Flood mapping by the US Federal Emergency Management Agency fails to capture events driven by intense rain bursts, leading to homeowners not understanding risk, an academic has warned.  

Climate change is worsening the situation, says Jeremy Porter, professor of quantitative methods in the social sciences at City University of New York.

The accuracy of US flood mapping is under the spotlight after flash floods in Texas this month killed 135 people.

Professor Porter says the maps focus on river channels and coastal flooding, and largely exclude the risk of flash floods.

“There are areas of the country that flood, some regularly, that don’t show up on the maps as at risk,” he said.

There is also political interference in FEMA’s mapping process.

“Local governments and developers sometimes fight to avoid high-risk designations to avoid insurance mandates or restrictions on development, leading to maps that may understate actual risks and leave residents unaware of their true exposure.”

New York City appealed against a 2015 FEMA flood insurance rate map update, leaving the current mapping project tied up in legal red tape and the city with maps that are 20 years old.

However, private groups are using technology to provide more accurate risk assessments. 

Professor Porter says advances in modelling and private risk data have allowed the real estate, finance and insurance industries to rely less on FEMA’s maps, and real estate portals are highlighting hidden vulnerabilities that are driving property-buying decisions.