Simulating the future climate of the Great Lakes using Regional Climate Models

1. Simulating the future climate of the Great Lakes using Regional Climate Models Frank Seglenieks Boundary Waters Issues Unit, MSC Methods of Projecting Hydrologic Impacts of Climate Change, Muskegon, MI 2012-08-27

2. Summary • Previous estimates of future levels of the Great Lakes • The Canadian Regional Climate Model • RCM downscaling – current climate • RCM downscaling – future climate • RCM downscaling – future lake levels • Initial results using NARCCAP • Future research

3. Previous studies of lake levels All methods use output data from Global Circulation Models (GCMs) based on various future carbon scenarios (A1B, A2, etc.). Unfortunately the GCMs have poor resolution, most don’t even see the lakes and therefore no lake processes are included.

4. early transient runs (GFTR2, HCTR2, MOTR2, CCTR2) early 2XCO2 runs (GISS, GFDL, OSU, CCC1) Previous studies of lake levels Lake level predictions made using GCM data resulted in estimates for much lower lake levels: Michigan – Huron Lake Levels: Decadal Mean MAX: 177.50 (Oct 1986) Lake Level(m) MIN: 175.58 (Mar 1964) Lofgren et al. 2002 Mortsch et al. 2000

5. Previous studies of lake levels This has been repeated often in the media: October 2, 2009: Study reports Indiana Dunes National Lakeshore threatened by climate change “Scientists project that Great Lake levels could fall by as much as several feet by 2090.” November 28, 2008 Climate Change, Water Sharing Could Damage Great Lakes “Most climate models predict that the water levels in the Great Lakes will fall …. Lake Huron could drop by as much as 4.5 feet.

6. Previous studies of lake levels In general GCMs predict higher precipitation, evaporation, and runoff over the Great Lakes. From IPCC AR4

7. The CRCM The Canadian Regional Climate Model (CRCM) was adapted to study climate change over the Laurentian Great Lakes as part of the International Upper Great Lakes Study (IUGLS). Need to study the effect of future climates on lake levels to evaluate regulation plans and adaptive management strategies. Hence data was only analyzed on a monthly basis. The CRCM runs were performed by the Ouranos group in Montreal.

8. The CRCM The Canadian Regional Climate Model (CRCM) reproduces the main characteristics of the climate system based on dynamical and thermodynamic equations. The Ouranos version uses CLASS 3.3 and a 1-D lake model. The outside boundary conditions are supplied by the various future climate results of the GCMs, this process is called dynamical downscaling. The smaller resolution of RCMs allow processes such as lake effect precipitation and precipitation recycling to be modelled (45 km instead of 200+ km). Future climate results for one run are also available on a much smaller time step (15 min instead of monthly)

9. The CRCM • CRCM AMMO grid forced around the outside with GCM data.

10. The CRCM • 3 GCMs used with various members • 8 total future climate sequences

11. RCM downscaling – current climate CRCM output was used to determine the components of the net basin supply (NBS): lake precipitation, lake evaporation, and incoming runoff for each lake. The lake precipitation and lake evaporation components of the water budget were directly calculated by the CRCM. Runoff into each lake is the most difficult component of the water budget to calculate. The runoff simulated by the CRCM had to be routed down the river system in order to properly simulate the timing of the runoff input into the lakes.

12. RCM downscaling – current climate Comparison was made between the CRCM results and data from the Great Lakes Environmental Research Laboratory (GLERL) based in Michigan. GLERL data is based on runs of their Area Ratio Method (ARM). Environment Canada is working towards running a coupled atmospheric-land surface model called GEM-Surf (formerly MEC/MESH).

13. RCM downscaling – current climate • Good agreement between current climate and reference datasets • Timing issue in lake evaporation

14. RCM downscaling – current climate • Runoff had to be routed so that it would better match measured inflow. • This changed the timing of the runoff, but did not change the volume.

15. RCM downscaling – current climate • Timing issue seen in NBS of all lakes.

16. RCM downscaling – future climate Now look at differences between the future (2041-2070) and current time slice (1961-1990). Both time slices use downscaled CRCM data. As this is dynamical downscaling, time series to not “line-up”.

17. RCM downscaling – future climate Annual total of differences for each component (positive numbers indicate higher future values).

18. RCM downscaling – future climate • Lake Superior • Large differences seen in seasonal patterns. • Generally wetter in the spring and drier in the fall.

19. RCM downscaling – future climate • More runoff during the winter, reduction in spring melt peak, not much change in summer/fall. Lake Michigan/Huron Lake Erie

20. RCM downscaling – future climate Superior Michigan/Huron Erie

21. RCM downscaling – future lake levels Change in lake levels in metres • Annual difference in future lake levels show very little overall change. • Even the range seen in the different models is not that drastic.

22. RCM downscaling – future lake levels • Very important to look at the monthly cycle of lake level, not just the annual differences. • Exaggerated season cycle seen for most models on most lakes. • Extreme monthly lake levels are what cause problems.

23. Michigan – Huron Lake Levels: Decadal Mean MAX: 177.50 (Oct 1986) MIN: 175.58 (Mar 1964) RCM downscaling – future lake levels • Nowhere near as dramatic a change in lake level as seen in earlier studies using GCM results directly.

24. Angel and Kunkel analysis • Angel and Kunkel analyzed over 500 GCMs. • Most variation seen between GCMs, than members of the same GCM, then downscaling method

25. Initial results using NARCCAP • North American Regional Climate Change Assessment Program (NARCCAP) – 6 RCMs, 4 GCMs. • Ideally 24 different combinations would be available • Only 12 were actually attempted • Only 8 actually had enough data to calculate lake levels

26. Initial results using NARCCAP • One RCM (RCM3) did not resolve the Great Lakes • Overall, only 6 RCM/GCM combinations are currently available (only 3 had complete data sets for all months): • CRCM – CCSM • CRCM – CGCM3 (same as previous analysis) • HRM3 – GFDL • HRM3 – HADCM3 • WFRG – CCSM • WFRG – CGCM3

27. Initial results using NARCCAP • Showing current climate results for Lake Michigan/Huron

28. Initial results using NARCCAP • Showing differences for Lake Michigan/Huron

29. Initial results using NARCCAP • Showing difference in runoff for all lakes

30. Future research • Complete analysis of output from NARCCAP RCMs (ie. look at temperature, ice, etc.) and extend to all lakes as well as Ottawa River • Use the precipitation and temperature data to run the WATFLOOD hydrological model to look at hourly flows • Analyze for changes of intensity of the future climate (ie. Precip return periods, drought). • Run a hydrological model that has a full energy balance (ie. MESH)

31. Questions?