For almost 20 years, homeowners in Harris County, Texas, have used the same federal flood maps to determine whether their homes were at risk.

Then came Hurricane Harvey in 2017, and about 70% of the flooded homes — an estimated 110,000 — found themselves outside the official high-risk zones. This meant most people whose homes flooded had never been warned, and most lacked flood insurance.

Since then, the federal government — specifically the Federal Emergency Management Agency (FEMA) — has been playing catch-up.

The latest draft flood maps for Harris County, released earlier this year, would expand the 100-year floodplain by about 50,000 acres, a 33% increase. This change would put more than 170,000 properties, worth around $50 billion, into high-risk areas for the first time.

The Cypress region was among the areas Harvey hit hardest, and the new draft maps would add 24,500 single-family homes and 6,100 multifamily units in the area to the floodplain.

This means homeowners with federally backed mortgages in these areas will eventually have to buy flood insurance, even if they never needed it before.

Is Harris County an exception or a sign of what’s to come?

About 10 million high-risk flood properties are missing from FEMA’s official maps across the country, according to a report by First Street Foundation. The maps homeowners use to check their risk are often based on outdated rainfall data, and updates happen slowly, one county at a time, with no set national schedule.

“Global awareness of flood risk remains limited,” reads the First Street report. “Many national maps are outdated or incomplete, pluvial and compound floods are often underrepresented, and existing global models rely on simplified methods that cannot capture real hydraulic behavior.”

If you haven’t gotten a letter about flood risk, that isn’t necessarily good news. It may be that no one has yet redrawn your county’s map.

Not just a Texas problem

Harris County stands out because it has the most detailed data, but the same pattern happens anywhere FEMA’s information is outdated.

North Carolina clearly shows this gap is real. State researchers found that more than 90,000 buildings flooded at least once between 1996 and 2020, and 43% of them were always outside FEMA’s mapped floodplains. Instead of waiting for federal updates, North Carolina created its own maps for five river basins, using models that include areas far from streams — places that standard maps often miss.

Florida is an example of how these updates roll out over time. Bay County’s new maps took effect in August 2024. Lee County has been updating its coastal zones since a 2022 federal decision, and Collier County is still working on its updates. More counties are waiting for their turn.

Right now, there’s no single “Florida flood map.” Instead, updates are happening slowly, county by county. The process will continue for years.

The Northeast is also seeing changes, though they’re less dramatic. FEMA’s coastal offices have been updating preliminary maps for New York and New Jersey, adjusting the boundaries between high-risk coastal zones and standard flood zones using more detailed building data. These are smaller changes than in Harris County, but the same idea applies: FEMA is updating old risk boundaries with newer information.

This highlights the temporary nature of FEMA’s flood maps.

Because states update their maps on different schedules without a national plan, homeowners can’t know if their county is next until FEMA releases a draft map. Checking individual addresses proactively offers a safer approach than waiting for a letter.

When FEMA actually drew the maps

Harris County, TX — Current effective maps date to 2007, based on rainfall data collected after Tropical Storm Allison in 2001. New draft maps released in February 2026 use post-Harvey rainfall data (Atlas 14), reflecting roughly a 30% increase in calculated rainfall rates. The maps are in draft/technical review now; finalization is expected to take another one to two years.
Lee County, FL — Received a Letter of Final Determination in 2022; new coastal maps became effective November 17, 2022. A narrower 2026 revision affecting six map panels in unincorporated Lee County is in progress now.
Bay County, FL — Updated maps became effective August 16, 2024.
Collier County, FL — Ongoing updates; no fixed effective date yet.
North Carolina — Supplemental “advisory” maps (not FEMA’s official FIRMs) released in April 2026 for five eastern river basins, built on flood-event data spanning 1996–2020.
New York/New Jersey — Ongoing, iterative refinements to preliminary maps and Advisory Base Flood Elevations; no single redraw date.

What actually triggers a mandatory flood insurance purchase

Getting added to a new draft map doesn’t, by itself, change anything. Harris County’s Flood Control District has been explicit that nothing changes right now regarding flood insurance requirements or development regulations — the draft maps exist solely for technical review. The mandatory-purchase trigger doesn’t fire until a map becomes “effective,” after the formal appeal window closes, and that might be months or even years away.

Once a map goes into effect, homeowners could see the following changes:

If the property is newly placed in a Special Flood Hazard Area and the mortgage comes from a federally regulated or federally backed lender, then flood insurance becomes mandatory.
If the property is no longer in a flood zone, homeowners aren’t required to have flood insurance, but that doesn’t mean the risk is gone. Across the country, about 10 million high-risk flood properties remain off FEMA’s official maps, and Harris County’s experience is a warning.

What’s next? How to check your home’s flood risk

Start with FEMA’s Flood Map Service Center (msc.fema.gov) — the official national source for both effective and preliminary maps, searchable by address.
Check if the county or state has a local flood tool. In Harris County, residents can compare old and new maps using the county Flood Control District’s interactive map. North Carolina has its own Flood Resiliency Blueprint Tool and Flood Risk Information System (FRIS), which provide more detail than FEMA’s maps, especially in the eastern river basins. Not every state has these tools, but where they exist, they’re usually more up to date and easier to use than FEMA’s national viewer.
Pay attention to public comment periods, not just letters. Mortgage lenders usually notify homeowners after a new map takes effect, but by then, the insurance requirement is already in place. Draft and preliminary maps are available to the public much earlier for property owners seeking to appeal a designation or to plan for higher costs.
If the property is now in a flood zone, get a flood insurance quote before it becomes mandatory. Comparing costs while the map is still in draft form gives homeowners time to shop around, budget, or challenge the designation, instead of rushing once the mortgage company asks for proof of coverage.
If the property is no longer in a flood zone, get an elevation certificate before canceling coverage, especially if the home has any history of flooding. This document uses real data to show whether the map change matches the actual risk for the property.