Houston High development High development High development Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)

As floodwaters from Hurricane Harvey recede in Houston, one thing that’s been revealed is that some of the damage — financial, physical, emotional — could have been avoided.

Flood hazard maps by the Federal Emergency Management Agency, showing the 100-year floodplain, an area with a 1 percent risk for flooding in any given year, mark where homeowners are required to have federally sponsored flood insurance. This is one of the few early warning signals the United States has for flooding. For Houston, those maps were thoroughly inadequate. Early assessments show many homes were flooded even though they were located far from the designated floodplains. Many homes in what’s known as the 500-year floodplain — with a 0.2 percent chance of flooding in a year — are also flooded.

Areas surrounding the Katy Prairies, sprawling grasslands in western Harris County, provide one such example. The region has been heavily developed over the past 30 years, sometimes overlapping or abutting floodplains. Local officials did not do enough to preserve native grasses, set aside open spaces or improve drainage.

100-year floodplain 500-year floodplain Building damage Building Damage Floodplain Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery); FEMA (building damage, through Sept. 2, 2017)

Damage around Katy was not restricted to floodplains identified by FEMA.

“It gives people a feeling of complacency if they are not required to buy insurance,” said Howard Kunreuther, the co-director of the Wharton Risk Management and Decision Processes Center at the University of Pennsylvania. He would like to see FEMA provide people the "gradation of their risk."

Less understandable is how often these flood maps were ignored in Houston, where policies encouraged development in flood-prone areas while reducing the region’s natural defenses to flooding.

And while the region has its own unique history, geography, economy and approach to growth, the lessons it will be learning in the coming weeks would apply to many other areas of the country.

FEMA flood risk zones Building Damage 100-year 500-year OUTSIDE floodPLAINS Spring Hockley HOUSTON Jersey Village 1 2 Highlands Katy Pasadena Baytown East Houston 2 1 Damaged buildings outside floodplains Source: FEMA (building damage); Beyond Floods (floodplains) FEMA flood risk zones Building Damage 100-year 500-year OUTSIDE floodPLAINS HARRIS COUNTY Spring Hockley HOUSTON Jersey Village 1 Highlands Katy 2 Pasadena East Houston Baytown 1 2 Damaged buildings outside floodplains Sources: FEMA (building damage, through Sept. 2, 2017); Beyond Floods (floodplains) FEMA flood risk zones 100-year 500-year Building Damage OUTSIDE floodplains HARRIS COUNTY HOUSTON Jersey Village 1 Highlands Katy 2 Pasadena East Houston 1 Damaged buildings outside floodplains Baytown 2 Sources: FEMA (building damage, through Sept. 2, 2017); Beyond Floods (floodplains)

Houston’s Rampant Development

With Houston’s economy booming, thanks in large part to oil and gas industries, residential and business development spread. As developers carved out new neighborhoods, they sometimes overlapped or abutted the floodplain — zones highly susceptible to flooding. Elsewhere, roads, parking lots, homes and businesses covered over wetlands and prairies that absorb flood waters.

An area east of Katy was submerged in floodwaters after rainfall breached the Addicks Reservoir. One neighborhood, Westlake Forest, was built in what the FEMA designated a floodplain.

Westlake Forest Neighborhood Civilians patrol for residents in need of evacuation in the Westlake Forest neighborhood of Katy, Texas. Alyssa Schukar for The New York Times FLOODPLAIN Westlake Forest Neighborhood Civilians patrol for residents in need of evacuation in the Westlake Forest neighborhood of Katy, Texas. Alyssa Schukar for The New York Times FLOODPLAIN Westlake Forest Neighborhood Civilians patrol for residents in need of evacuation in the Westlake Forest neighborhood of Katy, Texas. Alyssa Schukar for The New York Times FLOODPLAIN

A newer development located on the south side of Kingwood, a community in northeast Houston, was constructed throughout the late 1990s and 2000s directly inside the floodplain. Satellite photos show the area overwhelmed by floodwaters after the storm.

Other regions, like Cypress in northwest Harris County, or Willow and the Woodlands on the northern side of Houston, also show heavy development throughout the late 1990s and 2000s. Both areas experienced heavy flooding during the hurricane.

Kingwood 1984 Kingwood Major flooding Floodplain Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)

Cypress 1984 Cypress Major flooding Floodplain Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)

The Woodlands 1984 The Woodlands Major flooding Floodplain Sources: Beyond Floods and FEMA (floodplains); Google (satellite imagery)

FEMA maps are updated infrequently because Congress has not appropriated enough money for the work. The maps do not take into account the future impact of climate change or the impact of likely real estate development in the area. In addition, FEMA has not created flood maps for the entire country, leaving some home buyers unaware of flooding risks, said Larry Larson, a senior policy advisor at the Association of State Floodplain Managers.

A more nuanced view of flood risk may be possible. Data by Syndeste and Beyond Floods considers factors like previous flood damage and land cover as part of a risk assessment, showing many properties in downtown Houston not in the floodplain are still at significant risk.

FEMA flood risk zones 100-year 500-year Flood outlook score per block HIGH OR Very high LOW VERY LOW Greater Heights HOUSTON Rice Military Fourth Ward Sources: FEMA (floodplains); Beyond Floods (flood outlook) FEMA flood risk zones Flood outlook score per block 100-year 500-year HIGH OR Very high LOW VERY LOW Near Northside Greater Heights HOUSTON Rice Military Fourth Ward Downtown Hyde Park Sources: FEMA (floodplains); Beyond Floods (flood outlook) FEMA flood risk zones 100-year 500-year Flood outlook score per block HIGH OR Very high LOW VERY LOW Greater Heights HOUSTON Rice Military Fourth Ward Sources: FEMA (floodplains); Beyond Floods (flood outlook)

Damage for Many, Insurance for Few

Right now, more troubling is how ill-prepared even those in the current floodplain are to deal with Harvey’s aftermath. The vast majority of residents across the 30-county region struck hardest by hurricane Harvey also did not have insurance, according to Beyond Floods, a company that tracks and analyzes flood data.