Cities brace for this season’s colliding climate disasters

26 August 2022

Published by: https://www.bloomberg.com

USA – May to October has become known as the “danger season” — when the US is most at risk of experiencing back-to-back climate disasters like heat waves, wildfires, drought and storms.

As summer in the US approaches peak wildfire and hurricane seasons, with above-normal activity predicted for the latter, experts worry that persistent heat waves can pack a deadly one-two punch as they coincide with extreme storms and severe droughts.

Such a threat played out in August 2020, when a heat wave blanketed Louisiana right after Hurricane Laura hit, leaving residents in 100-degree Fahrenheit weather without power. Of the 31 storm-related deaths reported, eight were “heat-related” and nine were due to carbon monoxide poisoning, likely from a generator. Then in October, as parishes were barely recovering in the sweltering heat, Hurricane Delta came barreling up the Gulf Coast.

These days, disasters seldom happen in isolation, even as most response and aid programs still treat them as one-off events. Events are overlapping, and hitting cities one right after another. The period between May and October, dubbed “danger season” by the Union of Concerned Scientists (UCS), is when extreme weather hazards are most likely to collide. Senior scientist Juan Declet-Barreto at UCS worries that the slow start to this year’s Atlantic hurricane season could mean a pile-up of severe storms over the next two months.

Since May this year, 116 US counties were under multiple types of alerts from the National Weather Service during the same week, according to his analysis — the first of such snapshot from the group to approximate the risk of colliding events during this season. Nearly three-quarters had concurrent fire weather and heat alerts, particularly along the West Coast and the Great Plains. Eighteen counties were under flood and heat alerts within the same week, and 15 had fire weather and flood alerts.

“It really stresses the systems that are normally designed to handle one disaster at a time,” says Claire Knox, an expert on emergency and crisis management at the University of Central Florida.

The last two years in particular have made apparent the challenges of compounding, or co-occurring, disasters: Floods, extreme heat and wildfires coincided with a global pandemic, hitting cities just as Covid infections surged, and further straining local resources and complicating efforts to shelter displaced residents. The US is having one of the hottest summers on record, according to at least one energy metric.

Hazardous weather events are also increasingly triggering subsequent ones thanks to human-driven climate change, creating a domino effect of worsening impacts that then snowball into a catastrophe — a type of compounding event known as cascading disasters.

In the US, extended extreme heat and droughts are now twice as likely to coincide as in the 1960s and 1970s, with each event driving up the intensity of one another, and creating fuel for devastating wildfires. When a record-shattering heatwave blanketed the southwest US in 2021, for example, the severe drought that the region had been experiencing likely drove temperatures up by four degrees in some areas, according to a recent study out of Johns Hopkins University.

The heat, meanwhile, intensified drought conditions, creating a dangerous feedback loop. “One is amplifying the other, and both of them are amplifying each other,” says Mahmoud Osman, a hydroclimate engineer at Johns Hopkins, who led the study.

Extreme heat can also intensify wet weather events such as in eastern Kentucky this month, when a heat wave threatened to complicate rescue and recovery efforts just days after the area suffered historic flooding. Overseas in London and Paris, intense rainfall triggered flash flooding last week. Experts say weeks of drought and extreme heat likely amplified the intensity by drying up the land and making it less effective at absorbing water.

“In cascading events, the sequence, timing and order of events really matter,” says Amir AghaKouchak, a professor of environmental and civil engineering at the University of California, Irvine. He adds that some events can take place over years, making it harder for scientists to model or predict their risks.

How to prepare cities

The strain that compounding events put on cities have far-reaching consequences that can affect the capacity to respond to future disasters. Local governments usually have to front the initial cost of recovery efforts, before getting reimbursed by the Federal Emergency Management Agency, or FEMA. “What we find in our research is that it can take two to three years for local governments to be fully reimbursed from a previous disaster,” says Knox.

As multiple disasters hit, the delay stands to drain municipal reserves and divert funds from other vital operations, and can lead to haphazard efforts to repair or replace damaged infrastructure.

Compound disasters can also hamper cities from completing the four stages of emergency management (mitigation, preparedness, response, and recovery). “So you’re having to recover from the first event, as the second event starts. Now you’re back into response mode, while you’re trying to mitigate for the next one,” says Knox, adding that it could trigger staffing, technology and financial issues for the responding organizations.

Many cities today still treat weather hazards as independent events in disaster and urban planning in general, in part because preparations are often based on past disasters. Municipal agencies also tend to complete comprehensive risk analysis separately, rather than as an entire entity. That means despite mitigating measures, developers may still be permitted in flood areas, for example.

The upcoming challenge is to turn science into policy, says AghaKouchak. “I think cities and states need to spend more resources on planning for future extreme scenarios, exploring potential grey swan events,” he said. That is, events with high impact, but which may be perceived as rare. “It’s good practice to explore events that have never happened before, that can theoretically happen together.”

In the US, a lot of these changes, Knox says, will depend on whether the funding for disaster changes: “We’re having to rethink how we are designing our plans, including the funding structures,” she says. “We can’t continue expecting local governments to front the bill for all of these disasters and yet expect them to be resilient in the same breath.”