1. Effects of Climate Change on the Columbia River Basin’s Water Resources
JISAO Center for Science in the Earth System
Climate Impacts Group
and Department of Civil and Environmental Engineering
University of Washington
Nov, 2005
Alan F. Hamlet
Philip W. Mote
Nathan Mantua
Dennis P. Lettenmaier

2. Natural AND human influences explain the observations of global warming best.
Natural Climate Influence
Human Climate Influence
Red: observations of global average temperature
Grey: simulations with a climate model (huge computer program, like weather prediction model only run for hundreds of years)
Natural influence: volcanoes, solar variations – guesses before ~1970, better since then
Human influence: greenhouse gases, sulfate aerosols
it is possible to simulate the climate of the last 100 years, and the conclusion is that humans didn’t matter much before 1960 – the early warming and the cooling were largely natural, and the late-century warming was largely human-caused
All Climate Influences

3. Temperature trends (°F per century) since 1920
cooler warmer
3.6°F
2.7°F
1.8°F
0.9°F
Each dot represents a station with data going back at least to 1920, size of dot shows magnitude of linear trend. Open circles are negative trends - not many of those. Most trends in the 1-3F range. The regional average (using appropriate area-weighting) is 1.5F/century.
These data have been quality-controlled and corrected by the National Climate Data Center. This includes removing the “urban warming” effect, which is statistically estimated.

4. Annual Precipitation
(Western WA, OR, BC)

5. Hydroclimatology of the Pacific Northwest

6. Annual PNW Precipitation (mm)
Columbia River Basin
Useable Storage ~35 MAF
~50% of storage is in Canada
~Storage is 30% of annual flow
Snowpack functions as a natural reservoir
The Dalles
Elevation (m)

7. Effects of the PDO and ENSO on Columbia River
Summer Streamflows
PDO
Cool
Cool
Warm
Warm
high
high
low
low
Ocean Productivity

8. Warming Affects Streamflow Timing
Temperature warms,
precipitation unaltered:
Streamflow timing is altered
Annual volume may be somewhat lower due to increased ET
Black: Obs
Red: 2.3° C warming
Using a hydrologic simulation model we can evaluate the effects of warming on streamflow in isolation. Precipitation is held constant and temperatures are raised by about 4.1 F. The primary effect is on streamflow timing. Winter flows increase, summer flows decline. This effect is primarily related to changes in snow accumulation and melt. Increased temperatures also result in decreases the annual flows, although these effects are relatively small for this amount of warming (see Slide 10).

9. Precipitation Affects Streamflow Volume
Precipitation increases,
temperature unaltered:
Streamflow timing stays about the same
Annual volume is altered
Black -- Obs
Blue -- 9% increase in precip.
Using a hydrologic simulation model we can evaluate the effects of precipitation changes on streamflow in isolation. Temperature is held constant and precipitation is increased by about 9% in winter. The primary effect is on streamflow volume. Annual flows increase by about 10% percent.

10. Observed Hydrologic Changes

11. Trends in April 1 SWE
Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS (in press)

12. spring flows rise and summer flows drop
As the West warms,
spring flows rise and summer flows drop
Stewart IT, Cayan DR, Dettinger MD, 2005: Changes toward earlier streamflow timing across western North America, J. Climate, 18 (8):
Spring snowmelt timing has advanced by days in most of the West, leading to increasing flow in March (blue circles) and decreasing flow in June (red circles), especially in the Pacific Northwest.

13. Global Climate Change Scenarios and Hydrologic Impacts for the PNW

14. Four Delta Method Climate Change Scenarios for the PNW
Somewhat wetter winters and perhaps somewhat dryer summers

15. Changes in Mean Temperature and Precipitation or Bias Corrected Output from GCMs
ColSim
Reservoir
Model
VIC
Hydrology Model

16. The warmest locations are most sensitive to warming
+4.5% winter precip

17. Changes in Simulated April 1 Snowpack for the Canadian and U. S
Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin
(% change relative to current climate)
Current Climate
“2020s” (+1.7 C)
“2040s” ( C)
-3.6%
-11.5%
-21.4%
-34.8%
April 1 SWE (mm)

