Recent changes in national flood insurance policy outraged many homeowners who found properties moved into a floodplain for the first time–but in Ann Arbor the effect has been largely reversed, if only temporarily.

The Federal Emergency Management Agency’s revised floodplain boundary maps, released in 2012, moved tens of thousands of homes across the country into floodplains. That same year, Congress passed the Biggert-Waters Flood Insurance Reform Act. Hurricane Katrina in 2005, and Hurricane Sandy in 2012, had inundated FEMA’s National Flood Insurance Program, leaving it $24 billion in debt. Biggert-Waters required FEMA’s insurance premiums to reflect the “actual risk” of flood damage–resulting in huge rate increases for many owners of floodplain property.

Jerry Hancock, Ann Arbor’s storm-water and floodplains program coordinator, says some city homeowners who previously paid about $2,000 a year for flood insurance saw their premiums skyrocket in 2013. “We had a house where the floodplain was about three feet deep, and they had a basement,” Hancock recalls. “Their rates went up to about $8,500 a year–and that was less than what I expected based on what I saw from FEMA’s records.”

After an outcry in coastal states, Congress backtracked. The Homeowner Flood Insurance Affordability Act of 2014 either delayed or undid most of Biggert-Waters’ mandates. However, properties negatively affected by Biggert-Waters were already in the minority in Ann Arbor. With the redrawn FEMA maps, 116 Ann Arbor parcels and eighty-eight buildings moved into a floodplain–but 321 parcels and 452 buildings were moved out.

It’s a curious reversal of the national trend, and Hancock says a 2006 study conducted by the U-M is in large part responsible.

In anticipation of the 2008 renovation of the Wilpon Baseball and Softball Complex, the university hired engineering firm CH2M Hill to study floodplain conditions in the area. Allen Creek passes through the athletic campus in an underground pipe, and as of the last FEMA flood map update, in 1992, the area was considered to be within the creek’s 100-year floodplain. U-M environmental protection and permitting manager Stephen O’Rielly says CH2M Hill’s survey found that “the average 100-year flood water depth through this area was less than one foot, with no clearly defined channel”–qualifying the area for a low-risk FEMA Zone X rating, where flood insurance is not required.

The CH2M Hill study was submitted to the Michigan Department of Environmental Quality, and the data was incorporated into FEMA’s 2012 flood maps. Hancock estimates that 160 Ann Arbor parcels were moved out of an insurance-mandatory floodplain as a result.

However, Hancock says he has “more than a strong suspicion” that the floodplain will expand again the next time maps are revised. Since the agency did its analysis in 2006, he says, Washtenaw County has improved its contour data to show elevations at two-and-a-half-foot intervals rather than five-foot intervals. Furthermore, in 2013 the National Oceanic and Atmospheric Administration increased the 100-year, 24-hour rain event for our area from 4.36 inches to 5.1 inches–essentially rendering Ann Arbor’s worst-case flooding scenario 17 percent worse. “If you plug that different-sized storm into the same flood models, we also coincidentally have a lot better survey information since FEMA did their work,” Hancock says. “If you put both those things in, that whole area that was taken out before will come back in.”

But homeowners can probably breathe easy for a while yet. The Homeowner Flood Insurance Affordability Act directs FEMA to develop a regulatory plan addressing long-term flood insurance affordability issues, including assistance for those financially unable to purchase insurance. And given the two decades that elapsed between FEMA’s two most recent flood map revisions, Hancock says another redrawing likely won’t happen any time soon.