Metro

Melting may create a watery mess in the spring

Pedestrians try to avoid the huge snow accumulations in Hull.
John Tlumacki/Globe Staff
Pedestrians tried to avoid the huge snow accumulations in Hull.

It may seem like a distant reality, but in the coming weeks, as winter edges toward spring, the snow blanketing the ground will begin to melt.

And when it does, cities and towns across the state will be faced with a whole new set of problems, including flooding from storm water runoff overwhelming drainage systems and river ways.

“We’re already starting to talk about those concerns,” said Stephanie Dunten, a meteorologist with the National Weather Service.

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Dunten said the worst-case scenario would be a rapid increase in temperatures, accompanied by a sudden rainstorm.

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“It would be a big concern, so we’re keeping it in the back of our minds,” she said. “That would cause a lot of ice jams to break, flooding in the rivers, and runoff and urban flooding would be possible.”

For now, temperatures are expected to remain low for the next week, with the forecast including the threat of blizzard-like conditions this weekend.

But like the National Weather Service, officials from the Massachusetts Emergency Management Agency can’t help but keep a keen eye on the impact the historic snowfall could have on municipalities, once those huge mounds finally start to fade away.

“With more snow on the ground, the risk [of flooding] could be greater. But that being said, it really depends on the thaw,” said MEMA spokesman Peter Judge. “It’s something we are going to monitor much more carefully this year, because of the amounts of snow.”

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When it does get warmer, residents could experience flooded basements, backyards, and roadways, based on where they live and the history of flooding in those regions.

Judge said homeowners in low-lying areas may face greater risks. “Certainly you want to get flood insurance, if you don’t have flood insurance” he said. “Your normal insurance is not going to cover you if you lose things in your home, or there’s damage to your home from flooding.”

To measure the impact of potential flooding, the National Weather Service regularly studies the snow’s water equivalent using core samples from snowpacks. Experts melt the snow down after it’s trapped inside of a special tube, then measure the water, in inches, to make their predictions.

“From a flood-threat perspective, the melt of water content in the snowpack is very important to know,” said Nicole Belk, the National Weather Service’s in-house hydrologist.

Because many municipalities’ catch basins are probably buried under the current snow, Belk said, a sudden warm up could cause a “pretty quick incident of poor drainage flooding.”

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Varying elements contribute to the possibility of rapid snow melt, including high dew points, strong winds, and temperature shifts.

Weather experts said it’s ideal to have a “slow melt” as the warmer months approach, easing residents into the spring, rather than having it happen unexpectedly.

To reach that ideal, the temperatures need to be warm during the day, then drop below freezing at night, so whatever snow melts has time to drain.

In Cambridge, city officials are already beginning to think ahead.

“In terms of flooding, so much of it depends on when and how the snow melts. Obviously, a more gradual melt is preferable,” said city spokesperson Lee Gianetti.

Cambridge’s catch basins are currently covered in excess snow, so the amount of water they can handle depends on how quickly melting occurs.

“This can lead to localized street flooding,” Gianetti said. “We will continue to monitor streets over the next several weeks, and into spring.”

Boston officials are also keeping an eye on their drainage systems.

Jeanne Richardson, deputy director of communications for the city’s Water and Sewer Commission, said if the weather breaks, the snow melt could cause “ponding” in some neighborhoods, but because workers have been clearing away snow mounds and transferring them to designated “snow farms,” there’s no immediate concern.

“We will keep it on our radar,” said Richardson.

Snow and water content

Much of the water content of recent snowfalls in Boston is still on the ground unmelted. The chart shows water content as it was reported daily, which is not necessarily the amount remaining in the snowpack.

How much is it?

If 4.13 inches of water were collected from an area the size of Boston, it would fill 19 1/2 TD Gardens.

DATA: National Weather Service

David Butler, Chiqui Esteban/Globe Staff

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.