Outdated rainfall models put billions in new infrastructure at risk

Billions of dollars in federal funding from the Biden administration’s Infrastructure Investment and Jobs Act could be wasted because state highway and bridge projects are using an outdated government precipitation model to determine future flood risk, according to a new report from First Street Foundation, a nonprofit climate risk research and technology firm.

The government’s precipitation expectation model from the National Oceanic and Atmospheric Administration, or NOAA, is called Atlas 14. States use it widely to inform the engineering design of transportation infrastructure, such as roads and bridges, by predicting rainfall and, consequently, flooding.

But Atlas 14 is based on backward-looking data going as far as the 1960s and does not incorporate the effects of global warming into its model.

The First Street report compared the government’s precipitation forecasting standard, which is used by and sometimes mandated for state infrastructure projects, with much more current rainfall data that projects into the future.

It found a dangerously wide discrepancy between the two.

“All that money that is going into the infrastructure is being built to the wrong flood standard, meaning those roads will flood, those bridges will flood, and it is a big waste of money when it’s a once-in-a-generational spend that we’re actually using right now,” said Matthew Eby, founder and CEO of First Street Foundation.

NOAA confirmed that Atlas 14 does not incorporate the future effects of climate change in its model.

“It does not include any climate change information,” said Fernando Salas, director of the Geo-Intelligence Division for the NOAA/National Weather Service, Office of Water Prediction. “It leverages the best available historical precipitation data that was available the time that the study was performed.”

Critics of Atlas 14 say it has more problems than just backward-looking data, including “the removal of extreme precipitation observations and the use of inconsistent methods across the U.S. as Atlas 14 was created piecemeal over time,” according to the First Street report. Those extreme precipitation events are the ones that directly lead to flash floods and overwhelm stormwater infrastructure, the report says.

Extreme rainfall events have become heavier and more frequent across most of the United States because as temperatures warm, the atmosphere can hold more water. Since 1991, the amount of rain falling in very heavy precipitation events has been significantly above average, according to the 2014 National Climate Assessment. It found that heavy downpours increased 71% in the Northeast, 37% in the Upper Midwest, and 27% in the Southeast from 1958 to 2012. This has led to an increase in flooding.

NOAA officials are well aware of the issues with Atlas 14. The agency has received over $30 million in funding to modernize it to Atlas 15, “to not only use the best available historical information, but also leverage outputs from the various different climate…