Anchored in flood-prone areas in every American state are more than 2,500 sites that handle toxic chemicals, a New York Times analysis of federal floodplain and industrial data shows. About 1,400 are located in areas at highest risk of flooding.

As flood danger grows — the consequence of a warming climate — the risk is that there will be more toxic spills like the one that struck Baytown, Tex., where Hurricane Harvey swamped a chemicals plant, releasing lye. Or like the ones at a Florida fertilizer plant that leaked phosphoric acid and an Ohio refinery that released benzene.

More Than 2,500 Sites That Handle Toxic Chemicals Are Located in Flood-Prone Areas Across the Country. Site in area at high risk of flooding Site in area at moderate risk of flooding Wash. Me. Mont. N.D. Vt. Minn. Ore. N.H. Mass. Idaho S.D. N.Y. Wis. Mich. Wyo. R.I. Pa. Conn. Iowa Neb. N.J. Ohio Nev. Ind. Del. Ill. Utah W.Va. Colo. Md. Va. Kan. Mo. Calif. Ky. N.C. Tenn. Okla. Ariz. Ark. S.C. N.M. Ga. Ala. Miss. Fertilizer factory in White Springs, Fla. Texas La. Alaska Fla. The Houston area is home to more than 100 facilities that handle toxic chemicals and are located in flood zones. Hawaii Wash. Me. Mont. N.D. Vt. Minn. Ore. N.H. Mass. Idaho S.D. N.Y. Wis. Mich. Wyo. R.I. Pa. Conn. Iowa Neb. N.J. Ohio Nev. Ind. Del. Ill. Utah Md. W.Va. Colo. Va. Kan. Mo. Calif. Ky. N.C. Tenn. Okla. Ariz. Ark. S.C. N.M. Ga. Ala. Miss. Fertilizer factory in White Springs, Fla. Texas La. Alaska Fla. The Houston area is home to more than 100 facilities that handle toxic chemicals and are located in flood zones. Hawaii Wash. Me. Mont. N.D. Vt. Minn. Ore. N.H. Mass. Idaho S.D. N.Y. Wis. Mich. Wyo. R.I. Pa. Conn. Iowa Neb. N.J. Ohio Nev. Ind. Del. Ill. Utah Md. W.Va. Colo. Va. Kan. Mo. Calif. Ky. N.C. Tenn. Okla. Ariz. Ark. S.C. N.M. Ga. Ala. Miss. Texas La. Alaska Fla. Hawaii

Flooding nationwide is likely to worsen because of climate change, an exhaustive scientific report by the federal government warned last year. Heavy rainfall is increasing in intensity and frequency.

At the same time, rising sea levels combined with more frequent and extensive flooding from coastal storms like hurricanes may increase the risk to chemical facilities near waterways.

The Times analysis looked at sites listed in the federal Toxic Release Inventory, which covers more than 21,600 facilities across the country that handle large amounts of toxic chemicals harmful to health or the environment.

Of those sites, more than 1,400 were in locations the Federal Emergency Management Agency considers to have a high risk of flooding. An additional 1,100 sites were in areas of moderate risk. Other industrial complexes lie just outside these defined flood-risk zones, obscuring their vulnerability as flood patterns shift and expand.

Video shows the Chevron Phillips plant in Baytown, Texas underwater in the midst of historic #Harvey flooding. https://t.co/8Vc8S8au1m pic.twitter.com/PenjeFtp0i — ABC News (@ABC) August 29, 2017

The presence of chemical sites in areas vulnerable to flooding is a holdover from an age where the advantages to industry of proximity to rivers and oceans — for transportation and trade, or for a ready supply of cooling water — seemingly outweighed the risks.

“Waterfronts are changing as a result of sea level rise,” said Jeanne Herb, an environmental policy expert at Rutgers University who has researched hazards posed by climate-related flooding to industries in New Jersey. “More often than not, these are facilities are on the water for a reason,” she said. “So how do we make sure that there are protections in place? That’s the big question.”

Federal law does not explicitly require sites in floodplains that handle toxic chemicals to take extra precautions against flooding. Nor do most states or local governments have such requirements.

President Barack Obama signed an executive order in 2015 requiring planners of federally funded buildings, roads and other infrastructure to account for the impact of possible flooding from rising sea levels or more extreme precipitation. President Trump rescinded those rules last year.

The Times analysis focused on facilities on the federal toxic release database, which tracks sites handling chemicals that could be harmful to health and the environment if released. The list does not include properties like Superfund sites or wastewater facilities, or chemical sites where the predominant risks are fire or explosion, as opposed to toxic pollution.

The Times also examined reports of oil and chemical spills tallied by the National Response Center, which is run by the Coast Guard. Companies are required by law to report spills to the N.R.C., although that database has been criticized as incomplete.

Still, the data does provide a glimpse into the thousands of spills that occur across the country each year.

Texas: Chemical Plant

Area of detail San Jacinto River Chevron Phillips Cedar Bayou Channelview Baytown Houston Houston Ship Channel La Porte Galveston Bay San Jacinto River Area of detail Chevron Phillips Cedar Bayou Channelview Baytown Houston Houston Ship Channel La Porte Galveston Bay San Jacinto River Chevron Phillips Cedar Bayou Baytown Houston Ship Channel Area of detail Galveston Bay Site in area at high risk of flooding Site in area at moderate risk of flooding

By the time the murky flood waters had receded from the sprawling Chevron Phillips chemical plant in Baytown, 34,000 pounds of sodium hydroxide and 300 pounds of benzene — both highly toxic — had escaped through a damaged valve. The plant, a joint venture between Chevron and Phillips 66, is one of many that filled the region’s streets with a stew of chemicals, debris and waste in the days after Hurricane Harvey and its torrential rains.

