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USA: Communicating flood risk

Source(s):  First Street Foundation (FSF)

Millions of Americans face an increasing risk of flooding. According to NASA, 2018 and 2019 brought record setting precipitation, with the United States experiencing the most rainfall in a 12-month period ever, in the 124 years that records have been kept. Earlier this year, the North basins experienced rain and snow up to 200% above normal, creating a spring flood season that put 200 million people at risk within 25 states. As the 2019 hurricane season begins, there’s a 30% chance of above-normal hurricane activity in the Atlantic, with 5-8 hurricanes expected (winds of 74+ miles per hour).

Flood risk is increasing for Americans.

Scientists have a deep understanding of the potential risks of flooding, and continue to conduct research and run models to understand it even further, but too often that risk is not effectively communicated to the people who need to understand it most. For both coastal and inland residents, knowing and understanding flood risk is imperative to protecting their property. Without this knowledge, people exposed to dangerous flooding face being underinsured and unprepared for disasters.

How flood risk is communicated determines how it’s received; without effective communication, individuals cannot fully understand their risk and, because that risk is not adequately understood, appropriate action cannot be taken.

Scientists, elected officials, and communication experts have come together through one of the Wharton Risk Center’s Digital Dialogues to explore how flood risk can be more effectively communicated. Their ideas focus on how to better the general public’s understanding of risk and thereby empower property owners and municipalities to become better prepared for flood-related disasters.

Understanding risk

Communicating risk, especially changing risk, is challenging. However, it has been shown that risk is best understood when the communication is simple, tangible, relevant, and personal. Risk should be communicated in a way that is not only clear and quantifiable, but that leads people to recognize how they could be personally affected.

Likelihood of experiencing a flood, communicated over a short period of time.

Many environmental changes happen on a large timescale. In the scientific community, sea level rise projections often use the year 2100 as a benchmark. However, this far off projection may not be tangible for people. Experts agree that risk is better communicated within a shorter time period, for example the likelihood of experiencing a flood over the life of a mortgage. This makes the timeframe more short-term and the impact more personal.

More specifically, internal testing has shown that homeowners are most concerned about their flood risk when it’s communicated within a 15 year time frame and identifies the monetary impact of the flood damage. Additionally, most homeowners are more concerned about their most-likely risk scenario than they are a worst-case scenario. Providing the severity of risk, such as “high risk” or “medium risk,” is also optimally effective, as it helps provide context.

Federal Emergency Management Agency (FEMA) maps currently convey risk through broad zones, all holding equal amount of risk. Offering property-specific, detailed risk projections would be a drastic change from the current standard, but it would increase understanding of risk considerably among homeowners.

Probability and impact

While FEMA has traditionally communicated risk in terms of probability—such as odds out of 100 or 500 within the FEMA flood zone designations—internal testing shows that it’s more effective to communicate probability in terms of a percent chance within a specific time period, such as a 48% chance of flooding this year.

If the impact of flood-related events can be properly communicated, it vastly improves how people respond and prepare in the face of risk. In a survey conducted by the University of Chicago, surveyees were more responsive to impact information on a potential flood (e.g. potential monetary damage that a flood could cause to their home) than they were to probability information or the likelihood of a potential flood.

Because flood risk is changing—due to rising sea levels and warming sea surface and atmospheric temperatures—it’s important to create a realistic picture of what a future flood event could look like. Illustrating the “worst case scenario” based on past events will not accurately reflect what could happen now, or in the future. Understanding that the next-worst catastrophe will be something that hasn’t yet been experienced will more adequately inform people and help communities prepare. Without realistic comprehension of what an extreme flood event could look like, hundreds of thousands of homeowners could be at-risk but unaware.

For example, in 2017, Hurricane Irma’s storm surge impacted over 133,000 homes across Florida, causing extensive flooding and damage. According to tidal data in the region, relative sea level off the coast of Florida has risen approximately 7 inches since 1970. Research found that of the affected homes, approximately 57,000 would not have experienced flooding with sea levels from 1970, making it directly responsible for the impact on these properties. The same research also found that if Hurricane Irma were to hit at the sea level projected for 2050 by the Army Corps of Engineers (USACE)—approximately 15 inches above current levels—the storm surge would affect an additional 200,000 homes. In other words, a 1.26 foot increase in nearby sea levels would result in a 150% increase in the number of homes impacted by Hurricane Irma’s storm surge.

Increased awareness

In Bangladesh, the population’s response to potential flood risk has dramatically changed in the last 50 years. During the Bhola Cyclone event in 1970, devastating storm surge that was estimated at 20-30 feet high caused major flooding and killed over 300,000 people. Without knowing what type of damage the cyclone could cause, the country was unprepared.

Successful risk communication and adaptation saves lives in Bangladesh.

In recent years, Bangladesh has undergone a major transformation in the way that it handles flood mitigation and prepares for storms, embarking on the Bangladesh Delta Plan 2100, in partnership with the Netherlands government. When Cyclone Fani hit Bangladesh in April of 2019, the country sustained a minimal death toll due to increased awareness, understanding, and flood adaptation being implemented. Though some casualties were reported, an estimated 1.6 million people had successfully evacuated prior to Fani’s arrival. This demonstrates the drastic benefit that risk comprehension can have on a community.

These findings are important because they show that the next “worst case scenario” cannot be quantified by past data, only by future projections. This information allows home buyers, property owners, and communities to understand their true risk.

Similar catastrophic events took place in the United States, with Hurricanes Katrina and Sandy, leaving cities like New Orleans and New York in peril. However, these cities are using their increased understanding of risk to rebuild stronger, implementing new strategies to better protect people and property in the future. These efforts go far beyond knowing when to evacuate, with adaptation efforts that surround the concept of “living with water” that fortify and protect cities.

Effective communication

With sea levels projected to rise at unprecedented rates over the next 20 years, and both tropical cyclones and Category 4 and 5 hurricanes expected to increase in frequency and strength, it’s more important than ever for people to properly understand their flood risk. Communication that outlines this ever-growing risk in a simple, tangible, relevant, and personal way can reach the most important audiences.

People tend to be averse to the notion of risk, but when they understand what the potential impact will be, especially on a personal level, they are more likely to take action. If risk can be effectively communicated, residents and communities will be receptive enough to build awareness and take measures that save lives and property.



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  • Publication date 25 Jun 2019

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