There’s a familiar script when it comes to hurricanes: The high winds snap tree branches and even tree trunks and whip around anything else that’s light enough or not bolted down — including power lines and distribution poles. While this type of damage can lead to large-scale outages, it’s also relatively straightforward to fix. In many cases the power comes back on relatively quickly, more like days rather than weeks or months.
But when it comes to flooding, especially in areas that do not regularly deal with big storms, the damage can be more severe, long-lasting, and difficult to repair. This is largely because what’s at risk in these scenarios is not power lines but substations. These messes of transmission and distribution lines that channel high voltage power to homes and businesses are vulnerable to rising water, and repairs can’t begin until the floodwaters recede. Often they have to be replaced entirely, which is expensive and can lead to further delays as there’s a nationwide shortage of transformers. Just one substation can support thousands of homes — a single point of failure that, when it floods, takes all its customers down with it.
Duke Energy, whose grid in the Carolinas was pummeled by Hurricane Helene, has said the damage to its system encompasses “submerged substations, thousands of downed utility poles, and downed transmission towers,” and noted that much of the affected area is “inaccessible due to mudslides, flooding and blocked roads, limiting the ability to assess and begin repairing damages.” In an update published Saturday, it stated that while more than 2 million customers had seen their power restored, about 250,000 customers across North and South Carolina remained without electricity more than a week after the storm.
Workers are “encountering more severe damage on a larger scale than we’ve ever experienced,” Duke Energy storm director Jason Hollifield said in a statement. (Duke didn’t respond to my request for comment.) One Duke employee told the local television station in Asheville, North Carolina, which saw more than three months’ worth of rain fall over three days, that a local substation would have to be completely rebuilt, a process that could take months. In Western North Carolina, the area’s Representative Chuck Edwards has estimated that 117,000 customers still lack electricity, and that while some of them will likely get it back by Sunday, others “whose properties are inaccessible or not able to receive power may be without electricity for an extended period of time as Duke Energy works to rebuild critical infrastructure.”
To prepare for the onrushing Hurricane Milton, Duke is staging thousands of “line technicians, vegetation workers, damage assessors and support personnel” in Florida, the company said. The same problem remains, however: Line technicians will not prevent substations from flooding.
While the exact effect of climate change on hurricanes and other storm categories is an area of intense debate among climate scientists and meteorologists, there’s a rough consensus that warming will cause the storms to be wetter. That means utilities will have to update their old disaster response playbooks, or else prolonged outages when an especially wet storm arrives over a flood plain.
In most hurricanes, utilities are able to pre-position workers to restore power quickly, working on knocked down poles and wires, explained Jordan Kern, an assistant professor engineering at North Carolina State University. “When trees fall on distribution lines, those are, in normal situations, easy to repair,” he told me. But, Kern said, “If the substations are flooded, you can’t do anything until the flood waters go down. They can be without power for a long time.”
Wetter hurricanes will likely mean more severe and less predictable flooding happening far away from the coasts, bringing with it risks that utilities and local governments may be less prepared to face, with costs that will ultimately be born by anyone who pays for electricity, as expensive repairs and hardening of electrical infrastructure will likely be born by ratepayers.
“Rates will necessarily rise” to deal with the higher costs of adaptation and repairing infrastructure more complex than a wooden pole, Tyler Norris, a PhD student at Duke University’s Nicholas School of the Environment, told me while driving towards Asheville to help out family impacted by the storm.
While Helene has been an especially damaging storm, the risks of wetter storms and inland flooding away from the coastal areas that are prepared for frequent hurricanes have become more apparent in recent years. While Hurricane Irene in 2011 made landfall on Long Island, its most devastating effects were felt inland due to heavy rains, especially in Vermont.
North Carolina in particular has seen a rash of nasty hurricanes in the past 10 years or so, giving Duke ample recent experience with big storms — and some indication of what a warming world could bring.
During 2018’s Hurricane Florence, which knocked out power for around a million Duke customers, “at least 10 substations required de-energization due to flooding or flood risk where heavy rainfall and resulting inland flooding,” according to a 2022 Duke climate resiliency report. The report was meant to look at the effects of climate change to the Duke system by 2050 under two emissions scenarios outlined by the Intergovernmental Panel on Climate Change, one assuming emissions start falling by 2040, the other assuming continued (some might say unrealistically) high emissions.
Under the extreme scenario, the “overall vulnerability priority of Duke Energy substations to climate-driven changes in precipitation and inland flooding is high,” the report said, while under the “middle of the road” projection, “transmission infrastructure faces a medium priority vulnerability.” In both cases, however, “without adaptation planning … substations are at the highest potential risk, with extreme heat and flooding being the greatest concerns for existing assets.”
Duke said at the time that it had “implemented permanent flood protection measures at new substations located in flood plains and substations with a prior history of flooding.” For its existing fleet, priority was being given to those substations considered particularly “at-risk,” however the flood protection plan had “not yet been universally implemented at all existing substations in the flood plain.”
“What they characterized there falls significantly short of what we just saw,” Norris said. While he noted that Duke had listed risk to substations from inland flooding as high (albeit only under the extreme scenario), it had listed the risk to the distribution of power, i.e. poles and wires, as “low” under both scenarios. “There’s been a dramatic misestimate of risk here,” Norris said.
For Duke customers, especially in the more isolated parts of Western North Carolina, they may simply have to wait for workers and parts to arrive. Repairs that could normally happen quickly will likely happen slowly as workers struggle to reach areas whose roads have been washed away. Duke said that it’s now focusing on restoring the “backbone” of the transmission and distribution system, and then is moving on to restoring fallen poles in less densely populated areas.
And it will likely happen again. Kern noted that inland flooding especially is notoriously hard to predict compared to coastal flooding from hurricanes. “Flooding is so idiosyncratic,” he said. “It’s hard for anyone to predict how flooding will affect a region. Let alone electric utilities.”
