Ebony Small was walking toward her home in North Philadelphia and said she knew change was in the air.

"Oh yeah, I know it's coming," Small said just as the city's first major heat wave of the summer was about to get underway. "I watch the news every night. I just want to sit back and try and beat the heat. My plan is to just keep cool and check on my elderly neighbors."

Welcome to Swelterdelphia: Heat-trapping pockets of the city made extra steamy by block after block of black-roofed rowhouses, strip shopping centers, busy roads — but few trees or other sources of shade in between.  These areas even stay warmer at night because heat is released more slowly from all those structures.

In some neighborhoods, temperatures can get much higher than the city average on a hot day, according to data supplied to the city by David Hondula of Arizona State University, who analyzed satellite and temperature data from 2013 to 2015. In fact, there can be as much as a 20-degree difference.  His data reflect surface temperatures which are associated with air temperatures, although it's not always a one-to-one match.

Some of the hot spots:  Hunting Park in North Philadelphia, Point Breeze in South Philadelphia, and Cobbs Creek in West Philadelphia, all with lots of rowhouses.

Some of the coolest:  Roxborough, Chestnut Hill, and Mount Airy in the Northwest, and Somerton in the Northeast, all of which boast tree-lined streets and shady parks.

Let's say a shady Chestnut Hill street is 13 degrees lower that the city average on a hot day.  In Hunting Park at the same time, it might be 7 degrees higher than the average.

That's a 20-degree difference between two neighborhoods, and that can be perilous:  104 people have died from heat-related causes in the last decade. The city does not track deaths by neighborhood.

City officials fear climate change is exacerbating the problem.  Recent data show that Philadelphia's average temperature has risen 2 degrees Fahrenheit in the last 30 years.  Temperature rise will have a disproportionate impact on poorer and minority residents, given that the warmest neighborhoods also are the most economically stressed and majority black or Hispanic.

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A city report on the potential impact of climate change says Philadelphia "may experience four to 10 times as many days per year above 95°F, and as many as 16 days a year above 100°F by the end of the century, up from the 1950-1999 average of fewer than one. More of these hot days may arrive together as heat waves, increasing the risk of residents experiencing heat-related health problems such as dehydration, heat exhaustion, and heat stroke."

For her part, Small, 41, the North Philadelphia resident, says she'll start these hot days with a fan and turn on the air conditioner if it becomes unbearable.

But many city residents don't have air conditioners, and those who do often leave them off because it costs so much to run them, said Leroy Fisher, who works in the city managing director's office and handles community engagement in Hunting Park.  Fisher, 47, grew up in North Philadelphia and knows what people do to keep cool.  He recalls seeing a boy struck by a car as he was cooling off in front of an open fire hydrant.

"It's going to be horrible this weekend," Fisher said.  "Heat kills."

Fisher said efforts are underway to identify and map buildings that can be part of a network — including pools — residents could use to stay cool rather than a single cooling center.

While some escape to the Shore or mountains, those in the hottest parts of the city are often stuck in place.  Many would need bus fare to get themselves and their families to an established cooling center, such as a library.

Christine Knapp, director of the Office of Sustainability, said it will take a citywide effort to create the network.

"Eight of the last 10 years have been among the hottest we've had in Philly," Knapp said, explaining the urgency of the project.

"We'll be asking people: How do you cope with the heat? Where do you go?  Is anyone really going to pay for a bus to go to a library to cool down?  Do they want trees?  Do they want cool roofing or free transit on hot days?" Knapp said.

Some changes should be made quickly, she said. For example, she cited tree giveaway programs, such as TreePhilly, as a good start.  Many people rent and don't know they can still qualify to plant trees as long as they have clearance from a landlord.

Steven Alles, director of the division of disease control for the city's health department, said his office was also preparing.

Among the concerns: people who are afraid to open their windows at night.  Often, they'll keep windows sealed shut but turn on a fan, creating sort of a convection-oven effect.  Especially for seniors, there's another danger: failing to realize they are getting dangerously overheated.

"Heat in itself is a cause for attention by our office," Jeffrey Kolakowski, a representative of the Office of Emergency Management, wrote in an email.  The office monitors heat waves and has a heat plan for residents, who are asked to give the city contact information so someone knows they may need help.  Power outages caused by increased electric consumption are another concern. The office also conducts one-hour workshops on dealing with heat and other issues.

Anna Alston, 52, a Hunting Park resident, said she plans to stay inside with the air conditioner on for as long as the heat wave lasts.

"I don't like the heat," Alston said. "I'm telling you it gets so hot on this block you can fry an egg on it.  It's like the South here."

Across the street from her home, someone had already inflated a kiddie pool, blocking the sidewalk. The summer's first heat wave was underway.