Study: We’re not ready for extreme weather
Climate change has made precipitation more extreme, and national standards aren’t keeping up, according to a new study by researchers at First Street Foundation, a science and technology nonprofit.
Extreme rainfall intensities thought to occur only once every 100 years actually happen every 30 years in California, according to the research. This could mean more flooded highways, overtopping rivers and overwhelmed drainage systems than expected, the scientists said, because national precipitation standards guide engineering projects.
“We’re actually building infrastructure that’s out of date as soon as it’s completed,” said study co-author Jeremy Porter, head of climate implications research for First Street. “It’s not able to manage the risks that exist for that area.”
The new work compares extreme rainfall risk from First Street’s precipitation model with the national standard for precipitation frequency estimates, the National Oceanic and Atmospheric Administration Atlas 14.
In the western United States, California stands out with the most counties in the “extreme increase” category, especially in the northern half of the state and on the Central Coast. Sonoma County, for example, saw a 41.4% increase in extreme precipitation.
The research focuses on extreme rainfall over the span of one hour, rather than over the course of an entire day. The approach provides better insight into precipitationdriven flooding and flash floods, which happen on the scale of hours, said Jungho Kim, director of hydrological sciences at First Street and lead author of the study.
While First Street’s model is similar to the one used for NOAA Atlas 14, the underlying data is dramatically different. The data used for the national standard stretches back decades, with the records for most states averaging around the mid-1970s. First Street relied on data from just the past 20 years.
“We believe that represents current climate conditions,” Kim said.
The differences across California are likely due to regional climate variation and unique topographic features, Kim said. Some places even saw decreases in extreme hourly precipitation.
Overall, the updated approach reveals the much higher likelihood of extreme precipitation and associated flood risks across the country. As much as one-third of the U.S. population can expect to see a 1-in-100-year storm as often as three times in their lifetime, the authors wrote.
This has important implications for infrastructure designed for precipitation with 10- or 20-year return periods. Based on the new study, storms of that intensity actually occur as often as every two years, Kim said. That means roadways and drainage systems face much harsher conditions than intended.
“The fact that (infrastructure designed based on NOAA Atlas 14) is not sufficient now — I think it’s an important message,” said Ruby Leung, a climate scientist at Pacific Northwest National Laboratory, who wasn’t involved with the study.
More research is needed to conclude how extreme precipitation could change in the future, Leung said, as natural climate variability or patterns occurring on longer time scales could also be at play.
Leung is part of a scientific committee providing recommendations to NOAA on extreme rainfall. The agency is in the process of developing Atlas 15, an improved compendium of precipitation frequency estimates.
“We’re actually building infrastructure that’s out of date as soon as it’s completed.”
Jeremy Porter, study co-author and head of climate implications research for First Street Foundation