1. Streamflow Response to Climate: Why Geology Matters –Tim Mayer, US Fish and Wildlife Service Presented at the Oregon Water Conference Corvallis, OR May 24-25, 2011

2. Warmer temperatures, reduced snowpacks, earlier snowmelt and more winter rain v snow will lead to: Earlier timing of snowmelt runoff Decreased summer/fall baseflows Increased water temperatures Increased winter flooding

3. Purpose of Study To consider how climate change impacts to streams vary for different stream types, as defined by elevation and geology. Focus on the Pacific Northwest. Crater Lake Nat Park Mt Rainier Nat Park Olympic Nat Park

4. Surface-dominated and Groundwater-dominated Flow Regimes RiverType Elev Annual Pcp Annual Runoff (m) (cm/yr) (cm/yr) Little R, OR Surface Rain 860 156 89 Salmon R, CA Surface Snowmelt 1300 141 83 McCloud R, CA Groundwater 1500 143 87

5. USGS Grid Map of Baseflow Index (Wolock, 2003)

6. Stream Types and Summer Streamflow Contrast in summer flows in two Oregon rivers Groundwater-dominated stream Surface-dominated stream

7. Importance of Groundwater Basins (sub-watersheds) to Mainstem Flows on Three Major River Systems

8. Predicted v Observed Low Flow (P10) for 281 OR Streams Multiple Linear Regression Predictors: Drainage area, Pcp, Longitude, (BFI) no BFI r 2 = 0.56 w/ BFI r 2 = 0.86

9. Stream Types and Climate Change Impacts Earlier timing of snowmelt runoff and decreased baseflows

10. Mayer and Naman (2011) compared trends in monthly and annual streamflows from 1956 to 2005 among stream types.  Examined 10 rain basins, 5 snowmelt basins, and 11 groundwater basins (all with minimal regulation and diversion).

11. Mayer and Naman (2011)  Rain Basins – large and variable trends in monthly flows in winter, very small trends in summer.

12.  Snowmelt Basins – little or no change in monthly flows in winter, increases in early spring, decreases in late spring, very small trends in summer. Mayer and Naman (2011)

13.  Groundwater Basins – more uniform trends (mostly declines) in all months, less of a decline or even increases at some sites in Mar/ Apr, relatively large declines in summer/fall flows in comparison to surface-dominated streams. Mayer and Naman (2011)

14. “…absolute decreases in July-September baseflows are significantly greater, by an order of magnitude, in groundwater basins compared to surface-dominated basins…” Mayer and Naman (2011)

15. Stream Types and Climate Change Impacts Warmer Water Temperatures? Groundwater-dominated stream Surface-dominated stream

16. Stream/Air Temperature Relationship

17. Summer Stream/Air Temperature Relationship

18. 7 Stream Temperature Sites In the North Umpqua and Upper Rogue

19. August Stream/Air Temperature Relationships

21. Regression Results from August Stream/Air Temperature Relationships

25. Potential Climate Change Impacts to Groundwater-dominated Streams  Changes in timing and baseflows –Groundwater basins show some indication of earlier timing of snowmelt runoff due to reduced snowpack but timing changes are more subtle and spread out. The effects of reduced snowpacks are extended into summer, resulting in larger absolute decreases in summer baseflows.

26. Potential Climate Change Impacts to Groundwater-dominated Streams  Warmer water temperatures –Summer water temperatures are considerably cooler in groundwater-dominated streams and these systems may be less sensitive to increasing summer air temperatures than surface-dominated streams.

27. Questions? Crater Lake Nat Park Mt Rainier Nat Park Olympic Nat Park