PHILADELPHIA — The water trickled down quickly, enough to coat the sun-bleached concrete basin in a city park with a layer of wetness. A toddler danced, smiling as water from the park’s sprinklers rained down on her, keeping her cool.

It was a blistering midsummer day in July, the kind that as recently as 30 years ago would have proven disastrous for vast numbers of this city’s most vulnerable residents.

In the early 1990s, heat pounded Philadelphia’s most at-risk communities, killing or sickening scores. After a raft of changes, including the creation of an extensive heat warning system and opening “spraygrounds,” the city has been able to largely diminish the heat’s threat to its residents. And in a world where climate change is making extreme weather the norm, some say the city could be a model.

“We know climate change is here to stay,” said Drew Shindell, a professor of earth science at Duke University. “ … It’s still going to go on for decades, even if we take aggressive action. So it would make sense for more cities to adopt the kind of best practices the leading cities have put into place there.”

Philadelphia, largely bereft of greenery, faces hotter temperatures than more rural parts of Pennsylvania. The red-brick sidewalks and asphalt roadways that line the city’s landscape absorb more heat than natural foliage, creating a heat island effect.

Hot temperatures present a significant health risk, including the threat of heat stroke. When it’s hot, your heart rate climbs. The body kicks into overdrive, producing sweat to help itself cool down.

The effectiveness of this physiological response can diminish with age, experts say. High heat and humidity, coupled with chronic illness, can be a dangerous — and potentially fatal — combination, particularly for older individuals and those with preexisting conditions.

“It’s very different when you’re on oxygen or you’re on a diuretic or heart medicine or, you know, you’re a smoker or have existing heart disease,” said Jay Lemery, an associate professor of emergency medicine at the University of Colorado School of Medicine. “At that point, you know, that physiological stressor is just enough to put you over into crisis.”

In summer 1993, Philadelphia reported 118 deaths, far more than other cities experiencing similarly sweltering conditions. Victims, many elderly and secluded, often weren’t found for hours or days. Some didn’t have air conditioning or had closed their windows at the time of their death, a potential indicator that heat may have played a role in exacerbating prior medical conditions, officials said.

“Nearly all of those deaths are preventable,” said Kristie Ebi, professor in the Center for Health and the Global Environment at the University of Washington.

At the time, most cities tended to label a death as heat-related only when signs of hyperthermia — when body temperature becomes abnormally high — were evident.

Philadelphia was an exception. Led by then-medical examiner Haresh Mirchandani, who pushed investigators to search for additional signs of heat exposure during periods of extreme heat, the city was able to get a more accurate reading of the impact heat was having in its communities.

Soon, other cities began to take notice. Using broader criteria to track heat-related deaths, investigators in Chicago found that the blazing heat that swept over the city during a three-day stretch in 1995 claimed the lives of 739 people. It was “exactly what happened in Philadelphia in 1993,” Mirchandani, now deceased, told the Chicago Tribune at the time.

“With the Chicago heat wave of the ’90s, I think there was a recognition that, you know, urban heat could actually be really dangerous,” said Christine Knapp, director of Philadelphia’s Office of Sustainability. “I think there was a recognition that we could be in that kind of dangerous situation as well.”

Armed with a newfound understanding of the risks heat posed to its most vulnerable residents, Philadelphia officials sprang into action. The city implemented several strategies to insulate various communities from the threat of heat waves. In 1995, the city set up the Hot Weather-Health Watch/Warning System. The program provides the public with forecasts showing air mass projections. Air mass types linked with higher morbidity and mortality rates are noted, at which point the Philadelphia Department of Public Health steps in to provide emergency precautions and mitigation procedures for residents.

According to a 2004 report, such warnings save 2.6 people per day when issued. To date, the system has been implemented in more than 20 cities worldwide.

A public awareness campaign also sprouted in the aftermath of the scorching summers of the mid-1990s. Billboards paint downtown Philadelphia’s horizon, a constant reminder to residents of the risks attached to being outside in baking temperatures. Local news programs bombard Philadelphians with messages urging them to stay indoors during periods of excessive heat. Block captains and community organizers work to keep historically disadvantaged parts of the city abreast of changing climate projections.

“People need to be aware that heat is a killer,” Ebi said. “ … People need to understand that they have to pay attention, that they have to stay hydrated, that they find a way to keep cool.”

It’s an imperfect science, Shindell said. Climate change disproportionately affects low-income groups and people of color — both in this country and around the world. Neighborhoods such as Hunting Park, a Black and Hispanic enclave redlined heavily throughout the 20th century, face surface temperatures as much as 22 degrees higher than the largely White, grassier suburbs.

Meanwhile, homelessness still affects a large portion of Philadelphia’s residents. According to a report by the city’s Office of Homeless Services, about 5,700 people were experiencing homelessness in 2019. That number is expected to rise with the end of covid-19 eviction moratoriums.

The city offers a host of services for residents seeking relief from the heat. There are 10 cooling centers, public spaces where vulnerable populations can find temporary relief from the sun’s gaze. Most are public libraries, Knapp said.

And during the coronavirus pandemic, with many libraries closed to the public, city officials got creative. Drawing on Philadelphia’s expansive bus system, SEPTA, climate and health experts helped create cooling buses. Parked on street corners across the city, the buses provide shade, comfort and cool air for those looking to beat the heat.

Spraygrounds also provide a temporary reprieve for children and their families on hot days. Young children are especially vulnerable to excessive heat conditions, a consequence of their underdeveloped physiological system, Ebi said.

It’s the sprinklers that draw the most attention, not the candy-color-painted slides and circuslike monkey bars. Children frolic under the mist, returning to their parents wet, weary and, most importantly, cool.

There is Seger Park, located in the area formerly known as Seventh Ward, a sleepy suburb that was once a cultural hub for Black and immigrant communities in the 19th and early-20th centuries. Once immortalized in W.E.B. Du Bois’ landmark study, “The Philadelphia Negro,” the area is now primarily White and upscale.

Angel LeBron, 40, recently took his children, 23-month-olds Riley and Ajani, to the park. LeBron watched as Riley made her way around the playground. She stopped for a second, glancing at the streams of water converging in the middle.

She took a step closer, then another. Soon, she was sopping, unable to control her joy as water drenched her hair and T-shirt. LeBron, sitting on a cobalt blue bench with Ajani a few feet away, couldn’t stop laughing.

A longtime Kensington resident, LeBron has seen the increasingly unpredictable weather over the years. Precipitation patterns have proven more volatile, while the weather tends to stray between “super-duper hot” and “chillier” than what he’s experienced in the past.

Dustin Leyland, 42, agreed. Leyland lives about a block away from Starr Garden, another well-shaded sprayground located in the heart of Lombard Street.

A former Pittsburgh resident, Leyland has lived in Philadelphia since 2010.

“The summers are pretty similar, you know, very humid,” Leyland said. “You got to do something to keep cool.”

So, Leyland took his son, Berek, and his neighbor, Alex, to the park. A small building nearby is coated with streaks of bright yellow and forest-green paint. A mosaic of paper flowers shroud the metal “Starr Garden” sign emblazoned on the front.

The sprinkler appeared drab, in comparison. A murky mix of water, dirt and leaves pooled beneath the streams.

But Berek and Alex didn’t care. Equipped with bikes and helmets, the two circled around the pit for a few seconds. Then, they went in. They came out soaking and giggling as they peddled their way back to Leyland.

“It’s a great option. You know, especially [if] you don’t have … the place to, you know, use a hose or a sprinkler or something at their house,” Leyland said. “The only way they can do it is [to] get to the park.”