Experts

Experts: 50 inches of rain unlikely in NH, but much less still could be disastrous

By SHAWNE K. WICKHAM
New Hampshire Sunday News


September 02. 2017 11:59PM




People gather at a service station on Water Street in Concord, just south of the Gas House bridge, after being evacuated by boat from homes in the city’s south end. (UNION LEADER FILE)

Online resources

• For tips on family preparedness and to sign up for notification of emergencies, visit readynh.gov.

• The final report of the N.H. Coastal Risk and Hazards Commission can be found at nhcrhc.org.

The harrowing images from Houston have prompted some in New Hampshire to ask: Could it happen here?

Tom Hawley, a veteran meteorologist for the National Weather Service in Gray, Maine, says it’s “theoretically impossible we would get that kind of rain up here.”

“We just don’t have the moisture content available up here like they do down in the Gulf states,” he said.

Hurricanes typically die when they reach the cold ocean waters of New England. And by then, he said, “They usually are accelerating, and moving quite rapidly.”

Hurricane Harvey churned into the Texas coast last weekend and stalled there for days, dumping a historic 50 inches of rain in some areas.

If New Hampshire ever did get that much rain, Hawley said, “It would be Armageddon.”

Unlike Houston’s flat topography, our terrain would enhance the destruction, he said. Rain would rush down the mountains, into the smaller rivers, and flood the larger river basins.

“And it would be fast-flowing water that would literally pick up everything in its path and move it out,” Hawley said. “The houses would just be removed from their foundations and washed downstream.”

“It would be Noah’s flood. And it would take decades to recover.”

Perry Plummer, the state director of homeland security and emergency management, agreed New Hampshire isn’t likely to see Harvey levels of rain. But he said, “It doesn’t take 50 inches to cause widespread flooding and chaos.”

“Unfortunately, we’re in a time where the weather patterns have changed,” he said. “We need to be prepared for widespread flooding, whatever the number is.”

New Hampshire has seen catastrophic flooding before, most often when heavy spring rainfall combines with melting snow.

Old-timers remember the flood of 1936, when rain-swollen and ice-jammed rivers rose, engulfing homes and businesses around the state. Bridges were swept away and northern communities were cut off as flood waters washed out roads.

The March 19, 1936, edition of the Manchester Leader and Evening Union reported: “Rivers and lakes, lashed to demoniac madness by the relentless onslaught of a drenching 24-hour rain, swelled by millions of tons of melting snow, were on the most violent rampage within the mind of memory.”

The state later reported that 8,000 people had been driven from their homes, 26 bridges had been destroyed or damaged, and damage was estimated at $25 million. Then-Gov. H. Stiles Bridges appointed a state “rehabilitation committee,” and thanked those who assisted their neighbors.

Two years later, a hurricane again brought damaging rain and wind.

In 1987, April Fool’s Day rains on top of melting snow caused record floods in Maine, and heavy flooding here, according to Hawley.

And just this past July, flash flooding in Grafton County and southern Coos County caused an estimated $8 to $11 million worth of damage, earning a federal disaster declaration.

“That happened with just four or five inches of rain,” Hawley said. “Can you imagine 50 inches of rain? It’s just unimaginable to me.”

“Nobody would be living here anymore. Everything would be gone,” he said.

Plummer said the 9/11 attacks in 2001 and Hurricane Katrina in 2005, which caused an estimated $160 billion of damage to the Gulf Coast, were “industry-changing events.”

State and federal emergency management officials have beefed up notification systems to alert residents to emergencies, and done more planning to distribute supplies such as food and water, generators and clothing to disaster areas.

New Hampshire has a voluntary alert system that residents can sign up for at readynh.gov. And a serious disaster would trigger a federal notification system that sends messages to all cellphones, Plummer said.

New Hampshire has an “all-hazards” approach to emergency management,” Plummer said. “It doesn’t really matter if it’s a human-caused disaster or a terrorist attack or flooding or snow event or wind event, our structures are set up so we can respond to those events in a similar manner,” he said.

Flooding is still the most common disaster the state has to deal with, Plummer said. And state agencies constantly train for worse-case scenarios.

The state keeps updated flood inundation maps that predict which areas will likely flood if a hurricane hits. Mandatory evacuations here, Plummer said, are “possible but rare.”

Plummer’s worst nightmare? What he calls a “no-notice event.”

If a hurricane or another storm is approaching, he said, “We can pre-position food, we can pre-position generators when we have notice.”

But imagine a serious earthquake striking New Hampshire. “You can’t move people out; it just happens,” he said.

Cameron Wake, a research professor in climatology and glaciology at the University of New Hampshire, said Harvey took even the experts by surprise. “In the time we’ve been recording precipitation events, this has never happened.”

“We’ve been saying there’s a chance a real big storm will hit and cause enormous damage, but the notion of 50 inches of rain is just unbelievable.”

So while he would have said such a catastrophic storm would not happen in New Hampshire, Wake said, Harvey has caused him to rethink what’s possible.

Scientific data shows we’ve been getting bigger precipitation events, “where we get more of our rain falling in fewer events,” Wake said. Meanwhile, continued development is creating more impervious surfaces, such as roads, roofs and parking lots.

“So we’re combining the two together: large, extreme precipitation events with more impervious surfaces, which means more runoff, which both lead to bigger floods.”

Federal, state and local officials are constantly planning for disasters, Plummer said. But he said citizens need to plan as well.

Folks take for granted the emergency services we’ve come to rely on, he said. “We think even in a Houston or an earthquake, or even an Irene or Sandy, that we’re going to pick the phone up and first responders are going to be there in three minutes or five minutes – because they usually are,” he said.

But in an emergency like that, he said, “They’re not.”

Folks should be prepared to be “self-sustaining,” with enough food, water and medications to last for three days until help arrives, Plummer said. It’s also a good idea to have a plan for friends or relatives who live elsewhere to take you in if a disaster lasts longer than that.

Wake said Harvey changes everything: “The impossible is now possible.”

“Houston was completely and utterly unprepared for what just hit them, and we are not that different,” he said. “It doesn’t matter that it’s not 50 inches. If it’s 15 inches, that presents serious problems for us.”

Wake expects that New England will continue to see bigger “extreme” precipitation events. He points to the Mother’s Day flood in 2006 and Hurricane Irene in 2010.

“It’s happening now, and it’s going to continue to happen in the future. So we should start preparing not for the flood that’s happened in the past but for a bigger flood that’s going to happen in the future.”

Harvey is a grim reminder that the time to act is now, Wake said. “I would rather do that before the flood comes, and not after the flood comes and people die and lose everything that they own.”

After three years of study, the bipartisan New Hampshire Coastal Risk and Hazard Commission last year unanimously adopted 35 recommendations for strengthening communities’ resilience to storm surge, sea-level rise and extreme precipitation events.

Wake served on the commission and on a panel that provided technical expertise. He hopes this is one issue that can bring people together in common cause.

“Flood waters have no political persuasion or party,” he said. “When I talk to people around the region, they are really interested in their communities, their families and their jobs.

“And I would love to think we could get together to say that’s the kind of thing we need to start working to preserve.”

swickham@unionleader.com

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