Forecasts, Floods & the Challege of Communicating Risk

Emergency managers in the Gulf Coast and East Coast states got some good news last week when the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center said the 2015 Atlantic hurricane season will “likely be below-normal.”

While the prediction of a 70 percent chance of 3 to 6 hurricanes grabbed all the headlines, it’s NOAA’s forecast of a 70 percent chance of an “above average” Eastern Pacific hurricane season that piqued my interest. Statistically speaking, that translates into a 70 percent chance of 15 to 22 named storms, and 7 to 12 hurricanes, including 5 to 8 major hurricanes. The Eastern Pacific is circumscribed by NOAA as the region of the Pacific east of 140ºW north of the equator (see the National Hurricane Center website for updated storm outlooks).

Satellite photo of Hurricane Norbert (source: NASA)

When you think of hurricanes, you don’t think of Arizona. Wildfires yes, but not hurricanes. And yet tropical storms and hurricanes from the Eastern Pacific have had serious impacts on the state. Last September, remnants of Hurricane Norbert unleashed record rainfall and flash flooding across Arizona, including the Phoenix Metro Area. Not a week later, Hurricane Odile brought more rain and flooding.

Flooding is the most common natural disaster in the United States. In Arizona, wildland fire danger (e.g., fire restrictions) and flood risk are two measurements that people need to stay informed about.

On my way to the gym Saturday morning I heard a story on NPR about the recent floods affecting Texas. The reporter asked a man whose mobile home was damaged by the floods why he didn’t have flood insurance. “I never thought it would be this bad,” the man answered. “I was here in ’98 with that flood and that was the worst I’d ever seen. And they said it was a 500-year flood.” The interview made me think—on a Saturday no less—about how we contextualize flood impacts and the possible impact it has on people’s perception of flood risk.

The labels used to describe rain and flood events can be misleading. For example, a “100-year flood” isn’t a classification of flood that occurs once every 100 years; rather, it means there is a 1 percent chance that a flood of that magnitude will happen in a given year. The worry is that phrases like 100-year flood can give people a false sense of security, and negatively inform their perception of the threat and decision to buy flood insurance.

The man in the NPR interview thought he’d experienced an once-in-a-lifetime flood in 1998. He heard it explained as a 500-year flood and maybe took that to mean there wouldn’t be another flood like it for another 500 years, so why buy flood insurance.

I won’t pretend to have the answer; in fact, I’m not sure that labels like “100-year flood” are a substantive problem to communicating flood risk and/or persuading people to get flood insurance. But the fact that hydrologists aren’t enamored with terms like “100-year flood” because it “is a misinterpretation of terminology that leads to a misconception of what a 100-year flood really is” should count for something.

An easy solution is to explain flood impacts in terms of the annual risk (e.g., a 100-year flood would be called a .01% flood). Another option is to stop historicizing flood impacts and risk all together.

In the meantime, there are steps you can take to prepare for flooding, including:

·         Know the difference between a watch and a warning;

·         Research your home’s flood risk;

·         Talk to an insurance agency about insurance for your at-risk home or business;

·         Prepare for the possibility of an emergency that could cause an evacuation; and

·         Make FloodSmart® improvements around your home or business (e.g., elevate the furnace, water heaters and electrical panel).