1. Understanding the Effects of Climate Change on Water Resources in the Pacific Northwest
Alan F. Hamlet,
Philip W. Mote,
Dennis P. Lettenmaier
JISAO/CSES Climate Impacts Group
Dept. of Civil and Environmental Engineering
University of Washington

2. Recession of the Muir Glacier
On the left is a photograph of Muir Glacier taken on August 13, 1941, by glaciologist William O. Field; on the right, a photograph taken from the same vantage on August 31, 2004, by geologist Bruce F. Molnia of the United States Geological Survey (USGS).
According to Molnia, between 1941 and 2004 the glacier retreated more than twelve kilometers (seven miles) and thinned by more than 800 meters (875 yards).
Ocean water has filled the valley, replacing the ice of Muir Glacier; the end of the glacier has retreated out of the field of view. The glacier’s absence reveals scars where glacier ice once scraped high up against the hillside. In 2004, trees and shrubs grow thickly in the foreground, where in 1941 there was only bare rock.
Aug, 13, 1941
Aug, 31, 2004
Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia

3. Tmax
Canada
USA
PNW CA GB
Tmin
Figure 4
CRB

4. 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, 86 (1): 39-49

5. 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.

6. Projections for the Future Using
Global Climate Models

7. 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

8. Observed 20th century variability
Curves are fits to ln(CO2) for A2 (solid) and B1 (dashed)
Warming ranges are shown for 2020s, 2040s and 2090s relative to 1990s. Central estimates: 0.7C by 2020s, 1.7C by 2040s, 3.2C by 2090s. Pink box shows +/- 2 sigma for annual average temperature (sigma=0.6C). Red lines show previous generation of change scenarios.
Pacific Northwest

9. Observed 20th century variability%
+6%
+2%
+1%
Curves are fits to ln(CO2) for A2 (solid) and B1 (dashed)
Precip changes are shown for 2020s, 2040s and 2090s relative to 1990s. Central estimates: 1% by 2020s, 3% by 2040s, 6% by 2090s. Pink bar shows +/- 2 sigma for PNW annual precip.
Observed 20th century variability
-1 to +3%
-1 to +9%
-2 to +21%
Pacific Northwest

10. Hydroclimatology of the Pacific Northwest

11. Annual PNW Precipitation (mm)
Winter climate in the mountains is the key driver of streamflow.
Snowpack functions as a natural reservoir.
Elevation (m)

12. Hydrologic Characteristics of PNW Rivers

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

14. 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).

15. 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.

16. Hydrologic Impacts for the PNW

17. Schematic of VIC Hydrologic Model and Energy Balance Snow Model
6 km
1/16th
Deg.
6 km
PNW
Snow Model

18. The warmest locations that accumulate snowpack are most sensitive to warming
+6.8% winter precip

19. Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming
Increased winter flow
Earlier and reduced peak flows
Reduced summer flow volume
Reduced late summer low flow

20. Rain Dominant
Chehalis River

21. Warm Transient Snow
Hoh River

22. Cooler Transient Snow
Nooksack
River

23. Snowmelt Dominant
Skagit River

24. 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)
20th Century Climate
“2040s” (+1.7 C)
“2060s” ( C)
-3.6%
-11.5%
-21.4%
-34.8%
April 1 SWE (mm)

25. Effects of Basin Winter Temperatures
Northern Location
(colder winter temperatures)
Southern Location
(warmer winter temperatures)

26. Decadal Climate Variability and Climate Change

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

28. Regionally Averaged Cool Season Precipitation Anomalies

29. Impacts to the Columbia River
Hydro System

30. 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)

31. 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

32. Climate change adaptation may involve complex tradeoffs between competing system objectives
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,

33. Implications for Transboundary Water Management in the Columbia Basin
Climate change will result in significant hydrologic changes in the Columbia River and its tributaries.
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 as the flow regime changes.

34. Implications for the Columbia River Treaty
The Columbia River Treaty is focused primarily on conjunctive hydropower and flood control operations.
Arguably the greatest shortcoming of the agreement in the context of climate change adaptation is that currently the CRT does not encompass tradeoffs between the full range of management concerns facing the US and Canada.
Of particular concern is the need to encompass the different (and often competing) ecosystem needs in Canada and the US.
Does the Columbia River Treaty have the flexibility and scope needed to adapt to the water resources challenges of the 21st Century?

35. Overview of Some Water Resources
Impact Pathways

36. Water Supply and Demand
Changes in the seasonality water supply (e.g. reductions in summer)
Changes in water demand (e.g. increasing evaporation)
Changes in drought stress
Increasing conflicts between water supply and other uses and users of water
Energy Supply and Demand
Changes in the seasonality and quantity of hydropower resources
Changes in energy demand
Increasing conflicts between hydro and other uses and users of water
Instream Flow Augmentation
Changes in low flow risks
Changes in the need for releases from storage to reproduce existing streamflow regime.
Changes in water resources management related to water quality (e.g. to provide dilution flow or to control temperature)

37. Flood Control and Land Use Planning
Changes in flood risks
Changes in flood control evacuation and timing
Dam safety
Impacts in Estuaries
Impacts of sea level rise and changing flood risk on low lying areas (dikes and levies)
Impacts to ecosystem function
Changes in land use policy (coastal armoring, land ownership, FEMA maps)
Long-Term Planning, Water Resources Agreements, Water Law and Policy
Water allocation agreements in a non-stationary climate (e.g. water permitting)
Appropriateness of the historic streamflow record as a legal definition of climate variability
Need for new planning frameworks in a non-stationary climate
Transboundary implications for the Columbia Basin

38. Approaches to Adaptation and Planning
Anticipate changes. Accept that the future climate will be substantially different than the past.
Use scenario based planning to evaluate options rather than the historic record.
Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach.
Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time.

39. Overview of Some Existing Climate Change Water Planning Studies
Seattle Water Supply (Wiley 2004)
White River Basin (Ball 2004)
Snohomish Basin (Battin et al. 2007)
Columbia Hydro System (Hamlet et al. 1999; Payne et al. 2004, NWPCC 2005)
Ball, J. A Impacts of climate change on the proposed Lake Tapps-White River water supply, M.S.C.E. thesis, Dept. of Civil and Environmental Engineering, College of Engineering, University of Washington, Seattle.
Battin J., Wiley, M.W., Ruckelshaus, M.H., Palmer, R.N., Korb, E., Bartz, K.K., Imaki, H., Projected impacts of climate change on salmon habitat restoration, Proceedings of the National Academy of Sciences of the United States of America, 104 (16):
Hamlet, A. F. and D. P. Lettenmaier. 1999b. Effects of climate change on hydrology and water resources in the Columbia River Basin. Journal of the American Water Resources Association 35(6):
Payne, J. T., A. W. Wood, A. F. Hamlet, R. N. Palmer, and D. P. Lettenmaier Mitigating the effects of climate change on the water resources of the Columbia River basin. Climatic Change 62:
NW Power and Conservation Council, 2007, Effects of Climate Change on the Hydroelectric System, Appendix N to the NWPCC Fifth Power Plan,
Wiley, M. W Analysis techniques to incorporate climate change information into Seattle's long range water supply planning. M.S.C.E. thesis, Dept. of Civil and Environmental Engineering, College of Engineering, University of Washington, Seattle.