Median home sales prices in Massachusetts have skyrocketed, and that’s good news for owners looking to build equity or sell, but experts say those climbing property values and the increased severity and frequency of storms have left many owners underinsured or uninsured for flood risk.

One has to look only at the five tornadoes that hit Southern New England on Aug. 21 and this summer’s washed-out weekends for evidence of nature unleashed.

Meanwhile, condo and single-family home prices increased by at least 67 percent in Massachusetts between 2013 and 2022, according to The Warren Group, which tracks real estate data.

Doug Quattrochi, executive director of MassLandlords, said he was alarmed when he learned of the findings of First Street Foundation, a nonprofit dedicated to quantifying and communicating building-specific climate risk for properties and communities.

There are 114,552 properties in Massachusetts that have a 100-year flood risk in First Street’s modeling that aren’t in the Federal Emergency Management Agency’s flood zone, Jeremy Porter, head of climate implications for First Street, said via e-mail. These are the properties that meet the requirements in regard to risk but do not have flood insurance.

In the Back Bay, “there is a 60 percent chance of seeing 12 or more inches of floodwater in a [basement] unit over the next 30 years,’’ Porter wrote. “There is a 76 percent chance of seeing ‘any water’ (1 inch or more) in the unit over the same time period.’’

Quattrochi said the public needs to be better informed. “I feel like if people knew about that, they wouldn’t buy the place,’’ he said of the flood risk to the basement units. “They wouldn’t want to rent the place. They wouldn’t want to live there.’’

The overwhelming majority of homeowners think they need only the minimal amount of flood insurance if they own property in a flood plain identified on a FEMA map, he said, and some of those maps are old and represent historical storms and data, not what lies ahead.

According to a 2019 report from ValuePenguin by LendingTree: “Forty-seven percent of homeowners do not know what their insurance policies cover. In fact, nearly 20 percent have never reviewed their policies. Almost 50 percent of millennials believe their homeowner’s insurance covers flooding even though most policies do not.’’

Hundreds of thousands of Massachusetts residents actually have more than a 25 percent chance of being affected by flooding. “Over 400,000 Massachusetts residents live in a 100-year flood zone, which means more than a 1 in 4 chance of a flood during a 30-year mortgage period,’’ the state’s Environmental Public Health Tracking website warns. (You can map your risk by address at matracking.ehs.state.ma.us/planning_and_tools/flood-zones/flood-zones-tool.html.)

Corelogic, a property data analytics company, recently reported that “High-profile events such as Hurricane Ian and Hurricane Nicole could easily lead people to assume that Florida has the highest risk of loss potential. However, that designation actually goes to the Northeast, where there is a greater risk of insured loss due to the number of structures and their density.’’

The National Flood Insurance Program is the primary source of coverage for many residential homeowners, with more than 5 million policies. Joe Rossi, executive director of the Massachusetts Coastal Coalition and CEO of Joe Flood Insurance Brokerage, said if more homeowners understood the flood risk, they’d get the appropriate coverage.

According to FEMA, which administers the national program, just 1 inch of floodwater in a home can cause roughly $25,000 in damage.

“Most homeowners are not aware that their homeowner’s insurance policies for the most part don’t include flood damage,’’ Rossi said. “Roughly 40 percent of [National Flood Insurance Program] claims come from non-high-hazard zones, where many people might not have purchased coverage. Thirty-six percent of all flooding is inland flooding from non-coastal sources. Rainfall would be one example of that, and rainfall — increasingly urban rainfall — is a huge source of flooding.’’

Just ask the residents of landlocked North Andover about inland flood damage. The town reportedly sustained nearly $30 million in flood damage from power-packed rainstorms in August.

Rossi said many people who purchase an NFIP policy do so to satisfy their lender’s requirements, but often don’t understand that the coverage maxes out at $250,000 for a building with one to four units. That’s probably not enough to rebuild most homes in Massachusetts. (The program insures up to $100,000 for personal belongings.)

People who live a street or two back from the coastline have a false sense of security, Rossi said. “I remember in a nor’easter in 2018 the deck on a home in Scituate broke off and floated two blocks away and punctured a foundation’’ on a home inland, leaving it exposed.

Understanding what it would cost to fix or rebuild your home after a flood is crucial.

“The NFIP will cover debris removal and cleanup, and by the time you’re done with [that], you might not have any money left to fix the home. ... I have seen a cleanup claim on a small 2,000-square-foot ranch be $25,000 for just 2 inches of water.’’

Rossi said every homeowner should purchase flood insurance. “The average flood insurance claim is about $50,000, and the average claim from Hurricane Ian was about $104,000,’’ he said.

“Our models show risk is increasing for most natural disasters, and flood is certainly at the forefront.’’

Jim Morrison can be reached at JamesAndrewMorrison@gmail.com. Follow Address on Twitter @globehomes.