1. ASSESSING POTENTIAL IMPACTS OF CLIMATE CHANGE ON WATER RESOURCES: THREE WESTERN U.S. CASE STUDIES Dennis P. Lettenmaier Department of Civil and Environmental Engineering University of Washington CIG/CSES Seminar January 28, 2003

2. Outline of this talk 1)Climate variability and change context 2)Prediction and assessment approach 3)Accelerated Climate Prediction Initiative (ACPI) 4)Hydrology and water management implications for Columbia, Sacramento- San Joaquin, and Colorado River basins 5)Conclusions and comparative analysis

3. 1) Climate variability and change context

4. Humans are altering atmospheric composition

5. The earth is warming -- abruptly

6. Natural Climate InfluenceHuman Climate Influence All Climate Influences

8. Temperature trends in the PNW over the instrumental record Almost every station shows warming (filled circles) Urbanization not a major source of warming

9. Trends in timing of spring snowmelt (1948-2000) Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan +20d later –20d earlier

10. Trends in snowpack

12. 2) Prediction and assessment approach

13. Climate Scenarios Global climate simulations, next ~100 yrs Downscaling Delta Precip, Temp Hydrologic Model (VIC) Natural Streamflow Reservoir Model DamReleases, Regulated Streamflow Performance Measures Reliability of System Objectives

14. Reservoir Model Hydrology Model Coupled Land- Atmosphere-Ocean General Circulation Model

15. Accelerated Climate Prediction Initiative (ACPI) – NCAR/DOE Parallel Climate Model (PCM) grid over western U.S.

16. Bias Correction and Downscaling Approach climate model scenario meteorological outputs  hydrologic model inputs  snowpack runoff streamflow 1/8-1/4 degree resolution daily P, Tmin, Tmax 2.8 (T42)/0.5 degree resolution monthly total P, avg. T

17. Bias Correction from NCDC observations from PCM historical runraw climate scenario bias-corrected climate scenario month m Note: future scenario temperature trend (relative to control run) removed before, and replaced after, bias-correction step.

18. Downscaling observed mean fields (1/8-1/4 degree) monthly PCM anomaly (T42) VIC-scale monthly simulation interpolated to VIC scale

20. Overview of ColSim Reservoir Model Physical System of Dams and Reservoirs Reservoir Operating Policies Reservoir Storage Regulated Streamflow Flood Control Energy Production Irrigation Consumption Streamflow Augmentation Streamflow Time Series

21. Dam Operations in ColSim Storage Dams Run-of-River Dams VirginRegulated Flow In=Flow out + Energy H

22. Inflow Run of River Reservoirs (inflow=outflow + energy) Inflow Storage Reservoirs Releases Depend on: Storage and Inflow Rule Curves (streamflow forecasts) Flood Control Requirements Energy Requirements Minimum Flow Requirements System Flow Requirements System Checkpoint Consumptive use Inflow + C ol S im

23. 3) Accelerated Climate Prediction Initiative (ACPI)

24. GCM grid mesh over western U.S. (NCAR/DOE Parallel Climate Model at ~ 2.8 degrees lat-long)

25. Climate Change Scenarios Historical B06.22 (greenhouse CO 2 +aerosols forcing) 1870-2000 Climate Control B06.45 (CO 2 +aerosols at 1995 levels) 1995-2048 Climate Change B06.44 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.46 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.47 (BAU6, future scenario forcing) 1995-2099 Climate Control B06.45 derived-subset 1995-2015 Climate Change B06.44 derived-subset 2040-2060 PCM Simulations (~ 3 degrees lat-long) PNNL Regional Climate Model (RCM) Simulations (~ ¾ degree lat-long)

26. Future streamflows 3 ensembles averaged summarized into 3 periods; »Period 1 2010 - 2039 »Period 22040 - 2070 »Period 3 2070 - 2098

27. Regional Climate Model (RCM) grid and hydrologic model domains

28. ACPI: PCM- climate change scenarios, historic simulation v air temperature observations

29. ACPI: PCM- climate change scenarios, historic simulation v precipitation observations

30. 4a) Hydrology and water management implications: Columbia River Basin

31. PCM Business-as-Usual scenarios Columbia River Basin (Basin Averages) control (2000-2048) historical (1950-99) BAU 3-run average

32. RCM Business-as-Usual scenarios Columbia River Basin (Basin Averages) control (2000-2048) historical (1950-99) PCM BAU B06.44 RCM BAU B06.44

34. PCM Business-As- Usual Mean Monthly Hydrographs Columbia River Basin @ The Dalles, OR 1 month 12

35. CRB Operation Alternative 1 (early refill)

36. CRB Operation Alternative 2 (reduce flood storage by 20%) 15,000,000 20,000,000 25,000,000 30,000,000 35,000,000 40,000,000 45,000,000 50,000,000 55,000,000 ONDJFMAMJJAS End of Month Total System Storage (acre-feet) Max Storage Control Base Climate Change Change (Alt. 2) Dead Pool

