Science in the Earth System Climate Impacts Group
and Department of Civil and Environmental EngineeringUniversity of Washington
April, 2003
Climate Change Streamflow Scenarios for Critical Period Water Planning Studies
Changing Awareness of Climate Change in the Water Management Community
~1985: Global warming? ~1995: Is global warming real?~1997: What are the expected impacts of
climate change for our region and our water system?
~2002: How do we include climate change and climate uncertainty in long term planning to reduce risks?
Current Climate 2020s 2040s
The primary impact pathway in the western US: less snow
Snow Water Equivalent (mm)
Columbia River at The Dalles for “Middle-of-the-Road” Scenarios
Columbia River at The Dalles
0
100000
200000
300000
400000
500000
600000
oct
dec
feb
apr
jun
aug
Ave
rag
e F
low
(cfs
)
Base
2020s
2040s
Inflow to Chester Morse Lake
0
1000
2000
3000
4000
5000
6000
7000
8000
900010
/1
10/2
9
11/2
6
12/2
4
1/21
2/18
3/18
4/15
5/13
6/10 7/
8
8/5
9/2
Infl
ow
(ac
re-f
t)
Base
2020s
2040s
Effects to Moderate Elevation Basins in the Cascades
Project Motivation:
•Target existing planning processes at the watershed scale
•Make streamflow scenarios freely available to help reduce costs of including climate uncertainty in long-term planning
(Recommendations from regional stakeholders and policy makers attending a CIG sponsored climate change workshop Skamania, 2001)
Observed Streamflows
Planning Models
System Drivers
Critical Period Planning Methods for Water Studies
Columbia River at The Dalles
0100000200000300000400000500000600000700000800000
1925
1925
1925
1926
1926
1927
1927
1927
1928
1928
1929
1929
1930
1930
1930
1931
1931
1932
1932
1932
1933
1933
1934
1934
Observed Streamflows
Climate Change Scenarios
Planning Models
Long term planning for climate change may include a stronger emphasis on drought contingency planning, testing of preferred planning alternatives for robustness under various climate change scenarios, and increased flexibility and adaptation to climate and streamflow uncertainty.
Altered Streamflows
System Drivers
Incorporating Climate Change in Critical Period Planning
Project Goals:
•Create climate change streamflow scenarios that cover the same period of record and are numerically consistent with the historic record of streamflows traditionally used in water planning studies.
•Make these streamflow scenarios freely available on the web for a large number of river locations to facilitate the incorporation of climate change information into existing water planning efforts.
Choice of GCM Downscaling Methods for the Pilot Study
Although more sophisticated methods are also available, the “Delta” method of downscaling GCM results was chosen for the pilot applications.
•Good fit with producing alternate versions of the historic record used in critical period planning studies.
•Easy to understand and interpret (the project has an educational component).
•Captures much of the regional scale information from GCM simulations.
Precipitation Fraction, 2020s
0.5
0.75
1
1.25
1.5
1.75
J F M A M J J A S O N D
Frac
tion
hadCM2
hadCM3
PCM3
ECHAM4
mean
Delta T, 2020s
-1
0
1
2
3
4
5
J F M A M J J A S O N D
De
gre
es
C
hadCM2
hadCM3
PCM3
ECHAM4
mean
Delta T, 2040s
-1
0
1
2
3
4
5
J F M A M J J A S O N D
De
gre
es
C
hadCM2
hadCM3
PCM3
ECHAM4
mean
Precipitation Fraction, 2040s
0.5
0.75
1
1.25
1.5
1.75
J F M A M J J A S O N D
Fra
ctio
n
hadCM2
hadCM3
PCM3
ECHAM4
mean
Delta Method Climate Change Scenarios for the PNW
~ + 1.7 C ~ + 2.5 C
Somewhat wetter winters and perhaps somewhat dryer summers
ColSimReservoir
Model
VICHydrology Model
Changes in Mean Temperature and
Precipitation or Bias Corrected Output
from GCMs
Issues with Hydrologic Model Bias
Columbia River at The Dalles
0100000200000300000400000500000600000700000800000900000
1985
1985
1986
1987
1987
1988
1989
1989
1990
1991
1991
1992
1993
1993
1994
1995
1995
1996
1997
1997
1998
1999
1999
Str
ea
mfl
ow
(cf
s)
VIC
Observed
Quantile-Based Bias Correction (Wood et al. 2002)
0
5000
10000
15000
20000
25000
30000
35000
0 0.2 0.4 0.6 0.8 1
Probability of Exceedence
Flo
w (
cfs)
obs
vic
VIC Input = 19000
Bias Corrected Output = 10000
Bias Correction Objectives:
Result: Bias corrected hydrologic simulations are quite consistent with observed streamflows in absolute value and climate change signals are translated without significant distortion.
Raw Bias Corrected
Bias Corrected Time Series Plot for the Current Climate
Bias Corrected Time Series Plot for the Composite 2040 Scenario
Web-Based Data Archive
http://www.ce.washington.edu/~hamleaf/climate_change_streamflows/CR_cc.htm
Goals and Objectives of Two Regional-Scale Pilot Studies in the Pacific Northwest
Northwest Power Planning Council:
Primarily focused on reliability of the Columbia River hydropower system. Study will use the GENESYS model.Preliminary results in John Fazio’s talk this afternoon.
Idaho Department of Water Resources:
Primarily focused on groundwater/surface water interactions, sustainability of irrigated agriculture in the Snake River
basin, groundwater/surface water interactions and water allocation amongst different users and uses.
Current Streamflow Routing Locations
Some Selected Results for the Snake River Basin
(Composite Scenarios)
Planned Project Extensions
•Extend the period of record of the data to 1928-1999.
•Extend the number of climate change scenarios and the downscaling methods used.
Summary and Conclusions
Water policy workshops (Skamania 2001) have highlighted the need to inject climate change information into existing river basin planning activities where possible and to provide access to free streamflow scenarios to help reduce costs.
Because most planning studies currently use a critical period framework, our project produces “adjusted” realizations of the historic streamflow record based on simulations from a physically based hydrologic model driven by simple climate change scenarios.
The methods are flexible and portable and can be used to create streamflow scenarios deriving from different climate model scenarios, different downscaling methods, or different hydrologic models.