THE IMPACT OF CLIMATE CHANGE ON WATER SUPPLIES

1. THE IMPACT OF CLIMATE CHANGE ON WATER SUPPLIES Jim Doane PE Spring 2004

2. Order of Presentation • What is Current • Unprecedented issues for water supply planning • There will be temperature changes as a result of human activity • How these changes impact the hydrology of the Pacific Northwest • How these changes impact the Bull Run Water System

3. Order of Presentation • What is emerging • Worst case Pentagon Study on Climate Change (Leaked to British Press in Feb 2004) • Collapse of the Atlantic Ocean’s thermohaline circulation • Caused by Global Warming • Change in years instead of decades as presently predicted • Vast climate changes---both globally and locally • Colder, windier and drier and shorter growing season in the Northeast US. Less productive agriculture.

4. Order of Presentation • A longer growing season in the Southwest US. More productive agriculture if water can be provided. • Increased competition for water leading to international conflict. • http://www.ems.org/climate/pentagon_climatechange.pdf

5. Planning for Water Supply • Based on historical values • Demand….present demand plus growth (generally population based) • Supply • Historical Record • The longer the record, the higher the confidence • But the Past is no longer a good precursor of the future

6. TEMPERATURE CHANGES • From 2001 Work by the University of Washington • Dr. Philip Mote of the JISAO Climates Impacts Group

7. Assessments of Climate Change • Thousands of peer-reviewed papers • Peer-reviewed assessment: Intergovernmental Panel on Climate Change (IPCC) • Major reports in 1990, 1996, 2001 • National Academy of Sciences panel, 2001 underscored IPCC conclusions

8. Humans will keep increasing CO2 • carbon dioxide concentration has increased by ~32% • the carbon budget: nature has absorbed roughly half our emissions • there is no question that the increase is unnatural • from a very long term perspective, these changes are enormous

9. Evidence that Earth is Warming • Thermometers show warming of 0.4-0.8°C (0.7-1.4°F) since 1900 • Arctic permafrost is melting • Worldwide, most glaciers melting • Arctic ice thinning • Spring coming earlier (snow cover; blooming, leafing-out dates) • Borehole temperatures indicate warming • But: not every station shows warming; upper-air temperatures not increasing (satellites, balloons)

10. Global average temperature 0.8 0.4 degrees Celsius 0 -0.4 -0.8 1860 1880 1900 1920 1940 1960 1980 2000

11. Some Evidence that Humans are Responsible • Rate of warming unusual • Hard to explain as natural (volcanoes, solar, ocean) • Pattern of warming (and stratospheric cooling) consistent with human influence

12. The earth is warming -- abruptly

13. Natural Climate Influence Human Climate Influence All Climate Influences

14. Projections into the Future • Projections of future greenhouse gases (depends on socioeconomic projections) • Climate models: different “sensitivity” • Wide range of estimates: 1.4-5.8°C (2.5-10.4°F) by 2100, faster than any time in at least 10,000 years. • Estimates show Pacific Northwest will increase by 3-5°F by 2040.

16. Temperature trends in the PNW • Almost every station shows warming (filled circles) • Urbanization not a major source of warming

17. PNW average temperature

19. Temperature Change Conclusions • The bulk of the evidence points to a human influence on climate, with a global warming of 2.5-10.4F likely in the next 100 years. • Regional warming likely to be faster than average global warming (3-6°F by 2040s); main vulnerability: reduced snow leading to summer water shortages

20. Implications for Water Management • 2001 Work by University of Washington • Alan Hamlet, Andy Wood and Dennis Lettenmaier of the JISAO Climates Impacts Group

21. (mm) Summer Precipitation Winter Precipitation

22. Hydrologic Characteristics of PNW Rivers

23. Sensitivity of Snowmelt 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

24. 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)

25. Changes in Mean Temperature and Precipitation from GCMs ColSim Reservoir Model VIC Hydrology Model

26. Climate Change Scenarios 2020s

27. Climate Change Scenarios 2040s

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

29. Columbia River at The Dalles 2020s “Middle-of-the-Road” Scenario

30. Columbia River at The Dalles 2040s “Middle-of-the-Road” Scenario

31. Water Resources in the Columbia River Basin System objectives affected by winter flows Winter hydropower production (PNW demand) System objectives affected by summer flows Flood control Summer hydropower production (California demand) Irrigation Instream flow for fish Recreation

