1. Washington’s water resources in a changing climate
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
University of Washington
for
2009 University of Washington Water Center Annual Review of Research
Seattle
February 18, 2009

2. Washington State Climate Change
Impacts Assessment:
April 20, 2007: State Legislature of Washington passed HB 1303 which mandated the preparation of a comprehensive assessment of the impacts of climate change on the State of Washington to be performed by the UW Climate Impacts Group
The assessment was to be focused on the impacts of global warming generally, and specifically in relation to:
public health,
Agriculture (partner: WSU)
the coastal zone
forestry
Infrastructure (specifically stormwater)
water supply and management (partner: PNNL)
Salmon and ecosystems
energy

3. Projected annual changes in precipitation for PNW (averaged over 111o – 124o W, 41.5o – 49.5o N)

4. Projected annual changes in surface air temperature for PNW (averaged over 111o – 124o W, 41.5o – 49.5o N)

5. Assessment Overview: Study Region
In this study we focus on Washington State, but for hydrology we need to consider all of the drainages flowing into Washington as well. The hydrologic region impacting Washington includes parts of Bristish Columbia, Montana, Idaho, Wyoming, Oregon, and Washington. The region contributing to Washington is much of USGS Region 17. 5

6. We can characterize watersheds in Washington State as being one of three types: rain dominant, snowmelt dominant, and watersheds that receive both rain and snow. We have defined these watersheds using a metric of the ratio of peak snowpack to cool season precipitation (Oct – Mar).

7. Global Climate Models Hydrologic Models Energy Salmon Forests
2 different emissions scenarios
20 models using A1B (medium scenario)
19 models using B1 (low scenario)
Downscaled to regional projections of P and T for the 2020s , 2040s, 2080s
Hydrologic Models
Projections of future changes in
snowpack, streamflow, soil moisture, etc.
Energy
Salmon
Forests
Water Management
Infrastructure
Agriculture

8. Hydrologic Simulations
VIC typically applied to watersheds greater than 10000sq km or 3800sq mi.
Large Scale Model (VIC)
~12mi2 per cell
Fine Scale Model (DHSVM)
~6 acres per cell

9. Climate Change Projections (using “delta method”)
39 Climate Change Scenarios
- each is a monthly timeseries of P and T from
3 chosen projection windows
Mean DP & DT for 2040s ( )
Mean DP & DT for 2080s ( )
Mean DP & DT for 2020s ( )
2000
Overall Process for HB1303 Project:
Generally, a range of scenarios of climate change to 2100 are input to a hydrology model that provides projections of streamflow and other hydrologic variables.
-We are utilizing 100 year projections from approximately 20 GCMs, each of which has projections using 2 emissions scenarios. These emissions scenarios, A1B and B1, represent stabilization of CO2 by The B1 scenario is more ecologically friendly than A1B. They generally represent the range of possibly temperature changes into the future.
-The GCM scenarios, which are at a resolution of approximately 3-4 degrees, must be downscaled to the resolution of the hydrology model. We utilize 2 downscaling approaches including a statistical approach and an approach that incorporates results from regional climate models.
The downscaled GCM predictions and resulting hydrologic predictions provide a range of possibilities of future climate change which the various sectors can use to evaluate the impacts in their areas.
This is a more specific look at how we conduct an impacts assessment. The dynamics of the climate provides a basis of information from which we can make assessments of hydrology and other things. What we learn about the hydrology can then be applied to other sectors and these analyses provide a basis of information that policymakers can use in their decisions.
2050
2100
Historical daily timeseries ( ) perturbed by mean monthly DP & DT
(same mean DP and DT applied to each day in a given month)
New daily timeseries which incorporates historical daily patterns and future projections of precipitation and temperature

10. Focus Watersheds Columbia River Puget Sound Yakima River
Washington portion
Puget Sound
Green River
Snohomish River
Cedar River
Tolt River
Yakima River 10

11. Implications of 21st century climate change on Washington’s watersheds

12. Medium
Low
Elsner, M.M. et al. 2009: Implications of 21st Century climate change for the hydrology of Washington State (in review)

13. Weekly Snowpack Projections
Cedar River
Medium
Low
Yakima River
Medium
Low

15. Monthly Streamflow Projections
Snowmelt dominant
watershed
Rain dominant
watershed
Transient rain-snow watershed
The Chehalis River is not within our focus regions but lower parts of the watersheds in the Puget Sound, like the Cedar below Chester Morse reservoir, are rain dominant.

