Fairfax County, Va., in the Washington, D.C., metro region is considering a major code change to reduce the risk from floods.
The county is reviewing a proposal to base codes on 100-year storms instead of current 10-year storms. County staff cited the elevated risk of flooding in the county due to climate change as justification for the change.
Under the proposal, the county would require all future development to have proper drainage, pipe conveyance, and safety measures to be resilient to a 100-year storm event, adjusting for climate change. A “100-year storm event” is defined by the U.S. Geological Survey as one that statistically has a 1% chance of occurring in any given year. Such a storm would dump about 8 inches of rain over a 24-hour period on the county.
As the effects of climate change increase, that rainfall figure is likely to be adjusted in the future.