Phoenix is the deadliest heat city in the United States.

And that reality is a cocktail (Molotov cocktail) with various ingredients.

The obvious is that the capital of Arizona is located at the gates of the Sonoran desert, a giant of sand and saguaros that spreads on both sides of the border.

The other undeniable thing is climate change. Scientific evidence supports that the phenomenon generated by humans gives us, among other things, increasingly hot summers and more frequent extreme weather events.

And the special seasoning is constituted by an effect that makes it an island of cement and asphalt at times hotter than the surrounding arid vastness.

“We are in the middle of the desert and in a desert it is always hot, but the urban island effect makes it even worse,” Melissa Guardaro, a researcher at the School of Sustainability at Arizona State University and an expert in policies for mitigation and adaptation to extreme heat.

Phoenix is at the gates of the Sonoran desert.

Phoenix is at the gates of the Sonoran desert.

The “urban heat island effect”
The United States Environmental Protection Agency (EPA) defines it as the phenomenon in which an urban center becomes hotter than the periphery.

In a city of more than a million inhabitants, the average air temperature can be 1 to 12 ° C higher than in a less urbanized area in the vicinity, explains the agency.

And this is precisely what happens with Phoenix —with 1.6 million inhabitants, up to 4.4 million in its metropolitan area—, David Hondula, the director of the city’s Heat Response and Mitigation Office, confirms to BBC Mundo. , a pioneer in the US and whose example has been followed by Miami and Los Angeles.

“City nighttime temperatures have risen three to four times faster than daytime temperatures since the mid-20th century, and that’s a very clear and strong signal and consequence of urbanization,” he continues.

“And we talk about the weather as something mysterious and ambiguous that comes from the sky, but it’s also something that we modify (at the local level) with the way we are paving our streets,” he adds. “Urbanization, in fact, is a critical part of the issue.”

Natural environments are very efficient at removing the heat generated by solar radiation.

It is due to a process called evapotranspiration, by means of which the liquid water contained in the Earth’s surface returns to the atmosphere in the form of vapor. It is as if the skin of the planet sweats.

Trees and other vegetation are responsible for it. And even desert bushes are capable of cooling their surroundings, especially at night.

In contrast, everything that characterizes an urban environment—soaring glass buildings, bustling industry, vast expanses of concrete and asphalt—absorbs and amplifies the sun’s heat.

With decades of unstoppable urbanization, not only has cooling capacity been lost in Phoenix, but the problem has been made worse.

And it is that the heat is trapped between the tallest buildings, is absorbed by the asphalt and retained for hours after sunset, which means that the high daytime temperatures last until the night.

Human activity, such as factories, traffic, even the use of air conditioning, also produces residual heat that worsens the effect.

According to the National Weather Service (NWS), the average temperature for July in Phoenix was 34.9 °C (94.8 °F) and the maximum was 41.2 °C (106.2 °F). °F).

Although far from what the thermometer marked on the hottest day ever recorded (50 °C, 122 °F, in June 1990), two or three consecutive days with more than 90 °F is considered an extreme heat wave.

“And we anticipate that temperatures will continue above normal in the following months, as we have seen in the previous ones, well into the fall,” Tom Frieders, NWS meteorologist in Phoenix, tells BBC Mundo.

A sprawling giant
Phoenix’s expansion began decades ago.

According to city records, in 1950 it was 17 square miles in area. By 2010 it was already 517 square miles and had 1.4 million inhabitants.

It came from years of a real estate boom, at the height of which 60,000 new houses were built per year, according to data from the Arizona Department of Housing.

Today it continues to expand, nearing the edges of the desert, aided by immigration from the south, retirees seeking sun, workers drawn to tech companies, and middle-class families from California and other more expensive states seeking affordable housing.

According to the most recent data from the Census Bureau, it was the city that grew the most in demographic terms from 2020 to 2021, second only to San Antonio, Texas. It is the fifth largest city in the US and 42.6% of its inhabitants identify as Latino or Hispanic.

