The insurance industry hasn’t experienced a major hurricane since Superstorm Sandy. But independent agents and their clients can’t afford to get complacent—especially when it comes to the often-underestimated risk of storm surge.

More than 6.6 million homes on the Atlantic and Gulf coasts are at risk of hurricane storm surge inundation with a total reconstruction cost value of nearly $1.5 trillion, according to a 2015 storm surge analysis from global property information, analytics and data-enabled services provider CoreLogic.

What exactly is storm surge? According to the analysis, it’s a “complex phenomenon that occurs when water is pushed toward the shore through the force of powerful winds associated with cyclonic storms, and is further influenced by many different factors, including water depth and ocean floor terrain.” As a hurricane travels across the ocean, its winds act as a plow, piling up water at the front of the storm.

The faster the hurricane, the more damaging the storm surge—according to CoreLogic, each cubic yard of seawater weighs nearly one ton. Not surprisingly, the associated property damage can be extensive.

The data points to increasing year-over-year reconstruction cost value, which CoreLogic determines based on how much money rebuilding a property would require. The calculation takes into account labor and materials and assumes a worst-case 100% destruction. “We see new construction really driving some of that,” notes Tom Jeffery, senior hazard scientist at CoreLogic. “That’s going to ebb and flow year to year. Materials cost and labor cost will vary by geography and vary over time.”

And beyond property damage, “storm surge is responsible for a large number of deaths every year in the U.S. and globally,” Jeffery says. “That’s something you want to avoid by making people aware that they actually are in an area that has the potential to cause not just property damage but loss of life or harm to their person.”

It’s crucial for independent agents to educate homeowner clients about storm surge, “not just because they need to board up when [a storm] is coming in their direction, but because they really need to prepare with their insurance,” Jeffery says. “Boarding up may prevent some damage, but if your property is at risk, you really want to have it insured so that long-term you’re not on the hook for the cost of reconstruction entirely.”

At a regional level, the analysis finds that more than 3.8 million homes on the Atlantic Coast are at risk of storm surge in 2015, with a reconstruction value estimate of $939 billion. Meanwhile, about 2.8 million homes are at risk on the Gulf Coast, with a nearly $549 billion exposure to total destruction damage.

According to CoreLogic, Florida (2,509,812), Louisiana (760,272), New York (464,534), New Jersey (446,148) and Texas (441,304) account for more than 75% of all at-risk homes nationally. Compared to FEMA’s 100-year flood zone, CoreLogic’s data extends further inland and incorporates more homes.

“So we have people in these areas that may not even realize they’re susceptible to flood damage from storm surge,” Jeffery says. “When we look at Texas to Maine, we can go back in the historical record and find storms for any area along the coast. That doesn’t mean they’re very common in some places—storms in Florida are certainly is more common than you would find in Maine—but as an agent you can remind people that these things have happened in the past. There’s no guarantee that they will this year, but there’s no guarantee that they won’t either.”

When it comes to storm surge, that means agents need to prepare their clients for the unknown. “We know they’re going to happen again,” Jeffery says. “We don’t know when, we don’t know where, but we can certainly speculate that within most people’s lifetimes that are living there now, chances are good that they probably will see more storm activity in the future.”

Jacquelyn Connelly is IA senior editor.