Employees later pumped some of the tainted water into 80 steel tanks. But most of the product “was lost in the floodwater,” David Gray, an Environmental Protection Agency spokesman based in Dallas, said in an email.

A Chevron Phillips spokesman, Bryce Hallowell, declined to give further details of the spill. He stressed that the plant “was at the center of this incredibly powerful storm.”

The chemical site lies in a moderate-risk flood zone, defined by the government as having a 0.2 percent chance of flooding in any year. It was at least the third time in three years that the Chevron Phillips facility blamed heavy downpours for chemical leaks.

The spills underscore the vulnerability of America’s coastal industries to rising sea levels and extreme weather. This is the case along the Gulf Coast because the country’s oil, gas and petrochemicals industries are concentrated there.

At least 46 facilities reported an estimated 4.6 million pounds of airborne emissions beyond state limits between Aug. 23 and Aug. 30, 2017, the week spanning Harvey’s approach and landfall in Texas. The Chevron Phillips plant also reported one of the largest Harvey-related emissions of chemicals into the air.

But even as flooding risks increase, chemical companies continue to build in vulnerable areas. A boom in plastics manufacturing has brought billions of dollars of investment to the Gulf shoreline. The Chevron Phillips site had been in the midst of adding a new $6 billion ethane processor, one of the biggest investments in the Gulf’s fast-growing petrochemicals industry.

Despite repeated flooding, the chemicals manufacturer still considered the site, at Cedar Bayou, to be “the optimal location” for its new ethane facility, Mr. Hallowell said. He declined to detail protections that have been considered or installed, or whether they were designed to withstand future floods.

Florida: Fertilizer Plant

PCS Phosphate White Springs tallahassee suwannee river Lake City Area of detail Gulf of Mexico PCS Phosphate White Springs tallahassee Suwannee River Lake City Area of detail Gulf of Mexico Suwannee River tallahassee PCS Phosphate White Springs LAKE CITY Area of detail Gulf of Mexico Site in area at high risk of flooding

When Tropical Storm Debby brought torrential rain to north and central Florida in mid-2012, it triggered a release of phosphoric acid from a chemical plant in White Springs that produces phosphates, which are used to make fertilizer.

Flooding knocked out the power supply to its pumping system, causing water mixed with chemicals to spill into a storm-retention pond, which eventually also overflowed into a creek that feeds the Suwannee River. Released in large quantities into the environment, phosphates and phosphoric acid can cause uncontrolled algae and duckweed growth, causing oxygen levels in lakes and rivers to drop precipitously.

“It was like the biblical flood,” said Mike Williams, a spokesman for Nutrien, which runs the phosphates plant in an area dotted with high-risk flood zones, defined by the government as having a 1 percent chance of flooding in any given year. The plant had prepared for the storm by lowering water levels at the ponds, but the flooding was “well off the charts,” he said.

Since then, the plant has invested in pumps and backup generators that would allow it to more effectively control excess flood water. Still, “the lesson learned is that every now and then there will be something that’s more than we planned for,” Mr. Williams said.

Alabama: Plastics Plant

Alabama River Montgomery Catoma Creek Pintlala Creek Area of detail Sabic Innovative Plastic Alabama River Montgomery Catoma Creek Pintlala Creek Area of detail Sabic Innovative Plastic Area of detail Alabama River Montgomery Pintlala Creek Sabic Innovative Plastic Site in area at high risk of flooding Site in area at moderate risk of flooding

Floods, and the risks they pose to industrial sites, are not confined to the coasts or even to areas the government considers flood-prone.

Record-breaking rains brought flooding to wide swaths of Alabama in May, inundating storage ponds at a Sabic Innovative Plastics plant on the banks of the Alabama River. About 4,500 pounds of sodium hydroxide escaped into a tributary.

The same plant, which is not on land considered flood-prone under federal guidelines, had flooded in 2011, releasing 125 gallons of tetrachloroethylene, according to a cleanup agreement reached with regulators. Tetrachloroethylene is a carcinogen and can affect the nervous system.

Shelia Naab, a Sabic spokeswoman, said the plant had been inundated with “extraordinarily high levels of rain in a very short period of time” and that levels in its ponds had reached unprecedented levels. “We do not believe there was a significant environmental impact as a result of this incident,” she said. The plant has since updated a stormwater bypass that stops rainwater from overrunning its storage ponds, she said.

The flooding at Sabic underscores how floodplain designations may be increasingly outdated as rains intensify and weather patterns change.

Heavy rains in northern Ohio in June 2015 inundated Toledo Refining, near the banks of the Maumee River, causing a leak of several million gallons of wastewater from its treatment ponds. The site, run by PBF Energy, one of the country’s largest suppliers of transportation fuels and heating oil, also reported a release of benzene.

James Lee, a spokesman for the Ohio Environmental Protection Agency, said the leak was not thought to have reached major bodies of water. Toledo Refining did not respond to requests for comment.