Climate Change and Municipal Water Supplies

1. Climate Change and Municipal Water Supplies Presented by Lorna Stickel Portland Water Bureau and Regional Water Providers Consortium Project Manager

2. How are Municipal Water Supplies affected by Climate Change? • Water demands are increased by increases in temperature in the summer months, beyond the effects of growth. • The hydrology of sources is affected even more than the demands. • The competition for water resources is increased, thereby affecting water rights. • Summer instream flows are less affecting ESA species/HCP requirements and CWA permit requirements.

3. Topics for This Presentation • Past Regional Planning and Climate Change • Potential impacts of climate change on municipal supplies, some examples from the Portland metro area. • How municipalities might deal with climate change including more research that is needed.

4. Water Supply Planning in Portland Region • Most Water providers have not considered climate change directly in their Master Plans, however, two sources have had climate change studies conducted: • Bull Run - 2000 • Tualatin Basin - 2004 • Regional planning between 1993-2004 did not consider the direct effects of climate change, but did recognize the potential for impacts. • The RWSP Update of December 2004 does contain two pages on climate change and the two studies.

5. Regional Water Supply Plan • Planning for supplies in the Portland area included aspects of meeting drought needs within the Regional Water Supply Plan (RWSP) & Update through: • Water Demand Forecasting – Uses the actual climate patterns of the years 1940-2003 within an econometric model that predicts daily water demands. • Integrated modeling in Confluence allowed looking at weather events of the past so that those (eg. 1968 for peak season and 1981 for peak day) that drove demands higher were selected for analysis.

6. Regional Water Supply Plan • Conservation Programs selected that focus on summer peak season uses. • Interties have been constructed and more are proposed to connect sources better and to encourage conjunctive and efficient use of existing supplies. • Non-potable and reuse are also encouraged where feasible and cost effective.

7. Climate Change and Impacts to Municipal Sources of Supply • Impacts to Sources of Supply • Run of River – Changes in the periodicity of streamflows, more intense winter flows and lower summer flows • Storage – Reliability of storage projects changes • Demands are higher in the peak season • Less inflow affects both filling of some projects annually and reduces the amount of surface water inflow during the summer. • GW – Not sure of the impact on these systems, but if GW is pumped more to meet increased needs then declines in water levels could result and/or impacts on surface water sources could be greater. • The past 60 years of record shows great variability for surface water sources, climate change will result in seeing even more variability.

9. Bull Run Study: Impacts to Snowfall

10. Climate Change and Impacts to Municipal Water Demands • Demands • Temperature and rainfall are major factors that affect demand patterns during the peak season. • Even higher demands in peak season at the same time that supplies might be less. • Climate change likely to mean more severe demand patterns than seen in past, or greater frequency of “worst” weather years. • Fish & water quality instream needs also will compete more frequently with out of stream demands.

12. Bull Run Study : Impacts on Demand • Water demands shown to be less affected by climate change than hydrology • 8% increase in 2040 drawdown demand • 4% increase in 2040 average annual demand

13. Climate Change and Impacts to Municipal Water Systems • Most planning for water supplies is based on past history, and often not a very long history. • The synergy between lower summer streamflows, less summer rainfall and higher temperatures creates an effect that is going to stress municipal systems more than past. • If suppliers only evaluate the past history then we may be creating water supply systems that are not as reliable.

14. Dealing with Climate Change • Planning • Larger supplies as well as rivers that have multiple intakes should model climate change impacts as has been done for Portland’s Bull Run and for the Tualatin Basin. • Assess the effects on multiple sources at the same time if possible, more study is needed in the Portland area to include the Clackamas River particularly, but also the Willamette and the impacts on storage. • Include climate change effects on both the hydrology and water demand patterns. • Assess the role of curtailment, particularly in light of more extreme events (drought and flooding) and hardening of demand through conservation.

15. Dealing with Climate Change • Infrastructure Development & Use • Consider more conjunctive use of sources including surface, groundwater, and ASR. • Build more system interconnections and backup supplies for emergencies or more frequent shortages of primary supplies. • More close monitoring & modeling of short term system operations and put in place strategies for dealing with summer supplies in real time. • More storage may be necessary to capture the higher winter flow events.

16. Dealing with Climate Change Programmatic Actions • Assess the potential impacts of changing flood rule curves on multiple purpose projects. • Use Conservation Programs to moderate demand effects, particularly during the peak season. These programs can be justified to offset climate change effects on both demand patterns and instream resources. • Develop curtailment plans in a regional context. • Encouraging more active use of water markets and water banking to provide added flexibility to deal with change. • Public needs to be included in the decisions about system reliability in times of uncertainty about future supplies.

17. Better Knowledge Needed There is a lot that isn’t known about climate change impacts on municipal supplies: • Only limited studies have been done, and even then broad assumptions have to be made about the local effects. • The impacts on hydrology are the most important unknowns that need to be researched, particularly for urban water sources. • Summer climate change impacts on rainfall patterns are not as well predicted as temperature increases. • Reliable long term data needs to be collected and available for analysis. • Synergistic effects between flows, fish, flooding, hydro, and water demand patterns present a complex picture that needs more study. • The role of conservation and curtailment need to be better integrated into long term climate change impacts.

18. Parting Thought We need to be open minded to the reality that the future won’t be like our recent historic past. We don’t need to overreact, but we need to start now to incorporate the flexibility we will need to deal with the impacts of climate change on our water resources.