42. 4a) Hydrology and water management implications: Sacramento-San Joaquin River Basin

43. PCM Business-as-Usual scenarios California (Basin Average) control (2000-2048) historical (1950-99) BAU 3-run average

44. PCM Business-as-Usual Scenarios Snowpack Changes California April 1 SWE

45. PCM Business-As- Usual Mean Monthly Hydrographs Shasta Reservoir Inflows 1 month 12

46. Trinity Lake Storage: 2448 taf Lake Shasta Storage: 4552 taf Lake Oroville Storage: 3538 taf Folsom Lake Storage: 977 taf Whiskeytown Storage: 241 taf Sacramento River Basin Trinity Whiskeytown Shasta Oroville (SWP) Folsom Clear Creek American River Feather River Trinity River Sacramento River Dam Power Plant River Transfer Delta

47. Delta & San Joaquin R Basin Dam Power Plant River/Canal Transfer Eastman, Hensley, & Millerton New Don Pedro & McClure Delta New Hogan Pardee & Camanche Stanislaus River Tuolumne & Merced Rivers Delta Outflow Mokelumne River Calaveras River San Joaquin River Pardee/Camanche Reservoir Storage: 615 taf New Melones Res Storage: 2420 taf Don Pedro/McClure Storage: 3055 taf Millerton Lake Storage: 761 taf Sacramento-San Joaquin Delta Area: 1200 mi 2 Delta San Luis Reservoir CVP: 971 taf SWP: 1070 taf New Melones San Luis

49. Storage Decreases Sacramento Range: 5 - 10 % Mean: 8 % San Joaquin Range: 7 - 14 % Mean: 11 % Current Climate vs. Projected Climate

50. Hydropower Losses Central Valley Range: 3 - 18 % Mean: 9 % Sacramento System Range: 3 – 19 % Mean: 9% San Joaquin System Range: 16 – 63 % Mean: 28%

51. 4a) Hydrology and water management implications: Colorado River basin

52. Timeseries Annual Average Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098 hist. avg. ctrl. avg. PCM Projected Colorado R. Temperature

53. hist. avg. ctrl. avg. PCM Projected Colorado R. Precipitation Timeseries Annual Average Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098

54. Annual Average Hydrograph Simulated Historic (1950-1999)Period 1 (2010-2039) Control (static 1995 climate)Period 2 (2040-2069) Period 3 (2070-2098)

55. Projected Spatial Change in Runoff 90 % 86 % 82 % 83 %

56. April 1 Snow Water Equivalent

57. Natural Flow at Lee Ferry, AZ Currently used 16.3 BCM allocated 20.3 BCM

59. Storage Reservoirs Run of River Reservoirs CRRM Basin storage aggregated into 4 storage reservoirs –Lake Powell and Lake Mead have 85% of basin storage Reservoir evaporation = f(reservoir surface area, mean monthly temperature) Hydropower = f(release, reservoir elevation) Monthly timestep Historic Streamflows to Validate Projected Inflows to assess future performance of system

60. Water Management Model (CRRM) Multi Species Conservation Program year 2000 demands – upper basin 5.4 BCM – lower basin 9.3 BCM – Mexico 1.8 BCM Minimum Annual Release from Glen Canyon Dam of 10.8 BCM Minimum Annual Release from Imperial Dam of 1.8 BCM

61. Total Basin Storage

62. Annual Releases to the Lower Basin target release

63. Annual Releases to Mexico target release

64. Annual Hydropower Production

65. Uncontrolled Spills

66. Deliveries to CAP & MWD

67. Precipitation Annual Average Change (mm/yr) in: Evapo-transpiration Runoff mm / yr.

68. Colorado River Basin Annual Average Precipitation (mm/yr) (mm/yr) NE cell XX X SW cell NW cell

72. 5) Conclusions and Comparative analysis 1) Columbia River reservoir system primarily provides within-year storage (total storage/mean flow ~ 0.3). California is intermediate (~ 0.3), Colorado is an over-year system (~4) 2) Climate sensitivities in Columbia basin are dominated by seasonality shifts in streamflow, and may even be beneficial for hydropower. However, fish flow targets would be difficult to meet under altered climate, and mitigation by altered operation is essentially impossible. 3) California system operation is dominated by water supply (mostly ag), reliability of which would be reduced significantly by a combination of seaonality shifts and reduced (annual) volumes. Partial mitigation by altered operations is possible, but complicated by flood issues. 4) Colorado system is sensitive primarily to annual streamflow volumes. Low runoff ratio makes the system highly sensitive to modest changes in precipitation (in winter, esp, in headwaters). Sensitivity to altered operations is modest, and mitigation possibilities by increased storage are nil (even if otherwise feasible).