16. Weekly Streamflow Projections
Cedar River - inflow to Chester Morse Reservoir
Yakima River at Parker

17. Case study 1: Puget Sound Basin
Precipitation in fall-winter, water demand in summer
Water management systems:
Seattle - municipal, fish
Tacoma - municipal, flood control
Everett - municipal, hydropower
Reservoir capacities small relative to annual flow

18. Puget Sound Basin Seattle Tacoma Everett
Transition basins. Lower parts of basin already rain dominate. Upper, more snow dominated.
Variations in impacts within and between systems (A1B)
Seattle, M&I and environmental flows
Tacoma, flood control, more constrained storage
Everett, hydropower, more interannual variability

19. Puget Sound Basin municipal supply - current demand
M&I reliability measures, differ for all systems
Current demand, reliability little impact from future change (A1B)
Tacoma, water allocations closer to current system capacity
Everett, largest system capacity
Note: simulations prior to adaptations 1% 7% 0%

20. Puget Sound Basin municipal supply - changing demand1% 5%
23%
36%
With demand increases, climate change has more impact reliability
Importance of conservation measures/reduced demand
Systems respond different depending on storage capacity, basin transitions, system demands, adaptive capacity
Note: simulations prior to adaptations 7% 9%
10%
0% diff, all 100%

21. Puget Sound Basin operations beyond municipal supply
32% diff
Range of operating goals that must be balanced
Tacoma, likelihood of flood control years
Tacoma minimum instream flow reliability
Note: current demand and simulations prior to adaptations
36% diff

22. Case study 2: Yakima River Basin
Irrigated crops largest agriculture value in the state
Precipitation (fall-winter), growing season (spring-summer)
Five USBR reservoirs with storage capacity of ~1 million acre-ft, ~30% unregulated annual runoff
Snowpack sixth reservoir
Water-short years impact water entitlements
Elevation 8184 ft to 340 ft
Historic Temp and precip
22-76F, 80 in-140 in at 2300 ft, 27-90F, 0 in-10 in at 350 ft
61% -81% precip in October-March
This water is used in many ways…
-TWSA: multiple regression analysis uses correlations with precipitation, streamflow, snow measures, forecasts are made for precipitation levels of 50, 100 and %150 normal.
Water supply during growing season in lower basin primarily from snowmelt, depends on reservoirs for storage
Six USBR reservoirs with storage capacity of ~1 million acre-ft, ~25% unregulated runoff
Managed system vulnerable to drought with increasing water use and changing snowpack
DETAILS ON TWSA:
Max, Min, and Avg all from and 2007 values of:
(1) System Unregulated Flow Volume (system of reservoirs, sum of inflows),
(2) Observed Flow Volume (system of reservoirs, sum of outflows),
(3) Parker Unregulated Flow Volume (Yakima River NR Parker mean daily natural discharge),
(4) Parker Observed Flow Volume (Yakima River NR Parker mean daily regulated discharge)
(5) Yakima System Diversions (5 major irrigation diversions above Parker)
(6) Yakima System Storage (Reservoir system storage, mean daily reservoir volume)
REFERENCES:
(USBR, 2002)
KENNEWICK, WASHINGTON (454154)
LAKE KACHESS, WASHINGTON (454406)
Precipitation varies considerably across the basin throughout the year. Mean-annual precipitation ranges from 140 inches in the higher mountains of the northwestern part of the basin to less than 10 inches throughout the lower Yakima Valley. The amount of precipitation that occurs during the period of Oct ober to March period, both the arid and alpine parts of the basin ranges from 61-81% of the annual precipitation. The variation in annual precipitation can be large. The geographic variability of mean annual precip in high mts between inches in lower between 0-10 inches (USBR 2002, pg 2-2)
Water quality, generally high in upper basin. Degrades downstream. Many reaches in Federal Clean Water Act 303(d) list. Issues of turbidity, pesticides, low dissolved oxygen, elevated temperatures, metals, fecal coliform, low flows, and pH.
Air temps, inversely related to altitude. Min and Max occur in Jan and July. Values above from LAKE KACHESS ( Monthly Climate Summary, Average Min in Jan and Average Max in July)
-Reserviors been in place since 1930s
-Irrigation project serves 465,000 acres
-Basin drains about 4 million acres (Basin drains about 6150 sq miles)
-Yakima River flows about 215 miles
-Estimated unregulated runoff of Yakima Basin ( ) is 3.97 million acre-ft
FROM POSTER, AGU 2006
-The USBR Yakima Project supports approximately 464,000 irrigated acres (via four irrigation districts -- Roza, Yakima-Tieton, Sunnyside Valley and Kittitas -- and the Wapato Division).
-Most of the water in the Yakima River comes from snowmelt, and is caught in a series of reservoirs to ensure sufficient water supply throughout the season.

