Après moi, le déluge: Wildfire’s Dangerous Companion, from the Golden State to the Midi

December 15, 2021
by Serena Ingalls
2018 Montecito Debris Flow, California
2018 Montecito Debris Flow, California (Photo: Mike Eliason, Santa Barbara County Fire Department)

California and Southern France both have beautiful beaches, sunny weather, and landscapes seemingly tailor made for the silver screen. However, their similarities have a negative aspect as well: they are prone to wildfires.

They both have a Mediterranean climate, and follow similar trends regarding climate change, which predicts a trajectory of increasingly severe wildfires.

Californians are no strangers to the devastating impacts of wildfires. There are too many examples to name, but one notable example is 2018’s Thomas Fire, which impacted the community of Montecito. At the time, this was the biggest California wildfire in history.

Less than a month later, devastating debris flows that initiated in the burned areas of Montecito impacted the community, taking the life of twenty-three people.

The pattern of floods after fires is not unusual in these regions, and in California and Southern France, it is often a concern, as their climates have brief periods of extreme rain that can cause flash floods. The floods that follow wildfires are an example of a compound hazard, and there are different circumstances that can lead to compound hazards occurring.

“Fires can create a hydrophobic layer on the soil which can reduce infiltration during a storm,” explains Anna Serra-Llobet, a researcher at the University of California, Berkeley, Social Science Matrix, Center for Catastrophic Risk Management.

In other words, damage done by fires can effectively “[set] the stage for an intense runoff,” says Serra-Llobet.

Unfortunately, due to climate change, the severity of wildfires, floods, and compound hazards is set to increase over time in these regions. This is a huge concern.

Southern France is not yet as associated with devastating wildfires as California is, but “I think local actors and authorities are afraid of such new risks in Southern France,” says Johnny Douvinet, professor in Geography at Avignon University, member of the ESPACE CNRS scientific team, and young member of the French University Institute (IUF).

The compound hazards that exist in California and Southern France become even more complicated when the social components are taken into account. Montecito, as many other cities in California, is built on alluvial fans. However, despite knowledge of alluvial fan flooding, houses are often built there. This is in part due to the fact that alluvial fan flooding maps are not yet created for all California.

Wildfires and floods are not a risk per se, they become a risk when we put ourselves in harm’s way, for example building in high hazard areas, and developments if floodplains and alluvial fans are substantially increasing in both countries. Whenever an area with a high wildfire and flood risk is urbanized, that leaves a great possibility for casualties and damages, like the Thomas Fire and subsequent floods in Montecito, which killed 23 people and cost more than 1 billion dollars in damages.

So, in the face of daunting opponents such as wildfires and floods, and current urbanization trends in high risk zones, how does one proceed? International collaborative research is one way to approach the issue, and this is the path that Anna Serra-Llobet and Johnny Douvinet took.

Serra-Llobet and Douvinet met in 2018 when Serra-Llobet was working as a visiting researcher at the University of Aix-Marseille.

“We realized right away we had a really similar line of research topics and interests with floods as a common link,” says Serra-Llobet. With Douvinet working in France, and Serra-Llobet located in the US, the France-Berkeley Fund (FBF) was the perfect opportunity for an international collaboration.

The team was awarded an FBF research grant in 2019, and the pair also involved John Radke, associate professor at the University of California, Berkeley, College of Environmental Design and fire expert, Sarah Lindbergh, PhD student from the University of California, Berkeley, College of Environmental Design, as well as master students from the University of California, Berkeley, Environmental Planning Studio. The master students won a national student paper competition in 2021 for their work in the project, in particular for “thinking out of the box”.

“So what we wanted to do was look at how the US and France manage flood after fires, which type of maps they use, and how they can improve their current approaches, looking at the problem from different disciplines and through a more extensive comparative study of differences and similarities between the two approaches,” explains Serra-Llobet.

“It was useful to compare the experience observed in California and the problems and improvements we can support to implement the same practices in the South of France,” adds Douvinet, commenting on the best practices yet observed since the end of the 20th century, especially in relation to the fear of climate change worsening natural disasters in Southern France.

Their project involved a comparison of the two regions, and the California portion of the project specifically focused on Montecito. They collected hydrological data from Montecito. This data simulated the surface runoff that would occur based on conditions such as slope and stream networks, land use, and intensity of rainfall on burned areas. This information was then compared with existing models and experiments.

“We also collected a lot of data to analyze how the exposure has evolved over time, so we used historical information and we digitized the houses in different periods of time, for the case of Montecito in particular,” says Serra-Llobet. “We also used analyses of the plans, for example, to get more information about...why they are building where they are building....So the idea was not just focus on flood ‘hazard’ maps (which is what people normally do)…but also look at other aspects of flood risk which have to do with ‘exposure’ and ‘vulnerability.’”

