A man stays hydrated while sunning himself in Portland's Monument Square during a 2018 heat wave. Credit: Troy R. Bennett / BDN

People in Portland suffered more than most Mainers when temperatures hit the mid-90s at the end of June as climate change brings more extreme heat days and health risks that hit urban areas hardest, a new national analysis found.

Maine’s largest city could be nearly 6 degrees warmer this summer than areas surrounding it because of low tree cover and heat-absorbing infrastructure such as pavement, buildings and rooftops, according to data released Wednesday by Climate Central, a nonprofit science and journalism organization. This so-called urban heat island effect exacerbates rising temperatures, with Portland seeing four additional days of 90-degree-plus heat on average since 1979 as summer temperatures stretch into the shoulder seasons.

Even though Maine is generally considered a cooler state, it is experiencing the type of heat increases seen in larger cities like New York and Boston, which are about 2 degrees warmer than Maine. Portland residents may feel the effects more than people in a desert city like Las Vegas, Jen Brady, senior data analyst with Climate Central, said.

“If you drive out of Las Vegas, you’re not going to cool off much,” she said. “But if you drive 20 miles out of Portland, it might be a lot cooler.”

The Climate Central temperature estimates accounted for humidity, but did not include the effect of ocean breezes. Portland residents will feel increasingly uncomfortable day and night during the summer as temperatures have risen 2.3 degrees on average since 1970 and night temperatures are up 3.4 degrees, according to Climate Central.

The heat presents elevated risks in Maine, which is the oldest state in the nation by median age. Some 36 percent of heat-related deaths in the United States are people over age 65, who don’t adjust well to sudden temperature changes, according to the U.S. Centers for Disease Control and Prevention. Low-income groups that live in areas with more pavement than green areas also face greater health threats, according to Climate Central.

Heat events adversely affect quality of life and trap pollutants in the lower atmosphere, and higher cooling demand strains the electric grid and raises electric bills. Extreme heat is the leading weather-related cause of death over the past 30 years, according to the National Weather Service. The 1995 Chicago heat wave was one of the deadliest climate disasters in U.S. history, killing 739 people, mostly older Americans and poor.

This summer, Cumberland County emergency departments have seen 35 heat-related illness visits, or less than 1 percent of all visits, according to Maine CDC data. It is still important for older Mainers to take precautions to stay cool in the summer, Jane Margesson, an AARP Maine spokesperson.

Some 85 percent of the U.S. population lives in metropolitan areas and will feel the heat effects more during the summer months. Neighborhoods in a highly developed city can experience mid-afternoon temperatures that are 15 to 20 degrees hotter than nearby tree-lined communities or rural areas with fewer people and buildings, according to the data.

Strategies that could help mitigate the effects of rising temperatures include planting more trees, especially along paved streets, and planting rooftop gardens or using reflective materials, according to Climate Central.

The state and Portland are taking measures to adapt buildings and homes. On July 1, the state raised the minimum standards for new home insulation and ventilation in all cities and towns to improve energy efficiency.

Last November, Portland voters approved a “green new deal” referendum that would require projects receiving $50,000 or more in public funds to be built using strict environmental standards with solar-ready or living roofs while increasing pay and training standards for workers. Those strategies could make a big difference, Troy Moon, sustainability director for the city of Portland, said.

Portland could warm another 5 degrees by 2050, and Moon said the city accounted for that in its climate action plan completed last year. It calls for the city to reduce greenhouse gas emissions by 80 percent by 2050 and transition to 100 percent clean energy for municipal operations by 2040. That will include mitigation efforts such as planting more trees in pavement-heavy areas including Bayside and areas with large open parking lots while promoting heat pumps to cool homes.

“We are called the ‘Forest City,’ and we want to make sure we can improve and maintain our tree canopy because that’s a really important way to reduce the heat island effect,” Moon said.