Roughly Speaking Dan Rodricks: Commentary and conversation on life in Baltimore, Maryland and the USA

Could Harvey-size storm hit Chesapeake region?

In early spring, Don Boesch, Maryland’s top climate scientist, spoke at the State of the Gulf of Mexico Summit in Houston. The conference took place at a downtown hotel next to the Buffalo Bayou, the creek that had meandered quietly across Houston until last weekend, when unrelenting rains from Tropical Storm Harvey turned it into a massive lake.

During the panel discussion on March 28, Boesch, the longtime president of the University of Maryland Center for Environmental Science in Cambridge, made a point of displaying a color chart showing unusually warm waters in the gulf during the winter months.

“The Gulf had been warm all winter,” Boesch said this week. “It had never really cooled down.”

He used satellite readings of water temperatures to highlight the potential for big storms, warm water being a key ingredient of them. It’s one of the threats posed by climate change: The more the ocean temperatures rise, and the deeper the warming trend in the water column, the greater the threat of extreme storms.

The panel’s theme was not climate change — it was “Communicating Science in Order to Adaptively Manage” — but Boesch never misses a chance to raise the issue in his public comments, or to warn influential people of their responsibilities to slow it down.

“I showed how warm the Gulf was for that time of year to make the point that the folks down there need to bring climate change into their planning,” Boesch said. “It was the elephant in the room because of the politics [in Texas]. I didn’t know how prescient I was and how soon my warnings would come to pass.”

Climate change, Boesch and many other scientists point out, does not cause events like Tropical Storm Harvey. But it certainly makes them worse.

If you live anywhere near waters — the ocean, the bays, rivers, lakes and reservoirs — you probably wonder how your neighborhood, your town or city, or your business would fare in a massive storm like the one that hit Houston.

Imagine Baltimore, Annapolis, Havre de Grace, Rock Hall or Crisfield after 30 inches of rain, with more coming. All those places lie at sea level. They would be devastated by a storm like Harvey.

But is the premise correct? Could we even have a storm of that scale?

“Stationarity is dead,” cautioned Boesch. The phrase is taken from the title of a 2008 Science journal article about how climate change undermines assumptions previously based on weather history. It means that infrastructure planners, for example, can no longer assume the present is going to be like the past, because of climate change.

Nonetheless, Boesch offers Tropical Storm Agnes, in June 1972, as the nearest the Chesapeake region has come to anything like Harvey. Some 19 inches of rain fell on a large swath of Pennsylvania, and at least 10 inches hit the Baltimore area, with up to 15 inches elsewhere in Maryland. The storm killed people and destroyed property throughout the region. It left flooding from North Carolina to New York.

Stationarity might be dead, but Boesch warned we are likely to see a storm of Agnes’ scale again — only next time it will probably be worse.

Still, he said, it probably won’t be as bad as Harvey. The difference is in the level of warming taking place in the Gulf of Mexico versus the Atlantic Ocean.

“Tropical storms or hurricanes, like Agnes, that are centered over the coastal waters of the Atlantic, or even the Delmarva coast, pose the greatest risk of a deluge and flooding by fast water,” he said. “Like Harvey, these storms are able to continue to pick up more moisture from the warm ocean to resupply the rainfall.”

“The Atlantic is warming and will allow hurricanes to be better fueled as they reach this latitude, but it is not likely to warm to the temperature in the Gulf, especially deep below the surface,” Boesch said.

But if stationarity is dead, and if global warming has put us in uncharted — and unpredictable — waters, who says a Harvey-size storm couldn’t one day hit the East Coast, or the Chesapeake region?

“To allow the extreme rainfalls seen in Harvey, you need two things: Warm ocean water to supply the moisture and a very slow moving or stalled-out system,” Boesch said. “On both counts, the bay region is less vulnerable. The Atlantic waters are not as warm and the warm surface layer is not as deep.”

Hurricanes lose their power, Boesch noted, when their winds mix up the ocean waters, allowing cooler water to come to the surface. The cooler temperatures can make a storm stall.

“Scientific principles suggest that this means that our region is much less likely to experience Harvey-level rainfall,” he said. But rain levels greater than Agnes dumped 45 years ago, he was quick to add, are “clearly in the realm of possibility.”

drodricks@baltsun.com

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