32. Simulated Reliability of Water Resources Objectives for “Middle-of-the-Road” Scenarios

33. 1 Palisades 2 Milner 3 Oxbow 4 Ice Harbor 5 Kiona 5 4 3 1 2

34. Snake River at Milner

35. Snake River at Ice Harbor

36. Yakima River at Kiona

37. General Conclusions for the PNW PNW hydrology is predominantly controlled by winter conditions in the mountains. Warmer temperatures produce streamflow timing changes in most PNW basins. Changes in precipitation produce changes in streamflow volumes. Basins encompassing the mid-winter snow line are most sensitive to warming. Basins at high elevations with cold winter temperatures are less sensitive. The primary impact of warming in the PNW is loss of mountain snowpack. For the scenarios investigated, both warm/wet and warm/dry scenarios result in decreased snow water equivalent in the Columbia basin. Warmer temperatures generally results in higher winter flows, lower summer flows, and earlier peak flows Effects to the Columbia water resources system are largely associated with reduced reliability of system objectives affected by summer streamflows (water supply, irrigation, summer hydropower, instream flow).

38. General Conclusions for the PNW (cont.) There are significant uncertainties regarding changes in precipitation and the resulting intensity of reductions in summer streamflows and increases in the frequency of droughts. However, a consistent and robust result is that some reduction in summer streamflow and increase in drought frequency is present in all scenarios by the 2040s for the Columbia basin. The greatest impacts to the Columbia system are for the warm/dry scenarios, which produce the strongest reductions in summer streamflows and the greatest increases in drought frequency. The reductions in summer streamflows in these scenarios are likely to exacerbate existing conflicts over water, the impacts of regional growth, and weaknesses in infrastructure, water management practice, and management institutions.

39. The Impacts of Climate Change on Portland’s Water Supply Work by Joe Dvorak, Dennis Kessler, Azad MohammadiPortland Bureau of Water WorksRichard Palmer, Margaret HahnUW Dept of Civil EngineeringClimate Impacts Group, JISAOSpring 2002

40. Objectives Of StudyExamine the impacts of climate change on the Bull Run Watershed: • Bull Run Watershed hydrology • temporal and spatial analysis • Forecasted M&I demand • System performance

41. Portland’s Water Supply System • Serves ~ 840,000 people • Largest system in state; serving since 1895 • 42 BG annual demand • 115 MGD average daily demand • Bull Run Watershed • Dam No.1 (10 BG) • Dam No.2 (7 BG)

42. Bull Run Watershed • 107 square miles • 2350 feetelev. • Rainfall driven • 80 in./yr. rainfall • 170 BG/year yield • Peak Snowpack: • 16 inches Snow Water Equivalent (SWE) • Snowmelt typically occurs before June

43. Four Global Circulation Models Hydrological Model WaterSupply Model Methodology Three sets of models used in the study: Predicts changes to temperature and precipitation based on altered CO2 concentration. Uses GCMs to predict climate impacted runoff in watershed. Forecasts system performance based predicted watershed hydrology.

44. Results: Impacts to Climate • Average warming trends of ~1.5 OC for the 2020 decade and ~2 OC by 2040. • Increased winter precipitation, with less snowfall, but more rain • A decrease in late spring and summer precipitation

45. 2020 Climate Change Temperature Change for Climate Change Scenarios 4 2040 Climate Change 3.5 3 2.5 Degrees C 2 1.5 1 0.5 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Results: Impacts to Temperature

46. Results: Impacts to Snowfall

47. Precipitation Fraction for 2020 Climate Change Climate Change Scenarios 1.2 2040 Climate Change 1.15 1.1 1.05 Fraction Precipitation 1 0.95 0.9 0.85 0.8 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Results: Impacts to Precipitation

48. Results: Impacts to Hydrology • Average winter streamflows increase by 15% • Late spring streamflows decrease by 30% due to spring snowmelt being non-existent • 50 percent of the time, April to September flows may decrease by as much as 12.9 BG • Less impact to storage (0.1 - 3.6 BG) depending on drawdown timing (avg. 1.3 BG)

49. Results: Impacts to Streamflow

50. Results: Impacts to Streamflow(April to September)