1. Climate impacts on the Pacific Northwest environment: Hydrology and water resources
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
and
Climate Impacts Group
University of Washington

2. Characteristics of the current PNW climate

3. Annual PNW Precipitation
(mm)

4. Hydrologic Characteristics of PNW Rivers

5. A history of the PDO A history of ENSO warm warm cool

6. Columbia River Apr-Sep streamflow5 4 3
105 cubic feet per second 2 1
1900
1920
1940
1960
1980
2000

7. Sensitivity of Snow-dominated and Transient Rivers
to Changes in Temperature and Precipitation
Temperature warms,
precipitation unaltered:
Streamflow timing is altered
Annual volume stays about the same
Precipitation increases,
temperature unaltered:
Streamflow timing stays about the same
Annual volume is altered

8. 1998 cool PDO/warm ENSO

9. 1999 cool PDO/cool ENSO

10. 2001 cool PDO/ENSO neutral

11. Temperature trends in the PNW
US Historical Climate Network data
113 stations with long records
Almost every station shows warming
Urbanization not a major source of warming

12. Observed temperature trend

13. Historic Analogues for the Effects
of Climate Change

14. Unusually Warm Year
Ollalie Meadows (3700 ft elevation) WY 1992
Near Normal Precipitation Warm Temperatures ( F)
normal precipitation
normal snowpack

15. Effect of 1992 Winter Climate on Two PNW Rivers
Cedar River
Western Cascades
(caused predominantly by
warm temperatures)
Columbia River
at The Dalles
(caused both by warm
temperatures and
decreased precipitation)

16. Climate change: Predictions for
the next century

17. This figure shows 10-year average temperatures averaged for Washington, Oregon, and Idaho. The observed temperatures are compared with a simulation by one climate model (the CGCM1) for This plot underscores that the 1990’s were the warmest decade of the 20th century in the Northwest (as well as globally), by almost 1 degree, and that the rate of warming from 1970 to 2000 has been roughly what the CGCM1 simulates. Looking ahead to the 2020s and 2040s, we examined output from a total of 8 climate models and the warmest, average, and coolest of these 8 models are shown as red, yellow, and green. The average rate of warming is a bit less than 1 degree per decade. Even the coolest scenario still shows about 2F warming by the 2040s.

19. Precipitation changes
Most of the models we looked at also project modest increases in precipitation, mainly in winter.
Estimated climate change from 20th c. to 2040s using 8 climate model scenarios.

20. Climate models: The current climate

22. Interpreting the hydrologic effects

23. To evaluate the effects of these temperature and precipitation changes on the Northwest’s water resources, we have used the Variable Infiltration Capacity (VIC) model, developed at the University of Washington. VIC includes multiple soil levels, energy and water balance at the surface, and a sub-grid distribution of land surface types and infiltration values. We have implemented VIC over the Columbia River Basin at 1/8 degree by 1/8 degree horizontal resolution.
Source for this and the next 6 slides: Hamlet and Lettenmaier, 1999, J. Amer. Water Resources Assn.

24. The main impact: less snow
April 1
Columbia
Basin
Snow
Extent

25. Columbia Basin Average Snow Water Equivalent
HadCM2 (Warm/Wet) and ECHAM4 (Warm/Dry) Scenarios
Conclusion:
Both Warm/Wet and Warm/Dry scenarios result in reduced SWE

26. Other sectors (forests, fish, …)

27. Forests Vegetation carbon
Vegetation modeling for including effects of changes in
temperature
precipitation (seasonality?)
CO2 (uncertain)
Longer, hotter summers likely to take a toll on Northwest forests even with CO2 fertilization
This figure shows a simulation of North American vegetation using the MC1 model, a dynamic global vegetation model that includes equilibrium biogeography and disturbance components with related feedbacks. Assuming 35% increase in water use efficiency in an enriched-CO2 environment and significant benefits from increased winter precipitation, the model projects increases in vegetation carbon (biomass) for much of the region. However, the most heavily forested areas see decreases in this model. Big questions about WUE assumption.
Courtesy Ron Neilson, OSU

29. ???? and climate damage Floods Low summer streamflow, high temp
Green arrows: improvements, red arrows: declines
Decrease in floods in some basins, increase in others
Warmer, shallower streams in summer bad for juveniles
Estuary conditions: warming probably increases water column stability, decreases biological productivity
????
Estuary conditions: prey, predators, competitors

30. Impacts of climate change on the PNW
Highest confidence:
Models: warmer; higher snow line
summer water supply, drought
demand for water
conflicts over water resources
winter streamflow increases in snowmelt-driven basins
coastal flooding, inundation
salmon freshwater survival
energy production
Italics indicate an output from climate models
Length of arrow indicates magnitude of socioeconomic and ecological impact
Reduction in summer water supply: a direct consequence of snow line retreat, affects whole region
Demand: to overcome increased evaporative loss (mainly ag, also urban)
Conflicts: a consequence of reduced supply and increased demand
Winter streamflow: flooding only significant on west side, only affects small areas, very weather-dependent (rather than climate dependent)

31. Are we prepared for a changing climate?
Natural resource management presently assumes that
Climate does not change
If few of the region’s institutions are prepared to deal differently with a year whose climate is different from normal, how will they deal with a decade or a future whose climate is different from what they’ve experienced as normal?
In other words, what will it take for the PNW to become climate-wise?
But what if it does?

32. Adaptation pathways Assess the problem, identify vulnerabilities
Long-term planning for reduced summer water
Incorporate strategies into water policy
These come from White Paper #3