Another critical part of the project were the workshops. One of these workshops took place in February 2020 in Berkeley, and there are plans for a workshop in France as well, hopefully in spring 2022.

Workshop Participants

Workshop Participants at Moses Hall, on February 5, 2020 (From left to right: Louise Comfort, Jonathan (Yonni) Schwartz, Dave Winnacker, Anna Serra-Llobet, Rob Olshansky, John Radke, Renaud Vidal, Sarah Lindbergh, Matt Kondolf, Johnny Douvinet, Yiyi He, Jeremy Lancaster, Nicholas Sitar, Peter Norton, and Robert Lewin)

The team brought their own specific skill set to the collaboration; Douvinet is a geographer with strong technical skills in hydrology, Serra-Llobet is an environmental scientist specialized on flood risk management policies and environmental planning, and Radke is an expert on GIS (Geographical Information Systems) and wildfires, and Sarah Lindbergh works on compound hazards.

The project has revealed ways to improve approaches to compound hazards. For example, in cases of flooding, particularly in urban areas, there is concern about the dangers of debris flows. Debris flows can be deadly, and they should not be ignored, but at this time in the US and France, debris flow maps are not commonly used to inform land use and urban planning decisions. Serra-Llobet and Douvinet encourage the inclusion of debris flow maps alongside more traditional maps showing riverine and coastal flooding.

Through his experience in the workshop, Douvinet observed that the participants (practitioners and academics) had relevant “knowledge on risk but they do not work together; they have information, but they don’t know how to use it in real time...I think in France it’s the same problem, people working on their specific topic; they discuss together but they don’t know how they can use the information in real time.”

Douvinet, Serra-Llobet and Radke concurred that greater interdisciplinary research and coordination in flood risk management would have a positive impact in managing floods after fires.

One might think that natural disaster risk management in different regions can be approached in the same way. However, the researchers explain that differences in culture and governance have a huge impact.

“You cannot have a one size fits all solution, but there are definitely things that can be applied in both cases, like for example a process-based approach,” Serra-Llobet explains.

In terms of differences between countries, “one thing that’s really difficult to change is the culture, so we have very different ways of understanding what is important, what is not,” Serra-Llobet adds.

For example, in the US, property rights are an important value, but in the EU, people are more open to taking suggestions on building restrictions based on hazards that may exist for the greater good. Unlike France, building new developments in high hazard zones is highly discouraged in the US, but it is not explicitly forbidden, unless the community decides to do it, which is not very common.

The differences in the two countries can occasionally be helpful. For example, France will use SMS and Cell Broadcast in their emergency alert system starting June 2022, using the platform FR-Alert to help people evacuate, to send more appropriate messages, and to provide siren sounds. The US has done this since 2006 through the Integrated Public Warning and Alert Systems (IPAWS), set up following Hurricane Katrina in 2005. France can learn from the US’s example of such a system and see what works and what doesn’t before rolling out their own version.

Though their project has led to valuable research, it has not been without difficulty; their work was interrupted by the COVID-19 pandemic. This made it harder for Douvinet to work on research related to Montecito, since his stay in Berkeley was short.

There were, however, some unexpected benefits to this: stronger community bonds.

“The advantage of having the COVID kind of time is that, since the project was extended, it gave us a lot of time to build more relationship between academics and with the community of Montecito...Hopefully we can do something similar with the French community as well,” says Serra-Llobet. “We have been able to talk to the planning department in Santa Barbara County and show some of the results of our analysis and they might be willing to take them into consideration when they redo the local plans, so it’s been an advantage having this pause in the project that gave us more time to really build a relationship, which is necessary to make your results more actionable.”

In France, they plan to focus on Pignans, a commune in southeastern France. Pignans experienced flooding on August 25, 2021 after a severe wildfire. Continued comparative study of Southern France and California will help the team determine if their research can reveal which areas are likely to be affected by flash flooding after wildfires.

Like many research projects, the work Douvinet and Serra-Llobet have done has inspired further projects. Serra-Llobet has started an international project on residual risks involving France, between other countries, called RREFlood (The Residual Risks of Extreme Floods: A Challenge for Achieving the Sustainable Development Goals), which explores how our societies manage low-probability, high-consequence events, such as the 2018 Montecito debris flow, but in this case with special focus on the residual risk associated with structures such as levees or debris basins, since these structures can overtop or breach.

Douvinet is now working on France’s emergency warning system. He is collaborating with Louise Comfort, an expert in decision-making in crisis and disaster preparedness from the University of Pittsburgh.

The pair had some words of wisdom for other researchers considering applying to the France-Berkeley Fund.

“I totally recommend it,” says Serra-Llobet. “It’s a great way to learn from each other but also to create a long-term relationship...I think it’s a great opportunity for many researchers, especially the ones who are starting to build a connection between the two countries.”

“I think it’s a great opportunity to start new projects, new collaborations, and to discuss with other researchers,” concludes Douvinet.