How to plan better for New England floods
Changing rainfall patterns have increased the number and severity of floods. Better forecasts and improved flood management have helped, but planners need to do more to reduce risks and boost community resilience.
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In Pictures Springtime flooding in the US
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He analyzed 75 years' worth of data from US Geological Survey stream-flow gauges throughout New England – but selected from landscapes that have undergone little development, which can increase the rate of run-off and intensify floods.
The data point to a long-term increase in the number of floods. But they also point to what he calls a "stepwise" increase in the frequency of above-average floods, beginning around 1970. In some cases, he says, severity is well above the long-term average. By contrast, prior to 1970, floods typically fell below the long-term average severity.
"It's not just simply a gradual upward trend over 75 years," he says. "It's more like there are two distinct periods in the record that hinge around 1970."
Is climate change a factor?
At the moment, it's unclear whether this change represents a regional hydrological effect of global warming. Other researchers have documented trends in increased precipitation over several decades in the US, which is consistent with a warming atmosphere's ability to hold – and release – more moisture.
For now, he says, a feature of natural climate variability called the North Atlantic Oscillation looks as if it may be playing a role. Since 1970, it appears to have shifted to a regime in which it favors warmer, wetter winters in the US Northeast than it experienced before 1970, Collins says. The correlation is strong enough to warrant more work on it, he says.
Such trends imply a need to redouble efforts to reduce the risk to lives and property flooding in the region presents, researchers say.
While today's "best practices" widely applied would not have prevented the kind of damage March's flooding inflicted on New England, they can help reduce losses from lesser events, according to Paul Kirshen, a former Tufts University engineering professor who now works on climate-adaptation issues at the Battelle Memorial Institute's office in Duxbury, Mass.
Mimicking natural water flows
One concept, low-impact development, aims to engineer drainage systems – from those used in homes to those running beneath entire communities – in ways that mimic natural water flows. For homes, that could in part mean giving up a thickly paved driveway for gravel or paving stones that allow more water to sink into the soil
That may not help an individual's flooding problem during a given storm, Dr. Kirshen acknowledges. But it does help on a community-wide basis.
In addition, groups ranging from the Army Corps of Engineers to local communities and environmental groups are trying to find ways to make room for a storm's flow upstream, which eases the flood levels in more-populated areas downstream.
Dam removal also plays a role, adds Brian Graber, with the environmental group American Rivers, noting that historically, many of the region's dams were built to power mills, not control floods. Old and often in poor repair, many of these dams prompt evacuations during severe storms even when people living downstream are not experiencing flooding.