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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 September, 2004 Effects of Climate Variability and Change on Pacific Northwest Rivers: Implications for Water Management and Salmon in the Columbia River Basin

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 Hydroclimatology of the Pacific Northwest

4 Annual PNW Precipitation (mm) Elevation (m) The Dalles 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

5 Hydrologic Characteristics of PNW Rivers

6 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

7 A history of the PDO warm cool warm A history of ENSO 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Pacific Decadal OscillationEl Niño Southern Oscillation

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

9 Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (in review). Columbia River Flow and Drought Since 1750. Submitted to Journal of the American Water Resources Association. Tree ring reconstructions of Columbia River flows show the Dust Bowl was probably not the worst drought sequence in the past 250 years. red = observed, blue = reconstructed

10 Global Climate Change Scenarios and Hydrologic Impacts for the PNW

11 Humans are altering atmospheric composition

12 The earth is warming -- abruptly

13 Four Delta Method Climate Change Scenarios for the PNW ~ + 1.7 C ~ + 2.5 C Somewhat wetter winters and perhaps somewhat dryer summers

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

15 Current Climate 2020s2040s Snow Water Equivalent (mm) VIC Simulations of April 1 Average Snow Water Equivalent for Composite Scenarios (average of four GCM scenarios) The main impact: less snow

16 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

17 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

18 Changes in Natural Streamflow for the “Middle of the Road” Scenarios Current Climate--Blue 2020s--Green 2040s--Red Impacts in the upper basin (Canada) are delayed in comparison with the lower basin (USA).

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

20 Frequency of Drought in the Columbia River Comparable to Water Year 1992 (data from 1962-1997) x 2 x 4.7 x 1.3

21 Effects of Hydrologic Changes Increased Winter Flow Increases winter flooding in some basins Increased scouring events and sediment loads(?) Potential benefits to winter hydro production Reduced Snowpack and Earlier Snow Melt Reduces spring flooding in some basins Reduces summer water availability (limited storage) Reduces summer hydro production May change structure of mountain ecosystems Longer dry season may intensify forest disturbance (e.g. fire, pests) Late summer streamflows systematically lower Increased water temperatures (?)

22 Decadal Climate Variability and Climate Change

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

24 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

25 Monitoring Observed Climate Change Impacts

26 Source: Mote et al., Declining Mountain Snowpack in Western North America (BAMS, 2004) Trends in April 1 SWE 1950-1997

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

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

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

30 Fraction of Annual Streamflow Occurring from June-Sept Trends in Simulated Summer Water Availability for the N.F. Clearwater River at Dworshak Dam

31 Impact Pathways for Salmon Management and Recovery Efforts in the Columbia Basin and Opportunities for Adaptation

32 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 Managed Flow Augmentation

33 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, 233-256 Adaptation to climate change will require complex tradeoffs between ecosystem protection and hydropower operations

34 Flood Control vs. Refill Because so little storage is currently allocated to fish flows, reliability of refill is crucial to achieving acceptable levels of flow augmentation in summer. As streamflow timing shifts move peak flows earlier in the year, flood evacuation schedules may need to be revised both to protect against early season flooding and to begin refill earlier to capture the (smaller) spring freshet. Model experiments (see Payne et al. 2004) have shown that moving 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, 233-256

35 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.

36 Broad Strategies for Incorporating Climate Variability and Climate Change in Long-Term Planning Identify and Assess Climate Linkages Identify potential linkages between climate and resource management that could affect outcomes in the long term. What’s being left out? Are there future “deal breakers” in these omissions? (e.g. ocean productivity, glaciers maintaining summer streamflow in the short term) Design for Robustness and Sustainability Use modeling studies to test preferred management alternatives for robustness in the face of climate variability represented by paleoclimatic studies, conventional observations, decadal variability, and future climate change projections. Identify Limits and Increase Response Capability Use estimates of uncertainties or “what if” scenarios to find the performance limits inherent in preferred management alternatives. How can response capability be increased? Expect Surprises and Design for Flexibility to Changing Conditions Design contingency planning into management guidelines to allow for ongoing adaptation to unexpected (or uncertain) conditions without recursive policy intervention.

37 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 Refs on Climate Variability and Climate Change

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