We need to plan for extreme flooding in California

This year (2021) we have seen unprecedented flooding in Europe and on the East Coast. We’ve also just seen unprecedented flooding in British Columbia. As David Wallace Wells reports in “This Is What Happens When One Climate Disaster Follows Another,”

The impacts have been significantly greater than expected,” acknowledged Mike Farnworth, the deputy premier of British Columbia, echoing the language of bewilderment and disorientation that accompanied the heat dome this summer as well.

This is Canada. We aren’t just failing to address the growing climate crisis to come; we’re unprepared even for the impacts already here — in part because they keep surprising us with their intensity and in part because, in places across the global north, we can’t seem to fathom our genuine vulnerability.

In 2018, Daniel Swain, Baird Langenbrunner, J. David Neelin & Alex Hall published a study [1] of the increased  frequency of extreme flood events such as the Great Flood of 1862. Swain et. al. suggested “that California’s major urban centers (including San Francisco and Los Angeles) are more likely than not to experience at least one such extremely severe storm sequence between 2018 and 2060 on a business-as-usual emissions trajectory.”  We asked Swain if the new COP26 agreement changed this > 50-50 chance. Swain explained that the difference between the warming scenarios in the next few decades is quite minimal.  He said he hadn’t done the math, but thought it would be about the same.

One of the key lessons from the pandemic was that tabletop exercises for worst case scenarios were extremely important for response. Our comments on the Draft California Climate Adaptation Strategy recommended that the strategy explicitly address the need to do such scenario planning. In particular, we’ve recommended that Action 16 include development of response strategies, not just pre-positioning of resources.

Action 16: Integrate future climate risk into emergency management, response, and early warning systems.

  • Success Metric: Number of pre-positioned resources intended to anticipate and mitigate catastrophic wildfires and other climate-driven disasters
  • Timeframe: Under review
  • Agency/Agencies: CA Governor’s Office of Emergency Services

The success metric for reducing flood vulnerability for California should be percentage of the vulnerable urban and small community population that is protected, not permitted Flood-MAR projects. California Water Research has recommended that Action 5 should be revised:

Action 5: Reduce flood damages in California by helping regions prepare for new flood patterns.

  • Success Metric: Reduced flood damages in California
  • Timeframe: Under review
  • Success Metric: Number of new projects permitted to capture peak flow and improve groundwater recharge

At the COP26 conference in Glasgow, Secretary of Natural Resources Wade Crowfoot said,  “climate change has gotten existential for us.… I try to keep it very real. The time for talking is complete. It’s time for taking action.”

It is time for California to act on the climate crisis with the urgency that it demands. Whether people are displaced by climate change, or whether they even survive, will depend on the decisions that we make now.


[1] Swain, D., Langenbrunner, B., Neelin, J.D., Hall, A. Increasing precipitation volatility in twenty-first-century California. Nature Clim Change 8, 427–433 (2018). https://doi.org/10.1038/s41558-018-0140-y.


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