St. Louis ? Concentrated development in flood-prone parts of Missouri, California and other states has significantly raised the risk of New Orleans-style flooding as people snap up new homes even in areas recently deluged, researchers said Saturday.

Around St. Louis, where the Mississippi River lapped at the steps of the Gateway Arch during the 1993 flood, more than 14,000 acres of floodplain have been developed since then. That has reduced the region’s ability to store water during future floods and potentially put more people in harm’s way, said Adolphus Busch IV, a scion of the Anheuser-Busch brewing family who is chairman of the Great Rivers Habitat Alliance.

Similar development has occurred around Dallas; Kansas City, Mo.; Los Angeles; Omaha, Neb.; and Sacramento, Calif., said Gerald Galloway, a professor of engineering at the University of Maryland.

“The half-life of the memory of a flood is very short. You can already hear it in Washington, D.C.: New Orleans where?” Galloway said of the lack of action in the aftermath of Hurricane Katrina last summer.

The research was presented Saturday at the annual meeting of the American Association for the Advancement of Science.

‘Reinventing Katrina’

In California, development in the Sacramento-San Joaquin delta, where flood control efforts first started in the mid-1800s, represents a major risk to cities such as Stockton as they expand, said Jeffrey Mount, a professor of geology at the University of California, Davis.

“We are reinventing Katrina all over again,” Mount said.

Mount estimates a two-in-three probability in the next 50 years of a catastrophic levee failure in the massive delta region east of San Francisco.

Even a moderate flood could breach the delta’s levee system while a larger one, perhaps following an earthquake, would inundate the region, Mount said.

The Sacramento-San Joaquin delta, which covers 738,000 acres, receives runoff from more than 40 percent of California. Much of the land is below sea level and relies on more than 1,000 miles of levees for protection against flooding, according to the California Department of Water Resources.

“In California, we know that we have two kinds of levees: Those that have failed and those that will fail,” Mount said.

Bad decisions on land

The lack of coordination among local, state and federal officials after a flood was evident with Katrina. Similarly, even before a storm hits, coordination on issues such as land use and development is a problem, Galloway said.

“Local land decisions later result in cries for federal help. Does that make sense? No,” Galloway said, adding that the federal flood program was “rudderless.”

Nor do efforts to guard against floods automatically reduce risks, said Nicholas Pinter, a professor of geology at Southern Illinois University.

Pinter said as much as 85 percent of the Mississippi in St. Louis is confined behind levees, which have raised flood levels 10 feet to 12 feet higher than they were just a century ago. That parallels the situation in New Orleans, which suffered catastrophic flooding when levees failed in the wake of Katrina.

Bolstering levees may lure more people onto floodplains, Mount said. In California, the modest investment required to shore up a levee protecting farmland can result in a dramatic increase in the value of that land, Mount said. That in turn increases the likelihood a farmer will sell out to developers, ushering in the construction of houses on what had been floodplain.

“You actually spur development. It’s a self-fulfilling process,” Mount said.

In the St. Louis area, there has been an estimated $2.2 billion in new construction on land that was under water in the 1993 flood, Pinter said. New Orleans probably will not be immune to that same lack of foresight, he said.

“If you want to look at what probably – unfortunately – will happen in New Orleans in the next 10 years, look at what has happened in St. Louis in the last decade,” Pinter said.

Weather factors

The weather situation, too, may worsen, said Anthony Arguez, of the National Oceanic and Atmospheric Administration.

“As the climate warms, we expect more extreme precipitation events. That means what once might have been a 100-year flood might be a 50-year flood,” Arguez said.

Norbert Schwartz, director of the mitigation division of the Federal Emergency Management Agency’s Chicago office, did not dispute that there has been a “substantial” amount of construction on lands abutting levees across the United States.

But he said the national flood insurance program saves $100 billion in potential flood costs each year.