Rainfall extremes 'the new normal' for New England, hydrologist says

People try to stay dry as they walk to their buses at the SEAT bus stop on Water Street in New London during a rain storm Tuesday, March 28, 2017.  Precipitation extremes are expected to be the 'new normal' for New England, a weather scientists say. (Dana Jensen/The Day)
People try to stay dry as they walk to their buses at the SEAT bus stop on Water Street in New London during a rain storm Tuesday, March 28, 2017. Precipitation extremes are expected to be the "new normal" for New England, a weather scientists say. (Dana Jensen/The Day)

Haddam — David Vallee had his “religious experience” seven years ago to the day on Friday, standing on the steps of the church where he’d been confirmed as a boy to photograph 6 feet of water flooding the streets and stores in downtown West Warwick, R.I.

As the hydrologist in charge for the Northeast River Forecast Center in Taunton, Mass., seeing the 2010 floods in his hometown made him realize as never before that there’s a “new normal” when it comes to precipitation patterns and the ability of roads, bridges, spillways, storm drains and other infrastructure to deal with it.

“These extremes are very hard to manage,” said Vallee, whose agency, part of the National Oceanic and Atmospheric Administration’s National Weather Service, provides flood forecasting services to federal, state and local agencies in the Northeast. “Throughout most of New England, our infrastructure was built out in the 1950s and 1960s. From a stormwater management standpoint, we’re not designed for these extremes.”

Vallee gave the keynote talk at a symposium presented by the University of Connecticut’s Climate Adaptation Academy and the Rockfall Foundation, a Middletown-based nonprofit that promotes environmental education, resource conservation and sustainable development in the lower Connecticut River Valley and region. Titled, “Water: Too Much or Not Enough? From Rain Bombs to Drought,” it brought together about 60 land-use professionals to discuss the challenges of intense zigzags between floods and droughts brought on by climate change and urbanization for planners, public water systems, public health, agriculture and other areas.

Since 1958, Vallee said, New England has seen a 71 percent increase in the frequency of heavy rains that can lead to flooding, as measured by the number of storms that brought more than an inch of rain in a day. Along with more intense events, the total amount of annual precipitation overall also has been increasing, by about a half-inch per decade, in Connecticut, he said.

The increase in downpours and total precipitation, he said, has been brought about mainly by two factors related to climate change: shrinking sea ice in the Arctic, which is affecting jet stream winds, and overall warming of the Earth and oceans, which is sending more moisture into the atmosphere.

“Our weather systems now have much more moisture to work with,” Vallee said.

Another recent trend, he said, is for a slowing movement of weather systems that get “blocked up” in succession.

“These systems are getting stuck in a rut for weeks at a time,” he said. “We’re getting intense back-to-back-to-back precipitation events.”

He added, however, that climate change isn’t the only reason the region is seeing more flooding.

“It’s also about the urbanization of the landscape,” he said. The existing infrastructure, he said, “simply doesn’t have the capacity to move the volume of water” that’s coming in the extreme storms.

Even as the intense rainstorms are more frequent, “flash droughts” also are occurring, when rainfall is absent during the peak growing season months of May, June and July. Both the intense rainfall and the droughts, Vallee said, along with the warming average temperatures, are posing new challenges for agriculture.

“Our annual average temperatures today are more like what New Jersey or Delaware used to be in the 1930s,” he said. “The changes in the growing season have also brought changes in insect and bird life.”

After Vallee’s presentation, Michael Dietz, water resources educator for the Connecticut NEMO (Nonpoint Education for Municipal Officials) program, advocated using the tools and techniques of “low-impact development” to adapt communities’ vulnerability to the reality of more frequent flooding. Channeling water into rain gardens, “green roofs” with plantings and permeable surfaces for parking lots, courtyards and walkways means less runoff taxing storm drains and retention ponds, he said.

“No, one small rain garden isn’t going to save the world,” he said. “But when you start to have 15 to 20 of these in a small area, it can have an impact. Large cities are looking at using green infrastructure. These practices can help deal with this changing precipitation regime.”

j.benson@theday.com

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