18. Naturalized Flow for Historic and Global Warming Scenarios
Compared to Effects of Regulation at 1990 Level Development
Historic Naturalized Flow
Estimated Range of
Naturalized Flow
With 2040’s Warming
Regulated Flow

19. Decadal Climate Variability and Climate Change

20. Will Global Warming be “Warm and
Wet” or “Warm and Dry”?
Answer: Probably BOTH!

21. Water Resources Implications for the Columbia River Basin

22. Impacts on Columbia Basin hydropower supplies
Winter and Spring: increased generation
Summer: decreased generation
Annual: total production will depend primarily on annual precipitation
(+2C, +6%)
(+2.3C, +5%)
(+2.9C, -4%)
NWPCC (2005)

23. Warming climate impacts on electricity demand
Reductions in winter heating demand
Small increases in summer air conditioning demand in the warmest parts of the region
From a variety of charts in an NWPCC report ( see Fig.15), the monthly electricity demand during the winter is ~25000 MW; during the summer it's more like MW. So, the changes in winter demand in this figure are probably a reduction ~10% (as a maximum). This jives with some of the graphs from Sailor (I attached one) that calculates the sensitivity of electricity consumption for a 2 degree C warming to be a little less than 10%.
NWPCC 2005

24. Adaptation to climate change will require complex tradeoffs between ecosystem protection and hydropower operations
Source: Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer, and D.P. Lettenmaier, 2004, Mitigating the effects of climate change on the water resources of the Columbia River basin, Climatic Change, Vol. 62, Issue 1-3,

25. Flood Control vs. Refill
Maintaining an appropriate balance between flood protection and the reliability of reservoir refill is crucial to many water resources objectives in the Columbia Basin.
As streamflow timing shifts move peak flows earlier in the year, flood evacuation schedules may need to be revised both to protect against early season flooding and to begin refill earlier to capture the (smaller) spring freshet.
Model experiments (see Payne et al. 2004) have shown that moving flood evacuation two weeks to one month earlier in the year helps mitigate reductions in refill reliability associated with streamflow timing shifts.
Payne, J.T., A.W. Wood, A.F. Hamlet, R.N. Palmer, and D.P. Lettenmaier, 2004, Mitigating the effects of climate change on the water resources of the Columbia River basin, Climatic Change, Vol. 62, Issue 1-3,

26. Temperature thresholds for coldwater fish in freshwater
Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region
A monthly average temperature of 68ºF (20ºC) has been used as an upper limit for resident cold water fish habitat, and is known to stress Pacific salmon during periods of freshwater migration, spawning, and rearing
+1.7 °C
+2.3 °C

27. Implications for Transboundary Agreements
Snowpack in the BC portion of the Columbia basin is much less sensitive to warming in comparison with portions of the basin in the U.S. and streamflow timing shifts will also be smaller in Canada.
As warming progresses, Canada will have an increasing fraction of the snowpack contributing to summer streamflow volumes in the Columbia basin.
These differing impacts in the two countries have the potential to “unbalance” the current coordination agreements, and will present serious challenges to meeting instream flows on the U.S. side.
Changes in flood control, hydropower production, and instream flow augmentation will all be needed.
Long-range planning is needed to address these issues.

28. Conclusions
Climate change will result in significant hydrologic changes in the Columbia River and its tributaries.
These changes will not be equally distributed throughout the region or between different water management objectives.
With hydrologic changes, there will come a need to “rebalance” the system to compensate for these different impacts in each sector.
This “rebalancing” will take time and will involve complex (and contentious) tradeoffs between different management objectives.
We have the tools that we need to begin planning for a warmer future.
We should begin to include climate information in planning now to reduce the severity of future impacts as much as possible.

29. Selected References and URL’s
Climate Impacts Group Website
White Papers, Agenda, Presentations for CIG 2001 Climate Change Workshop
Climate Change Streamflow Scenarios for Water Planning Studies
Northwest Power and Conservation Council Columbia Basin Hydropower Study
Refs on Climate Variability and Climate Change