The key thing, Stephens adds, is for warnings to tell people whether they should evacuate or stay where they are. “One of the big challenges we have with floods is that when sirens go off, people don’t know if they’re supposed to shelter in place or evacuate,” she says. “You must tell them an action at the end [of the warning]. Just saying ‘You’re in danger’ or ‘This is happening in your community’. People read that message and go, ‘Ok, what do I do with this?'” 

Psychologists at the University of Houston recently tested an update of a flood warning system available on a popular Houston weather blog. One hundred people living on the Gulf Coast were asked how likely they were to take protective measures, such as gathering supplies or charging phones, after being given a warning. The alerts for one group came from the previous colour-coded rating system which told them only the flood risk faced (for example, “1 green” was “street flooding only” and “5 purple” was “historic regional flooding”). The other group was given a new version with examples of how to act for each stage of flood risk, for example, “never drive into flooded roadways” or “be prepared to shelter in place for multiple days”. People in the second group did a better job of planning for the storms, the researchers said.

Targeted alerts  

But even if there are clear instructions about what to do, it’s important that the type of communication is tailored to different users, says Liz Saccoccia, water security associate at the World Resources Institute, a non-profit based in Washington DC. “Women, disabled, elderly, different levels of literacy, and those without phone service or radio communication will need different communication methods,” she says. 

The content of the message “also needs to be tailored to groups’ specific risk tolerance”, says Saccoccia. For example, Stephens, who is carrying out (as yet unpublished) research into flood communication in Texas, has found that the NWS warning phrase, “Turn around don’t drown” doesn’t tend to resonate with young men.