What climate models should I use in my analysis? What are the priority models?

Thirty-two global climate model (GCM) simulations produced by institutions across the world served as a basis for California’s climate projections for California’s Fourth Climate Change Assessment, and thus for much of the data currently available on Cal-Adapt. These 32 GCMs are from the Coupled Model Intercomparison Project, version 5 (CMIP5).

Although the daily data from all 32 downscaled models, under two RCPs, can be used for the most comprehensive assessment and should be considered whenever possible, this may not always be practical. Subsets of these GCMs were therefore developed to provide much of the benefit of using all 32 GCMs but at a significantly reduced data volume.

The Department of Water Resources Climate Change Technical Advisory Group reduced the larger ensemble of 32 GCMs to a more manageable set of 10 GCMs as being most suitable for California water resource climate change studies where all 32 GCMs cannot be used. Additional variables were downscaled for these 10, including wind speed, specific and relative humidity, and surface solar radiation. Four models that span the temperature and precipitation changes from the 10 were identified for studies that cannot accommodate the 10.

These four models can be described as producing:

  • A warmer/drier simulation (HadGEM2-ES)
  • A cooler/wetter simulation (CNRM-CM5)
  • An average simulation (CanESM2)
  • A simulation that is most unlike the first three for the best coverage of different possibilities (MIROC5)

Cal-Adapt’s default settings provide outputs for these subsets of 10 and 4 GCMs, depending on the hazard. The average of values across different model projections is considered more likely than any individual model value, and the full range of values the models present can help you to evaluate potential extreme events and conditions. State guidance, including in the Office of Planning and Research’s Adaptation Planning Guide, Phase 2 and California Ocean Protection Council Sea Level Rise Guidance, recommends evaluating a range of future climate scenarios appropriate for planning decisions and respective risk aversion level.

To learn more about climate models, check out the Get Started section on climate models.

For more details on the selection of climate models for impact studies, see:

Pierce, D. W., J. F. Kalansky, and D. R. Cayan, (Scripps Institution of Oceanography). 2018. Climate, Drought, and Sea Level Rise Scenarios for the Fourth California Climate Assessment. California’s Fourth Climate Change Assessment, California Energy Commission. Publication Number: CNRA-CEC-2018-006.

You can also read guidance provided in the California Adaptation Planning Guide, version 2.0.