1. Implications of Climate Change for Water Resources Management in the Columbia River Basin
Alan F. Hamlet,
Philip W. Mote, Nate Mantua,
Dennis P. Lettenmaier
JISAO/CSES Climate Impacts Group
Dept. of Civil and Environmental Engineering
University of Washington

2. Example of a flawed water planning study:
The Colorado River Compact of 1922
The Colorado River Compact of 1922 divided the use of waters of the Colorado River System between the Upper and Lower Colorado River Basin. It apportioned **in perpetuity** to the Upper and Lower Basin, respectively, the beneficial consumptive use of 7.5 million acre feet (maf) of water per annum. It also provided that the Upper Basin will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 7.5 maf for any period of ten consecutive years. The Mexican Treaty of 1944 allotted to Mexico a guaranteed annual quantity of 1.5 maf. **These amounts, when combined, exceed the river's long-term average annual flow**.
      

3. What’s the Problem?
Despite a general awareness of these issues in the water planning community, there is growing evidence that future climate variability will not look like the past and that current planning activities, which frequently use a limited observed streamflow record to represent climate variability, are in danger of repeating the same kind of mistakes made more than 80 years ago in forging the Colorado River Compact.
Long-term planning and specific agreements influenced by this planning should be informed by the best and most complete climate information available, but frequently they are not.

4. Hydrologic Impacts of Warming:
Reduced snowpack
Earlier snowmelt
Increased winter flow
Decreased summer flow
Earlier peak flow

5. 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

6. 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.

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

8. 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)

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

10. 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
“2020s” (+1.7 C)
“2040s” ( C)
-3.6%
-11.5%
-21.4%
-34.8%
April 1 SWE (mm)

11. 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

12. Frequency of Drought in the Columbia River Comparable to Water Year 1992
(data from )
x 4.7
x 2
x 1.3
x 1.3

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

14. Water Resources Implications for the Columbia River Basin

15. 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)

16. 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

17. Managed Flow Augmentation
The flow needed to provide acceptable flow velocity for juvenile transport is frequently higher than natural flow, particularly in late summer (I.e. use of storage is required). Climate change increases the amount of storage required to meet flow targets.
Currently very little storage is allocated to fish in comparison with hydropower.
In a conflict between hydro or irrigation and fish flow, the current reservoir operating policies are designed to protect hydro and irrigation (fish flow storage allocation for main stem and Snake River flow targets is at the top of a shared reservoir storage pool)
The Columbia River Treaty does not provide explicitly for summer flow in the U.S. (transboundary issues). Compare with guaranteed winter releases associated with flood control.
Hydro storage
Fish flow storage

18. 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,

19. Flood Control vs. Refill
Streamflow timing shifts can reduce the reliability of reservoir refill
Full
Model experiments (see Payne et al. 2004) have shown that moving spring 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,

20. Temperature thresholds for coldwater fish in freshwater
Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region
A monthly average air 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

21. Water Temperature
Higher air temperatures and increased residence time in reservoirs due to summer streamflow reductions are likely to systematically increase water temperatures throughout the basin. In unmanaged tributaries these impacts may be difficult or impossible to mitigate. (land use)
In managed basins, stored cold water in reservoirs may be exhausted more rapidly than now, reducing the ability to mitigate high stream temperatures using releases from storage, particularly in late summer. Cold water storage at Dworshak dam is a particular concern since it is one of the few dams available to control stream temperatures in the lower Snake and is sited in a sensitive area.

22. Implications for Transboundary Agreements 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.

23. 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