The definition of a 100-year flood could soon be more destructive than what was once thought.

New preliminary data from a National Oceanic and Atmospheric Administration study could lead to big changes in floodplain maps and future development across the Houston area.

The official data will not be complete until May 2018 and is expected to be published in August 2018.

The new definition of a 100-year flood in Harris County could mean an increase of four to six inches of water.

Several things could change, according to Houston flood czar Steve Costello. Restrictions could be placed on future construction and design for commercial developers, floodplain designations would be changed, homes in a newly-designated flood plain would have to pay flood insurance and there could potentially be a decrease in some property values.

“Based on the NOAA study there’s a high probability that that 100-year event will be much larger,” Costello said. “There’s still a question of whether or not there’s going to be 18 inches or something less. At the end of the day, it’ll migrate to between 15 to 18 inches, somewhere in there.”

Jeff Lindner with the Harris County Flood Control District tweeted Monday that he questions some of the data and methodology used for the study, but says it shows some interesting trends.

The study must first pass through peer review before it becomes official.

Costello says it could takes years before new floodplain maps become effective.