As Hurricane Florence ground its way through the Carolinas this past weekend, climate watchers couldn’t help but notice that the size and behavior of the storm have been eerily reminiscent of Hurricane Harvey, which devastated Houston last year. What made these two hurricanes so destructive was their slow pace and the fact that they were supercharged with moisture from bathtub-warm oceans. It’s a deadly combination that leads to epic, record-setting amounts of rainfall and unprecedented flooding, amplifying damage from the high winds and storm surge typically associated with hurricanes.
Once Florence leaves the Carolinas and the floods have receded, the nation will rally to clean up what will likely be of one of its top five most destructive hurricanes. Florence will add to this century’s staggering storm damage, caused by 22 hurricanes or tropical storms that led to more than $700 billion in damages in the United States (adjusted for inflation).
Is this part of a trend? Most certainly. The National Oceanic and Atmospheric Administration has a detailed analysis of billion-dollar US weather disasters since 1980. Clearly, weather impacts are getting much more expensive—and much more frequent.
What does this mean for California? First, like all other states in the nation, California relies upon the federal government to help with disaster preparedness, response, and recovery. The increase in the number of natural disasters and their growing costs affect the ability of federal agencies to respond. And the most important tool in mitigating flood risk—flood insurance—relies on an insolvent National Flood Insurance Program that will surely be hit hard by Florence.
Second, while it is tempting for Californians to write off Florence as a weather problem that affects the Gulf Coast and Atlantic states, this would be a mistake. We have our own hurricane-equivalents here, called atmospheric rivers. These can produce rainfall rates similar to those found in hurricanes, and they are responsible for most of our floods.
California is no stranger to extreme floods that rival hurricanes in terms of damages. The Great Flood of 1861‒62 affected the entire state and turned the Central Valley into a lake. If that same flood were to happen today, studies by the US Geological Survey suggest that more than $700 billion in damages would occur (equal to all the damages from all hurricanes nationwide in the past 18 years) and more than 1.5 million Californians would be displaced. Research by Daniel Swain, a climate scientist at UCLA, suggests that the risk of this scale of flooding is increasing as global warming intensifies. Indeed, his work has shown that the probability of a flood similar to the 1861‒62 flood occurring in California by mid-century is greater than the probability that it won’t.
Florence is a sobering hurricane that will likely be one of the worst in history. California would do well to heed some of its key lessons. As discussed in our recent report and highlighted by California’s Fourth Climate Assessment, flood risk is increasing due to climate warming. The 2017 crisis at Oroville Dam is an expensive reminder that California needs to upgrade its aging water management infrastructure. This will require finding new and innovative ways to fund flood management improvements.
California should also expand its efforts to steer new development away from high flood-risk areas through better land-use planning that incorporates increasing risk.
No matter how well California prepares, there will always be floods that overwhelm defenses, damage homes and businesses, and threaten lives. The state needs to continue to improve emergency preparations for floods and to encourage those who live in areas at risk of flooding to purchase insurance.
California has been a leader in reducing its contribution of greenhouse gases. But more work is needed to ensure its water supply and flood management systems are able to withstand a more volatile climate. California must act now to weather floods of the future.