23. Key Findings: Puget Sound Basin
Primary impacts of climate change will be a shift on average in the timing of peak river flow from late spring to winter
With current demands, system reliability able to accommodate changes
With demand increases, system reliability reduced, conservation measures matter
Other aspects of system performance complicate management decisions such as environmental flows, flood control, and hydropower
Photo courtesy of

24. Yakima Basin Methods

25. Yakima River Basin
Unregulated

26. Yakima River Basin Unregulated
Basin shifts from snow to more rain dominant

27. Yakima River Basin Unregulated Regulated
management
model
Unregulated
Regulated
Basin shifts from snow to more rain dominant

28. Yakima River Basin Basin shifts from snow to more rain dominant
Water prorating, junior water users receive 75% of allocation

29. Yakima River Basin 2080s 2020s historical
Basin shifts from snow to more rain dominant
Water prorating, junior water users receive 75% of allocation
Junior irrigators less than 75% prorating (current operations):
14% historically
32% in 2020s A1B (15% to 54% range of ensemble members)
36% in 2040s A1B
77% in 2080s A1B

30. Crop Model - Apple Yields
There are similar impacts for cherry producers. Note the difference between yiled with and without CO2 fertilization effects
Yields decline from historic by 20% to 25% (2020s) and 40% to 50% (2080s)

31. Key Findings Yakima River Basin
Future projections indicated that reservoir system will be less able to supply water to all users, especially those with junior water rights
Earlier and shorter growing season - apples 12 days earlier, cherries 22 days earlier season start, month earlier harvest
Yields decline - under A1B emissions scenario, average apple and cherry yield are likely to decline by 20% to 25% (2020s) and 40% to 50% (2080s) for junior water holders
Crop values decline - value of apple and cherry production is likely to decline by 5% ($20 million) in 2020s,16% ($70 million) in the 2080s
Growing season effects are the average of the 4 scenarios for the 2080s, compared with historical
Growing season figures are the average of the four 2080 scenarios (A1B and B1 for No Co2 and with CO2) compared with historical

32. Shifts in energy production and demand

33. Changes in precipitation maxima

34. Likely reducing survival rates for incubating eggs and rearing parr
Models project more winter flooding in sensitive “transient runoff” river basins that are common in the Cascades
Likely reducing survival rates for incubating eggs and rearing parr
A warmer climate is likely to have impacts on flooding, stormwater, and wastewater management. Rising snowlines with warmer temperatures will increase runoff during storm events as more precipitation falls as rain and less as snow. The reduction in spring snowpack due to warmer temperatures, by itself, will likely reduce the risk of springtime flooding, but that factor will be opposed by the likely increases in spring soil moisture that come with early snowmelt.
Theory and climate modeling studies also suggest that a warmer climate will bring an increased intensity of precipitation with individual storms, and if this general impact takes place in Washington it will increase the risk of urban flooding and combined sewer overflows.
WACCIA 12 Feb 2009

35. Summer base flows are projected to drop substantially (5 to 50%) for most streams in western WA and the Cascades
The duration of the summer low flow season is also projected to increase in snowmelt and transient runoff rivers, and this reduces rearing habitat
WACCIA 12 Feb 2009

36. Warming trends of air and water temperatures across Washington State
Left map illustrates the historic conditions for Washington state.
Right panels shows the A1B middle scenario projections for temperatures in the 2040s
Continuous colors are air temperatures
Dots are for sites where we modeled water temperatures
Reds refer to warmer temperatures, unfavorable for salmon
Blues are cooler temperatures, favorable for salmon
Several blue dots in western Washington historically turn to yellow in the future
But more dramatically, the shift of yellow and orange dots to red for eastern Washington 36

37. Historical, three future time horizons for A1B emissions scenario
The B1 emissions scenario projections look similar, but the effects occur later in time
Again the regions of warming air temperatures in red, is dramatic for eastern Washington by the 2080s
And the blue areas are limited only to the highest elevations by the end of the century
Although the number of blue dots decreases in western Washington, it is not as extreme as in eastern Washington
Focusing in on a couple of sites that might present thermal barriers to migrating salmon in the warmer summer weeks… 37

38. Spatial distribution of the number of weeks projected to present thermal barriers for migrating salmon
Bubble size is proportional the the number of weeks exceeding 21C
By the 2080s much of the Columbia Basin and some sites in western Washington as well (like Lake Union and the Stillaguamish at Arlington) will have longer periods
Presenting thermal barriers for salmon. 38

39. Conclusions
Broad consensus among models that PNW temperatures will rise, continuing (and amplifying) 20th C trends
Precipitation changes less clear, both historically and projected, although some indication of slightly wetter conditions in coming decades, esp. in winter
Dominant hydrologic signal is reduction in SWE, and streamflow timing shifts – esp. in transient basins
Direct effects of warming on western WA water supply systems are nonetheless modest, mostly because of demand reductions achieved over last ~10-20 years
Impacts on the already-overallocated Yakima basin are more severe than on westside water systems
Other water-related sectors (fish habitat, energy, infrastructure) are generally negatively impacted, although specifics vary