At the same rate, the county in which it sits, Maricopa, is also growing, whose population increased by 18% in a decade, to exceed 4 million.

And all this growth raises concerns about how it will continue to guarantee water to all its residents while brutal droughts and hot summers drain rivers and reservoirs, in addition to multiplying the urban island effect and its consequences on the health of its inhabitants.

health consequences
This year Phoenix’s first extreme heat wave was recorded in June, with highs of 110°F (over 43°C) for four consecutive days and several daily records broken.

But by then the county medical examiner was investigating 30 cases from April as possible heat-related deaths.

And the most recent data from the Maricopa County Health Department shows that 17 heat-related deaths were recorded in the first week of July and another 126 cases are under investigation. Most occurred in Phoenix, and two-thirds were people who were outdoors.

Heat-associated deaths include those that can be directly attributed to exposure to high temperatures and those in which heat was not the primary cause of death but contributed to it.

In the last decade, the number of deaths of this type has more than tripled in Maricopa, the county in which Phoenix sits, adding 662 in recent years, including 388 last summer. They are respectively the deadliest county and city by heat in the country.

While death is the most extreme of its consequences, such brutal heat can also impact health, especially in certain population groups such as the elderly and those with certain chronic diseases.

And not just physics. Several investigations conclude that extreme heat can generate stress and exacerbate mental illness.

But these consequences, and the heat itself, are not the same for everyone.

The inequality of heat
To shake off the infamous title of deadliest city for heat, Phoenix has a comprehensive plan that includes establishing “cooling centers,” a network of public pools and water distribution throughout the season.

It also has innovative programs such as paving 70 kilometers with a mixture designed by the local university that cools at night and thus helps temperatures drop 12 degrees compared to ordinary asphalt, or covering the roofs of a chemical that reflects light and reduces the need for air conditioning.

And it has invested six million to plant trees in the poorest (and hottest) neighborhoods.

It is that “in some parts of the Phoenix metropolitan area it can be up to 13 °F more than in others,” Professor Guardaro tells BBC Mundo. “And you don’t have to do scientific research to prove it, just get in the car and drive from one part with green areas with automated irrigation to another one full of cement and without parks,” she adds.

“Those (more impoverished) areas are much hotter, which makes it an equity issue.”

He cites research he carried out two years ago on adaptability to heat in different parts of the city. After speaking with dozens of residents, today he groups them into three categories: one, those for whom the heat is “an inconvenience”, who go from their homes with air conditioning to their school/work/shopping center also with air conditioning in their ditto cars.

The second group includes those who, knowing that their electricity bill is going to increase between January and August, save for it; they are those for whom heat is “a manageable problem.”

And for those in the third group, rising temperatures are a catastrophe. “They have to choose between two bad options: do I pay for the air conditioning or the rent? If I don’t pay for the air, then my son is going to have an asthma attack and we will have to face medical expenses,” Guardaro illustrates.

“For these people, $200 per season (what it would cost them to cool the house for those months) can be the limit between being evicted or not, suffering medical episodes or not.”

“It’s your future”
At a time when energy prices are skyrocketing across the country, Phoenix has the highest inflation rate among large cities (12.3%), according to Bureau of Labor statistics.

And Arizona is among a handful of states that don’t allow local governments to enact rent controls or require developers to include affordable housing in new construction.

According to city data, at least 64% of heat deaths in 2020 were homeless. And a county-level survey conducted earlier this year showed the rate of homelessness increased by 35% during the pandemic.

“The homeless are without a doubt the group most at risk,” acknowledges Hondula, a professor with experience in urban planning and in researching the impact of high temperatures on urban life.

“So the most important investments to reduce the number of people getting sick or dying from heat in our city have to be in affordable housing programs and homeless programs.”

Be that as it may, “it seems to me that many cities should be looking at Phoenix,” adds Guardao.

“Because it is the future that awaits them.”

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