Coupled with projected sea level rise driven by global warming, reef decline could see flooding increase four-fold by century's end, they reported in the journal Nature Communications.
Without coral to help absorb the shock, a once-in-a-century cyclone would wreak twice the havoc, with the damage measured in the tens of billions of dollars, the team calculated.
"Coral reefs serve as natural, submerged breakwaters that reduce flooding by breaking waves and reducing wave energy," said Michael Beck, lead scientist at The Nature Conservancy research and environmental group, and a professor at the University of California in Santa Cruz.
"Unfortunately, we are already losing the height and complexity of shallow reefs around the world, so we are likely already seeing increases in flood damages along many tropical coasts," he told AFP.
Not all coral reefs are declining, and reefs can recover from bleaching, overfishing and storm impacts, Beck noted.
"But the overall pattern of signficant losses across geographies is clear."
Much of the world's 71,000 kilometres (44,000 miles) of coastline with shallow reefs -- concentrated in the tropics -- has been decimated by coastal development, sand mining, dynamite fishing and runoff from industry and agriculture.
Coral is also highly sensitive to spikes in water temperature, which have become sharper and more frequent with climate change.
A marine heatwave in 2016, for example, killed off nearly 30 percent of Australia's iconic Great Barrier Reef. Damage from yet another bout of destructively warm water in 2017 has yet to be assessed.
Global coral reefs risk catastrophic die-offs if Earth's average surface temperature increases two degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels, earlier research has shown.