Tsunami Data Point to Value of Reefs in Warming Era

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Scientists who have studied the 2004 Indian Ocean tsunami conclude that coral reefs helped to save many people. Recent computer models have confirmed what eyewitnesses reported: Shorelines behind reefs fared much better. That raises both the value of reefs as well as alarm over their rapid disappearance. And with climate change expected to raise sea levels, the data also suggest that reefs might help protect low-lying areas from higher wave surges.

MELISSA BLOCK, host:

Scientists have been studying the tsunami, not just to understand how it happened, but also to learn how to protect people in the future. One of the conclusions that they've come to is that coral reefs are more valuable than people realized.

NPR's Christopher Joyce has that story.

CHRISTOPHER JOYCE: Joe Fernando grew up in Sri Lanka, then moved to the U.S. to study engineering. Now he teaches fluid dynamics at Arizona State University. After the tsunami struck, he went back to Sri Lanka, to a place called The Safari Lodge along the coast. He vacationed there just six months before. Now it was a ruin. One-hundred-seventy-five people at the Lodge had died when the tsunami rolled inland, yet just a mile or two down the coast, the tsunami barely made it beyond the beach. He wondered why the difference.

Professor JOE FERNANDO (Arizona State University): So talking to people around there, they basically thought this might be something to do with the heavy coral poaching going on in the area.

JOYCE: Coral poachers blasted reefs with dynamite to kill fish and to strip hard coral to sell to tourists or to make into a local whitewash for buildings.

Professor FERNANDO: When I was coming back from there, I saw two big trucks with coral reefs, broken coral reefs they were carrying.

JOYCE: Fernando hired divers to examine the reefs offshore in about ten places along the coast. One in particular was Acurala. It was here that the tsunami swept a train off its tracks and killed 1700 people on board. Local residents told Fernando that the coastline there did have a reef.

Professor FERNANDO: And then when I put the divers down and they found that the coral reefs basically were, I mean, substantially destroyed.

JOYCE: Not by the tsunami, he says, most reefs weather that just fine. But by poaching before the disaster. Fernando saw the same pattern along the coast. Broken reefs allowed the tsunami to penetrate farther inland. Fernando acknowledges that this field research is patchy, but scientists at Princeton University have also been working on this. They created mathematical models to simulate the tsunami.

In open ocean, the tsunami is hardly noticeable, perhaps only a foot or two high but moving hundreds of miles an hour. As it reaches a coastline, shallow water makes the waves slow down, bunch up and rise as much as 20 or 30 feet high in the 2004 event.

Princeton geophysicist Michael Oppenheimer says the computer models simulate what happens when a big tsunami encounters a coral reef just offshore.

Dr. MICHAEL OPPENHEIMER (Princeton University): As it turns out, the amount of energy that the coral reef drains out of the tsunami wave before it gets to the beach determines how far up on the beach the tsunami can ride and therefore how many houses it can destroy, how many people it can kill, how many trees it can take away, how much agricultural land it can drown.

JOYCE: Reefs that rise closer to the surface and ones with large lagoons between the reef and the beach appear to work better as break waters. Oppenheimer says it's not just the reef's hard surface that slows the wave, but also the branching coral of a healthy reef.

Dr. OPPENHEIMER: You want something that has the feel of, say, a wire brush rather than something that looks like, say, velvet. And so it, as the tsunami runs over that stiff surface which is sticking up like a bunch of antlers or prongs, it loses a lot of its energy.

JOYCE: The Princeton team published their findings in the journal Geophysical Research Letters. They calculate that a reef could cut a tsunami's coastal run-up - the elevation on land the waves ultimately reach - by half. Tsunamis are rare, but Oppenheimer says reefs will also protect coastlines from storm surges. Many scientists predict that such storm surges will worsen as a warming climate makes sea levels rise.

Coral reefs are disappearing, however. Sedimentation from coastal development, warmer ocean water and dynamite fishing are killing them. There is one bright spot, though. Arizona State's Joe Fernando reports that in Sri Lanka, the tsunami experience has convinced the government to crack down on reef poaching.

Christopher Joyce, NPR News.

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