The deadly rain and windstorm that swept through Maine on Monday downing trees, cutting power to half the state, washing away roads and bridges, and flooding communities is the latest example of bad weather made worse by climate change.

Although the damage was caused by wind and rain, it was the unseasonably warm weather that Maine is experiencing due to an increase in heat-trapping greenhouse gases in the atmosphere that gave the wet winter storm its powerful punch, scientists say.

“The temperatures yesterday in Maine were three times more likely because of climate change, because of all the CO2 that we’ve pumped into the atmosphere,” said Andy Pershing, director of climate science at Climate Central. “And it was the heat that made this storm so powerful.”

Warm air can hold more moisture than cold air, Pershing explained. For every degree of increase, the atmosphere can hold about 4% more water per unit area. An unseasonably warm atmosphere feeds off the moisture provided by the nearby Gulf of Maine.

On Monday, Maine was primed for stormy weather, Pershing said. Portland almost hit 60 degrees, much higher than the seasonal norm of 25-34 degrees. When the storms rolled through, the unseasonably high temperatures made the bad weather worse, he said.

In a traditional winter storm, with temperatures down in the 20s and 30s, the atmosphere would not have been able to hold as much moisture, leading to less overall precipitation. And that precipitation would have come in the form of snow, not torrential downpours as it did at times Monday.

Climate change is when average weather conditions vary significantly over long periods, becoming warmer or wetter over decades or centuries. Blaming climate change for a single weather event is not easily done, and requires an in-depth analysis that has yet to occur on Monday’s storm.

But meteorologist Chris Legro of the National Weather Service in Gray said “it fits with the science” that global warming is causing an increase in the frequency and the power of the storms being recorded around the planet as carbon emissions increase.

Parts of Maine received 6 to 8 inches of rainfall during the 24-hour storm, which began late Sunday and ended late Monday, Legro said. The highest rainfall total of the storm was recorded in Newry, which logged a record-setting 7.6 inches of rain.

That rainfall total qualifies as a 500-year flood in Newry, Legro said. That doesn’t mean that Newry won’t see another storm like that for another 500 years – it means a flood of that size or greater has a 1-in-500 chance, 0.2%, of occurring in any given year.

At times, the rainfall rates on Sunday approached thunderstorm levels of 4 to 6 inches per hour, Legro said, although the storms tended to move in and out quickly. Certain areas were hit by multiple waves of these storms, however, leaving the ground saturated and causing heavy runoff.

Those record-setting rainfall totals don’t tell the whole story, Legro said. High temperatures also caused an inch or two of snow melt in Maine’s western mountains, which increased the flood risk in the lower-lying areas in that part of the state.

“This was a really interesting event because it was warm, it was powerful and it was really, really wet,” said Pershing, the former chief scientific officer at the Gulf of Maine Research Institute. “And climate change makes all of those things more likely.”

IMPACTS ALREADY BEING SEEN

The increasing frequency of extreme weather is already having impacts across Maine and the Northeast.

According to the new National Climate Assessment, the number of extreme rain or snow events in the Northeast is up 62%, the largest increase in the nation. Two-inch rain days were up 49% when comparing averages between 1958 and 2022, while 5-inch days were up 102%.

How does Maine stack up? The assessment’s conclusions about the Northeast are based on data from 13 states, from Maryland and West Virginia to Maine. It doesn’t specify how many heavy rain days any one state within the region has racked up.

An independent review of five long-term weather stations in Maine conducted by the state climatologist, Sean Birkel, shows some of the regional extreme precipitation trends hold true in Maine: The number of 2-, 3-, and 4-inch rain days are increasing.

Five-inch rain days may have doubled in the Northeast, but in Maine, they’re declining, Birkel said – but they’re so rare that the decline has little statistical value. Since 2000, Portland has had three 5-inch rain days, and Bangor has had one; Augusta, Caribou, and Farmington have had none.

The National Climate Assessment predicts extreme precipitation will continue to increase in frequency and ferocity under all global warming scenarios heading into the future. Its Interactive Atlas Explorer projects steep increases in extreme rain for parts of Maine in dire warming scenarios. For example, Aroostook County will see an 83% jump in extreme rain days, the biggest of any U.S. county, under the 7.2-degree Fahrenheit warming scenario.

Extreme precipitation events and subsequent flooding can cause a variety of costly problems including property damage, lost tourism days, sewer overflows that contaminate drinking water and private wells, and shellfish bed closures.

Extreme precipitation poses a risk to homeowners in an underinsured state like Maine, where less than 1% of housing units are covered by flood insurance. The federally run National Flood Insurance Program covers about 12% to 14% of annual flood damages in the U.S., leaving millions at financial risk.

In its 2020 report “The Cost of Doing Nothing,” the Maine Climate Council estimated climate-related flooding from overflowing rivers and streams could cause up to $2.4 billion in total building losses and wipe out another $2.6 billion a year in jobs.

The Maine Department of Transportation spent Tuesday assessing and repairing wind, rain and flood damage, spokesman Paul Merrill said. As of Tuesday afternoon, Maine had closed 100 state roads and three dozen bridges due to downed trees and power lines, flooding and infrastructure damage.

DAYS TO ASSESS DAMAGE

It could take days to know the extent of the storm’s damage. Inspections and damage assessments can’t be done until the water recedes, which is expected over the next day or so, Merrill said. Many roads and bridges cannot be safely accessed by road crews until power lines have been secured.

Although all counties have been impacted by this storm, more than half the road closures occurred in Oxford, Franklin, Somerset, and Kennebec counties. Flooding and damage are worst near the Sandy, Swift, Carrabassett, Kennebec and Androscoggin rivers and their tributaries.

And at least two of these rivers – the Kennebec and Androscoggin – weren’t expected to peak until early Wednesday. That means those two major Maine rivers haven’t even crested, much less begun to recede, especially where the Androscoggin joins the Kennebec or where the Kennebec empties into the Gulf of Maine.

The Maine Department of Transportation began to incorporate extreme precipitation events into its design standards and planning process about seven or eight years ago when staff started to note an increase in the number of culverts being lost, chief engineer Joyce Taylor said last month.

Before that, the agency used to design its culverts and other transportation projects to withstand a 25-year storm, but now it designs its new projects to be ready for a 100-year storm, Taylor said. While not indestructible, these new projects have all withstood Maine’s increasingly extreme weather.

The agency is about to conduct a statewide vulnerability assessment of its infrastructure, especially its inland culverts, to see which ones need to be made bigger to allow for more water to pass during one of these forecasted extreme precipitation events – even if the structures themselves aren’t old.

An estimated 2,300 of Maine’s road culverts valued at $76.6 million are in danger of being overtopped.

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