Alan F. Hamlet Philip W. Mote Dennis P. Lettenmaier JISAO Center for Science in the Earth System Climate Impacts Group and Department of Civil and Environmental Engineering University of Washington Feb, 2005 The Impacts of Climate Change on Pacific Northwest Climate and Streamflow: Implications for Puget Sound, Strait of Georgia, and Coastal Watersheds

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**.

Hydroclimatology of the Pacific Northwest

Annual PNW Precipitation (mm) Elevation (m)

Winter Precipitation Summer Precipitation (mm)

Hydrologic Characteristics of PNW Rivers

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 Sensitivity of Snowmelt and Transient Rivers to Changes in Temperature and Precipitation

Ollalie Meadows SNOTEL 3700 ft elevation WY 1995 (normal year)

Ollalie Meadows SNOTEL 3700 ft elevation WY 1992 (Warm Year)

Ollalie Meadows SNOTEL 3700 ft elevation WY 2005 (very warm year)

A history of the PDO warm cool warm A history of ENSO Pacific Decadal OscillationEl Niño Southern Oscillation

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

Watersheds in the Cascades are even more sensitive due to combined temperature and precipitation effects.

Observed Climate Change and Hydrologic Impacts for the PNW

The earth is warming -- abruptly

Source: Mote et al. (2004) Trends in April 1 SWE

Decadal Climate Variability Doesn’t Explain the Loss of SWE Due to Warming with Relative SWE Trends Due to Temperature Effects Alone (% per year)

Trends in timing of peak snowpack are towards earlier calendar dates Change in Date

As the West warms, winter flows rise and summer flows drop Figure by Iris Stewart, Scripps Inst. of Oceanog. (UC San Diego)

March June Relative Trend (% per year) Trends in fraction of annual runoff (cells > 50 mm of SWE on April 1)

Trends in Simulated Average APR 1 SWE for the Cascades in WA and OR ( ) Effects of TMP and PCP -54% Effects of TMP -26%Effects of PCP -28% SWE (mm)

Summer Water Availability is Declining 55 years Figures courtesy of Matt Wiley and Richard Palmer at CEE, UW

Global Climate Change Scenarios and Hydrologic Impacts for the PNW

Natural Climate InfluenceHuman Climate Influence All Climate Influences Natural AND human influences explain the observations best.

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

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

April 1 SWE (mm) Current Climate“2020s” (+1.7 C)“2040s” (+ 2.5 C) -44%-58% Changes in Simulated April 1 Snowpack for the Cascade Range in Washington and Oregon

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

Effects to the Cedar River (Seattle Water Supply) for “Middle-of-the-Road” Scenarios

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

Natural Streamflows at Dworshak Sustainable management of PNW salmon populations will very likely have to cope with flow variability associated with both “warm and wet” and “warm and dry” scenarios at different times. Such conditions can be incorporated in planning as a test for sustainability though adverse periods, rates of recovery during favorable periods, etc. Warm PDO 2040 Cool PDO 2040

Impacts of Climate Change on Puget Sound Fresh Water Inputs

Caveats Runoff from Vancouver Island and fresh water inputs to the Strait of Georgia are not included. Effects of deep ground water, changing urbanization, consumptive water use, dams, and water management are not considered.

Elevation (m) Digital Elevation Model of the Puget Sound Drainage Basin at 1/8 th Degree

Current Climate2040s (+2.5 C)

Changes in (Runoff + Baseflow) to Puget Sound for Comp2040 Scenario (+ 2.5 C)

May-Sept -8% June-Sept -13% Observed changes in Seasonal Fraction of Annual Flow in the Fraser River (Note small changes in consumptive use not accounted for in these data) Cumulative Trends over 82 years:

Implications for Puget Sound, Georgia Basin, and Coastal Watersheds The timing of natural runoff in many near-coastal watersheds of the PNW is very sensitive to small increases in temperature via changes in moderate-elevation snow dynamics. The seasonal timing of runoff originating from low elevation areas, by comparison, may be relatively insensitive to temperature changes. In PNW watersheds with significant snow accumulation we should expect systematic decreases in spring snowpack, increases in runoff in winter (which in some instances may result in greater flooding), earlier peak streamflow in spring, and reduced runoff in summer. Late summer low flows should also systematically decrease, while water temperature should systematically increase. Runoff to coastal areas in summer may also become more variable and more strongly linked to summer climate as warming progresses, because the current linkage to winter climate (via the snowpack) is weakened. The seasonal timing of fresh water inputs to the Strait of Georgia from the Fraser River are less sensitive to rising temperatures than are fresh water inputs to Puget Sound, but show analogous changes in the seasonality of flow. Effects of groundwater, urbanization, consumptive water use, and water resources management need further study. Integrated studies using linked hydrologic and oceanographic models are needed to begin to understand the ecological implications.